Jérémy J Kiszka
email: jeremy.kiszka@gmail.com

Kevin Charlot

Nigel E Hussey

Michael R Heithaus

Benoit Simon-Bouhet

Frances Humber

Florence Caurant

Paco Bustamante

Jeremy J Kiszka
email: jeremykiszka@gmail.com

Benoit Simon- Bouhet

Trophic ecology of common elasmobranchs exploited by artisanal shark fisheries off south-western Madagascar inferred from stable isotopes

Keywords: artisanal fisheries, sharks, trophic ecology, δ 15 N, δ 13 C, ontogenetic shift, sex differences

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Predicting the community-level consequences of changes in the abundance of a particular species, due to natural or anthropogenic factors, requires an understanding of its trophic interactions and trophic similarity amongst species (i.e. the level of trophic redundancy). In both terrestrial and marine environments, the removal of predators across multiple trophic levels has been shown to disrupt ecosystem function (reviewed in [START_REF] Estes | Trophic downgrading of planet earth[END_REF]. Declines of top marine predators, such as sharks, have been widely documented [START_REF] Ferretti | Patterns and ecosystem consequences of shark declines in the ocean[END_REF] and have raised international concern [START_REF] Dulvy | You can swim but you can't hide: the global status of and conservation of pelagic sharks and rays[END_REF][START_REF] Worm | Global catches, exploitation rates, and rebuilding options for sharks[END_REF]), but there is a paucity of data regarding trophic relationships among species within this predatory guild. For coastal ecosystems, it has been proposed that predator declines could initiate trophic cascades, whereby their removal disrupts the natural population abundances, or behaviours, of consecutive lower trophic level species [START_REF] Myers | Cascading effects of the loss of apex predatory sharks for a coastal ocean[END_REF][START_REF] Heithaus | Predicting ecological consequences of marine top predator declines[END_REF], Burkholder et al. 2013). Elasmobranchs are upper trophic level predators in many marine ecosystems, but there is considerable variation in diets and relative trophic position among species [START_REF] Wetherbee | Food consumption and feeding habits[END_REF][START_REF] Hussey | Rescaling the trophic structure of marine food webs[END_REF]. The presence of a diverse marine top predator community, such as elasmobranchs, including an abundance of sympatric and ecologically interacting species, may be important in structuring some marine communities [START_REF] Heithaus | Unravelling the ecological importance of elasmobranchs[END_REF]. It is unclear, however, whether diverse marine top predator faunas represent trophically redundant species [START_REF] Myers | Cascading effects of the loss of apex predatory sharks for a coastal ocean[END_REF] or inhabit unique foraging niches with differential impacts on overall community structure [START_REF] Kinney | Communal or competitive? Stable isotope analysis provides evidence of resource partitioning within a communal shark nursery[END_REF], Heithaus et al. 2013).

Although 95% of global fishers are artisanal [START_REF] Pauly | Major trends in small-scale fisheries, with emphasis on developing countries, and some implications for the social sciences[END_REF], detailed information on fisheries catch composition is limited due to a lack of monitoring and reporting as a result of restricted financial and logistical capacity. In developing countries, artisanal fisheries are the principal fishing practice and are consequently of considerable social and economic importance to regional human populations. These fisheries, however, can negatively impact the abundance and species composition of vulnerable species such as elasmobranchs [START_REF] Pinnegar | The shifting baseline phenomenon: a global perspective[END_REF]. Continued unregulated exploitation can lead to declines of key species with consequences extending to the broader food web, including commercial species that are critical to the livelihoods of local populations. Along the coast of Madagascar, elasmobranchs are heavily exploited both for subsistence (meat) and commercial (fins) purposes with an active and developed export market [START_REF] Mcvean | The traditional shark fisheries of southwest Madagascar: a study in the Toliara region[END_REF][START_REF] Robinson | A first description of the artisanal shark fishery in northern Madagascar: implications for management[END_REF]). Between October 2001and October 2002, 13 species were identified from a total of 1164 individual elasmobranchs caught off the southwestern region of Madagascar. Hammerhead sharks (mostly Sphyrna lewini, and to a lesser extent S. mokarran and S. zygaena) represented 29% of the catch by number and 24% of the total wet weight with an estimate of over 123 metric tons landed [START_REF] Mcvean | The traditional shark fisheries of southwest Madagascar: a study in the Toliara region[END_REF]. Hammerhead sharks (Sphyrna spp.) are globally threatened, with S. lewini currently classified as Endangered (IUCN Red List). Currently, no baseline ecological data exists for elasmobranchs from this region, but a decline in elasmobranch abundance has been observed for the most exploited species [START_REF] Mcvean | The traditional shark fisheries of southwest Madagascar: a study in the Toliara region[END_REF]. This decline of elasmobranchs from the coastal waters of south-western Madagascar could have adverse effects on both fishing communities and marine ecosystems. To assess this possibility, there is a need for information on these species including their trophic interactions and levels of trophic redundancy in the elasmobranch community.

Nitrogen and carbon stable isotopes provide chemical tracers of the diets and foraging habitats of organisms in a given ecosystem. Because offshore or pelagic-derived food webs tend to be 13 Cdepleted compared to inshore or benthic food webs [START_REF] Hobson | Tracing origins and migration of wildlife using stable isotopes: a review[END_REF], carbon isotope values (δ 13 C) can be used to indicate the foraging habitat of a species. In addition, the relative position of the consumer in the food web can be estimated from nitrogen isotopes values (δ 15 N) because of the enrichment of 15 N through successive trophic transfers [START_REF] Hobson | Tracing origins and migration of wildlife using stable isotopes: a review[END_REF][START_REF] Caut | Variation in discrimination factors (∆ 15 N and ∆ 13 C): the effect of diet isotopic values and applications for diet reconstruction[END_REF][START_REF] Hussey | Rescaling the trophic structure of marine food webs[END_REF]. To date, carbon and nitrogen stable isotopes have been used to elucidate aspects of elasmobranch trophic and foraging ecology, including niche breadth and separation [START_REF] Kinney | Communal or competitive? Stable isotope analysis provides evidence of resource partitioning within a communal shark nursery[END_REF][START_REF] Speed | Trophic ecology of reef sharks determined using stable isotopes and telemetry[END_REF][START_REF] Vaudo | Dietary niche overlap in a nearshore elasmobranch mesopredator community[END_REF], Heithaus et al. 2013), individual foraging specialization [START_REF] Matich | Contrasting patterns of individual foraging specialization and trophic coupling in two marine apex predators[END_REF], and ontogenetic and sex variation in trophic interactions and habitat use (e.g. [START_REF] Hussey | Stable isotope profiles of large marine predators: viable indicators of trophic position, diet and movement in sharks?[END_REF][START_REF] Carlisle | Using stable isotope analysis to understand the migration and trophic ecology of northeastern Pacific white sharks (Carcharodon carcharias)[END_REF]). Long-term integrated stable isotope values also provide information on the role of elasmobranchs within a food web [START_REF] Mcmeans | Diet and resource use among Greenland sharks (Somniosus microcephalus) and teleosts sampled in Icelandic waters using δ 13 C, δ 15 N, and mercury[END_REF][START_REF] Vaudo | Dietary niche overlap in a nearshore elasmobranch mesopredator community[END_REF]. In this study, we used stable isotopes to assess trophic relationships, isotopic niche breadth and overlap, as well as ontogenetic variation in trophic interactions among the most commonly caught elasmobranch species in artisanal fisheries operating in the coastal waters off south-western Madagascar (Table 1), including the scalloped hammerhead shark S. lewini, the sliteye shark Loxodon macrorhinus, the giant guitarfish Rhynchobatus djiddensis and the silky shark Carcharhinus falciformis.

