Fernandez Castro

Aurélie Clodic

Rachid Alami

Elisabeth Pacherie

V Fernandez Castro
email: victor.fernandez-castro@laas.fr

Commitments in Human-Robot Interaction

come

Introduction

A central challenge in human-robot interaction is to devise robots capable of interacting with humans to perform socalled joint actions, social interactions where two or more participants coordinate their actions in space and time to bring about a change in the environment [START_REF] Sebanz | Joint action: bodies and minds moving together[END_REF]. The notion of commitment plays a pivotal role in understanding joint action [START_REF] Cohen | Teamwork[END_REF]Bratman 1992;Gilbert 2009). In order to perform a joint action, co-agents need to establish and handle commitment regarding the shared goals and plans involved in the joint action. However, the study of commitments in the context of human-robot collaborative task achievement is quite new.

As a first approximation, a commitment is in place when an agent (the author of the commitment) has given an assurance to an another agent (the recipient of the commitment) that she will act in a certain way, when, as a result, the recipient has formed an expectation regarding the actions of the author, and when there is mutual knowledge by both parties that this is the case. In order to build our framework of commitments, we discuss two specific philosophical approaches that emphasize different, though complementary, aspects of commitments: (1) The functional approach and (2) The normative approach. The first emphasizes the function of commitments, how expectations reduce different forms of uncertainty. The second emphasizes how such a function is carried out; namely, by creating obligations towards one's co-agents and their corresponding entitlements to demand that these obligations be satisfied. In order to demonstrate how these approaches can give hints on the implementation of strategies for HRI, we consider a use-case, in which a robot guide takes a visitor to its destination (e.g. Rackham at the Space City Museum [START_REF] Clodic | Rackham: An interactive robot-guide[END_REF]). Although there is already previous research on commitments in social robotics, this work is a first step towards generating a framework that gives theoretical support to this previous research and at the same time generates new avenues for future investigations.

Two Philosophical Aspects on Commitments

Establishing commitments requires the participants involved to generate reliable expectations about the content of the commitment, for instance, making a promise that one will perform a particular objective or giving implicit signals that one act in a particular way. But why do we generate such expectations? Why do we need to establish such commitments?

The Functional Approach

Arguably, what distinguishes a joint action (e.g. walking together) from the mere coordination of behavior (two people randomly walking at the same pace) is that the partners are committed to achieve a goal together (Gilbert 2006). Furthermore, such a participatory commitment comes often with other contralateral commitments (Roth 2004) associated to the general goal or the plan necessary to achieve it (e.g. not speeding up, or waiting for your partner if he's left behind).

The necessity of establishing these different commitments comes from the fact that even assuming that the partners desire the outcome to be the case, different sources of uncertainty could prevent the joint action from being carried out. As [START_REF] Michael | On Commitments and Other Uncertainty Reduction Tools in Joint Action[END_REF] argue, participants can face three sources of uncertainty during joint action:

1. Motivational uncertainty: participants may not know whether or not the partner is motivated to engage in the joint action. Thus, they cannot be sure how convergent their respective interests are or whether or not they shared a goal. 2. Instrumental uncertainty: participants may not know whether or not they agree about how to proceed; for instance, how the participants must distribute their roles or when and where they must act. 3. Common ground uncertainty: it may happen that the instrumental beliefs and motivations are not mutually manifested. Thus, even if the participants share a goal or they agree about how to proceed, they might not know that this is the case.

But how do commitments reduce these sources of uncertainty? According to the functional approach supported by [START_REF] Michael | On Commitments and Other Uncertainty Reduction Tools in Joint Action[END_REF], generating commitments reduces uncertainty by stabilizing expectations regarding actions, beliefs and motivations and thus, facilitating the prediction of the other co-actors, which makes the joint action more fluent and efficient. In their view, the key aspects of commitments are related to how the expectations are generated, and thus, how the commitments are established. For instance, how co-agents generate expectations through implicit and explicit communication [START_REF] Austin | How to do things with words[END_REF]Siposova, Tomasello, and Carpenter 2018) or repetition (Gilbert 2006;Michael, Sebanz, and Knoblich 2016).

The Normative Approach

In a recent paper, Fernandez Castro and Pacherie (2019) have focused on a different aspect of commitments, namely, how they create obligations towards one's co-agents who are entitled to demand that these obligations be satisfied, giving rise to expectations that the agent will act as committed or that, if not, co-agents will demand that she does. This view shares with the functional approach the idea that expectations are the central element of commitments. However, they argue that the expectations generated by commitments are of a special kind: normative expectations.

In philosophy of mind, several authors (Greenspan 1978;Paprzycka 1999;Wallace 1998) or frustration triggers reactive attitudes: blame1 , request for justification or sanctions. These types of expectations are connected to the notion of holding someone on a demand. That is, the normal response to its frustration is to impose a negative reaction to the other agent for not acting as expected. Such negative reactions are more emotionally loaded and aimed at regulating the other's behavior. For instance, you can feel entitled to sanction your friend when he frustrates your expectation that he will cede his seat to an older person on the subway.

On the normative view, commitments serve to create for oneself, or the other agent, normative expectations, so we can ensure that every participant behaves as expected. In this view, the key aspect of commitments is how we display different communicative and behavioral strategies to make explicit our obligations towards our partner and their own obligations towards us; for instance, by blaming, making the other aware of what is expected or apologizing when something goes wrong.

At this point, it is worth noticing that the two approaches are not necessarily incompatible. In fact, to the extent that they emphasize different aspects of how agents handle commitments, they can be regarded as complementary. In our view, managing commitments involves both generating expectations that facilitate the reduction of uncertainty and displaying repairing and regulative strategies when such expectations are frustrated.

Related work

Several computational models of commitment management have already been proposed. Joint intention theory [START_REF] Cohen | Intention is choice with commitment[END_REF] introduces the notion of commitment in relation to the goal of the collaborative task: "if a team is jointly committed to some goal, then under certain conditions, until the team as a whole is finished, if one of the members comes to believe that the goal is finished but that this is not yet mutually known, she will be left with a persistent goal to make the status of the goal mutually known". Shared Plans theory [START_REF] Grosz | Collaborative plans for complex group action[END_REF] uses individual intentions to establish commitment of collaborators to their joint activity. Interestingly, Shared Plans theory proposes also the notion of agent's commitments to its collaborating partners' abilities, as well as the notion of helpful behavior and contracting action. Other works emphasize grounding as a kind of commitment (Clark 1996;Clark 2006): "Once we have formulated a message, we must do more than just send it off. We need to assure ourselves that is has been understood as we intended to be." Clark also proposes to consider on one side basic joint activity or joint activity proper and on the other side the coordinating joint actions based on communicative acts (Clark 2006). In the same vein, [START_REF] Klein | Common Ground and Coordination in Joint Activity[END_REF] describes "basic compact" as a kind of contract that need to be shared by the cooperative agents.

