Alexandra Gross

Kiszka Jeremy
email: jeremy.kiszka@wanadoo.fr

Van Canneyt Olivier

Richard Pierre

Ridoux Vincent
email: vincent.ridoux@univ-lr.fr

A preliminary study of habitat and resource partitioning among co-occurring tropical dolphins around Mayotte, south-west Indian Ocean

Keywords: dolphins, ecological niche, habitats, stable isotopes, south-west Indian Ocean, Mayotte

Mayotte in the southwest Indian Ocean is characterized by high dolphin diversity. They may coexist within a fairly small area around the island because they exploit neither the same preferential habitats nor the same resources. This preliminary study aimed to investigate ecological niche segregation among these delphinid communities: the Indo-Pacific bottlenose dolphin, Tursiops aduncus, the pantropical spotted dolphin, Stenella attenuata, the spinner dolphin, Stenella longirostris, and the melon-headed whale, Peponocephala electra. Two approaches were used. Habitat preferences were investigated by analysing dolphin sighting data and associated physiographical characteristics. Resource partitioning was explored by analysing C and N stable isotopes in skin and blubber biopsies. Only T. aduncus, which showed clear association with coastal habitats in the lagoon, differed from the others in terms of habitat preferences, characterised by shallow depth and slope, and proximity to the coast. All other species shared similar oceanic habitats immediately outside the lagoon, these being of higher depth and slope, greater distance from the coast and were not discernable by discriminant analysis. The two Stenella species and the melon-headed whale displayed very high overlap in habitat physiographic variables. The analysis of stable isotopes confirmed the ecological isolation of T. aduncus and revealed a clear segregation of P. electra compared to the two Stenella that was not apparent in the habitat analysis. This may reflect ecological differences that were not observable from diurnal surface observations.

Introduction

In biological communities, each species has its own unique niche, which provides the conditions and resources needed for its survival. A shared resource in limited supply will bring about competition between members of the same species (intra-specific competition) or between individuals of different species (inter-specific competition). Competition can take two different forms: interference, which is a direct, often aggressive, interaction between individuals, or exploitation-competition, in which individuals interact with each other indirectly, by responding to a resource level which has been depressed by the activity of competitors [START_REF] Begon | Ecology -Individuals, Populations and Communities[END_REF].

A niche occupied by a species in the absence of competitors is termed its fundamental niche, whereas in the presence of competitors, species may be confined to a realized niche, which is shaped by the presence of competing sympatric species [START_REF] Begon | Ecology -Individuals, Populations and Communities[END_REF]. Hence, the coexistence of potentially competing species is often made possible by the differentiation of their realized ecological niches. The first mechanism that allows for niche differentiation is resource partitioning. In this case, different species living in the same habitat exploit the resources differently. For example, predators of different size may feed on prey of different size, hence minimising the overlap between the various predators' prey size ranges. Prey specialization presumably allows for niche partitioning in areas of sympatry [START_REF] Ballance | Cetacean Ecology[END_REF]. The second mechanism involves spatial (microhabitat differentiation) or temporal separation in the availability of the different resources (these become available at different times of the day or different seasons of the year; [START_REF] Huisman | Biological conditions for oscillations generated by multispecies oscillations[END_REF].

Small delphinids belong to numerous species which have similar morphological characteristics. This situation suggests that fine-scale mechanisms allow for the partitioning of habitats and resources when and where the different species live in sympatry. A study of the cetacean community of Great Abaco, Bahamas, has shown that the ecological niches of the four species that permanently live there do not overlap [START_REF] Macleod | Diversity, relative density and structure of the cetacean community in summer months east of Great Abaco, Bahamas[END_REF]. These species capture prey at different depths of the water column. Other cetacean species are observed in the study area only during the season when prey abundance is sufficiently high to support their presence, while they are competitively excluded for the rest of the year [START_REF] Macleod | Diversity, relative density and structure of the cetacean community in summer months east of Great Abaco, Bahamas[END_REF]. Indeed, the spatial distribution of marine predators is mainly determined by the distribution and availability of their prey, these in turn varying according to physical, chemical and biological characteristics of the water masses [START_REF] Forcada | Distribution[END_REF].

