Marcelo Ruaro
email: marcelo.ruaro@univ-ubs.fr

Kevin J M Martin
email: kevin.martin@univ-ubs.fr

Fernando G Moraes
email: fernando.moraes@pucrs.br

Software-Defined Networking for Many-cores

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I. INTRODUCTION

Software-Defined Networking (SDN) makes the NoC simple by removing the communication control logic from the hardware level (router), bringing it to the software level. An SDN Controller (Controller) manages NoC path definition, enabling the NoC to support new communication services, as QoS, power management, and faulttolerance (FT), by implementing them as controller's software rules rather than on dedicated hardware designs. Figure 1(a) shows an example of a typical Processing Element (PE) architecture of a manycore [START_REF] Ruaro | A systemic and secure sdn framework for noc-based many-cores[END_REF]. The NoC implements a Multiple Physical Network (MPN) concept, with three disjoint subnets, and consequently, three routers to implement each subnet. One Packet-Switching (PS) router allows link sharing and is suitable for non-priority flows. SDN Routers (SR) implement Circuit-Switching (CS) [START_REF] Liu | MultiCS: Circuit switched NoC with multiple sub-networks and sub-channels[END_REF], supporting dedicated paths configured by the controller, and making them suitable for real-time flows. In this sense, PS paths act like roads, allowing sharing best-effort packets, while CS paths (managed by SDN) act like rails, supporting timing constrained packets. The number of SRs is configurable. The SRs of MPN have a low design cost with one SR requiring, on average, 25% of the area and power of a typical PS router [START_REF] Ruaro | Sdn-based circuitswitching for many-cores[END_REF].

Figure 1(b) shows the steps to establish a dedicated path in an SDN-based many-core. The controller can either run in dedicated PE [START_REF] Ellinidou | Sspsoc: A secure sdn-based protocol over mpsoc[END_REF], or as a high priority task [START_REF] Ruaro | Sdn-based circuitswitching for many-cores[END_REF]. The controller abstracts the network management to a system manager (M), which performs application admission and task mapping. Due to such abstraction, when M needs a path between a source (S) and a target (T) communicating task, it performs a path request to the controller (step 1). The controller searches the path guided by the network status and its current management policies (step 2). The example in Figure 1(b) explores a theoretical scenario where the controller searches the shortest path between S and T, avoiding hot-spot areas (in red) and faulty routers (router 3x3). After finding a path, the controller physically configures the path (step 3) by sending a configuration packet to the respective SR. The configuration packet uses the PS subnet to reach the desired PE where the SR is located. The NI (Network Interface) of that PE receives the configuration packet by the SDN configuration logic (SCL), which handles the packet and configures the respective SR. The configuration ends when the controller configures all SR bellowing to the path. After the configuration, the controller sends an acknowledgment packet to M (step 4), which sets S and T to use the path (step 5) effectively. Table I presents related works on SDN for many-cores. There is a noticeable increasing academic interest and recognition of this subject. The lines filed in blue show the authors' contributions for this subject. The main motivation for investigating the SDN paradigm for on-chip communication comes from its advantages over traditional hardware-centered implementations [START_REF] Ruaro | Sdn-based circuitswitching for many-cores[END_REF], [START_REF] Kostrzewa | Self-aware network-on-chip control in real-time systems[END_REF]- [START_REF] Ruaro | Software-Defined Networking Architecture for NoC-based Many-Cores[END_REF]:

Hardware complexity reduction: each SDN router implements a simple hardware logic used only to support the router's configuration and packet forwarding [START_REF] Ruaro | Sdn-based circuitswitching for many-cores[END_REF]. There is no need to implement the logic for routing and arbitration of packets or another kind of control like power, QoS, and FT. Less hardware means less area, power, and lower temperature, helping against the dark silicon effect;

Management flexibility: due to software implementation, the SDN allows for changing and updating policies that define the routing path without the necessity to design a new circuit [START_REF] Berestizshevsky | Sdnoc: Software defined network on a chip[END_REF];

Real-time guarantees: SDN combined MPNs, allows for a dedicated path for each real-time application flow, thus ensuring QoS through communication isolation [START_REF] Ruaro | Self-Adaptive QoS Management of Computation and Communication Resources in Many-Cores SoCs[END_REF];

Multi-objective management: SDN allows multi-objective management due to its panoramic overview of the NoC status. Different adaptive and management goals can be implemented and managed by the controller, which can decide to configure the NoC at runtime to fulfill real-time application needs of system budgets [START_REF] Ruaro | Multiple-objective management based on a distributed sdn architecture for many-cores[END_REF].

II. DISTRIBUTED SDN

One of the big challenges of SDN is regarding the scalability to search and configure paths at runtime. In [START_REF] Ruaro | Distributed sdn architecture for noc-based many-core socs[END_REF], the authors proposed a cluster-based approach, where one controller is in charge of a cluster of PEs instead the whole systems. Controllers work in parallel for local (intra-cluster) paths. For global (inter-cluster) paths, the controllers execute a synchronization protocol inspired by VLSI routing, with global and detailed routing phases.

Work Year Organization

Objective Model [START_REF] Cong | A configurable, programmable and software-defined network on chip[END_REF] 2014 At router level Architecture Noxim [START_REF] Sandoval-Arechiga | Software Defined Networks-on-Chip for multi/many-core systems: A performance evaluation[END_REF] 2016 Centralized Architecture Noxim [START_REF] Ruaro | Sdn-based circuitswitching for many-cores[END_REF] 2017 Centralized Architecture RTL [START_REF] Berestizshevsky | Sdnoc: Software defined network on a chip[END_REF] 2017 Centralized Architecture OMNET++ [START_REF] Fathi | A Centralized Controller as an Approach in Designing NoC[END_REF] 2017 Centralized Architecture RTL [START_REF] Scionti | Towards a Scalable Software Defined Network-on-Chip for Next Generation Cloud[END_REF] 2018 At PE level Power Mininet [START_REF] Kostrzewa | Self-aware network-on-chip control in real-time systems[END_REF] 2018 Centralized QoS RTL [START_REF] Ruaro | Software-Defined Networking Architecture for NoC-based Many-Cores[END_REF] 2018 Centralized Architecture RTL [START_REF] Ruaro | Self-Adaptive QoS Management of Computation and Communication Resources in Many-Cores SoCs[END_REF] 2019 Centralized QoS RTL [START_REF] Ruaro | Distributed sdn architecture for noc-based many-core socs[END_REF] 2019 Distributed Scalability RTL [START_REF] Ruaro | A systemic and secure sdn framework for noc-based many-cores[END_REF] 2020 Distributed Security RTL [START_REF] Ruaro | Sdn-based secure application admission and execution for many-cores[END_REF] 2020 Distributed Security RTL [START_REF] Ruaro | Multiple-objective management based on a distributed sdn architecture for many-cores[END_REF] 2020 Distributed Faults+QoS RTL Figure 2 evaluates the scalability of the approach, by varying the system size and the number of SDN routers (CSn) inside a PE. Figure 2(a) presents the total latency: time to establish the maximum number (worst-case) of simultaneous paths into the system. The distributed SDN (D-SDN) values are normalized in relation to centralized (C-SDN). In summary, the C-SDN presents a better total latency for smaller systems, on average, lower than 256 PEs, while D-SDN outperforms C-SDN for the larger system sizes. Figure 2(b) presents the average setup latency (ASL) per path. For system sizes below 1024 PEs on average, it is possible to observe that the D-SDN presents a higher ASL. Note that the C-SDN ASL increases with the system size, due to the larger path search space. This result unveils that SDN can be adopted in larger systems by distributing the management role/load among controllers.

III. SDN FOR QOS AND FAULTS

This experiment evaluates the multi-objective adaptation using SDN, handling QoS and fault-tolerance simultaneously. Figure 3(a) shows an MPEG application mapping, where blue arrows represent the communication between MPEG tasks. Red arrows represent disturbing flows and the two red rays faulty CS routers. Figure 3(b) presents the MPEG iteration latency measured at the output task. The communication between tasks starts in PS mode. As there is no disturbing traffic, the NoC can meet latency threshold. At 800,000 cc, disturbing flows start, generating an increase in the iteration latency (t1 in Figure ), and consequently, triggering a CS setup for the affected MPEG flows At 936,116 cc, the MPEG flows communicate using CS mode, restoring its QoS constraint.

At 1,800,000 cc, faults occur at CS routers in the cores executing ivlc and idct tasks, which makes the controller to switch the affected flows to PS mode. As the disturbing traffic is still active, the iteration latency increases, generating latency misses and making the controller to setup CS again (t2 in Figure ). As the controller is aware about the faulty CS routers, it sets CS using different subnets than previously. After 1,984,991 cc, all affected flows of MPEG meet the QoS constraint latency by using CS.

IV. SDN FOR SECURITY

Authors in [START_REF] Ruaro | A systemic and secure sdn framework for noc-based many-cores[END_REF] present a systemic and secure SDN framework (SDN-SS). The work describes the iteration between the hardware, operating system, and user's tasks to serve a data-sensitive application for dedicated and secure paths. The originality of SDN-SS includes (i) a step-by-step framework description addressing the phases required to support a secure SDN management; (ii) a secure SDN router configuration protocol; (iii) a protocol to change the subnet at runtime. Experimental results show the framework's capability to avoid DoS and spoofing attacks while presenting a low SDN router configuration overhead, corresponding up to 2% of a related work delay and a small impact over the user's task communication.