Several implementations using commitments have also been proposed2 , for instance, Collagen architecture (Rich, Sidner, and Lesh 2001;[START_REF] Sidner | Explorations in engagement for humans and robots[END_REF]) in collaborative conversation. In human-robot interaction, we can find implementations of commitments in different settings such as in Human-Robot Interaction Operating System [START_REF] Fong | [END_REF], robot behavior toolkit [START_REF] Huang | The repertoire of robot behavior: Enabling robots to achieve interaction goals through social behavior[END_REF], robot tutelage [START_REF] Hoffman | Effects of anticipatory action on human-robot teamwork: Efficiency, fluency, and perception of team[END_REF] or linked to supervision, communicative acts and grounding [START_REF] Clodic | A management of mutual belief for human-robot interaction[END_REF], (Clodic 2007).

In the framework of Rackham, a robot guide at the Space City museum 3 from 2002 to 2005 [START_REF] Clodic | Rackham: An interactive robot-guide[END_REF], we also already used the notion of commitments. In that experiment, we defined a set of commitments to the task : Rackham commitment to the task (obtained when the robot decided to do the task), Rackham's belief concerning the visitor's belief about Rackham commitment to the task (obtained once the robot told the visitor that it will perform the task), Rackahm's belief concerning the visitor commitment to the task (obtained once the visitor agrees to do the task). However, commitments were mostly used at task setup and not really handled during task execution.

The model we propose hereafter takes inspiration from this work. It could be seen as complementary to these models, theories and implementation as it helps to focus on the way we could define and manage commitments during the execution of the task and not just on how commitments can be established at the beginning of the task. The Rackham experiment [START_REF] Clodic | Rackham: An interactive robot-guide[END_REF]) allowed us to note the importance of the quality of interaction. We noticed that: "a continuous interaction all along the mission is fundamental to keep visitor interest. The robot must continuously check the presence of the guided person, show him that it knows where (s)he is (...)". At that time, it was difficult for us to model that since it was not really part of the task by itself and was done in an intuitive way. In one sense, we think that the theoretical framework we propose here will help us to capture and flesh out this intuition.

Implementing Commitment Framework

We have not yet implemented the proposed framework. Here, we are introducing it using an example, a robot guide such as Rackham at the Space City Museum. In that example, once the destination has been chosen, there should be a joint task of "go to the destination" where Rackham should "execute trajectory" whereas the visitor should "follow the robot". Regarding commitments, we propose that managing commitments is a social skill which requires capacities that are independent of the capacities required to perform the particular actions in place (e.g. execute trajectory for Rackham and follow the robot for the visitor). In our case, that means that commitment management could be modeled as something aggregated to the actions of the task and linked to expectations.

Given the lessons of the functional and the normative approach, we advance that the function of commitment as a reduction of uncertainty and its normative aspect must be two fundamental elements of the framework. Such elements are present in two different moments of the joint action. First, its function as a reduction tool is exhibited in the repertoire of 3 http://www.laas.fr/robots/rackham actions dedicated to insuring the mutual understanding that the commitment is in place before and during the interaction. Second, its normative aspect becomes evident when the commitment is frustrated and certain reactions, responses, and repairs became necessary. In what follows, we present how our framework would depict these two moments.

Generating Commitments

Considering a commitment as a reduction tool implies that ascribing or representing a partner as undertaking a commitment must be tied to a repertoire of actions aiming at insuring the establishment of a mutual understanding of the expectations involvede.g. social signals and cues or regulative actions. Such actions can vary depending on whether or not the actor is the agent expecting the other to perform the action (assigning a commitment) or the agent who should act as expected (undertaking the commitment). In our example, Rackham can expect the human to follow him and undertake the commitment of adapting the speed to human pace (which can also be modeled as the human expectation regarding the robot). For a sake of simplicity, from the robot point of view, such difference can be represented in terms of assignations of expectations:

• Expectation (Human follows)

• Expectation (Robot adapts speed)

Given the function of commitments, the robot must be able to actively provide different cues that facilitate human understanding of the expectations in place, but also, he must be able to monitor that the human is behaving as he should (See Figure 1). In the guiding example, when Rackham expects the human to follow (Expectation (Human follows)), he must possess the following capacities:

• Exhibiting/Signaling the expectation Rackham must provide reliable cues regarding what he expects from the visitor in order to make him aware of it. One way of establishing such a signal is through verbal communication, for instance, saying "I accompany you to your destination, please follow me".

• Monitoring: Rackham must be able to recognize the visitor's action and be sure he is behaving as expected, that is, monitoring that the visitor is following.

Certainly, the type of reliable signals in place varies with the assignation of expectations. In this case, when the expectation involves the robot itself, he must be sure that the human knows what he is going to do, so the human does not face any type of uncertainty regarding robots behavior. Furthermore, the dynamic nature of joint actions requires the participants to reinforce the pertinent expectations. In our example, thus, assignation of expectations to the human (Robot adapts speed) must be tied to the following capacities:

• Anticipating Expectation: Rackham must make clear that he is capable of adapting to the speed to the human, for instance, using verbal expressions like indirect speech acts (Are you in a rush? We can go faster if you want). 2) When the robot assigns a commitment to itself (he must adapt speed (Robot adapts speed)), the following capacities are required: Anticipating expectations to make the human aware of the robots obligations ; Reinforcing expectations: to make the human aware that the robot that he keeps committed to the task.

• Reinforcing Expectation: Rackham must maintain the human expectation that the robot will adapt to his speed. For instance, exhibiting some back and forth movement that makes the human aware that Rackham is still committed to the task.