MATERIALS AND METHODS

Study sites and sample collection

Shark samples were collected at 5 fish villages (landing sites) in south-western Madagascar: Andavado aka, Nosy Be, Nosy Hao, Lamboara and Nosy Andriamitaroka (Fig. 1). Southern areas (Andavadoaka, Nosy Be, Nosy Hao, Lamboara) are characterised by 2 distinct fringing and barrier reef systems separated by a 5 km wide passage or channel in which several patch reefs are situated.

The northern area (Nosy Andriamitaroka) is characterised by a shallow underwater shelf, approx. 30 km in width and generally less than 20 m deep. A scattered coral bank lies at the seaward periphery adjacent to the continental shelf drop-off. Sharks were caught by traditional fishers using longlines and gillnets from traditional non-motorised sailing pirogues (6 to 8 m long). Longlines consisted of an anchor line 50 to 100 m long and a buoyed surface line, 50 to 100 m long, with three 12 m long snoods approx. 25 m apart which are attached to the surface line [START_REF] Mcvean | The traditional shark fisheries of southwest Madagascar: a study in the Toliara region[END_REF]. Gillnets, the most commonly used gear, are approx. 50 m long and 4.5 m deep with a mesh size of 20 to 25 cm. The nets are typically set on the bottom, in water approx. 30 m deep, and are generally baited with fish. Trained local data collectors surveyed the 5 fish landing sites year round from April 2009 to May 2010 to collect elasmobranch muscle samples for stable isotope analysis.

White muscle tissue samples from the dorsal region of freshly landed sharks were collected from the most commonly recorded species, and were frozen at -20°C until further processing. Basic morphometric measurements, including total and fork length (TL and FL, respectively) and sex were recorded for each individual sampled.

Stable isotope analyses

Elasmobranch white muscle tissue was freeze-dried, ground into a homogeneous powder and lipids were removed by 2 successive extractions (1 h shaking in cyclohexane at room temperature and subsequent centrifugation) prior to analysis to standardize data among individuals and across species within the food web (Hussey et al. 2012a). This process also removes urea and trimethylamine oxide (TMAO) present in shark tissues, which can potentially affect δ 15 N values (Hussey et al. 2012b). A small sub-sample of tissue (0.35 to 0.45 mg) was weighed and stable isotope measurements performed with a continuous-flow isotope-ratio mass spectrometer (Delta V Advantage, Thermo Scientific) coupled to an elemental analyser (Flash EA1112, Thermo Scientific). Reference gases were calibrated against International Reference Materials (IAEA-N1, IAEA-N2 and IAEA-N3 for nitrogen; NBS-21, USGS-24 and IAEA-C6 for carbon). Results are expressed in the δ notation relative to Pee Dee Belemnite and atmospheric N2 for δ 13 C and δ 15 N, respectively, according to the equation: δX = [(Rsample/Rstandard) -1] × 103, where X is 13 C or 15 N and R is the isotope ratio 13 C/ 12 C or 15 N/ 14 N, respectively. Replicate measurements of a laboratory standard (acetanilide) indicated that analytical errors were <0.1‰ for δ 13 C and δ 15 N. Percent C and N elemental composition of tissues were used to calculate the sample C:N ratio, and indicated satisfactory lipid removal efficiency (mean ± SD C:N = 3.12 ± 0.2).

Data analysis

Assumptions regarding normality and homogeneity of variance were not met following Shapiro-Wilks and F tests. Non-parametric Kruskal-Wallis (H) tests were consequently used to examine the difference in stable isotopes values (δ 15 N and δ 13 C) among species. Wilcoxon (W) signed rank tests were performed to assess differences in δ 13 C and δ 15 N values between sexes and ANCOVA was used to test the influence of size and species on δ 13 C and δ 15 N values of the 2 most commonly sampled species (S. lewini and L. macrorhinus). The ANCOVA is a general linear model with a continuous outcome variable (δ 15 N and δ 13 C values) and 2 or more predictor variables where at least one is continuous (size; FL) and at least one is categorical (species). In order to compare isotopic niches and infer habitat (δ 13 C) and resource (δ 15 N) separation among the 4 species, we used the recently developed SIBER metric (Stable Isotope Bayesian Ellipses using R; [START_REF] Jackson | Comparing isotopic niche widths among and within communities: SIBER -Stable Isotope Bayesian Ellipses in R[END_REF]. Corrected standard ellipses (SEAc) are calculated from the variance and covariance of the data matrix and represent core niche or dietary isotopic space while accounting for small sample sizes per species and variable sample sizes among species. The OVERLAP command within SIBER was used to calculate the percentage of core niche overlap among species δ 13 C and δ 15 N ellipse space [START_REF] Jackson | Comparing isotopic niche widths among and within communities: SIBER -Stable Isotope Bayesian Ellipses in R[END_REF]. Data were analysed using R v. 2.12.0 (R Development Core Team 2010).

RESULTS

Over the 12 mo study period, 84 Loxodon macrorhinus, 40 Sphyrna lewini, 20 Rhynchobatus djiddensis and 7 Carcharhinus falciformis samples were obtained. The size range of individuals sampled was highly variable among species, with juveniles making up the majority of individuals, especially for S. lewini and R. djiddensis (Table 2, Fig. 2). The δ 13 C value was lowest for S. lewini (mean ± SD; -15.9 ± 1.19‰) and highest for C. falciformis (-14.4 ± 2‰), while the mean δ 15 N was lowest for L. macrorhinus (11.7 ± 0.59‰) and the highest for C. falciformis (12.9 ± 1.36‰; Table 2). Stable isotope values found in this study were graphically compared to other teleost fishes with known trophic level and habitat (see [START_REF] Daly | Comparative feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the southwest Indian Ocean inferred from stable isotope analysis[END_REF], including offshore pelagic, coastal pelagic and coastal demersal species (Fig. 3). Based on these data, C. falciformis and S. lewini do not have truly oceanic isotopic values. Conversely, it seems that L. macrorhinus and R. djiddensis are coastal consumers foraging in benthic and inshore habitats (Fig. 3).

Mean isotopic values varied among the 4 species for both δ 13 C (H = 10.8; df = 3; p = 0.01) and δ 15 N (H = 10.8; df = 3; p = 0.01; Fig. 3). At the individual level, δ 13 C and δ 15 N data were tightly clustered for L. macrorhinus and R. djiddensis but were more dispersed for S. lewini and C. falciformis (Figs. 3 & 4). Isotopic ellipse size was highly variable among species, with R. djiddensis having the smallest isotopic niche (0.3) and C. falciformis the largest (5.4) (Fig. 4). Ellipse sizes for S. lewini and L. macrorhinus were 4.1 and 1.9, respectively. Isotope niche overlap, based on the measure of ellipse overlap was high for R. djiddensis compared with C. falciformis (93.2%) and L. macrorhinus (73.2%), and to a lesser extent S. lewini (13.3%, Table 3). Higher isotopic niche overlap was also found between L. macrorhinus and both S. lewini (48.3%) and C. falciformis (46.2%), but most other comparisons yielded low niche overlap values (Fig. 4; Table 3).