V. CONCLUSION

This paper presents an overview of the possibilities in exploiting SDN for many-cores. The SDN is a new open-topic and as demonstrated by results can contribute to reach a scalable and runtime multiobjective management at communication level.

  Interface PS = Packet-Switching router SR = SDN Router SCL = SDN Configuration Logic

Fig. 1 .

 1 Fig. 1. (a) SDN-based communication in an MCSoC. (b) Overview of the Processing Element. Source: [1].

Fig. 2 .

 2 Fig. 2. Comparison between D-SDN and C-SDN.

Fig. 3 .

 3 Fig. 3. (a) MPEG mapping with disturbing flows, and faulty CS routers; (b) MPEG iteration latency. Source: [10].

TABLE I STATE

 I -OF-THE-ART WORKS OF SDN FOR MANY-CORES.


Ben Amor

W Taouali

E Faulques

M Bourass

D Khlaifia

A Haj

K Alimi

M Chemek

S Benamor

A Hadj Said

Photo-physical effects of the chemical insertion of the dimethyl-amine moiety on the newly synthesized oligophenylene (OMPA)

Keywords: 4-(methoxyphenyl)acetonitrile, Dimethylformamide Dimethyl Acetal (DMFDMA), Optical properties

Photo-physical effects of the chemical insertion of the

dimethyl-amine moiety on the newly synthesized oligophenylene (OMPA)

I-Introduction

Since the discovery of the light-emitting properties in thephenylene-based conjugated polymers in 1990 [1], potential device applications have been developed, going from optical switching to solar cells [2]. Furthermore, progress in the studying of the fundamental physics of these conjugated polymers provides crucial underpinnings to technological research. These signs of progress have been developed experimentally and using newly computational tools [3][4][5]. In this frame, the comprehension of the correlation between structure and photo-physical properties will provide useful information to design new materials with desired properties and functionalities. Indeed, the photo-physical properties of organic-based materials could be tuned by modulating their electronic structures [6][7][8]. This purpose could be achieved by incorporating appropriate electron-donating or electron-withdrawing groups in the structure of the starting monomer or of the final polymer. Unfortunately, the choice of monomers with appropriate groups is limited since not all of these groups are necessarily tolerant of the synthetic pathway of the polymer. Thus, the post-synthetic covalent modification of the polymeric backbone, by grafting different molecular moieties, is a more versatile strategy that offers more possibilities for controlling the chemical structure of the final material. However, this strategy is not always successful with long polymeric chains because of the steric hindrance effect, solubility problems, and applicability limitation due in particular to low PL quantum yield efficiencies in the condensed state [9]. A way to circumvent these problems is to design small molecules or oligomers that could be used as active layers in organic solar cells, light-emitting diodes, or other sensors [10][11][12]. Previously, we have synthesized new oligophenylene derivatives by electro-oxidative oligomerization of the 4-(methoxyphenylacetonitrile) monomer (referred to as MPA) [13]. The obtained oligomer, oligo [4-(methoxyphenyl)acetonitrile] n , (OMPA), was also successfully characterized by various experimental techniques [13]. Besides, DFT calculations were undertaken to describe the possible mechanism of the electro-oxidative oligomerization. The theoretical and experimental analysis showed that the average length chain is at about 5 units (5-MPA) [13,14]. Optical absorption measurements were carried out at room temperature (RT) using a Varian Cary 5G spectrophotometer. Continuous-wave photoluminescence measurements (PL) were collected on a Jobin-YvonFluorolog 3 spectrometer using a Xenon lamp (450W). Time-resolved photoluminescence experiments (TRPL) were carried out at room temperature with a regeneratively amplified femtosecond Ti:Sapphire laser system (Spectra-Physics Hurricane X) generating 100 fs pulses at 800 nm with a repetitive rate of 1 kHz and an average power of 1W. The laser line is frequency-tripled to obtain an excitation line ƛ exc = 266 nm. Optical measurements of the samples (OMPA and OMFA) were investigated in dilute chloroform solution and as thin films. For optical measurements, a diluted chloroform solution of OMPA and OMFA (C= The voltammetric study was performed with a Voltalab10 apparatus from a Radiometer driven by the Volta Master software. The working electrode was a 2 mm diameter platinum disk, the reference electrode was an SCE (Tacussel SR110) and the counter electrode was a platinum wire. The preparative electrolyzes were carried out in a two-compartment cell, under nitrogen, at a controlled potential versus an SCE (Tacussel C12). The potentiostat and the current integrator were Tacussel (PRT 1-100 and IG 5 respectively). The working electrode and the counter electrode were a 4 cm 2 and a 0.25 cm 2 platinum gauze, respectively. The separation between cell compartments was realized by a number 4 glass frit.

In
Quantum chemical computations were performed using DFT [15] implemented in Gaussian 16 program [16]. All calculations on the studied molecules of this work were done at the Performance Computing Center Bordeaux University. Molecular geometries were optimized in theground statewith the Becke-3-Lee-Yang-Parr (B3LYP) exchange-correlation functional [17], LSDA(SVWN5) [14], and PBE0 functional combined with the 6-311G (d,p) basis set [18].LSDA(SVWN5) was used in modelling the unmodified oligomer (OMPA), and it overestimates its experimental vibrational, electronic and optical properties. [14]. PBE0 functional was successfully tested for several small molecules [19][20]. The calculated absorption spectrum of the investigated oligomer was obtained by the Time-Dependent Density Functional Theory (TD-DFT) method. The NBO calculations were performed using NBO 3.1 program as implemented in the Gaussian 16 package. The molecular electrostatic potential mapping (MEP) and the contour plots of the different orbitals were also visualized and obtained from the fully optimized state on the ground state using the GAUSSVIEW program [START_REF] Dennington | GaussView, Version[END_REF].

III-Chemical synthesis procedure:

The unmodified oligomer OMPA was electrochemically prepared by the electrolysis of (4-methoxyphenyl) acetonitrile at a controlled potential of 1.8 V as described in our previous work [13]. In this part, we will firstly describe the modification of the chemical structure of The same previously described experimental procedure was used for the oligomer OMPA modification. The modified oligomer was filtered after precipitation in diethyl ether.

The yieldobtained was about 60%. The oligomer obtained exhibits good solubility in commonly used organic solvents such as chloroform (CHCl Particularly, in the 13 C NMR spectra, we note the appearance of the signal at 42 ppm, corresponding to the methyl carbons of the dimethyl-amine group. Added to that, the signal at 23 ppm, corresponding to benzylic carbons observed in the 13 C NMR spectrum of OMPA with high intensity [13], appears in the 13 C NMR spectrum of OMFA with weak intensity, and evidenced the quantitative or partial modification. The obtained material Oligo((Z)-3-

(diméthylamino)-2-(4-méthoxyphenyl) acrylonitrile) denoted (OMFA)

IV-Experimental investigations IV-1-Electrochemical measurements

Cyclic voltammetry measurements were performed using a three-electrode cell setup with 0.1 M tetrabutylammoniumtetrafluoroborate (Bu4NBF4) as a supporting electrolyte in degassed acetonitrile. We studied the electrochemical behavior of the oligomers to understand their electrochemical stability in p and n-doped states. Figure 1 illustrates the cyclic voltammograms of the OMFA oligomer. The E HOMO and the E LUMO were calculated with the empirical method [START_REF] Janietz | [END_REF][23], where: E HOMO (eV) = -(E onset oxi + 4,4) and E LUMO (eV) = -(E onset red + 4,4) with the onset potentials were measured vs. an ECS electrode. E onsetoxi and E onset red were estimated from the obtained cyclic voltammograms (E onsetoxi = 1.4 eV,E onset red = -0.9 eV).

Energy gap was also deduced by E H-L = E HOMO -E LUMO which is estimated to be 2.33 eV. The electrochemical obtained data of the prepared oligomers are presented in Table 2.

IV-2-Infrared observation

Unmodified and modified oligomers (OMPA and OMFA) are characterized by infrared spectroscopy using the Kbr technique. Normalized infrared spectra of both oligomers are presented in Figure 2 for the range 600-2400 cm -1 . Noting that the characteristic vibrations of OMPA are presented and assigned in Figure 1 following the results presented in our previous paper [13]. The chemical condensation of the OMPA oligomer induces a partial effect on the infrared vibrational properties (see Figure 2). In fact, under the Knoevenagel condensation, a new peak appears at around 1388 cm -1 assigned to the C-H vibration of the CH 3 -N-CH 3 introduced group. We notice the disappearance of the peaks located at 1083 and 1670 cm -1 which are observed in the infrared spectrum of the unmodified OMPA oligomer. Meanwhile, a slight shift of the aromatic C=C vibration from 1610 to 1620 cm -1 appears. Also, a decrease in the intensity of several collected mode vibrations and especially for the C-H vibration at 760-815 cm -1 and that for C≡N vibration at 2200-2250 cm -1 was observed. These observed trends are the results of the partial grafting of the dimethyl acetal group to obtain the OMFA oligomer.

IV-3-Steady-state optical absorption spectroscopy

The normalized optical absorption spectrum of OMFA oligomer in solution is depicted in Figure 3A. As mentioned previously [13], unmodified OMPA absorbs in the UV region with optical absorption bands located at 240, 270, and 340 nm (Figure 3C). From the obtained optical absorption spectrum, the onset of absorption wavelength λ onset is at about 405 nm.