Repairing

Of course, expectations can be frustrated or fulfilled, and this is where the normative aspects of commitments are made explicit. As the normative approach emphasizes, commitments enable participants to hold others on demand and regulate and influence their actions when a particular action is frustrated. This gives to social robotics an important element to improve social interaction by using commitment management as a mechanism for reparation. Given our representation of expectations (Expectation (Human follows)/Expectation (Robot adapts speed)), we can assume two plausible violations in the context of our example:

• The violation of Expectation (Human follows): the visitor does not follow. • The violation of Expectation (Robot adapts speed): the robot is going too slow (or too fast) or the human bump into the robot Now, considering the first type of violation, the robot must be able to execute two different actions: reaction and repair. The reaction is necessary to make the human understand that the expectation has been frustrated, and thus, that he is responsible for his commitment. Furthermore, such a reaction must be a facilitator for negotiating a re-engagement or repair. In our example, we can implement these two actions as follows:

• Reaction: when the expectation is frustrated (e.g. the visitor does not follow), Rackham must be able to react to the violation in a way that makes the visitor aware that he should be following. For instance, Rackham could stop, look back and adopt a posture of wait-and-see attitude.

• Repair: Rackham must be equipped with repairing strategies that facilitate the re-engagement in the task, for instance, approaching the visitor and asking whether everything is all right. Such a reparation would facilitate the conclusion of the general task, but also, it would make the human aware of his obligations to the robot, reinforcing the motivation for interaction.

Concerning the violation of the robot expectation, the necessary abilities of the robot should differ in several respects. In addition to being able to react and repair in a different way to when it is the human who is at fault, the robot must be able to recognize plausible signals that it is not behaving as expected 4 . In our example, these capacities can be regarded as follows:

• Recognition of reactions: when the expectation is frustrated (e.g. Rackham goes too fast or too slow), the robot must be able to notice when the visitor does not follow anymore or, on the contrary, bumps into the robot because it is too slow. Moreover, Rackham must be able to recognize some natural reactions to violation of expectations, like verbal petitions such as "Hey!" or "Wait for me!. • Reaction: the recognition that the robot has violated an expectation must trigger an excusing reaction to make the visitor aware that it knows that it has violated the commitment; for instance, apologizing to the visitor. • Repair: the reaction must be followed by a repair strategy of the commitment to ensure that the joint action takes place; for instance, slowing down or speeding up according to the human's needs.

Future Work

In the previous sections, we have proposed that designing social robots with the capacity for managing commitments can facilitate human-robot interaction. Our central 4 Certainly, we could provide more autonomy to the capacity of the robot to handle commitments by given the capacity of evaluating the situation and recognize that he may not be fulfilling the expectation, and thus, reacting and repairing before the human expresses his discontent. contention is that such a capability, understood as necessary for, but independent of, joint action, plays a central role in the reduction of different types of uncertainties and as a way of enabling participants to react to frustrations of expectations that may undermine the task. Drawing on philosophical approaches to commitments, we have proposed that a commitment management mechanism must be composed of different sub-capabilities for signaling, recognizing signals, monitoring actions, reacting to violations, and repairing different expectations on both the human and robot side. In this section, we would like to propose two lines of development that, we believe, could enrich our framework and open future research avenues.

First, an important way to in which our framework could be extended is by considering the capacity for selecting different signaling strategies depending on the partner. Conforming to expectations or commitments strongly depends on a variety of motivational sources including emotions [START_REF] Fehr | Social neuroeconomics: the neural circuitry of social preferences[END_REF]Sugden 2000;[START_REF] Colombo | Caring, the emotions, and social norm compliance[END_REF]), pro-social dispositions (Godman 2013), need to belong (Fernandez Castro and Pacherie 2019) or reputation management (Michael, Sebanz, and Knoblich 2016). These types of motivations are important when deciding on and selecting the appropriate signal for a particular expectation. For instance, a robot should be capable of deciding on the most appropriate way to ask someone to do something (e.g. using a flat or jovial tone of voice) depending on the assumed mo-tivation in the context (e.g. reputation in a context of work vs pro-social disposition in a playful context). Moreover, ideally, taking into account these motivational components would not only help the robot to select the appropriate signal for a particular expectation but also, to identify and adapt to the particular type of signal used by the human. Being capable of distinguishing someone's motivation and readiness to interact (e.g. distinguish a good teammate from a bad teammate) would provide the robot with better means of adapting and reacting to possible violations during the joint action.

Second, another future direction of research for our framework would be to explore more robust and flexible ways of dealing with the reactions to violations of expectations. Following the functional approach to the notion of commitment, we can advance that an important number of frustrations of expectations would depend on one of the different types of uncertainties (motivation, instrumental or common ground). One plausible improvement of our framework would be dedicated to designing robots capable for determining which source of uncertainty causes the violation and being able to select different repair strategies and reactions depending on the source. To give an example, if Robot could determine the reason why the visitor does not follow it, e.g. motivation: the visitor found a friend; instrumental: the visitor found an obstacle, it could adapt its answer depending on this factor, for instance, waiting for the human, or approaching her and giving assistance.

Conclusion

Managing commitments is a central aspect of joint action, and thus, it should be taken into consideration in the design of social robots. In order to do that, we have explored how different philosophical approaches to commitment can provide useful suggestions to roboticists for designing more efficient robots capable of engaging in joint actions. We have presented two complementary proposals that emphasize different behavioral and cognitive aspects of commitments that we must concentrate on for the study of joint action for human-robot interaction.

To design capacities for managing commitments, we must give to the robot abilities to signal its expectations on the one hand and to monitor humans expectations, reactions and signals on the other. We must also give the human different means of understanding the robot's expectations, reactions and signals on the one hand and of conveying his expectations to the robot on the other. These monitoring and signaling abilities should not be considered part of the action in itself but are needed for the interaction. In this sense perhaps, we should design a kind of code to help the management of these aspects on both the robot's and on human side (e.g. a kind of common interface that is understandable by every robot).

Finally, we have advanced two different research avenues that may enrich our framework. First, one may explore how to design more flexible and adaptable signals depending on the assumed source of motivation behind the joint action. Moreover, such a detection of motivation may help the robots to adapt in case of violation. Second, we have speculated that, when there is a violation of expectation, the source of the violation could come from the different uncertainties explored by the functional approach. As a result, a plausible line of investigation may research how to design the ability to determine the source of violation and adapt depending on the source.