For S. lewini and L. macrorhinus, ANCOVA confirmed that the 2 species were significantly distinct in their δ 15 N values, and that there was an effect of individual size (F3,116 = 30.75, p < 0.0001, Fig. 5). Smaller individuals of both species had similar δ 15 N values, but there was an increase in δ 15 N with size in S. lewini (R2 = 0.49, p < 0.0001) that was not observed in the smallerbodied L. macrorhinus. In contrast, ANCOVA found no influence of species and size on δ 13 C values (F3,116 = 2.05, p = 0.11; Fig. 5). Intraspecific variation in δ 15 N and δ 13 C values was high for both S. lewini and L. macrorhinus (Table 2; Fig. 5), especially for δ 13 C, highlighting potentially inter-individual differences in diets and/or foraging habitats. There was no difference between male and female δ 13 C values for either species (S. lewini: W = 161.5; p = 0.60 and L. macrorhinus: W = 871.5; p = 0.77) or for δ 15 N values of S. lewini (W = 150; p = 0.39). For L. macrorhinus, males had significantly higher δ 15 N values (mean = 11.8 ± 0.54‰) than females (mean = 11.5 ± 0.62‰; W = 675; p = 0.04).

DISCUSSION

These data provide the first investigation of trophic interactions, isotopic niches, ontogenetic and gender variation in the foraging ecology of 4 heavily exploited elasmobranch species from a datapoor region, the Mozambique Channel off south-western Madagascar. Sphyrna lewini, Loxodon macrorhinus, Rhyncho batus djiddensis and Carcharhinus falciformis are among the most commonly caught species by artisanal fishers over continental shelf waters in this region (~75% of species landed in the sampled region; F. Humber unpubl. data), and likely constitute a large proportion of the elasmobranch biomass. These species also account for a high percentage of the catch of artisanal fisheries off northern Madagascar, where concern over exploitation rates has recently been documented [START_REF] Robinson | A first description of the artisanal shark fishery in northern Madagascar: implications for management[END_REF]. Sampling covered a range of sizes (FL range 62 to 260 cm) for L. macrorhinus and C. falciformis, but consisted of mostly juvenile S. lewini and R. djiddensis, likely reflecting artisanal shark fisheries overlapping with nursery areas. It is possible, however, that long-term exploitation of elasmobranchs in this region, primarily for the fin trade, has altered the size structure of populations.

In order to correctly interpret stable isotope values in the tissues of juvenile sharks, especially those with long turnover rates (e.g. muscle), it is critical to understand the dynamics of maternal provisioning [START_REF] Mcmeans | Diet and resource use among Greenland sharks (Somniosus microcephalus) and teleosts sampled in Icelandic waters using δ 13 C, δ 15 N, and mercury[END_REF]. Previous studies of mother-offspring differences of stable isotopes ratios in placentatrophic sharks have shown that embryos are generally enriched in δ 15 N but fractionation of δ 13 C is variable among species (McMeans et al. 2009, Vaudo et al. 20s10).

Based on data from the literature (size at birth and growth parameters; [START_REF] Compagno | FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark specimen known to date. Part 2. Carcharhiniformes[END_REF][START_REF] Compagno | Rhinobatidae[END_REF], all animals from our study were likely more than 1 yr old. Therefore, maternal influences should have very limited impacts on isotopic values of the individuals in this study.

Stable isotope data indicated that, although the 4 species differed in their relative trophic position (indicated by mean δ 15 N values), δ 13 C values suggested considerable overlap in the food webs where species were foraging. There were, however, differences in how trophic interactions varied with size for S. lewini and L. macrorhinus and between sexes of L. macrorhinus. The 4 focal species are morphologically and ecologically distinct in terms of body size and feeding apparatus, diet consumed, and habitat use patterns (see Table 1). C. falciformis and S. lewini are wide-ranging and occur in oceanic, epipelagic and continental shelf habitats. They feed mostly on epipelagic and pelagic fish, cephalopods and crustaceans [START_REF] Compagno | FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark specimen known to date. Part 2. Carcharhiniformes[END_REF][START_REF] Bonfil | The biology and ecology of the silky shark, Carcharhinus falciformis[END_REF]). Juvenile S. lewini reside in coastal nursery grounds [START_REF] Simpfendorfer | Utilisation of a tropical bay as a nursery area by sharks of the families Carcharhinidae and Sphyrnidae[END_REF] that probably extend over the continental shelf off south-western Madagascar, as observed off south-eastern Africa [START_REF] Diemer | Distribution and movement of scalloped hammerhead Sphryna lewini and smooth hammerhead Sphyrna zygaena sharks along the east coast of southern Africa[END_REF]. R. djiddensis also occurs over the continental shelf, but, in contrast to S. lewini and C. falciformis, is adapted to shallow coastal waters (i.e. closer to more 13C-enriched benthic sources) and is thought to have relatively restricted home range and to feed mostly on molluscs and crustaceans [START_REF] Darracott | Availability, morphometrics, feeding and breeding activity in a multi-species, demersal fish stock of the Western Indian Ocean[END_REF][START_REF] Compagno | Rhinobatidae[END_REF]. L. macrorhinus is a poorly known continental shelf species that lives in intertidal areas up to 80 m depth and which feeds on teleosts, coastal cephalopods and crustaceans [START_REF] Compagno | FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark specimen known to date. Part 2. Carcharhiniformes[END_REF]. Despite these marked differences, there was considerable overlap in δ 13 C values among the 4 species. The larger variation in δ 13 C values observed in L. macrorhinus and S. lewini compared to R. djiddensis likely indicate the diversity of habitats and feeding areas encountered with larger home ranges, especially for the more pelagic S. lewini. The inability of δ 13 C values to discriminate known interspecific variation in seasonal finescale vertical (pelagic vs. benthic) and horizontal (oceanic vs. coastal) distributions likely relates to the slow turnover rate of muscle tissue (>250 d; [START_REF] Kim | Isotopic incorporation rates for shark tissues from a long-term captive feeding study[END_REF]. Such limitations of carbon isotopes in resolving fine-scale foraging patterns of seabirds and marine mammals have been reported in various ecological contexts [START_REF] Cherel | Resource partitioning within a tropical seabird community: new information from stable isotopes[END_REF][START_REF] Méndez-Fernandez | Foraging ecology of five toothed whale species in the Northwest Iberian Peninsula, inferred using δ 13 C and δ 15 N isotopic signatures[END_REF]. For example, despite obvious differences in habitat preferences of small cetaceans off the Iberian Peninsula (e.g. depth distributions; [START_REF] Pierce | Trends in cetacean sightings along the Galician coast, north-west Spain, 2003-2007, and inferences about cetacean habitat preferences[END_REF], similar δ 13 C values were recorded among species [START_REF] Méndez-Fernandez | Foraging ecology of five toothed whale species in the Northwest Iberian Peninsula, inferred using δ 13 C and δ 15 N isotopic signatures[END_REF].