Using the following formula = onset  1242 [24], the optical bandgap is estimated to be 3.06 eV. From the optical absorption spectra of the OMFA oligomer, we deduce that going from OMPA to OMFA no change of the short optical transitions is detected at 240 nm. While the chemical modification induces firstly a redshift of the optical absorption band located at 270 nm to 290 nm, secondly the π-π* optical transition shifts from 340 nm to 380 nm for the OMFA. Added to that, a red-shift of λ onset is observed from 405 nm for unmodified OMPA to 457 nm for OMFA, indicating a decrease in the optical bandgap from 3.06 to 2.71 eV for the OMFA oligomer. To give information on the eventual solid-state effects on the optical properties, the optical absorption spectrum of the OMFA oligomer thin film is presented in Figure 3B. The thin film was obtained by drop-casting a prepared solution of OMFA on a silica substrate. Going from solution to solid-state, a redshift of the detected optical transition was observed, especially the maximum absorption from 380 nm in solution to 398 nm in a solid-state. Elsewhere, the onset of absorption increase from 450 nm to 490 nm inducing a decrease of the optical bandgap from 2.71 eV to 2.53 eV in a solid-state.

IV-4-Steady-state photoluminescence spectroscopy

The photoluminescence excitation spectrum (PLE) recorded for the maximum emission (480 nm) of the OMFA oligomer in chloroform solution was obtained by varying the excitation wavelength from 250 to 450 nm (Figure 3A). The PLE spectrum presents a maximum optical band at 380 nm, reproducing also the π-π* optical transition observed in the optical absorption spectra of OMFA obtained in solution.

Figure 4 presents the photoluminescence dependence on the wavelength excitation light:

PLE maps OMPA and OMFA oligomers obtained by varying the excitation wavelength in the UV range under 2 nm steps. By analyzing the obtained PLE maps, a drastic change was observed in the emission properties going from OMPA to OMFA PLE maps. Under shortwavelength excitation (λ exc =260-320 nm), vibronic photoluminescence spectra with maximum emission at around 360 and 480 nm were obtained in the case of OMPA. For OMFA, a vibronic emission profile was also obtained under UV excitation (260-300 nm)

However, oppositely with that of OMPA, a weak transition at around (300-400 nm) and an intense one at around 500 nm are observed. Moreover, under higher excitation wavelength (λ exc varying for 320 to 440 nm) a broader unstructured emission profile was obtained for both oligomers. Meanwhile, going from OMPA to OMFA a red-shift of the maximum emission was obtained, indicating an enhancement of the effective conjugation lengths [24,25].

Moreover, we present in Figure 5 the photoluminescence spectra of OMPA and OMFA under both short (λ exc =290 nm) and high excitation wavelength (λ exc =360 nm). From these spectra, we confirm the assumption derived from PLE maps of the studied oligomers. In fact, under 360 nm excitation, PL spectra of OMPA and OMFA present a structure less and broad profile.

PL spectra of OMFA present a red-shift at around 60 nm compared to that of OMPA. Under λ exc = 290 nm excitation, a vibronic PL profile occurs for both oligomers with two emission transitions at around 360 and 490 nm. A strong decrease of the PL maximum emission located at 350 nm was obtained when going from OMPA to OMFA. From these observations, we can deduce that the grafting of the dimethyl-amino group changes dramatically the optical properties and also modify the photo-generated excitonic species. These trends could result from modification of the effective conjugation length under the chemical grafting.

IV-5-Time-resolved photoluminescence investigation

In this part, time-resolved photoluminescence (TRPL) spectroscopy has been used to better understand the possible photo-physical mechanism such as inter and intra-exciton formation and migration of the photo-generated species into the prepared oligomers. In Figure 6, we present TRPL decays of OMPA and OMFAobtained under laser excitation wavelength at λ exc =266 nm. Figures 6A and 6B depict the normalized TRPL dynamics in the 1ns range for both oligomers deposited in thin films by drop-casting the oligomer solution onto silica and in diluted chloroform solution in the range 0-5 ns on a semi-logarithmic scale, respectively.

The dynamics of the photo-excited states of all samples are fitted by a bi-exponential model [26] assuming that the total population of photogenerated species is n

= A 1 n 1 + A 2 n 2 ,
where A 1 and A 2 are proportional to the PL intensity from levels 1 and 2, respectively, the average decay time τ mean writes as τ mean = [A 1 (τ 1 ) 2 + A 2 (τ 2 ) 2 ] / [A 1 (τ 1 ) + A2 (τ 2 )]. The lifetimes presented in Table 1 show two-decay components: a fast one (τ 1 ) attributed to the nonradiative recombination, and a slow component (τ 2 ) that can be ascribed to the radiative recombination after the interaction. For oligomers prepared in solution, TRPL decays tend to be monoexponential with slower decay time. TRPL decays of thin films present a faster dynamic with biexponential behaviors. The calculated average lifetime τ mean for OMFA in dilute chloroform solution is 2.3 ns and 0.18 ns in the thick film, while for OMPAτ mean , it reaches 2.1 ns in dilute chloroform solution and 0.15 ns in the thick film. The dramatic decrease of τ mean for both oligomers going from solution to thin films is a signature of the increase of the effective conjugation length [27] in the condensed state due to the alignment of the oligomer chain onto the silica substrate, upon chloroform evaporation. In a diluted solution, oligomer chains are well separated favoring the formation of singlet intra-chain excitons under laser excitation. In this state, strong intermolecular interactions are negligible and inter-chain migration of the photo-generated species is precluded [28]. Consequently, a strong PL emission is observed in the solution state associated with a slow decay mechanism.

Furthermore, in thick film oligomer chains are aggregated in bundles favoring inter-oligomer interaction, which enhances the formation of non-emissive inter-chain photo-generated species migrating rapidly through the material. Consequently, quenching in the emission could be observed with faster decay dynamics.

IV-6-Thermal investigations

Thermal properties of the modified and unmodified oligomers were investigated by thermogravimetric analysis (TGA) under nitrogen atmosphere.

IV-7-Theoretical investigations

In this section, DFT quantum chemical calculations are performed to study the effect of the dimethyl-amino group on the optoelectronic properties of the as-synthesized oligomer and to rationalize the obtained experimental observations. In this part, we are going to study the effect of the chemical insertion on simple monomer units (MPA) and the oligomer OMPA.

The study on the simple monomer is presented in the supplementary data.

Based on our previous paper [14], the 5-MPA oligomer overestimates the experimental properties of the unmodified OMPA oligomer [14]. On the optimized 5-MPA, we graft a dimethyl-amine chemical group (Figure 8). The chemical structure of modified and unmodified 5-MPA is optimized on the ground state with DFT tools and using various functionals. The results listed in shown in the previous paper [29], the calculated frequencies using the used basis set must be corrected with the scale factor 0.988. The obtained calculated infrared spectrum is presented with the experimental one in Figure 1. It is seen that the theoretical infrared spectrum reproduces experimental one on the obtained band positions and intensities. Also, the theoretical optical absorption spectrum is computed by TD-DFT/LSDA/6-311G(d,p) on chloroform solution and presented with the experimental one (Figure 3D). The obtained simulated optical absorption spectrum reproduces the experimental one with a slight difference in shape. For most of organic conjugated polymer, the first calculated (TD-DFT) vertical electronic transition corresponds to the HOMO->LUMO transition, which energy commonly considered as the optical energy gap [30]. In our case, using Gauss sum software [START_REF] O'boyle | cclib[END_REF] on the obtained TD-DFT calculation, the vertical electronic transition is found at 498 nm with a weak oscillator strength f (0.012), and correspondingto HOMO->LUMO transition (96%). The optical energy gap is deduced to be 2.50 eV reproducing the experimental one ( =2.71 eV).

These obtained results confirm our choice and validate the obtained structure model of the modified OMPA (OMFA).

From the fully optimized chemical structure, frontier orbitals such as HOMO and LUMO are computed with 0.02 isovalue and presented in Figure 8. Also, HOMO and LUMO energy levels are computed. The chemical insertion of the dimethyl-amine on the focused site induces a change in the frontier orbitals distribution HOMO/LUMO (Figure 8). 2).

A focused study shows that a change in the electronic properties has a direct impact on the photo-physical properties [34]. To further showing the charge distribution on the optimized chemical structure of the OMFA oligomer, the molecular electrostatic potential (MEP) of the optimized OMFA is presented in Figure 9. The obtained surface visualizes the charged regions of the studied molecule [35]. Areas with blue color (high electrostatic potential)

indicate the absence of electrons while areas with red colors (low electrostatic potential) indicate an abundance of electrons [36]. It is seen that the dimethyl group presents blue color confirming the donating character of the added group, while the C≡N group presents intense red color confirming the accepting character of this site. These trends are confirming by NBO calculation on the OMFA optimized chemical structure. The donor group presents a positive NBO atomic charge, while the acceptor one presents a negative value [36]. NBO analysis shows that the dimethyl-amino added group presents positive NBO atomic charge (0.162), which confirm the addition of a donating moiety on the molecule, while C≡N group presents a negative NBO atomic charge (-0.133) confirming that C≡N group is an acceptor site on the molecule.