Figure 1 :

 1 Figure 1: Framework for generating commitments for a guiding task: 1) When the robot assigns a commitment to the human (the human must follow (Human follows)), the following capacities are required: Exhibiting expectations to make the other aware of her obligations; Monitoring expectations: observe and analyse the other agent behavior and detect if she violates expectations.2) When the robot assigns a commitment to itself (he must adapt speed (Robot adapts speed)), the following capacities are required: Anticipating expectations to make the human aware of the robots obligations ; Reinforcing expectations: to make the human aware that the robot that he keeps committed to the task.

Figure 2 :

 2 Figure2: Framework for repairing when a case of violation is detected: 1) When the robot detects a violation of the human, he must React to violation of expectations to make the other aware that their obligations are not satisfied; Repair the joint action. 2) In the case of the robot violation, he must Recognize reactions in order to detect the violation; React to make the human aware that he knows that he made a mistake; and Repair the joint action.

The notion of blame must be understood in very general terms and without moral burden in here; that is, as a reaction that serves to sanction negatively a conduct, whether this conduct is a violation of a moral norm or not.

In the robotic domain, it is the word "engagement" and not "commitment" which is often used. For the sake of simplicity we will continue using the term "commitment" in the paper

Acknowledgments

This work was supported by the ANR JointAction4HRI project (jointaction4hri.laas.fr), grant ANR-16-CE33-0017 of the French Agence Nationale de la Recherche.


Philippe Béarez

Laurie Bouffandeau

Fishing for survival: The forgotten slaves of Tromelin Island (Indian Ocean)

Keywords: Shipwreck, maritime archaeology, subsistence strategy, ichthyoarchaeology, fish 1 |

Fishing for survival: The forgotten slaves of Tromelin

Island (Indian Ocean)

understand how humans are able to overcome the obstacles to survival. Moreover, a better understanding of the survival capacity of a human group on a small isolated island can provide useful information on the lifestyles and resilience of the first coastal inhabitants in a given area.

Several famous shipwrecks on tropical Indo-Pacific islands are known but little information is available concerning the daily subsistence of the survivors. For example, in 1629, the ship Batavia from the Dutch East India Company, with more than 300 people on board, was wrecked on the Houtman Abrolhos archipelago, 60 km from the Western Australian mainland [START_REF] Green | The VOC ship Batavia wrecked in 1629 on the Houtman Abrolhos, Western Australia[END_REF]. Their search for drinking water is described but nothing is known about their fishing activities.

Maritime and shipwreck archaeology are even less developed in the western Indian Ocean [START_REF] Lane | Maritime and shipwreck archaeology in the western Indian Ocean and southern Red Sea: An overview of past and current research[END_REF]. At Tromelin, we have a rare opportunity to document the marine resources exploited for survival on a small island by a relatively well-known number of people over a known period of time of 15 years.

On November 17, 1760, l'Utile, a cargo ship belonging to the French East India Company, departed from Bayonne, France, with 140 crew members, whose mission was to supply the colonies of the Indian Ocean [START_REF] Guérout | Tromelin. L'Île aux esclaves oubliés[END_REF]. After their safe arrival at Mauritius Island, the ship was sent to Foulpointe, Madagascar, to bring back rice and beef.

However, the captain decided to fraudulently embark 160 Malagasy slaves to be sold at Rodrigues Island before joining Mauritius. The ship, having deviated from its route, was shipwrecked during the night of July 31, 1761, on the edge of the Isle of Sands, today called Tromelin Island (Fig. 1). The 45 m-long ship ran aground and broke over the coral reefs surrounding the deserted island; 70 slaves drowned locked in the hold, and 18 sailors were carried away by the stormy sea. The 210 survivors who reached the beach recovered any debris from the wreck, especially food and drink. Although they tried to organise themselves to survive, dehydration killed 8 further slaves before a well of brackish water was dug. Over the next two months, camps separating the slaves from the crew were set up, an oven and a forge were built, and the few available food resources on the island were exploited: birds, sea turtles and marine fishes. Faced with the lack of help, the French crew left Tromelin on September 27, 1761, aboard a makeshift boat, La Providence, built using debris from l'Utile.

They abandoned 80 survivors on the island [START_REF] Guérout | Tromelin. Mémoire d'une île[END_REF], promising to return to seek them: the Malagasy slaves were to be trapped there for 15 years and many died. Guérout and Romon (2015: 112) consider that after three years, only 13 survivors occupied the island for the 12 remaining years. On November 29, 1776, the 8 remaining survivors, 7 women and a 7-month-old infant, were eventually rescued by the corvette la Dauphine under the where they were declared free [START_REF] Guérout | Tromelin. L'Île aux esclaves oubliés[END_REF]. testimonies as well as the historical written sources allowed Max Guérout (Groupe de Recherche en Archéologie Navale: GRAN) to shed light on this event [START_REF] Guérout | Tromelin (Océan Indien)[END_REF]. With the collaboration of Joe Guesnon (GRAN) and Thomas Romon (Institut National de Recherches Archéologiques Préventives: INRAP), terrestrial and underwater archaeological excavations were conducted in Tromelin in 2006Tromelin in , 2008Tromelin in , 2010Tromelin in and 2013, as , as part of a project sponsored by the UNESCO project, 'Forgotten Slaves', documenting the slave trade in the Indian Ocean, particularly in Madagascar [START_REF] Guérout | Tromelin (Océan Indien)[END_REF].