Unfortunately, isotopic data on prey from specific habitats and food webs could not be collected during our study. Such data would provide even greater insights into the diets, foraging habitats and home ranges of the species studied here (e.g. [START_REF] Daly | Comparative feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the southwest Indian Ocean inferred from stable isotope analysis[END_REF][START_REF] Kiszka | The foraging ecology of coastal bottlenose dolphins based on stable isotope mixing models and behavioural sampling[END_REF]. However, data from neighbouring areas (e.g. coastal waters of Mozambique; [START_REF] Daly | Comparative feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the southwest Indian Ocean inferred from stable isotope analysis[END_REF]) can provide insights into habitat use by our focal species off SW Madagascar. Based on these regional data, none of the most pelagic species, especially C. falciformis and S. lewini had truly oceanic isotopic values. Indeed, both species from south-western Madagascar had higher δ 13 C values than those measured in pelagic teleosts [START_REF] Daly | Comparative feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the southwest Indian Ocean inferred from stable isotope analysis[END_REF]). This pattern is similar to published data on carbon and nitrogen isotope values from the same region for C. falciformis. Both δ 15 N and δ 13 C were significantly higher for C. falciformis off south-western Madagascar than was found further north in the Mozambique Channel (Rabehagasoa et al. 2012; see Table 2). This could be due to spatial variation in diets of C. falciformis in this region. However, the individuals we sampled were significantly larger than those analysed by Rabehagasoa et al. (2012). Therefore, ontogenetic shifts in diets, which have been documented for this species [START_REF] Compagno | FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark specimen known to date. Part 2. Carcharhiniformes[END_REF][START_REF] Cabrera-Chávez-Costa | Food habits of the silky shark Carcharhinus falciformis (Müller & Henle, 1839) off the western coast of Baja California Sur, Mexico[END_REF], Rabehagasoa et al. 2012), may also explain the observed differences with C. falciformis feeding on higher trophic level prey at larger sizes. Moreover, higher δ 13 C values observed in this species in our study area may either reflect an increasing relative importance of coastal prey with age, or a larger prevalence of coastal prey in the diet of C. falciformis (where the continental shelf is broader). In contrast, based on a comparison of data from a variety of pelagic and coastal teleost fish species from the coastal waters of Mozambique, it seems that L. macrorhinus and R. djiddensis are truly coastal consumers foraging in inshore and benthic habitats [START_REF] Daly | Comparative feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the southwest Indian Ocean inferred from stable isotope analysis[END_REF].

Interestingly, δ 13 C values measured in S. lewini and R. djiddensis from south-western Madagascar were similar to those from north-western India [START_REF] Borrell | Trophic ecology of elasmobranchs caught off Gujarat, India, as inferred from stable isotopes[END_REF]) and KwaZulu-Natal, South Africa (for S. lewini only; [START_REF] Hussey | Stable isotope profiles of large marine predators: viable indicators of trophic position, diet and movement in sharks?[END_REF]). However, δ 15 N values of both S. lewini and R. djiddensis were significantly lower off south-western Madagascar (Table 2), compared to those measured in India for the same species [START_REF] Borrell | Trophic ecology of elasmobranchs caught off Gujarat, India, as inferred from stable isotopes[END_REF]). This regional variation highlights the need for region-specific isotopic data to evaluate the trophic inter actions, including for wideranging consumers such as large elasmobranchs.

Differences in trophic interactions among these 4 highly exploited elasmobranchs suggest these species are not trophically redundant. This is consistent with previous studies from other geographic locations, where elasmobranchs were segregated based on their relative trophic position or mean δ 15 N values [START_REF] Cortés | Standardized diet compositions and trophic levels of sharks[END_REF][START_REF] Borrell | Trophic ecology of elasmobranchs caught off Gujarat, India, as inferred from stable isotopes[END_REF], Heithaus et al. 2013[START_REF] Hussey | Rescaling the trophic structure of marine food webs[END_REF].

Such isotopic segregation within a community has been documented in a number of coastal, oceanic and reef-associated elasmobranch species (e.g. [START_REF] Kinney | Communal or competitive? Stable isotope analysis provides evidence of resource partitioning within a communal shark nursery[END_REF][START_REF] Speed | Trophic ecology of reef sharks determined using stable isotopes and telemetry[END_REF], Rabehagasoa et al. 2012), but not in assemblages where species show morphological, taxonomic and habitat similarities over small spatial scales [START_REF] Vaudo | Dietary niche overlap in a nearshore elasmobranch mesopredator community[END_REF]). The highest degree of overlap in δ 15 N values was found between individuals of R. djiddensis and L. macrorhinus, species that both occur in shallow waters of the continental shelf. Overlap in diet would therefore be expected, although fine scale niche partitioning (concealed by isotope analyses) may occur.

Detailed stomach content data collected over a seasonal cycle would be required to determine this. S. lewini and L. macrorhinus also exhibited a moderately high degree of niche overlap, but the former had a significantly higher mean δ 15 N value (related to an ontogenetic diet shift with size). Juvenile S. lewini and L. macrorhinus of all size classes had similar δ 15 N values, also related to their occurrence in coastal waters and the potential for high niche overlap. It is important to note that establishing isotopic baselines and system end points for carbon and nitrogen stable isotopes in this region would be required to further elucidate the trophic ecology and roles of these species.

The isotopic niche sizes varied among species, with δ 15 N and δ 13 C values tightly clustered for L. macrorhinus and R. djiddensis but more dispersed for S. lewini and C. falciformis. The large variability in S. lewini and L. macrorhinus isotopic values may indicate either a high level of generalist feeding behaviour or, more likely, because of the long turnover times of muscle tissue, consistent differences in average trophic interactions of individuals within generalist populations.

Such behaviour has been found in juvenile bullsharks C. leucas in a nursery area of Florida [START_REF] Matich | Contrasting patterns of individual foraging specialization and trophic coupling in two marine apex predators[END_REF]) and has been suggested for a number of other elasmobranch taxa such as batoids [START_REF] Vaudo | Dietary niche overlap in a nearshore elasmobranch mesopredator community[END_REF]. In contrast, L. macrorhinus and R. djiddensis may be more specialized at the population level or individuals may all have similarly generalized diets over the time period that muscle isotopic values are integrated. The small sample size for C. falciformis may have influenced the standard ellipse (SEAc) size through artificially inflating the size of the niche area [START_REF] Jackson | Comparing isotopic niche widths among and within communities: SIBER -Stable Isotope Bayesian Ellipses in R[END_REF]. Given the observed variability in the data, however, this bias is likely minimal. Stable isotope analyses of multiple tissues with different turnover rates would address questions related to individual foraging specialisation (Matich et al. 20s11) and elucidate more intricate seasonal differences [START_REF] Kinney | Communal or competitive? Stable isotope analysis provides evidence of resource partitioning within a communal shark nursery[END_REF].