V-Conclusion

Using the Knoevenagel condensation reaction we have modified the backbone of our electrosynthesized (OMPA). Experimental and theoretical investigations show that the insertion of the dimethyl-amino group changes their electronic and photophysical properties as a result of an intramolecular charge transfer that occurred between thedonor dimethylamino and the acceptor cyano groups. The induced charge transfer leads to a decrease of the electronic and optical bandgaps. Therefore, enhancing the charge transfer in new organic oligomers should induce lower optical band gaps. Finally, we showed that the post-synthetic chemical modification of our oligophenylene is a versatile molecular engineering tool enabling the design of new materials with modulated functionalities and photophysical properties.

  this paper, we have modified the chemical backbone of the OMPA synthesized oligomer by the Knoevenagel condensation with the dimethylformamide dimethyl acetal (DMF-DMA). Photo-physical properties of the new oligo [3-(dimethylamino)-2-(4methoxyphenyl)acrylonitrile] (OMFA) were studied by the means of optical absorption, steady-state, and time-resolved photoluminescence techniques and compared to those of the unmodified OMPA. We present the chemical modification route and the effect of the grafting of the dimethyl-amino group on the photo-physical properties of the synthesized OMPA as well as DFT calculations to better understand the photophysical and electronic properties of this compound. II-Experimental and theoretical details 4-Methoxyphenyl acetonitrile,N,N-Dimethylformamide dimethyl acetal, and tetraethylammoniumtetrafluoroborate were purchased from ACROS. Chloroform and dichloromethane were purchased from PROLABO. Diethyl ether, ethanol, petroleum ether, and acetonitrile were purchased from PANREAC.

the 4 - 2 :Scheme 1 :

 421 Scheme 2: MFA chemical synthesis processThe13 C NMR spectrum of MFA, presents main chemical signals at:δ= 42,51, 55.43,

3 :

 3 Scheme 3: Chemical synthesis of OMFA oligomerThe analysis of the 1 H and13 C NMR spectra of the modified oligomer confirmed that

  Figure 7 shows the weight loss versus temperature of OMPA and OMFA. Both oligomers present small weight loss (at around 10%) under 247°C, which is, most probably, due to the departure of residual solvents used in the synthesis part and also unreacted used substance under chemical reactions. Until T1= 485 °C a second stability level for OMPA is observed, the insertion of the dimethyl acetal chemical group induces the decrease of the T 1 from 485 °C to 440 °C due to the degradation of the dimethyl-amine moiety from the backbone of the oligomer. Finally, fast degradation is observed under 485 °C for OMPA and 440°C for OMFA and until at around 600°C. It is seen that the use of the partial insertion of the chemical CH 3 -N-CH 3 induces a slight decrease in the stability of the oligomer.

  For 5-MPA optimized structure, HOMO and LUMO are localized on different sites on the chemical structure. Under the insertion of the dimethyl-amine group, the HOMO and LUMO distributions change. The HOMO localizes essentially on the dimethyl-amine group and in the grafted corresponding phenyl ring (See Figure8), while the LUMO localizes on the other part of the molecule. On the molecule containing the donor-acceptor system, HOMO electron distributions are localized on the donor fragment, while LUMO ones are localized on acceptor fragments[32][33]. These trends suggest that the insertion of dimethyl units localizes a donor fragment near the modified phenyl ring, and the acceptor one on the other side of the molecule. The change of the local distribution induces an increase of E HOMO and a decrease of E LUMO , and the energy gap E H-L = E HOMO -E LUMO decreases from 3.14 to 2.37 eV (see Table

  Table 2 indicate that DFT/LSDA/6-311G (d, p) overestimates the E HOMO , E LUMO , and the energy gap E H-L = E HOMO -E LUMO . Similar observations are found for unmodified OMPA[14]. In Figure8, we present the optimized chemical structure of OMPA and OMFA using DFT/LSDA/6-311G(d,p). Based on the optimized OMFA chemical structure, the theoretical infrared spectrum is computed by DFT/LSDA/6-311G(d,p). As it is

Acknowledgments

This work has been supported by the Tunisian-French cooperative action CMCU/07G1309. The authors are grateful to Dr. F. Massuyeau for their help in experimental measurements at IMN Nantes. France. The authors acknowledge Bordeaux University's High-Performance Computing Center(http://theo.ism.u-bordeaux1.fr/overview.php) for supporting theoretical calculations done in this work


PhD Jean-Marc M Roussel
email: jean-marc.roussel@inrae.fr

Guillaume Longin

Guy Fontenelle

Louis Bonneau De Beaufort

Chrystelle Delord

Sophie Launey

Raphaelle Rinaldo

Gilles Lassalle

Pierre-Yves Le Bail

Bonneau De

Le Bail

When subsistence fishing meets conservation issues: survey of a small fishery in a neotropical river with high biodiversity value

Keywords: French Guiana, inland fishery survey, catch per unit effort, fish size, resource decrease French Guiana, inland fishery survey, catch per unit effort, fish size, resource decrease

The inland fisheries sector is central for subsistence in many regions worldwide. The exploitation of fish resources is expected to increase along with the growing human population, with underlying conservation issues in regions with high biodiversity value. The small fishery of the Maroni River, French Guiana, is a hotspot of biodiversity and endemism where resource depletion is suspected. We surveyed 754 boat landings in seven villages located in the upper half of the watershed, representing > 6,300 fish during the study period (November 2013 -September 2014). Fishers used canoes with outboard engines almost exclusively (75%) and fished within 32 km of their villages. Most fish were caught in trammel nets (81%); the 20 most-landed species represented more than 87% of catches. Depending on the village, daily catches and biomass averaged 6-14 fish and 1.7-13 kg per boat landing, respectively. Seven control sites located outside of the fishing grounds were fished to identify potential differences in catch per unit effort and fish size. Per 100 m2 of trammel net, mean catches ranged from 4-13 and 8-29 fish in the villages and control sites, respectively, while fish biomass ranged from 0.9-4 and 3.2-7 kg in villages and control sites, respectively. For all species combined, fish caught at control sites were bigger than those landed in villages. This difference was significant for nine of the most-landed species. Differences in fishing techniques and fish catches between villages illustrated the gradual disappearance of the ancestral subsistence fishing. Our results support indications that the fish community in the upper Maroni River is harvested intensively, address the issue of sustainability of the fishery there, and call attention to the need to conserve the river's remarkable biodiversity.

Introduction

Small-scale fisheries are an important part of the fisheries sector in coastal marine areas and freshwater [START_REF] Allison | The livelihoods approach and management of small-scale fisheries[END_REF]FAO, 2008). They provide many human communities with animal protein and income (FAO, 2008;[START_REF] Béné | Are fishers poor or vulnerable? Assessing economic vulnerability in smallscale fisheries[END_REF][START_REF] Hallwass | Fishing Effort and Catch Composition of Urban Market & rural villages in Brazilia, Amazon[END_REF], but they remain difficult to survey. They are usually based on several fish species, many fishing techniques, and a variety of landing sites, which make it challenging to monitor them [START_REF] Salas | Challenges in the assessment and management of small-scale fisheries in Latin America and the Caribbean[END_REF][START_REF] Chuenpagdee | Small is beautiful? A database approach for global assessment of small-scale fisheries[END_REF][START_REF] Castello | Accounting for heterogeneity in small-scale fisheries management: The Amazon case[END_REF]. The lack of essential information, such as fishing pressure and fish stocks, is a clear limitation to developing a sustainable approach to small-scale fisheries [START_REF] Dimitriadis | A rapid assessment of trends in the multispecies small-scale fishery of Palamos (Catalonia, Spain)[END_REF]. Usually, no data on regular landings (e.g., logbooks, samples, and statistics) exist to assess fish stocks or forecast fishing strategies, unlike the large amount of data collected for larger commercial fisheries worldwide [START_REF] Hilborn | Quantitative Fisheries Stock Assessment: Choice, Dynamics and Uncertainty[END_REF][START_REF] Gray | Evaluation of fishery-dependent sampling for monitoring a small-scale beach clam fishery[END_REF]. In addition, conventional fisheries science often fails to address small fisheries because their social context is usually complex [START_REF] Berkes | Alternatives to Conventional Management -Lessons from Small-Scale Fisheries[END_REF], notably in poor or developing countries where subsistence fishing may occur.

Subsistence fishing is defined as an activity that meets the nutritional needs of the fishers, its family and eventually the community where he lives. It usually involves low-technology gears, which may be part of traditional or cultural practices, and it is not primary conducted for commercial purpose [START_REF] Berkes | Alternatives directions and methods[END_REF]. The current context of globalization, however, enhances new eating habits and the use of more efficient fishing gears such as trammel nets and motor boats. In that case, the sale of fish surplus to obtain money in return can be more regularly observed, and the line between subsistence and commercial fishing becomes blurred. For instance, small inland fisheries are key sources of food for many people along large tropical rivers [START_REF] Mosepele | Classical Fisheries Theory and Inland (Floodplain) Fisheries Management; Is there need for a paradigm shift. Lessons from the Okavango Delta, Botswana[END_REF][START_REF] Begossi | Small-scale fisheries in Latin America: Management Models and Challenges[END_REF][START_REF] Welcomme | Inland capture fisheries[END_REF], but some communities have started to shift toward the consumption of commercial food products and progressively left subsistence fishing for commercial fishing. Therefore, ensuring the sustainability of these small inland fisheries requires understanding the processes that occur during the transition from ancestral to modern lifestyle and their consequences on fish stocks.