The archaeological study of Tromelin, the extreme conditions prevailing on the island and the peculiar human context related to the shipwreck of L'Utile, offers a rare opportunity to enrich our knowledge on the survival behaviours of the displaced Malagasy people and their ability to rapidly adapt to hostile conditions. The diet of the survivors relied almost exclusively on nesting green sea turtles and colonies of terns (Laroulandie & Lefèvre, 2014 and unpublished data) and marine fishes. The aim of this ichthyoarchaeological study is to document the fish exploitation strategies implemented by the shipwrecked survivors. The quantification, the taxonomic identification of the fish remains and the analysis of their spatial distribution provided data that allowed us to characterise what part fish played in their diet and the fishing techniques they likely used.

| CONTEXT

Tromelin Island (54° 31' E, 15° 53 S) is a small, oval coral island of about 1 km², measuring 1500 x 700 m (Fig. 2). It is composed of white sand, microdunes and scattered coral blocks surrounded by beach sandstone slabs and storm slopes. The highest point of the island is in the north and culminates at 8.5 m altitude [START_REF] Marriner | The forgotten slaves of Tromelin (Indian Ocean): New geoarchaeological data[END_REF]. The island of Tromelin is surrounded by a reef flat nearly 400 m wide, with furrows corresponding to tidal F o r P e e r R e v i e w channels exposed at low tide and ending in a coral reef and a sandy outer slope. The foreshore area is subject to heavy surf, violent currents and breakers, especially on the south coast of the island [START_REF] Marriner | A geomorphological reconnaissance of Tromelin Island, Indian Ocean[END_REF]. The area is also affected by tropical disturbances and cyclones are common. Tromelin is swept by the prevailing trade winds and the swell can penetrate up to 250 m inside the island during the most intense storms. Palaeostorm levels are clearly visible in the sedimentary records: brutal cyclones cause the movement and spreading of sand, forming storm leashes. The layer associated with the 18th century's occupation has been preserved and sealed by a sterile level of storm deposit composed of beach sand [START_REF] Guérout | Tromelin. L'Île aux esclaves oubliés[END_REF]. The vegetation of the island is very limited, and trees are absent. However, there are velvet shrubs (Tournefortia argentea), which can grow up to 2.5 m tall, herbaceous meadow (Boerhavia diffusa), which are subservient to microdunes, as well as purslane (Portulaca oleracea), and the Durand potato (Ipomoea pes-caprae). Almost no plant remains have been recovered at the site (M.-P. Ruas pers. comm.). Terrestrial fauna is also restricted [START_REF] Paulian | Observations sur la faune terrestre de l'île Tromelin[END_REF] but well represented in the archaeological records. Rare remains of small mammals and rats, and a pig canine, probably exogenous, have been discovered and are under analysis. Avifaunal remains are dominated by the sooty tern (Onychoprion fuscatus), which no longer breeds on the island, with noddy (Anous sp.), tropicbird (Phaethon sp.), booby (Sula sp.) and frigatebird (Fregata sp.) also represented in the assemblages [START_REF] Laroulandie | The use of avian resources by the forgotten slaves of Tromelin Island (Indian Ocean)[END_REF].

Marine archaeofauna unearthed on the site is much more diverse and consists of fishes, crustaceans, molluscs, including giant clams (Tridacna spp.), and green sea turtle (Chelonia mydas). Indeed, Tromelin is part of the Indo-Pacific biogeographic zone and is endowed with a rich marine biodiversity. Yet, scientific surveys and inventories for Tromelin are rare and its fish fauna is poorly known.

All of the post-shipwreck related areas were investigated during the four archaeological campaigns, including those on the beach, constituting the crews' and slaves' occupation zones during the first two months, and Site 5, called "High Point", in the north of the island (Fig. 3). Disturbances related to the construction of the meteorological station and the uncertain state of conservation of structures built by the slaves led to the implementation of emergency excavation strategies specific to preventive archaeology. Some areas have been opened with an excavator; others were searched by hand and sometimes screened. The stratigraphy of the site, except in the sector where disturbances were recorded, was relatively clear and marked out by layers resulting from climatic phenomena [START_REF] Marriner | The forgotten slaves of Tromelin (Indian Ocean): New geoarchaeological data[END_REF]. The lithified storm deposit C5 is a non-anthropized layer, which lies on the coral substrate. It is in the C4 cultural level, corresponding to the occupation of the shipwreck survivors between 1761 and 1776 and divided into 3 sub-levels (C4a, b and c), that most of the remains have been uncovered. It is partly sealed with a storm level, called C3. Layer C2 constitutes a palaeosol posterior to the rescue of the slaves but anterior to construction of the meteorological station, between 1776 and 1950, sometimes disturbed in its lower part (C2b).

Layer C1 is composed of the embankment resulting from the construction of the meteorological station, post-1950 (Guérout & Romon, 2015: 146).

| MATERIAL AND METHODS

The totality of the 4282 Teleostei and Chondrichthyes bones studied here were unearthed in Site 5, between 2006 and 2013. These remains stem from sediments collected in sectors corresponding to the habitat of the Malagasy people after the departure of the French crew. The sediments were sieved through meshes of different sizes (2, 3 and 5 mm) according to the sectors and structures. These protocol differences did not allow for a spatial analysis. The fish bones were relatively well-preserved and with low rate of fragmentation; the sand layer which fixed the occupation level enabled good preservation by protecting the remains from climatic hazards. Several cut marks and burning traces were also observed on some remains and have been specified and recorded. All anatomical elements were considered in the analysis, cranial as well as post-cranial [START_REF] Reitz | Zooarchaeology[END_REF][START_REF] Bouffandeau | Fishing at Arapus-Mangaasi, Efate, Vanuatu (2800-2200 BP): New methodological approaches and results[END_REF]; however, no otoliths were found. Taxonomic identification, by morphological comparison was attributed to species level whenever possible, using the osteological reference collection housed at the National Museum of Natural History, Paris. This collection includes more than 850 Indo-Pacific fish specimens (ca 90 families, 220 genera, 475 species). Publications presenting regional ichthyofaunal lists [START_REF] Terashima | Field guide to coastal fishes of Mauritius[END_REF][START_REF] Letourneur | An updated checklist of the marine fish fauna of Reunion Island, South-western Indian Ocean[END_REF] were also necessary to guide the identifications and target local taxa within the rich Indo-Pacific biodiversity. The quantitative approach was based on counts and weights: the total Number of Remains (NR), composed of all identified or unidentified bone elements; the Number of Identified Specimens (NISP), and the Weight of Identified Specimens (WISP). The counts of the Minimum Numbers of Individuals (MNI) were performed by excavated units and then aggregated by levels. We used the MNI per combination [START_REF] Poplin | Remarques théoriques et pratiques sur les unités utilisées dans les études d'ostéologie quantitative, particulièrement en archéologie préhistorique[END_REF].

The body weight of each identified individual was visually estimated by comparison with the specimens available in the reference collection, in order to obtain average dimensions of the fishes composing the assemblage and refine the interpretations. By combining medium weight of individuals and MNI for each species we could roughly evaluate the total biomass of fish, from which we could obtain the edible biomass, by taking the 50% of the total weight (Torry Research Station, 1989).