Ontogenetic and sex differences in diets and habitat preferences are related to age-and sex-specific energy requirements, vulnerability to predators, and social considerations, and have been documented for a diversity of taxa (e.g. [START_REF] Beier | Sex differences in quality of white-tailed deer diets[END_REF][START_REF] Breed | Sexual segregation of seasonal foraging habitat in a non-migratory marine mammal[END_REF]), including elasmobranchs [START_REF] Lowe | Ontogenetic dietary shifts and feeding behavior of tiger sharks, Galeocerdo cuvier, in Hawaiian waters[END_REF][START_REF] Estrada | Use of isotopic analysis from vertebrae in reconstructing ontogenetic feeding ecology in white sharks[END_REF], Hussey et al. 2011, Rabehagasoa et al. 2012). Such ontogenetic niche shifts can impact population dynamics, community structure, and ecosystem function [START_REF] Hammerschlag-Peyer | A hypothesis-testing framework for studies investigating ontogenetic niche shifts using stable isotope ratios[END_REF], Hussey et al. 2011). Relative trophic level, inferred by δ 15 N values, significantly increased with body length in S. lewini, suggesting a dietary change with age in this species that likely reflects moving from more coastal to pelagic habitats and foraging large predators in the system to incorporate in food web models to examine long-term effects of removing trophically distinct species within artisanal fisheries. macrorhinus.

Fig. 1 :Fig. 2 :

 12 Fig. 1: Map of the study area, in south-western Madagascar.

Fig. 3 :

 3 Fig. 3: Stable isotope values (in ‰, δ 15 N and δ 13 C) in lipid-treated shark muscle (means ±SD and

Fig. 4 :

 4 Fig. 4: Individual stable values (in ‰, δ 15 N and δ 13 C) of C. falciformis, L. macrorhinus, R.

Fig. 5 :

 5 Fig. 5: Relationships between δ 15 N (left) and δ 13 C (right) and fork length (cm) in S. lewini and L.

Table 1 :

 1 Review of ecological characteristics ( * minimal depth range, ** major prey type) of elasmobranch species investigated in this study.

	Species	Habitat	Depth range (m)* Diet**	References
	Rhynchobatus djiddensis	Benthic	0 -200	Small fishes, molluscs and crustaceans	Darracott (1977), Compagno (1986)
	Loxodon macrorhinus	Demersal	0 -80	Small demersal fishes and cephalopods, crustaceans	Compagno (1984)
	Carcharhinus falciformis	Epipelagic, oceanic	0 -500	Large squids, pelagic fishes, pelagic crabs	Compagno (1984), Bonfil (2008), Cabrera-Chavez et al. (2010)
	Sphyrna lewini	Coastal and oceanic	0 -275	Pelagic to demersal fishes, squids and elasmobranchs	Compagno (1984), Baum et al. (2007), Hussey et al. (2011)

Table 2 :

 2 Number of sampled sharks, mean FL (Fork Length), size range, sex ratio, percentage of mature individuals in sampling of our study based on length of maturity from[START_REF] Compagno | FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark specimen known to date. Part 2. Carcharhiniformes[END_REF], and mean (SD) stable nitrogen, carbon isotope values and C:N ratios.

	Species	n sampled	Fork Length (cm)	Sex ratio	% of mature	δ 15 N	δ 13 C	C:N
			Mean	Range	(m:f)	individuals	Mean ± SD	Mean ± SD	Mean ± SD
	Loxodon macrorhinus	84	83.7	62 -100	1:1	85	11.66 ± 0.59	-15.4 ± 1.01	3.14 ± 0.18
	Carcharhinus falciformis	7	162.9	73 -260	0.9:1	29	12.89 ± 1.36	-14.37 ± 1.2	3.02 ± 0.1
	Rhynchobatus djiddensis	20	86	65 -190	0.8:1	5	11.92 ± 0.42	-14.66 ± 0.43	3.13 ± 0.1
	Sphyrna lewini	40	96.5	58 -172	0.8:1	5	12.42 ± 1.05	-15.89 ± 1.19	3.1 ± 0.2

Table 3 :

 3 Percentage of niche overlap among the four species investigated in both δ 15 N (above the diagonal) and δ 13 C (below the diagonal) space.

	Species	R. djiddensis	L. macrorhinus	S. lewini	C. falciformis
	R. djiddensis	*	12.8	1.1	5.7
	L. macrorhinus	73.2	*	22.4	16.1
	S. lewini	13.3	48.3	*	19.3
	C. falciformis	93.2	46.2	26.6	*

Acknowledgements

Our particular thanks are addressed to sample and data collectors in south-western Madagascar, working on behalf Blue Ventures. We are grateful to G. Guillou and P. Richard (University of La Rochelle, UMR LIENSs), for running the stable isotope analyses. This work has been supported financially by LIENSs and the CPER 13 (Contrat de Projet Etat-Région).

on higher trophic level prey [START_REF] Compagno | FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark specimen known to date. Part 2. Carcharhiniformes[END_REF][START_REF] Borrell | Trophic ecology of elasmobranchs caught off Gujarat, India, as inferred from stable isotopes[END_REF], Hussey et al. 2011). Spatial segregation has been documented for a diversity of elasmobranch species [START_REF] Compagno | FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark specimen known to date. Part 2. Carcharhiniformes[END_REF], including through the use of stable isotopes (e.g. [START_REF] Hussey | Stable isotope profiles of large marine predators: viable indicators of trophic position, diet and movement in sharks?[END_REF]. In our study, differences in δ 15 N values between male and female L. macrorhinus indicate that males feed at a higher relative trophic position compared to females. Whether this reflects foraging on different prey taxa or sexual segregation remains to be elucidated. We did not detect sex differences in isotopic values of S. lewini, which contrasts with results from individuals captured off the coast of KwaZulu-Natal, South Africa [START_REF] Hussey | Stable isotope profiles of large marine predators: viable indicators of trophic position, diet and movement in sharks?[END_REF]. Off South Africa, δ 13 C values of males and females between 120 and 160 cm (precaudal length) supported sexual segregation, with females most likely spending more time in oceanic waters [START_REF] Hussey | Stable isotope profiles of large marine predators: viable indicators of trophic position, diet and movement in sharks?[END_REF].

CONCLUSIONS

In summary, these data suggest that complex trophic structuring occurs in this highly exploited elasmobranch assemblage. Differences in trophic interactions appear to be driven by a combination of interacting factors including habitat use, home-range size, diets, and variation in all of these factors across size classes, sexes and individual behaviours. Consequently, species-specific population declines as a result of continued unregulated exploitation have the potential to lead to intricate species-specific cascades within the coastal waters of south-western Madagascar. More detailed sampling of the food web, however, is required to examine isotopic variation in prey items consumed by the 4 species and to determine if benthic and pelagic and coastal/offshore ecosystems can be readily distinguished. Given the IUCN Red list categories for 2 of the species ('Vulnerable', R. djiddensis; 'Endangered', S. lewini), local management is imperative to regulate regional fisheries. More data is also required on the biological parameters of these populations and other


Laurent Besacier
email: laurent.besacier@imag.fr

Lane Schwartz

Automated translation of a literary work: a pilot study

Current machine translation (MT) techniques are continuously improving. In specific areas, post-editing (PE) can enable the production of high-quality translations relatively quickly. But is it feasible to translate a literary work (fiction, short story, etc) using such an MT+PE pipeline? This paper offers an initial response to this question. An essay by the American writer Richard Powers, cur-

Introduction

The task of post-editing consists of editing some text (generally produced by a machine, such as a machine translation, optical character recognition, or automatic transcription system) in order to improve it. When using machine translation in the field of document translation, the following process is generally used: the MT system produces raw translations, which are manually post-edited by trained professional translators (post-editors) who correct translation errors. Several studies have shown the benefits of the combined use of machine translation and manual post-editing (MT+PE) for a document translation task. For example, [START_REF] Garcia | Translating by post-editing: is it the way forward[END_REF] showed that even though post-editing raw translations does not always lead to significant increases in productivity, this process can result in higher quality translations (when compared to translating from scratch). 1 Autodesk also carried out an experiment to test whether the use of MT would improve the productivity of translators. Results from that experiment [START_REF] Zhechev | Machine translation infrastructure and post-editing performance at Autodesk[END_REF] show that post-editing machine translation output significantly increases productivity when compared to translating a document "from scratch". This result held regardless of the language pair, the experience level of the translator, and the translator's stated preference for post-editing or translating from scratch.