Tropical regions host many endemic species and high biodiversity [START_REF] Abell | Freshwater Ecoregions of the World: A New Map of Biogeographic Units for Freshwater Biodiversity Conservation[END_REF], which reinforces the need to manage the inland fisheries sustainably for conservation. On the Maroni River in French Guiana, the small inland fishery faces the challenges of modernization, resource decrease, and conservation issues. The watershed hosts 264 strictly freshwater fish species, of which 17% are endemic [START_REF] Bail | Updated checklist of the freshwater and estuarine fishes of French Guiana[END_REF]. Nearly 60 of these species are regularly fished, of which 20 are endemic. Despite the high biodiversity value of these fish communities, the fishing pressure there has never been assessed, and no data exist on fish stocks and their dynamics. Part of native people still depend on fish resources for their daily diet, and several villages and communities are aware of the risk of declining resources, and the potential threat to food availability in the future [START_REF] Longin | Fishers' perceptions of river resources: case study of French Guiana native populations using contextual cognitive mapping[END_REF]. Consequently, Parc Amazonien de Guyane (the French national park of Amazonia), which manages this territory, is currently unable develop suitable management policies to protect fish resources and ensure subsistence fishing for people living along the Maroni River.

The present study aimed to define the small fishery of the upper Maroni River (UMR) by bridging the information gap between fish resources and fishing activity. To do so, a conventional fisheries survey (e.g., [START_REF] Pido | A rapid appraisal approach to evaluation of community-level fisheries management systems: Framework and field application at selected coastal fishing villages in the Philippines and Indonesia[END_REF][START_REF] Rochet | Ecosystem trends: evidence for agreement between fishers' perceptions and scientific information[END_REF][START_REF] Cerdeira | Fish catches among riverside communities around Lago Grande de Monte Alegre, Lower Amazon, Brazil[END_REF][START_REF] Hallwass | Fishing Effort and Catch Composition of Urban Market & rural villages in Brazilia, Amazon[END_REF][START_REF] Hallwass | Fishers' knowledge identifies environmental changes & fish abundance trends in impounded tropical rivers[END_REF] was combined with participatory monitoring (e.g., [START_REF] Ticheler | Participation of local fishermen in scientific fisheries data collection: a case study from the Bangweulu Swamps, Zambia[END_REF][START_REF] Silvano | Beyond fishermen's tales: contributions of fishers' local ecological knowledge to fish ecology and fisheries management[END_REF][START_REF] Rochet | Ecosystem trends: evidence for agreement between fishers' perceptions and scientific information[END_REF][START_REF] Hallwass | Fishing Effort and Catch Composition of Urban Market & rural villages in Brazilia, Amazon[END_REF][START_REF] Hallwass | Fishers' knowledge identifies environmental changes & fish abundance trends in impounded tropical rivers[END_REF] that included native fishers. Our objectives were to map the fishing grounds of several villages in the UMR, and analyze the abundance and biomass of fish landed, as well as their seasonal variability per species. We estimated potential impacts of the fishery on fish populations by assessing differences in the catch per unit effort (CPUE based on surface of trammel nets) and size of catches between villages and remote, control sites located outside the fishing grounds.

We also explored the transition from ancestral to modern lifestyles by comparing the two major indigenous communities in the UMR: the native Amerindian, who still have a subsistence lifestyle, and the Bushinengue, descendants of African slaves who escaped and established independent communities, and who recently began to adopt a modern lifestyle [START_REF] Delpech | Les Aluku de Guyane à un tournant de l'économie de subsistance à la société de consommation[END_REF].

Methods

Study area

The study was performed in the UMR, a river 610 km long that flows between Suriname and French Guiana (Fig. 1). Approximately 5,500 people live in Maripasoula City, the main town in the region, including natives from several communities and Europeans. The commune of Maripasoula City has a regional airport, and food stores are supplied by plane from Cayenne, the capital of French Guiana. Daily fishing activity is low in Maripasoula City, and fish landings are difficult to monitor due to the scattered distribution of landing locations. Conversely, daily fishing activities occur in 21 small villages located along the UMR. Two communities live in the area: Bushinengue (Aluku ethnic group) and Amerindians (Wayana and Teko ethnic groups), who live downstream and upstream of Maripasoula City, respectively. Bushinengue fishers have access to the zone of Abattis Cottica (Fig. 1), which is known to be a productive, fish-rich area (Le Bail, personal communication). After reaching agreement with the traditional chiefs, we selected seven villages to represent these ethnic groups and the hydromorphological characteristics of the UMR watershed (Fig. 1). The landings of 134 fishers (101 Amerindians, 33 Bushinengue, i.e., 55% of the fisher population) were surveyed from November 2013 to September 2014 (Supplementary Table S1).

Data collection

The survey focused on fishing trips that lasted a maximum of 24 h (hereafter, "one-day fishing trips"). We did not consider other techniques, such as traditional poisoning using a substance derived from lianas or multi-day fishing expeditions, which occur on an occasional basis only [START_REF] Longin | Fishers' perceptions of river resources: case study of French Guiana native populations using contextual cognitive mapping[END_REF]. The survey included four 15-day sampling periods: in November, to represent the end of the long dry season; in February, to represent the end of the short wet season; in May-June, for the middle of the wet season; and at the end of August, for the beginning of the long dry season. To describe all fishing activity adequately, we hired one fisher in each village to act as his village's advisor. The advisor's role was to collect information on daily catches during the four periods of the survey. Advisors were trained for 1-3 days to become comfortable with following the protocol.

For each boat landing, the power of the engine was noted, and the fisher was asked to locate his fishing ground on a grid map (5 km × 5 km squares) with toponyms. The type and number of fishing gear in the boat were noted: nets (gillnet or trammel), active lines (hand-held line, wooden cane, rod and reel), sight fishing (trident, bow, spearfishing gun, cast-net), or passive gear (baited traps, longlines). Length, height, and mesh size were noted for nets, and the actual fishing period (day only, night only, or 24 h) was noted for each type of fishing gear. The advisor then detailed the daily catches. Each fish was taxonomically identified to the species level using a practical illustrated booklet with the 61 largest species living in the Maroni River, based on information from [START_REF] Planquette | Atlas des Poissons d'Eau douce de Guyane (tome 1). Collection Patrimoines Naturel[END_REF], [START_REF] Keith | Atlas des Poissons d'Eau douce de Guyane. Tome 2, Fascicule I: Batrachoidiformes, Mugiliformes, Beloniformes, Cyprinodontiformes, Synbranchiformes, Perciformes, Pleuronectiformes, Tetraodontiformes[END_REF], [START_REF] Bail | Atlas des poissons d'eau douce de Guyane. Tome 2, Fascicule II: Siluriformes[END_REF], and Le [START_REF] Bail | Updated checklist of the freshwater and estuarine fishes of French Guiana[END_REF]. Correspondence between scientific names and the Aluku, Wayana and Teko common names was based on [START_REF] Grenand | Revision of vernacular names for the freshwater fish of French Guiana[END_REF]. Then, fish total length (nearest cm, from fish nose to end of caudal fin) and weight (nearest dg) were measured using a measuring tape and spring balance, respectively.

Seven control sites located on major tributaries of the UMR (i.e., Litani, Marouini, Tampok, and Waki) were surveyed from August 2014 to March 2016 to estimate impacts of the fishery on fish populations. A minimum of two days of travel by boat was required to access each control site from the nearest village, including exiting the water to pass rapids. Since there was no other village in the vicinity, we assumed that fishing pressure was very low compared to sites around villages. The control sites (Fig. 1) were: Apsik Icholi and Eléüéletpe (64 and 96 km upstream of Pidima village, respectively), Langa Soula and Wayo Gaan Soula (90 and 126 km upstream of Antecume-Pata village, respectively), Saut Tampok and Saut Pierkourou (33 and 130 km upstream of Kayodé village, respectively) and Saut l'Inspecteur (74 km upstream of Kayodé). Four to five consecutive nights of sampling were performed at each site, where nearly 1 km of river was prospected. The fish community was fished using trammel nets, which were set in the evening and checked in the morning. Nets (1.5-2.0 m high, length >30m, 6-22 cm inner-outer panels mesh size) were chosen to match with characteristics of prevalent trammel nets used by fishers in villages, for subsequent comparisons. Nets were positioned in deep or in shallow zones, with very low flow or close to turbulent areas, parallel or perpendicular to the bankside to cover the range of aquatic habitats available. The sampling effort, expressed as the cumulative length of trammel nets set at night, was 860 m, 1,120 m, 1,470 m and 1,690 m respectively on Waki, Litani, Tampok and Marouini. Each fish was taxonomically identified to the species level, then measured (nearest mm) and weighed (nearest g).

Data analysis

Only eight boat landings corresponded to 24h fishing trips; the corresponding data were not considered in subsequent analysis. Chi-squared tests were performed to identify significant differences in numbers of one-day fishing trips between seasons and between communities.

Data were analyzed to identify the 20 most abundant fish species landed in the fishery.

Confusion was suspected between Myloplus rubripinnis and M. ternetzi at landing, so the two species were considered as a single group (M. rubripinnis/ternetzi) for the rest of the analysis.

Based on fishing grounds reported by fishers on the grid map, catches located within a 10 km radius of each other were then combined to perform maps of catches. For each species, lengthweight curves were plotted; erroneous records, i.e., individuals showing obvious mismatch between length and weight data, were discarded (1% of data). Moreover, 8% of the fish were gutted before landing, and we used the length/weight curves to estimate total weight of the fish.