The horizontal distribution of the fish remains in the levels was also examined, since it is likely to reveal potential functional areas and/or particular fish processing and consumption methods by the occupants of the site.

Finally, we took advantage of the many underwater photographs taken by the divers during the underwater prospections and excavations around the island. Most of the coral, benthic and pelagic fish taxa, visible on the photographs could be identified with the help of fish guides [START_REF] Terashima | Field guide to coastal fishes of Mauritius[END_REF][START_REF] Taquet | Poissons de l'océan Indien et de la mer Rouge[END_REF]: surgeonfishes (Acanthuridae), triggerfishes (Balistidae), jacks (Carangidae), sharks (Carcharhinidae), butterflyfishes (Chaetodontidae), stingrays (Dasyatidae), wrasses (Labridae), snappers (Lutjanidae), moray eels (Muraenidae), angelfishes (Pomacanthidae), damselfishes (Pomacentridae) and groupers (Serranidae). In some instances these photographs helped us to be more confident with species attribution of fish bones, especially for large individuals of jack, snapper and triggerfish.

| RESULTS

| Assemblage composition

Out of the 4282 studied fish remains, 889 were taxonomically identified (NISP), representing 1/5 of the assemblage in terms of number of remains and 2/3 (760 g) of the total fish bone weight (Tab. 1). The MNI was estimated at 518. Table 1. List of taxa identified with their numbers of remains, MNI and bone weight.

The relatively low identification rate, despite good conservation, can be explained by the strong representation of non-diagnostic elements such as scales (NISP = 1326), or fin elements such as spines and pterygiophores (Tab. 2). Vertebrae, whose identification is more challenging, were also present in significant number (NISP = 666). However, the fact that there is no perceptible imbalance between the number of cranial and postcranial elements, along with the occurrence of numerous scales, seems to indicate that the fish were brought back whole to the habitat zone and scaled on site.

Table 2. Distribution of fish skeletal parts.

The good preservation of fish bones enabled the reliable identification to species level in several cases (Tab. 1; Fig. 4). Among the identified taxa, a clear majority belong to the Teleostei or bony fish (Fig. 5), whereas Chondrichthyes, such as sharks (NISP = 3) and rays (NISP = 1) are poorly represented. The diversity within teleosts is important, since at least 22 families and 41 genera compose the assemblage. The modern species observed during the underwater prospections (N = 62) correspond well to those identified in the archaeological material (Tab. 1; Tab. 3). Carangidae, or jacks, largely dominate the faunal spectrum (Fig. 6), in NISP (49%), MNI (42%) and WISP (66%). However, it is not surprising that these carnivorous pelagic fishes, frequently encountered around coastal reefs and oceanic islands, are well represented as they are a common prey of anglers. The diversity of the identified carangids is quite high (at least 7 species), although the genus Caranx dominates. Among this genus, many identified specimens exceed 10 kg and, in some cases, 20 kg, which likely indicates the exploitation of giant trevallies (Caranx ignobilis), often found frequenting the drop-offs.

Several blue jacks (Caranx melampygus), which usually swim along the shorelines, were also identified in the assemblage. Within the assemblage, four other families represent more than 5% of the MNI: Serranidae, Acanthuridae, Balistidae and Lutjanidae. These taxa are usually connected with substrates close to the shore and can even be observed in surge zones, in particular surgeonfishes, such as Acanthurus lineatus. Several individuals of large dimensions were also noticeable in these families, especially the carnivorous ones. A few serranids in our sample reached nearly 30 kg, most likely Epinephelus tukula (potato grouper); balistids weighed up to 4 or 5 kg, like Balistoides viridescens (titan triggerfish); and some of the lutjanids, such as Lutjanus bohar (red dog snapper), weighed 7 kg. It should also be noted that some large specimens occurred in more accessory families, such as parrotfishes, with Scarus ghobban at 7 to 8 kg, or porcupinefishes, with Diodon hystrix at 3 kg.

As for the rest of the identified fish, the sizes are variable but many show small dimensions, with weights ranging from a few dozen to a few hundred grams. Among these are reef-associated fishes, such as Pomacentridae (damselfishes), Chaetodontidae (butterfly fishes) and Bothidae (flatfishes).

Finally, it is interesting to mention the mysterious presence of two remains of what seems to be a sailfish (Istiophorus platypterus). The two remains, part of a rostrum and a fragment of caudal vertebra, are quite distant from each other (sectors 19 and 21) but could have belonged to the same individual. This large pelagic species is very combative, which raises questions as to its method of capture, especially as it weighed at least 50 kg. The occurrence of this species in the vicinity of an oceanic island such as Tromelin, where depths of 1000 m are attained at only 2.5 km from the island's coastline [START_REF] Marriner | The forgotten slaves of Tromelin (Indian Ocean): New geoarchaeological data[END_REF], is easily conceivable. However, it is highly unlikely that an individual just washed up on shore, and it is more probable that it was harpooned in open water because it often swims near the surface, showing its sail.

Considering the estimated weights and MNI, the total fish biomass could be approximately 1000-1200 kg, which constitutes an edible biomass of about 500-600 kg.

| Stratigraphic and spatial distribution

In all structures where the same stratigraphy could be found, most of the fish bones were concentrated in the C4 layer, which yielded 74% of the identified remains. Another 12% of the NISP stem from layer C2b. The remaining 14% were recovered from the sector S21-TR1312. In all cases, Carangidae (jacks) dominate with a NISP between 47% and 64%, and the order of the main families remains unchanged: Carangidae, Serranidae, Acanthuridae, Balistidae, Lutjanidae. As expected for larger sample sizes, taxonomic diversity is higher in layer C4, which also shows the largest number of remains. However, a different pattern is visible in sector S21-TR1312: the proportion of jacks is the highest but only a restricted number of large-sized individuals are present (i.e. 2 specimens of big-head trevallies, weighing respectively 12 kg and 18 kg). Remarkably, this sector yielded solely cranial elements but no vertebrae. One of the two remains of sailfish, a fragment of rostrum bearing burning traces, was also uncovered in this area. Could it have been a disposal zone for nonvaluable fish parts?