These results from academia [START_REF] Garcia | Translating by post-editing: is it the way forward[END_REF] and industry [START_REF] Zhechev | Machine translation infrastructure and post-editing performance at Autodesk[END_REF] regarding translation in specialized areas lead us to ask the following questions:

• What would be the value of such a process (MT + PE) applied to the translation of a literary work?

• How long does it take to translate a literary document of ten thousand words?

• Is the resulting translation acceptable to readers?

• What would the official translator (of the considered author) think of it?

• Is "low cost" translation produced by communities of fans (as is the case for TV series) feasible for novels or short stories?

This work attempts to provide preliminary initial answers to these questions. In addition to our experimental results, we also present a new transla-tion (into French) of an English-language essay (The Book of Me by Richard Powers).

This paper is organized as follows. We begin in §2 by surveying related work in machine translation in the literary domain. In §3, we present our experimental methodology, including the choice of literary work to be translated and the machine translation, domain adaptation, and post-editing frameworks used. In §4, we present our experimental results, 2 including an assessment of translation quality using automated machine translation metrics. In §5, we attempt to assess machine translation quality beyond automated metrics, through a human assessment of the final translation; this assessment was performed by a panel of readers and by the official French translator of Richard Powers.

Related Work

While the idea of post-editing machine translations of scientific and technical works is nearly as old as machine translation (see, for example [START_REF] Oettinger | A Study for the Design of an Automatic Dictionary[END_REF]), very little scholarship to date has examined the use of machine translation or post-editing for literary documents. The most closely related work [START_REF] Voigt | Towards a literary machine translation, the role of referential cohesion[END_REF] that we were able to identify was presented at the ACL workshop on Computational Linguistics for Literature 3 ; since 2012, that workshop has examined the use of NLP in the literary field. [START_REF] Voigt | Towards a literary machine translation, the role of referential cohesion[END_REF] examine how referential cohesion is expressed in literary and nonliterary texts and how this cohesion affects translation (experiments on Chinese literature and news). The present paper, however, tries to investigate if computer-assisted translation of a complete (and initially un-translated) short story, is feasible or not.

For the purposes of this paper, we now define what constitutes a literary text. We include in this category (our definition is undoubtedly too restrictive) all fiction or autobiographical writing in the form of novels, short stories or essays. In such texts, the author expresses his vision of the world of his time and life in general while using literary devices and a writing technique (form) that allows him to create effects using the language and to express meanings (explicit or implied).

Methodology

For this study, we follow a variant of the post-editing methodology established by [START_REF] Potet | Collection of a large database of French-English SMT output corrections[END_REF]. In that work, 12,000 post-edited segments (equivalent to a book of about 500 pages) in the news domain were collected through crowdsourcing, resulting in one of the largest freely available corpora of postedited machine translations.4 It is, for example, three times larger than that collected by [START_REF] Specia | A dataset for assessing machine translation evaluation metrics[END_REF], a well known benchmark in the field. Following [START_REF] Potet | Collection of a large database of French-English SMT output corrections[END_REF], we divide the document to be translated into three equal parts. A translation/post-edition/adaptation loop was applied on the three blocks of text according to the following process:

• The first third of the document was translated from English to French using Moses [START_REF] Hoang | Moses: Open source toolkit for statistical machine translation[END_REF], a state-of-the-art phrase-based machine translation system. This machine translation output was then post-edited.

• The post-edited data from the third of the document was used to train an updated domainadapted English-French MT system. Given the small amount of post-edited data, adaptation at this point consisted only in adapting the weights of the log-linear SMT model (by using the corrected first third as a development corpus). A similar method is suggested by [START_REF] Pecina | Simple and effective parameter tuning for domain adaptation of statistical machine translation[END_REF] for domain adaptation with a limited quantity of data (we are aware that other more advanced domain adaptation techniques could have been used but this was not the central theme of our contribution),

• Then, the second third of the text was translated with the adapted MT system, then the results were post-edited and a second adapted MT system was obtained starting from the new data.

This second system was used to translate the third and last part of the text, Our methodology differs in two important ways from [START_REF] Potet | Collection of a large database of French-English SMT output corrections[END_REF]. First, our study makes use of only one post-editor, and does not use crowdsourcing to collect data. Second, once the postediting was completed, the final text was revised: first by the post-editor and then by another reviewer. The reviewer was a native French speaker with a good knowledge of the English language. The time taken to post-edit and revise were recorded.

Choice of literary document

To test the feasibility of using machine translation and post-editing to translate a literary work, we began by selecting an essay written in English which had not yet been translated into French. The choice of text was guided by the following factors:

(a) we had a contact with the French translator of the American author Richard Powers 5 (author of the novel The Echo Maker which won the National Book Award and was a finalist for the Pulitzer Prize) (b) In his writing, Powers often explores the effects of modern science and technology, and in some ways his writings contain commonalities with scientific and technical texts. We hypothesized that this characteristic may somewhat reduce the gap between translation of scientific and literary texts.

Via his French translator (Jean-Yves Pellegrin), Powers was informed by e-mail of our approach, and he gave his consent as well as his feeling on this project (Richard Powers: ".../... this automated translation project sounds fascinating. I know that the field has taken a big jump in recent years, but each jump just furthers the sense of how overwhelming the basic task is. I would be delighted to let him do a text of mine. Such figurative writing would be a good test, to be sure. .../... "The Book of Me" would be fine, too.").

We selected an essay by Powers, entitled The Book of Me, originally published in GQ magazine. 6 The essay is a first-person narrative set in 2008, in which Powers describes the process by which he became the ninth person in the world to see his genome fully sequenced. Although the topic is genetics and 5 http://en.wikipedia.org/wiki/Richard_ Powers 6 http://www.gq.com/ news-politics/big-issues/200810/ richard-powers-genome-sequence in spite of the simple, clinical style used by the author, The Book of Me is truly a work of literature in which the author, who teaches narrative technique at the university level, never puts aside his poetic ambition, his humour and his fascination for the impact of science and technology on the society.

MT system used

Our machine translation system is a phrase-based system using the Moses toolkit [START_REF] Hoang | Moses: Open source toolkit for statistical machine translation[END_REF].