Data from trammel nets of similar size (6-22 cm inner-outer panels mesh size, 1.5-2.0 m high, length >30m) that were set at night were used to compare the catches of villages and control sites. The number of catches was converted into CPUE (i.e., number or biomass of fish caught per 100 m 2 of trammel net per night) for all species pooled. Although the advisors in each village were trained to collect data, fish body-length data were marginally biased since the caudal fin was sometimes excluded. Thus, fish weight data was preferred for subsequent analyses. For all sites combined, fish body-weight distributions by species were divided into three equal thirds (small, medium, and large fish), and the percentage of individuals in each of the three categories was calculated for each species. Data were then aggregated (all species combined) to assess differences in fish weight between villages and control sites. Differences in fish body-weight between village and control sites were also compared by species when catches of a species reached at least 100 fish in village and 100 fish in control site (sites combined) and were distributed equally among seasons. Non-parametric Wilcoxon rank-sum tests were performed to identify significant differences in species body-weight between village and control sites.

Results

Fishing grounds

A total of 647 Amerindian and 107 Bushinengue boat landings were surveyed (Supplementary Table S1). On average, Amerindians traveled a maximum distance of 16.5 km (ca. 45 min depending on the flow and outboard engine power) vs. 32.5 km for Bushinengues (90 min).

Bushinengue and Amerindian fishing grounds did not overlap (Fig. 1). Fishing grounds of Loca and Papaïchton were completely intertwined and included the zone of Abattis Cottica.

Conversely, Amerindian fishers preferred fishing grounds within 5-10 km of their villages. Some Amerindian fishing grounds overlapped, except for fishers from Kayodé, who fished only the Waki and Tampok Rivers (Fig. 1).

Fishing techniques

Regardless of the community, 75% of one-day fishing trips were performed using canoes with outboard engines, most of which were 10-25 horsepower, although a few were 40-60 horsepower (Supplementary Fig. S2). The Bushinengues rarely used paddling (5% on average), which the Amerindians used slightly more often (17% on average) to reach fishing grounds near their village, especially in Pidima, Antecume-Pata, and Twenké. Fishers favored the use of nets (81%) and passive gears (10%), active lines and sight fishing being less observed (Supplementary Fig. S2). Passive gears were more frequently used in Kayodé (28% of the fishing technics reported), while sight fishing was mostly observed in Twenké (17% of the fishing technics). The trammel net was the most popular fishing gear; both the Bushinengue and Amerindian communities used 30-50 m long trammel nets of 1.5-2 m high and 6-22 cm (inner-outer panels) mesh size.

The average number of one-day fishing trips per fisher was similar for Amerindians and Bushinengues (Supplementary Fig. S3), but the frequency varied greatly among the fishers: some fished almost every day (up to 6 days per week), while others fished less than once per week. The number of one-day fishing trips did not differ among seasons (Chi-squared test, p=0.83, Supplementary Fig. S3). Amerindians tended to fish equally at night (55%) or during the daytime (45%), while the Bushinengues preferred to fish at night (72%) (Supplementary Fig. S3). Night fishing trips lasted ca. 12 h, which generally corresponds to the duration of night at the UMR's latitude; fishers usually set trammel nets at dusk and picked them up at dawn.

Fish catches

The villages landed 63 species throughout the study period, representing 6,366 individual fish.

The 20 most-landed species represented 87% of individual fish landed (Fig. 2, and see Online Supplementary Appendix B for a brief description of each species), of which Pseudancistrus barbatus alone represented more than 12% of all catches (in number). Overall, 59% of all catches came from three fish families: Serrasalmidae (25% -Myloplus rubripinnis/ternetzi, Myloplus rhomboidalis, Myloplus planquettei, Tometes lebaili, Serrasalmus rhombeus, Acnodon oligacanthus), Doradidae (19% -Platydoras costatus, Doras micropoeus), and Loricariidae (16% -P. barbatus, Hemiancistrus medians, Hypostomus gymnorhynchus). The large fish Hoplias aimara represented 33% of biomass landed (but only 4% of numbers), while all species of Serrasalmidae, Doradidae, and Loricariidae represented 24%, 8% and 4% of the biomass landed, respectively. For all species combined, nets caught 81% of the fish. However, some species were caught mainly with other techniques, such as Hemisorubim platyrhynchos (68% by longline), M. planquettei (76% by rod and reel, and 11% by spearfishing gun), H. aimara (41% by baited traps), A. oligacanthus and H. gymnorhynchus (19% and 15%, respectively, by cast-net), and T. lebaili (25% by spearfishing gun). Among the 20 most-landed species, 7 were caught more during the dry season, 9 during the wet season, and 4 species were caught evenly in all seasons (Fig. 3).

Differences in catches between villages and communities

Amerindians landed 77% of all catches during the survey (Fig. 4), using mostly nets (78% of catches, of which 96% were with trammel nets), passive gears (11%, essentially longlines) active lines (6%), and sight fishing (5%). Bushinengues caught fish using mostly nets (90%, of which 93% were with trammel nets), passive gears (7%, essentially traps) and active lines (3%), and but never sight fishing. For all fishing techniques combined, the mean number of catches per boat landing ranged from 6-9 fish in Amerindian villages vs. 13-14 fish in Bushinengue villages (Supplementary Table S4). During the entire survey, 2,929 kg of fish was landed in total (1,943 kg, i.e. 3.0 kg per boat landing by Amerindian, and 986 kg, i.e. 9.2 kg per boat landing by Bushinengue) (Fig. 4). Fishers from the Bushinengue village of Papaïchton landed the largest fish biomass per one-day fishing trip (13 kg), while other villages landed a mean of 1.7-4.0 kg (Supplementary Table S4). Amerindians used mainly nets (47%), active lines (13%), longlines (35%), and sight fishing (5%) to catch the biomass they landed, while Bushinengues used mainly nets (56%), traps (39%), and active lines (5%) to catch the biomass they landed.

H. aimara represented 24% and 50% of the fish biomass landed by Amerindians and Bushinengues, respectively, and Bushinengues often caught them with baited traps (54%). Both communities successfully used active lines to capture other large fish species (e.g. T. lebaili, M. planquettei, M. rhomboidalis, S. rhombeus, B. falcatus) (33% and 8% of the biomass landed by Amerindians and Bushinengues, respectively). Amerindians specifically targeted H. platyrhynchos using longlines and H. gymnorhynchus using cast-nets. Amerindians used sightfishing techniques to catch 25% of the biomass of A. oligacanthus and T. lebaili.

CPUE and fish body-weight

The mean area of trammel nets set at night ranged from 72 to 171 m² in Amerindian villages (for Pidima and Kayodé, respectively) but reached 338 and 385 m² in the Bushinengue villages of Papaïchton and Loca, respectively (Supplementary Fig. S3 and Table S5). However, the lowest CPUEs (4-7 fish per 100 m 2 of trammel net) were recorded at Loca, Papaïchton, and Kayodé, while a mean of 8-13 fish per 100 m 2 of trammel net were caught in other Amerindian villages (Fig. 5A, Supplementary Table S5). In comparison, the CPUE at control sites ranged from 8-29 fish per 100 m 2 of trammel net (Fig. 5A, Supplementary Table S5). For biomass, the lowest yield was recorded at Loca and the highest at Papaïchton (0.9 and 4.0 kg of fish per 100 m 2 of trammel net, respectively), while the yields for Amerindian villages showed intermediate values (1.5-3.1 kg). Yields ranged from 3.2-7.0 kg per 100 m 2 of trammel net at the control sites (Fig. 5B, Supplementary Table S5).

For all fish species combined, fish caught by trammel nets at control sites tended to be larger than fish landed in villages (Fig. 5C) except for Papaïchton and Kayodé. Thirteen species were caught in sufficient numbers to compare fish CPUE and body-weight between villages and control sites (Fig. 6). No significant difference (Wilcoxon test, p>0.05) was found for five species (Ageneiosus enermis, Doras micropoeus, H. gymnorhynchus, Leporinus friderici, S. rhombeus); other eight species were significantly lighter (p<0.05, Wilcoxon test) around villages than at control sites (Fig. 6). Mean body mass was particularly lower around villages for Brycon falcatus (-146 g, i.e. 32% lower), Cynodon meionactis (-41 g, 24% lower), M. rhomboidalis (-400 g, 64% lower), P. costatus (-179 g, 47% lower), P. barbatus (-28 g, 26% lower), and Semaprochilodus varii (-373 g, 56% lower). Weight differences were also significant but less pronounced for M. rubripinnis/ternetzi and H. aimara (Fig. 6).