The quantitative distribution of remains per sector (Tab. 4; Fig. 3) offers little information, due to the sieving parameters not being homogeneous. For example, sectors 17 to 21, excavated in 2013, were sieved by means of a smaller mesh size than the other ones, which could explain why they yielded an important number of remains. It is, however, noticeable that sector 17 provided the largest NR for the whole of Site 5, with a total of 1487 remains, out of which 1482 belong to layer C4 (NISP = 232 or 27%). The other structures that yielded significant numbers of remains (> 5%) are, in descending order of importance: S19, S21, S06, S15, S11 and S20. All of them are outlying sectors: does this indicate a disposal pattern, or a choice by the occupants to keep the central area of their habitat clean? Table 4. Distribution of fish remains by sector. Given the total number of fish remains found in the excavations (NR = 4282), it appears that fish were not the primary source of protein for the castaways, but that birds and sea turtles also played an important role (Laroulandie & Lefèvre, 2014 and unpublished data). However, these figures must be put into perspective by considering the large sizes of some of these fishes: a grouper of at least 30 kg, jacks of 20 to 25 kg, and snappers and parrotfishes of about 10 kg, as well as one or two sailfishes of about 50 kg. Considering the estimated weights and MNI, the total fish biomass could be approximately 1000-1200 kg, which constitutes an edible biomass of about 500-600 kg. If we consider that only 13 survivors occupied the island for 12 years [START_REF] Guérout | Tromelin. L'Île aux esclaves oubliés[END_REF], that would mean ca 3.5 kg of fish flesh per person per year, which is certainly not a negligible amount within the diet of the castaways.

| DISCUSSION

The capture of these big fishes would have required venturing out to the open sea and, for carnivorous specimens, to fish using lines and hooks. Indeed, four hooks from sector S03 and a spear tip from sector S19, were found, attesting to angling and harpooning activities (Fig. 7).

But although building a craft to go fishing during calm sea days might have been possiblethe shipwrecked people could have taken advantage of the debris of the wreck or driftwood stranded on the shore for its construction -it would still have been necessary to overcome their probable apprehension of the ocean. Angling is the most likely technique for the capture of several carnivorous species present in the studied material, such as jacks, groupers and snappers. The occurrence of the latter species, Lutjanus bohar (see Fig. 3), is also mentioned in the logbook attributed to Hilarion Dubuisson de Keraudic, the ship's official log keeper (M. Guérout pers. comm.): "Nous avons pris deux grandes sardes". The term "sardes" probably corresponds to the name given to snappers in the Caribbean (Cuvier & Valenciennes, 1828: 440) where some of the crew members might have worked previously; its relationship with bonitos (Sarda spp.) seems less likely.

The fishing of small-size fishes could have been practiced along the shore in calm weather, taking advantage of the low tide and tidal pools; indeed, some of the small reef fishes identified in the assemblage might have been captured by hand in these intertidal pools. The origin of the slaves is not known with certainty; thus, it is difficult to define if they were accustomed to the marine environment and fishing. However, anthropologists suggest, after analysis of the strontium and barium of two skeletons uncovered at the site, that they possibly originated from Madagascar -the highlands for one individual, and the coastal zone for the second [START_REF] Guérout | Tromelin. L'Île aux esclaves oubliés[END_REF]. It is therefore likely that those among the Malagasy people or the French sailors who knew how to fish transmitted their knowledge and techniques to the entire group during the first two months. On this permanently swept coast fishing is opportunistic, as it is often the case in extreme situations and environments. It appears that selection by size or specific distinctions were not made during the capture of the fish and all accessible biotopes seem to have been exploited. The survivors showed an amazing ability to adapt, which is also visible in the use of raw materials and reuse of objects recovered from the wreckage.

| CONCLUSION

This study allows us to glimpse aspects of the life of the slaves on a remote and desolate island. At the same time, this example illustrates the importance of such studies for the understanding of the ability of humans to adapt and survive to complex conditions in hostile environments.

The ichthyoarchaeological data provides insight into the use of marine resources through fishing on a desolated island. It reveals that ichthyological resources also played a key role in the subsistence of the Malagasy shipwreck survivors on Tromelin, besides those of sea turtles and birds. And although one would have expected that fish, a permanent resource, would have played a major role in their diet, access to this rough sea from a small island with almost no reef flat, by people that were, at least at the beginning of their stay, probably little experienced as mariners, would have been difficult. In this sense, shipwreck archaeology has much to contribute to the understanding of behavioural adaptation to survival and, beyond that, to the exploitation of marine resources by human groups during dispersal along coastal routes.

  Jacques Marie Boudin de Tromelin and taken to Mauritius Island,

Figure 1 .

 1 Figure 1. Location of the main islands east of Madagascar within the southwestern Indian Ocean..

Figure 2 .

 2 Figure 2. Aerial view from the south of Tromelin Island (© Richard Bouhet / AFP).

Figure 3 .

 3 Figure 3. Layout of the excavation of Site 5.

Figure 4 .

 4 Figure 4. Some diagnostic fish bone remains from Site 5 of Tromelin : (A) precaudal vertebra of Caranx ignobilis; (B) precaudal vertebra of Epinephelus sp.; (C) caudal vertebra of Naso sp.; (D) precaudal and caudal vertebrae of Pomacentridae; (E) caudal vertebrae of Bothus sp.; (F) right maxilla of Caranx ignobilis with cut marks; (G) neural process of a caudal vertebra of Istiophorus platypterus; (H) tooth of Balistoides viridescens; (I) dermal spine of Diodon hystrix; (J) dentary of Gymnothorax sp.; (K) right palatine of Lutjanus bohar; (L) epibranchial 4 of Scarus sp. -Scale bar = 1cm.

Figure 5 .

 5 Figure 5. Main large species identified among the fish material and observed at Tromelin (from left to right and top to bottom): Caranx ignobilis; Caranx melampygus; Epinephelus tukula; Acanthurus lineatus; Balistoides viridescens; Lutjanus bohar. Copyright: Joël Mouret.

  Table 3. List of the 62 fish species observed at Tromelin based on underwater photos taken during underwater prospections.

Figure 6 .

 6 Figure 6. Distribution (NISP) of fish taxa from among the fish material from Tromelin site.

Figure 7 .