Our system is trained using the data provided in the IWSLT machine translation evaluation campaign [START_REF] Federico | Overview of the IWSLT 2012 evaluation campaign[END_REF], representing a cumulative total of about 25M sentences:

• news-c: version 7 of the News-Commentary corpus,

• europarl: version 7 of the Europarl corpus7 [START_REF] Koehn | Europarl: A parallel corpus for statistical machine translation[END_REF],

• un: the United-nations corpus,8

• eu-const: corpus which is freely available [START_REF] Tiedemann | News from OPUS -a collection of multilingual parallel corpora with tools and interfaces[END_REF],

• dgt-tm: DGT Multilingual Translation Memory of the Acquis Communautaire [START_REF] Steinberger | DGT-TM: A freely available translation memory in 22 languages[END_REF],

• pct: corpus of Parallel Patent Applications9 ,

• gigaword: 5M sentences extracted from the Gigaword corpus; after cleaning, the whole Gigaword corpus was sorted at sentence level according to the sum of perplexities of the source (English) and the target (French) based on two French and English pretrained language models. Finally, the 5M subset was obtained after filtering out the whole Gigaword corpus with a cut-off limit of 300 (ppl). This leads to a subset of 5M aligned sentences.

Prior to training the translation and language models, various pre-processing steps are performed on the training data. We begin by filtering out badly aligned sentences (using several heuristics), filtering out empty sentences, and sentences having more than 50 words. Punctuation is normalized, and we tokenize the training data, applying specific grammar-based rules for the French tokenization. Spelling correction is applied to both source and target side, and certain words (such as coeur) are normalized. Abbreviations and clitics are disambiguated. Various additional cleaning steps (as described in the list above) were applied to the Gigaword corpus. Many heuristics (rules) were used in order to keep only good quality bi-texts.

From this data, we train three distinct translation models on various subsets of the parallel data (ted; news-c+europarl+un+eu-const+dgt-tm+pct; giga-word5M). The French part of the same corpus is used for language model training, with the addition of the news-shuffle corpus provided as part of the WMT 2012 campaign [START_REF] Callison-Burch | Findings of the 2012 workshop on statistical machine translation[END_REF]. A 5-gram language model with modified Kneser-Ney smoothing is learned separately for each corpus using the SRILM toolkit [START_REF] Stolcke | Srilm: An extensible language modeling toolkit[END_REF]; these models are then interpolated by optimizing perplexity on the IWSLT dev2010 corpus. The weights for the final machine translation system are optimized using the data from the English-French MT task of IWSLT 2012. The system obtains BLEU [START_REF] Papineni | Bleu : A method for automatic evaluation of machine translation[END_REF] scores of 36.88 and 37.58 on the IWSLT tst2011 and test2012 corpora, respectively (BLEU evaluated with case and punctuation).

The training data used is out-of-domain for the task of literary translation, and as such is clearly not ideal for translating literary texts. In future work, it would be desirable to at least collect literary texts in French to adapt the target language model, and if possible gain access to other works and translations of the same author. Additionally, in future work we may examine the use of real-time translation model adaptation, such as [START_REF] Denkowski | Real time adaptive machine translation for post-editing with cdec and transcenter[END_REF].

Post-editing

We use the SECTra w.1 post-editing interface of [START_REF] Huynh | SECTra w.1: an online collaborative system for evaluating, post-editing and presenting MT translation corpora[END_REF]. This tool also forms the foundation that gave rise to the interactive Multilingual Access Gateway (iMAG) framework for enabling multilingual website access, with incremental improvement and quality control of the translations. It has been used for many projects [START_REF] Wang | Online production of HQ parallel corpora and permanent taskbased evaluation of multiple MT systems[END_REF], including translation of the EOLLS encyclopedia, as well as multilingual access to dozens of websites (80 demonstrations, 4 industrial contracts, 10 target languages, 820k post-edited segments).

Figure 1 shows the post-editing interface in advanced mode. In advanced mode, multiple automatic translations of each source segment (for example, from Google, Moses, etc.) can be displayed and corrected. For this experiment, the output of our Moses system was prioritized when displaying segment translations.

Post-editing was done by a (non english native) student in translation studies at Univ. Grenoble-Alpes.

4 Experimental results

Corpus and post-editing statistics

The test data, The Book of Me (see §3.1), is made up of 545 segments comprising 10,731 words. This data was divided into three equal blocks. We apply machine translation and post-editing to the data, as described in §3.2 and §3.3.

Table 1 summarizes the number of source and target (MT or PE) words in the data. Not surprisingly, a ratio greater than 1.2 is observed between French target (MT) and English source words. However, this ratio tends to decrease after post-editing of the French output. The post-editing results reported in Table 1 are obtained after each iteration of the process; the last stage of revision is thus not taken into account at this stage.

Performance of the MT system

Table 2 summarizes machine translation performance, as measured by BLEU [START_REF] Papineni | Bleu : A method for automatic evaluation of machine translation[END_REF], calculated on the full corpus with the systems resulting from each iteration. Post-editing time required for each block is also shown. The BLEU scores, which are directly comparable (because evaluated on the full corpus), show no real improvement of the system. It therefore appears that adaptation of weights alone (which resulted in improvements in [START_REF] Pecina | Simple and effective parameter tuning for domain adaptation of statistical machine translation[END_REF]) is ineffective in our case. However, post-editing time decreases slightly with each iteration (but again, the differences are small and it is unclear whether the decrease in post-editing time is due to the adaptation of the MT system or to in- creasing productivity as the post-editor adapts to the task). In the end, the total PE time is estimated at about 15 hours.

Analyzing the revised text

Reading the translated work at this stage (after PE) is unsatisfactory. Indeed, the post-editing is done "segment by segment" without the context of the full corpus. This results in a very embarrassing lack of homogeneity for a literary text. For this reason, two revisions of the translated text are also conducted: one by the original post-editor (4 hours) and one by a second French-English bilingual serving as a reviewer (6 hours). The final version of the translated work (which has been obtained after 15+4+6=25 hours of work) provides the basis for more qualitative assessments which are presented in the next section. The difference between the rough post-edited version (PE -15 hours of work) and the revised version (REV -25 hours of work) is analyzed in Table 3. It is interesting to see that while the revision takes 40% of the total time, the revised text remains very similar to the post-edited text. This can be observed by computing BLEU between the post-edited text before and after revising; the result is a BLEU score of 79.92, indicating very high similarity between the two versions. So, post-editing and revising are very different tasks. This is illustrated by the numbers of Table 3: MT and PE are highly dissimilar (posteditor corrects a lot of MT errors) while PE and REV are similar (revision probably focuses more on important details for readability and style). More qualitative analysis of the revised text and its comparison with post-edited text is part of future work (and any reader interested in doing so can download our data -see footnote 2 on page 2).

5 Human evaluation of post-edited MT able on github (see footnote 2 on page 2).

After three questions to better understand the profile of the participant (How old are you? Do you frequently read? If yes, what is your best reading genre?), the first portion asks readers five questions about readability and quality of the translated literary text:

• What do you think about text readability?

• Is the text easy to understand?

• Does the language sound natural?

• Do you think sentences are correct (syntactically)?

• Did you notice obvious errors in the text?

The second portion (7 questions) verifies that certain subtleties of the text were understood

• What is the text about?

• Who is the main character of the story?

• Who is funding the genome sequencing?

• Retrieve the right sequence of steps for genome sequencing?

• How many base pairs are in the genome?

• When the novel was written, how many people had already fully sequenced their genome?

• Which genetic variant is associated with a high risk for Alzheimer's disease?