Discussion

Fish species richness in the tropical freshwater of Southeast Asia, Africa, and South America is among the highest worldwide [START_REF] Abell | Freshwater Ecoregions of the World: A New Map of Biogeographic Units for Freshwater Biodiversity Conservation[END_REF], which creates regional hotspots with high biodiversity value and conservation issues. Studies have shown causal correlations between biodiversity and ecosystem services [START_REF] Tittensor | A mid-term analysis of progress toward international biodiversity targets[END_REF], and conservation plans commonly focus on both issues. Among important ecosystem services, inland fisheries provide low-cost protein in areas where alternative food sources and employment are infrequent. Poor or developing nations generally rely the most on these inland fisheries, among which the importance of high-yield river fisheries has been demonstrated [START_REF] Mcintyre | Linking freshwater fishery management to global food security and biodiversity conservation[END_REF]. Such small fisheries are challenging to study, however, since they involve many fishers, fishing techniques, landing sites and fish species [START_REF] Salas | Challenges in the assessment and management of small-scale fisheries in Latin America and the Caribbean[END_REF][START_REF] Chuenpagdee | Small is beautiful? A database approach for global assessment of small-scale fisheries[END_REF][START_REF] Castello | Accounting for heterogeneity in small-scale fisheries management: The Amazon case[END_REF]. In addition to ongoing environmental threats (e.g., habitat loss, pollution, climate change), intensive harvesting of the most biodiverse rivers is a major concern for the conservation and sustainability of these fisheries. Usually, no data on regular landings (e.g., logbooks) exist, as they do for commercial fisheries worldwide, and in the best cases, coarse description of fisheries precludes rigorous assessment of effects of fishing on natural resources [START_REF] De Graaf | The scale of inland fisheries, can we do better? Alternative approaches for assessment[END_REF].

The upper Maroni River (UMR) is a good example of a small continental fishery that provides subsistence fishing in a context of high biodiversity, including conservation issues and suspected resource depletion. Traditional fishing techniques are documented for the UMR fishery [START_REF] Hurault | Extrait de lettres au Sous-Préfet de Saint-Laurent-du-Maroni[END_REF][START_REF] Martin | La proie, l'animal personne ou l'ennemi des hommes: nommer, classer, penser et se nourrir d'animaux sur le haut-Maroni des Wayana (Guyane française)[END_REF], but information on the fishery remains mostly in narrative form and geographically limited [START_REF] Moretti | Les nivrées ou plantes ichtyotoxiques de la Guyane française[END_REF][START_REF] Chapuis | La personne wayana entre sang et ciel[END_REF][START_REF] Pagezy | Valeur patrimoniale de Serrasalminae hervivores du Haut Maroni (Guyane française) : approches biologiques et socioculturelles en pays wayana[END_REF][START_REF] Froese | Keep it simple: three indicators to deal with overfishing[END_REF][START_REF] Richard-Hansen | Mise en place d'un Observatoire de l'exploitation des ressources naturelles dans le sud de la Guyane[END_REF][START_REF] Martin | La proie, l'animal personne ou l'ennemi des hommes: nommer, classer, penser et se nourrir d'animaux sur le haut-Maroni des Wayana (Guyane française)[END_REF]. Therefore, our detailed description of the fishery of the Bushinengue and Amerindian communities could serve as a baseline for future monitoring in the following decades. By combining a conventional survey and participatory monitoring of native fishers, we assessed potential impacts on fish stocks by comparing yield inside and outside the boundaries of the UMR fishery. For all species combined, fish abundance per unit effort was lowest in villages in which large linear nets were set up, especially Loca, Papaïchton, and Kayodé. Similarly, fish biomass per unit effort was lower around villages than at control sites. This apparent decrease in yield in the fishing grounds could indicate intensive harvest, but the causal correlation between fishing pressure and fish abundance is not elucidated here since we did not consider other environmental pressures (e.g., poor water quality, habitat degradation), which could have decreased fish abundance around villages [START_REF] Longin | Fishers' perceptions of river resources: case study of French Guiana native populations using contextual cognitive mapping[END_REF].

Moreover, the dominant species in catches may differ among fishing grounds based on their habitat preferences, behavior, and the season. For instance, Prochilodus rubrotaeniatus uses to move to feeding grounds downstream [START_REF] Agostinho | Ecologia e Manejo de Recursos Pesqueiros em Reservatorios, Notas de estudo de Ecologia. Universidade Federal Rural de Pernambuco (UFRPE)[END_REF], and H. medians remains within fast-flowing habitats (Le [START_REF] Bail | Atlas des poissons d'eau douce de Guyane. Tome 2, Fascicule II: Siluriformes[END_REF] that are more frequent downstream of Loca and Papaïchton in the Abattis Cottica (Fig. 1). D. carinatus, L. friderici, and M. rubripinnis preferred lentic environments (authors' personal observation; [START_REF] Boujard | Growth in four populations of Leporinus friderici (Bloch, 1794) (Anostomidae, Teleostei) in French Guiana[END_REF][START_REF] Planquette | Atlas des Poissons d'Eau douce de Guyane (tome 1). Collection Patrimoines Naturel[END_REF], which are more common around Elahé and Kayodé. Indeed, caution is necessary when analyzing aggregated yield data since they are difficult to understand in multispecies fisheries [START_REF] Lorenzen | Aggregated yield and fishing effort in multispecies fisheries: an empirical analysis[END_REF]. In our case, catch per unit effort data by species was not possible since many zero values (i.e., each species was caught in a small number of nets only) in the data hampered analysis of differences between villages and control sites.

Analyzing differences in fish body-weight revealed an additional sign of intensive harvest in the UMR fishery. Several studies support that prolonged periods of exploitation are associated with both a decline in fish catches and fish size [START_REF] Haedrich | Changes over time of the size structure in an exploited shelf fish community[END_REF][START_REF] Froese | Keep it simple: three indicators to deal with overfishing[END_REF][START_REF] Hutchings | Life history consequences of overexploitation to population recovery in Northwest Atlantic cod (Gadus morhua)[END_REF]. Theoretical and empirical studies also illustrate how life history traits can be reshaped in harvested fish populations, notably toward slower somatic growth, smaller body size and earlier maturation of individuals [START_REF] Bouffet-Halle | Density-dependent natural selection mediates harvestinduced trait changes[END_REF]. All species combined, we found a decrease in fish weight classes, especially around the Amerindian villages of Pidima, Antecume-Pata, Twenké, and Elahé (Fig. 5). This general trend was confirmed by the analysis of spatial differences in body-weight by species. Differences were particularly obvious for the large and highly targeted M. rhomboidalis; fishers rarely landed large individuals (>0.5 kg), while large individuals represented half of the captures of this species outside the fishery grounds. Individuals of another highly targeted but small species, P. barbatus, were 25% lighter around villages than outside the fishery grounds. Similar patterns were observed for B. falcatus and P. costatus, which also suggests that these species are harvested intensively. Converging patterns of body-size declines were reported for other neotropical freshwater fish species, including Prochilodus nigricans (Bonilla-Castilo et al., 2018), Arapaima sp. (Castello et al., 2011b), and several species of Loricariidae, Pimelodidae, Scianidae and Serrasalmidae (Castello et al., 2011a). In the Maroni River, H. aimara was the largest fish species landed. It was smaller on fishing grounds too, even if the difference with control sites was not as stronger as anticipated for this popular species. The influence of a strong exploitation on H. aimara body weight could have been masked, however, by the presence of larger individuals in large downstream habitats, which are more suitable for this predatory species.

The case of S. varii seems different: small fish were caught almost only inside the fishery grounds, suggesting a different age-class distribution across the survey areas. For instance, a closely related species that lives in the Amazon watershed, S. insignis, is a migratory species that spawns in floodplains [START_REF] Araujo-Lima | Chapter 6 -Migratory Fishes of the Brazilian Amazon[END_REF][START_REF] Goulding | Ecosystembased management of Amazon fisheries and wetlands[END_REF]. For other species such as A. inermis and L. frederici, however, body weight did not differ between villages and control sites. They were caught mainly during the rainy season, when they reach flooded forests for feeding [START_REF] Agostinho | Ecologia e Manejo de Recursos Pesqueiros em Reservatorios, Notas de estudo de Ecologia. Universidade Federal Rural de Pernambuco (UFRPE)[END_REF], and it is possible that long-distance movements of individuals between village and control sites decreased differences in body weight. Moreover, H. gymnorhynchus is a small species (<20 cm long) with an elongated shape that is difficult to capture with nets so results for it should be considered with caution. Finally, fishers do not target S. rhombeus, an aggressive piranha that lives in deep habitats, because it is dangerous and causes serious damage to nets. Therefore, fishing pressure on it would be too low inside the fishery grounds to cause differences in body weight.

For several reasons, the exploitation rate in small-scale fisheries is expected to increase.

Poor communities depend more on freshwater fisheries than on marine or aquaculture sources [START_REF] Mcintyre | Linking freshwater fishery management to global food security and biodiversity conservation[END_REF], and the growing population generally increases pressure on natural resources. Moreover, there is a general trend for more efficient techniques, and motor boats and nets are replacing traditional techniques [START_REF] Isaac | A pesca no Baixo Amazonas[END_REF]Castello et al., 2011a;[START_REF] Hallwass | Fishing Effort and Catch Composition of Urban Market & rural villages in Brazilia, Amazon[END_REF]. During our investigations on the UMR, we observed traditional gear in fishers' homes, such as bows and arrows, spears, wooden traps, and canes, but they rarely used them.

Comparing the Amerindian (Wayana and Teko) and Bushinengue (Aluku) communities in the UMR illustrates this rapid transition from ancestral to modern lifestyles in French Guiana.

Bushinengue began adopting a modern lifestyle before Amerindian did. They rarely used paddling and preferred motor boats to reach distant fishing grounds during one-day fishing trips. They usually used trammel nets and caught more fish per fishing trip, but captured the fewest fish per unit area of trammel net. Despite the intense fishing pressure in this community, fish are no longer a main source of protein in the Bushinengue diet [START_REF] Longin | Fishers' perceptions of river resources: case study of French Guiana native populations using contextual cognitive mapping[END_REF].