 7 Figure 7. Fishing artefacts, fishhooks (T08.PH5.272 & T08.PH5.273) and spear point (T13.PH5.1035), recovered during the excavation of the Tromelin site. Scale bar = 1 cm

Figure 1 :Figure 2 :Figure 3 :

 123 Figure 1: Location of the main islands east of Madagascar within the southwestern Indian Ocean. 413x204mm (300 x 300 DPI)

Figure 4 .Figure 5 .Figure 7 .

 457 Figure 4. Some diagnostic fish bone remains from Site 5 of Tromelin : (A) precaudal vertebra of Caranx ignobilis; (B) precaudal vertebra of Epinephelus sp.; (C) caudal vertebra of Naso sp.; (D) precaudal and caudal vertebrae of Pomacentridae; (E) caudal vertebrae of Bothus sp.; (F) right maxilla of Caranx ignobilis with cut marks; (G) neural process of a caudal vertebra of Istiophorus platypterus; (H) tooth of Balistoides viridescens; (I) dermal spine of Diodon hystrix; (J) dentary of Gymnothorax sp.; (K) right palatine of Lutjanus bohar; (L) epibranchial 4 of Scarus sp. -Scale bar = 1cm. 169x129mm (300 x 300 DPI)

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			International Journal of Osteoarchaeology
	Taxa	NISP	MNI	WISP (g)	Thalassoma spp. gen. sp.		1 4	1 3	0.30 0.49
	CARANGIDAE Caranx ignobilis Caranx melampygus Table 2	86 83	25 56	47.32 334.12	Bothus spp. BOTHIDAE		13	7	1.73
	Caranx sexfasciatus	2	2	1.53	SCARIDAE
	Caranx spp. Trachinotus baillonii BONE Trachinotus blochii Trachinotus cf. africanus Trachinotus spp. scale unidentified fragment	70 10 NISP 8 1 55 1326 54 10 5 1 27 906	70.31 WISP (g) 1.86 1.56 0.13 11.54 34.54 parasphenoid Scarus ghobban BONE Scarus spp. Chlorurus cf. sordidus NISP gen. sp. 213.99 basioccipital	8 8	4 WISP (g) 6 1 15.01 4 6 1 1 1 4.87	11.49 12.27 0.05 0.06
	Elagatis bipinnulata Carangoides cf. fulvoguttatus spine	4 1	3 1 863	0.61 0.07 156.29 urostyle DIODONTIDAE Diodon hystrix	8	2	2 4.15	2.81
	gen. sp. vertebra	116	34 666	33.25 416.29 scapula Diodon spp.	7	6	6 2.18	2.15
	SERRANIDAE pterygiophore		61	gen. sp. 23.81 supracleithrum	5	2	2 3.75	0.36
	Epinephelus spp. Cephalopholis cf. argus Cephalopholis spp. scute	75 1 15	40 1 12 46	52.95 0.29 1.55 14.59	HOLOCENTRIDAE Sargocentron spp. posterior gen. sp. ceratohyal	4	3 1	3 1 1.91	1.40 0.06
	gen. sp. ACANTHURIDAE preopercle cleithrum Acanthurus xanthopterus Acanthurus triostegus Acanthurus lineatus Acanthurus spp. Naso spp. Ctenochaetus spp. hyomandibula dentary opercle Zebrasoma spp. gen. sp. BALISTIDAE Balistoides viridescens Sufflamen spp. gen. sp. LUTJANIDAE Lutjanus bohar Lutjanus spp. gen. sp. POMACENTRIDAE Abudefduf spp. gen. sp. KYPHOSIDAE Kyphosus vaigiensis Kyphosus cf. bigibbus premaxilla maxilla quadrate anguloarticular pharyngeal bone posttemporal anterior ceratohyal palatine tooth vomer	5 F 5 39 35 o r 3 3 2 2 2 1 49 38 22 8 3 3 F o r 33 31 31 F o r P 3.58 24.71 ectopterygoid ANGUILLIFORMES gen. sp. 25.41 epibranchial 2.24 0.12 0.99 14.73 13.17 0.34 EXOCOETIDAE gen. sp. LETHRINIDAE gen. sp. 18.38 subopercle 40.00 neurocranial bone 15.95 glossohyal e e r R e v i e w 2 1 0.06 12 8 1.07 13 7 31.06 3 3 0.28 50 20 9.09 4 4 3.12 30 22 42.96 3 3 4.98 9 4 1.05 24 16 3.82 8 7 2.33 3 3 1.78 ISTIOPHORIDAE Istiophorus platypterus BELONIDAE Tylosurus cf. crocodilus P e e 28 31.96 urohyal 26 42.88 rostrum 24 9.86 supraoccipital 21 35.69 basipterygoid P e e CHAETODONTIDAE Chaetodon spp. r r gen. sp. GERREIDAE gen. sp. HEMIRAMPHIDAE gen. sp. POMACANTHIDAE Pomacanthus spp. Total TELEOSTEI 3 3 3 2 2 2 1 1 1 R e v i e w 18 17.46 metapterygoid 1 17 5.83 postcleithrum 1 R 16 2.27 tail spine 1 12 7.91 lacrymal 1 11 2.41 hypural plate 1 9 8.35 TOTAL 4282 e v i e w	2.55 3 2.49 3 2 1.09 4.48 0.57 2 2 0.17 1.98 0.70 0.51 1 1 1 1 1 516 0.22 0.17 0.15 0.06 0.05 1195.62 885 4 3 3 2 2 1 1 2 2 1	0.26 0.15 0.23 10.94 0.11 0.06 0.01 0.10 0.03 0.21 759.62
	Kyphosus spp.	15	12	7.87	CARCHARHINIDAE
	MURAENIDAE				gen. sp.		3	1	0.31
	Gymnothorax spp. gen. sp.	12 8	8 6	7.13 4.64	DASYATIDAE gen. sp.		1	1	0.15
	LABRIDAE Coris spp.	6	3	0.39	Total CHONDRICHTHYES	4	2	0.46
	Cheilinus spp.	4	3	0.29	TOTAL		889	518	760.07
	Thalassoma purpureum	1	1	0.22

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Acknowledgements

We would like to thank Max Guérout and Thomas Romon for giving us the opportunity to study the fish bone material, as well as Véronique Laroulandie for involving us in this project.

Special thanks are also due to Joel Mouret for authorising us to utilise his underwater pictures taken at Tromelin. Thanks to Jill Cucchi for copy-editing, and to the anonymous reviewers for their valuable comments.