The text is considered to be overall readable (5 Very Good and 3 Good), comprehensible (8 yes, 1 not) and containing few errors (8 seldom, 1 often). The easiest comprehension questions were well handled by the readers, who all responded correctly (4 questions). However, three questions led to different answers from the readers:

• 2 readers responded incorrectly to a seemingly simple question (Who funded the genome sequencing of Powers?)

• The question At the time the story was written, how many people's genomes had been sequenced? was ambiguous since the answer could be 8 or 9 (depending on whether Powers is counted), giving rise to different responses from readers

• Only 4 of 9 readers were able to give the correct sequence of steps in the process of genome sequencing; the translated text is not unclear on this point (the errors are on the part of the readers); this mixed result may indicate a lack of interest by some readers to the most technical aspects of the text.

In short, we can say that this survey, while very limited, nevertheless demonstrates that the text (produced according to our methodology) was considered to be acceptable and rather readable by our readers (of whom 3 indicated that they read very often, 4 rather often, and 2 seldom). We also include some remarks made in the free comments:

• "I have noticed some mistakes, some neologisms (I considered them to be neologisms and not mistranslations because they made sense)"

• "Very fluid text and very easy reading despite precise scientific terms"

• "I found the text a little difficult because it contains complex words and it deals with an area I do not know at all."

The views of R. Powers's french translator

To conclude this pilot study, the views of a tenth reader were solicited: the author's French translator, Jean-Yves Pellegrin, research professor at Paris-Sorbonne University. His comments are summarized here in the form of questions and answers.

Readability? "The text you have successfully reproduces faithfully the content of the article by Powers. The readability bet is won and certain parts (in particular those which relate to the scientific aspects of the described experiment) are very convincing."

So the MT+PE pipeline seems also efficient for obtaining quickly readable literary texts, as it is the case for other domain specific data types.

Imperfections? "There are, of course, imperfections, clumsy expressions, and specific errors which require correction" Top mistakes?

• "The most frequent defect, which affects the work of any novice translator, is the syntactic calque, where French structures the phrase differently .../... One understands, but it does not sound very French"

• "Another fairly common error is the loss of idiomatic French in favor of Anglicisms." Sometimes these Anglicisms can be more disturbing when flirting with Franglais, 11 such as translating 'actionable knowledge' as 'connaissances actionnables' (p. 18) instead of 'connaissances pratiques / utilisables'."

11 Frenglish

• "A third defect is due to not taking into account certain cultural references .../... For example, Powers made several references to the topography of Boston that give rise to inaccuracies in the translation: 'Charles River' for example (p. 12) is not 'une riviere' but 'un fleuve'; that is why we translate by 'la Charles River' or simply 'la Charles'"

The errors mentioned above are considered as not acceptable by a professional translator of literary text. These are hard problems for computer assisted translation (move away from the syntactic calque, better handle idioms and multi-word expressions, take into account cultural references).

Could this text serve as a starting point for a professional literary translator? "Instinctively, I am tempted to say no for now, because from his first cast the translator has reflexes that allow him to produce a cleaner text than the one you produced .../.... however, this translator would spend more than 25 hours to produce the 42 pages of 1500 characters that comprise Power's text. At a rate of 7 pages per day on average, it would take 6 eight-hour days. If, however, I could work only from your text (while completely forgetting Powers's) and I could be guaranteed that your translation contains no errors or omissions from the original, but just that it needs to be improved, made more fluid, more authentically French, things would be different and the time saved would be probably huge."

As expected, the professional translator of literature wants to control the whole translation process. But the last part of his comment is interesting: if the meaning was guaranteed, he could concentrate on the form and limit going back and forth between source and target text. Thus, working more on quality assesment of MT and confidence estimation seems to be a promising way for future work on literary text translation. Based on the translation speed rates provided by Pellegrin, we can estimate the time savings of our technique. Our computerassisted methodology can be said to have accelerated the translation factor by a factor of 2 -our process took roughly 25 hours, compared to the 50 hours estimated for a professional literary translation.

Collected Data Available Online

The data in this article are available at https://github.com/ powersmachinetranslation/DATA. There one can find:

• The 545 English source and French target (MT, PE) segments mentioned in Table 1 • The translated and revised work (REV in Table 3), in French, that was read by a panel of 9 readers

• The results of the survey (9 readers) compiled in a spreadsheet (in French)

Comments and open questions

We presented an initial experiment of machine translation of a literary work (an English text of about twenty pages). The results of an MT+PE pipeline were presented and, going beyond that, the opinions of a panel of readers and a translator were solicited.

The translated text, obtained after 25 hours of human labor (a professional translator told us that he would have needed at least twice that much time) is acceptable to readers but the opinion of a professional translator is mixed. This approach suggests a methodology for rapid "low cost" translation , similar to the translation of TV series subtitles found on the web. For the author of the literary text, this presents the possibility of having his work translated into more languages (several dozen instead of a handful, this short story by Richard Powers has also been translated into Romanian using this same methodology). But would the author be willing to sacrifice the quality of translation (and control over it) to enable wider dissemination of his works? For a reader who cannot read an author in the source language, this provides the ability to have faster access to an (admittedly imperfect) translation of their favorite author. For a non-native reader of the source language this provides a mechanism for assistance on the parts he or she has trouble understanding. One last thing: the title of the work The Book of Me has remained unchanged in the French version because no satisfactory translation was found to illustrate that the author refers both to a book but also to his DNA; this paradox is a good illustration of the difficulty translating a literary work!

Thanks

Thanks to Manuela Barcan who handled the first phase of post-editing machine translations in French and Romanian during the summer of 2013. Thanks to Jean-Yves Pellegrin, French translator of Richard Powers, for his help and open-mindedness. Thanks to Richard Powers who allowed us to conduct this experiment using one of his works.

Figure 1 :

 1 Figure 1: Post-editing interface in advanced mode

Table 1 :

 1 Iteration (no. seg) English (no. words) French MT (no. words) French PE (no. words)

	Iteration 1 (184)	3593	4295	4013
	Iteration 2 (185)	3729	4593	4202
	Iteration 3 (176)	3409	4429	3912
	Total (545)	10731	13317	12127

Number of words in each block of the English source corpus, French machine translation (MT), and French post-edited machine translation (PE).

Table 2 :

 2 BLEU after tokenization and case removal on full corpus, and time measurements for each iteration

	5.1 The views of readers on the post-edited
	translation
	Nine French readers agreed to read the final trans-
	lated work and answer an online questionnaire. The
	full survey is available on fluidsurveys.com. 10 . A pdf
	version of the test results and a spreadsheet file con-
	taining the results of the survey are also made avail-
	10 https://fluidsurveys.com/
	surveys/manuela-cristina/
	un-livre-sur-moi-qualite-de-la-traduction/
	?TEST_DATA=

Table 3 :

 3 Automatic Evaluation (BLEU) on full corpus between unedited machine translation (MT), post-edited machine translation (PE), and revised post-edited machine translation (REV).

The work of[START_REF] Garcia | Translating by post-editing: is it the way forward[END_REF] is somewhat controversial, because the manual translation without post-editing appears to have been done without allowing the translator to use any form of digital assistance, such as an electronic dicitonary.

http://www-clips.imag.fr/geod/User/ marion.potet/index.php?page=download

http://www.statmt.org/europarl/

http://www.euromatrixplus.net/multi-un/

http://www.wipo.int/patentscope/en/ data/pdf/wipo-coppatechnicalDocumentation. pdf