Bushinengue live in large villages of more than 1,000 inhabitants (Loca has ca. 1200 and Papaïchton 2900), and fishers represented less than 2% of the population (Supplementary Table S1). The annual biomass of landed fish extrapolated from our data is ca. 14 t, i.e., 10 g per person per day. This low intake of animal protein from the river indicates that the Bushinengue diet has mostly shifted toward imported and/or processed food, and that subsistence fishing has mostly disappeared in their community. Conversely, Amerindians live in smaller villages (35-180 inhabitants) in which fishers represent nearly 30% of the population, which indicates that each family still eats fish from the fishery. The same extrapolation results in an annual biomass of landed fish of 27 t, i.e., 115 g per person per day. Protein intake from the river remains substantial, but has obviously decreased since the early 1960s, when [START_REF] Hurault | La vie matérielle des Noirs réfugiés Boni et des Indiens Wayana du Haut-Maroni[END_REF] reported that the Amerindian Wayana ate 200-560 g of fish per person per day, depending on the season.

Nevertheless, many native people in the UMR region still depend on fish resources from the river for their daily diet, and they are increasingly concerned about the risk of overexploitation and resource depletion [START_REF] Longin | Fishers' perceptions of river resources: case study of French Guiana native populations using contextual cognitive mapping[END_REF].

Conclusion

Our investigation confirms that a high fishing pressure on fish populations in the UMR region is a plausible scenario. Most importantly, we found that yields were consistently low within the fishery grounds, and that some highly targeted species showed typical signs of a prolonged period of exploitation, especially a decrease in body weight. Our study focused only on oneday fishing pressure, but multi-day fishing trips are increasingly popular and are supported by powerful motor boats, generators, and freezers that allow fishers to go farther on the river and to store fish. Based on the continued increase in the human population (+6.2% per year from 2011[START_REF] Gray | Evaluation of fishery-dependent sampling for monitoring a small-scale beach clam fishery[END_REF], INSEE, 2019) ) and the shift from traditional fishing technics to modern and more efficient ones, indications that the fish community is harvested intensively should alert local authorities and managers. This seems to hold true even in the current context of the modernization of eating habits and progressive loss of subsistence fishing. Our results call attention to the need to conserve this unique biodiversity of the UMR, and they address the sustainability of the fishery there. The participatory approach that we used in this study has already informed fishers about the intensive pressure on fish resources from their river, the threat to their unique ecological heritage, and the need to set up management rules toward a sustainable fishery in the Maroni River.

Figure 1 .

 1 Figure 1. Fishery survey of the upper Maroni River (French Guiana). Control sites and fishing grounds that correspond to the maximum distance per one-day fishing trips around each village are shown.

Figure 2 .

 2 Figure 2. (A) Number of catches and (B) biomass landed for the 20 most-landed species by main type of fishing gear.

Figure 3 .

 3 Figure 3. Percentage of catches for the 20 most-landed species by season. Font colors indicate species caught mainly in the dry season (tan), wet season (blue), or throughout the year round (black).

Figure 4 .

 4 Figure 4. (A) Number of catches and (B) biomass landed by Bushinengue and Amerindian fishers by main type of fishing gear.

Figure 5 .

 5 Figure 5. Spatial distribution of all fish species caught with trammel nets in the village and control sites: (A) number of fish per 100 m² of net, (B) fish biomass (in kg) per 100 m² of net, and (C) fish body-mass classes. Circle sizes represent the number of captures used for calculations at each site.

Figure 6 .

 6 Figure 6. Individual body-weight of the 13 most-landed fish species at control sites (white) and village fishing grounds (gray). Error bars represent 1.5 times the interquartile range. Stars denote significant differences between village and control sites (Wilcoxon test; * p < 0.05; ** p < 0.01).

Figure

  Figure

Acknowledgements

Our thanks first go to all the Wayana, Teko, and Aluku fishers from villages in the upper Maroni River (Antecume-Pata, Elahé, Kayodé, Loca, Papaïchton, Pidima, Twenké, and Talwen) who agreed to contribute to the survey by showing their catches at landing and providing information on their fishing trips. This program would not have been possible without the strong involvement of the following group of advisors: Raymond Essimon (Pidima), Pitoma Mekouanali (Antecume-Pata), Sébastien Amaïpetit (Twenké), Etulano Yamo (Kayodé), Mones Tokotoko (Elahé), Marc Pinson and Alfred Dja-ba (Papaïchton). We are grateful to researchers who know French Guiana, with whom we were able to exchange knowledge during this study, and who provided us with valuable advice: Damien Davy (CNRS), Francis Dupuy, Marie Fleury (MNHN), Pierre Grenand, Marianne Palisse (Université de Guyane), Emmanuel Martin, Jean Moomou (Université des Antilles), and Cécile Richard (Office Français pour la Biodiversité). A friendly thanks to all colleagues who contributed to fish surveys at the control sites: Sébastien Le Reun, Régis Vigouroux (Hydreco), Raphaël Covain (MHNG), Jean-Luc Baglinière, Damien Fourcy, Catherine Le Penven, and Marie Nevoux (UMR ESE-INRAE).

Thanks to Pierre Joubert and Maïlys Le Noc (Parc Amazonien de Guyane) for compiling data.

Finally, this study would not have been possible without logistical support from the Parc Amazonien de Guyane or technical and translation assistance provided by Lanaki Cognat, Apaïkassi Nanuk, and Hervé Tolinga. This study was funded by the Parc Amazonien de Guyane under contract R&D-2003-06, with financial support from the DREAL and the Office de l'Eau de Guyane

Supplementary material for on-line publication only

Click here to access/download Supplementary material for on-line publication only FISH10476_AppendixB.pdf

Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:


Maria Sayu Yamamoto

Md Khadijeh Sadatnejad

Rabiul Islam

Fabien Lotte

Toshihisa Tanaka

Reliable outlier detection by spectral clustering on Riemannian manifold of EEG covariance matrix

teaching and research institutions in France or abroad, or from public or private research centers.

Reliable outlier detection by spectral clustering on Riemannian manifold of EEG covariance matrix

Maria Sayu Yamamoto 1,2* , Khadijeh Sadatnejad 1 , Md. Rabiul Islam 2 , Fabien Lotte 1 Toshihisa Tanaka 2 1 Inria Bordeaux Sud-Ouest, Talence, France; 2 Tokyo University of Agriculture and Technology, Koganei-shi, Japan *200 avenue de la Vieille Tour, 33405 Talence cedex, France. E-mail: yamamoto18@sip.tuat.ac.jp Introduction: Automatically identifying and rejecting artifact-contaminated trials is a key problem to design robust BCIs. Here, we propose a novel outlier detection method based on Riemannian Geometry (RG), a promising approach for BCI classification [START_REF] Yger | Riemannian approaches in brain-computer interfaces: a review[END_REF]. With RG, EEG signals are represented and processed as Sample Covariance Matrix (SCM), which is also known to reduce EEG artifacts influence. State-of-the-art outlier detection methods in RG include Riemannian Potato (RP) [START_REF] Barachant | The Riemannian potato: an automatic and adaptive artifact detection method for online experiments using Riemannian geometry[END_REF] and Median-Based Trimming (MBT) [START_REF] Uehara | Robust averaging of covariance matrices by Riemannian geometry for motor-imagery brain-computer interfacing[END_REF]. However, both suffer from the need of a threshold to determine outliers, and both always reject some samples as outliers, even when there is none. Thus, we propose Riemannian Spectral Clustering (RiSC), to detect outliers by clustering SCMs into non-outliers and outliers by similarity, without thresholds.

Material, Methods and Results: First, RiSC computes the graph of SCMs similarities using the Riemannian distance between SCMs. Then, the graph nodes are clustered using spectral clustering [START_REF] Luxburg | A Tutorial on Spectral Clustering[END_REF], and all clusters except the most numerous one are rejected as outliers. We compared the classification accuracy of a Minimum Distance to Mean classifier [START_REF] Yger | Riemannian approaches in brain-computer interfaces: a review[END_REF] without outlier rejection (baseline) and after rejecting outliers from each class training data using RP, MBT and RiSC. We used EEG signals from 78 subjects from [START_REF] Roc | Would Motor-Imagery based BCI user training benefit from more women experimenters? 8th Graz Brain-Computer Interface Conference[END_REF][START_REF] Jeunet | Why standard brain-computer interface (BCI) training protocols should be changed: an experimental study[END_REF], who performed right or left-hand motor imagery. The first two runs were used for training and the remaining runs for testing. Results showed no significant differences between methods (repeated measure ANOVA, p = 0.093). Mean classification accuracy (%) was 59.5±10.2, 59.8±10.1, 59.4±9.99 and 59.5±10.1 for the baseline, RiSC, RP and MBT respectively. RiSC did not detect any outlier for most (68 out of 78) subjects. However, when it removed outliers, this increased accuracy for all but one subject (mean gain: 2.39 ± 2.24 %). On the other hand, RP and MBT detected outliers in all subjects, but this decreased accuracy for 46 and 34 out of 78 subjects respectively. Discussion: RiSC did not detect outlier for most subjects, which may suggest EEG contamination was already reduced using SCM. Thus, RiSC might be useful on more contaminated data. Contrary to RP and MBT, RiSC did not inadvertently reduce accuracy by rejecting clean data as outliers. Significance: Describing EEG as SCMs and detecting their outliers by spectral clustering seem to be a robust method that usually does not lead to inadvertent decrease in classification accuracy.