The dietary ecology of marine mammals and their trophic level can be determined using different methods: traditional methods analyse faeces and regurgitated food of living animals, as well as the stomach contents of dead animals (from strandings or by-catch; e.g. [START_REF] Pusineri | Food and feeding ecology of the common dolphin (Delphinus delphis) in the northeast Atlantic and comparison with its diet in neritic areas[END_REF]. A more recent method for studies of dietary ecology is stable isotope analysis of blubber, skin or muscle samples (Bearhop et al., 1993). The carbon and nitrogen isotope ratios ( 13 C/ 12 C and 15 N/ 14 N, expressed hereafter as δ 13 C and δ 15 N) of a consumer reflect those of its diet, with a slight retention of the heavier isotope and excretion of the lighter one [START_REF] Das | Marine mammals from the southern North Sea: feeding ecology data from δ13C and δ15N measurements[END_REF]. As a consequence, tissues will be enriched with heavy isotopes at every trophic level. The minor stepwise trophic enrichment of the carbon-isotope ratio limits its use in assessing trophic levels, but enhances its use in tracking carbon sources through a food chain. The carbon isotope ratio of secondary and tertiary consumers should thus reflect the source of carbon at the base of their food chain [START_REF] Kelly | Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology[END_REF]. The higher enrichment of the nitrogen isotope ratio of consumers compared to their prey makes it very useful for the determination of their trophic level [START_REF] Kelly | Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology[END_REF]. Thus, both ratios help elucidate trophic relations and habitat use.

Mayotte, a volcanic island in the northern Mozambique Channel (southwest Indian Ocean), is characterized by the permanent presence of more than 20 species of cetaceans [START_REF] Kiszka | Cetacean diversity around the Mozambique Channel island of Mayotte (Comoros Archipelago)[END_REF]. Of these, the most important in coastal waters are the Indo-Pacific bottlenose dolphin, Tursiops aduncus (Ehremberg, 1833), the pan-tropical spotted dolphin, Stenella attenuata (Gray, 1846), the spinner dolphin, S. longirostris (Gray, 1828), and the melon-headed whale, Peponocephala electra (Gray, 1846). The island has a great variety of marine ecosystems offering a large diversity of habitats: coasts, mangroves, an extended lagoon (1100 km 2 ), different kinds of reefs (fringing, pinnacles, and barrier), a steep insular slope with many submarine canyons and seamounts, and the open ocean [START_REF] Quod | The Comoros archipelago[END_REF]. At least twelve species of delphinids may coexist in a fairly small area around the island because they exploit neither the same habitats nor the same resources [START_REF] Kiszka | Cetacean diversity around the Mozambique Channel island of Mayotte (Comoros Archipelago)[END_REF]. The present study aimed to investigate ecological niche segregation among the resident dolphin community of Mayotte, especially the Indo-Pacific bottlenose dolphin, the pantropical spotted dolphin, the spinner dolphin and the melon-headed whale. We concentrated on these four species as they are of fairly similar size and can be found within the same proximity around Mayotte, in closely-related habitats within a small area and at all seasons [START_REF] Kiszka | Cetacean diversity around the Mozambique Channel island of Mayotte (Comoros Archipelago)[END_REF]. This is particularly so for the two Stenella species and the melon-headed whale which are all encountered immediately outside the barrier-reef and in the channels, whereas existing literature suggests that they would be more differentiated habitat-wise, with the spinner dolphin feeding offshore but resting inshore, the melon headed whale being an oceanic squid-eater and the Indo-Pacific bottlenose dolphin dwelling in nearshore coastal habitats [START_REF] Norris | The Hawaiian Spinner Dolphin[END_REF][START_REF] Silva | Rest, nurture, sex, release, and play: diurnal underwater behaviour of the spinner dolphin at Fernando de Noronha Archipelago, SW Atlantic[END_REF][START_REF] Perryman | Melon-headed whale Peponocephala electra[END_REF][START_REF] Wells | Bottlenose dolphins Tursiops truncatus and T. aduncus[END_REF]. Two approaches were used for the study: a comparison of habitat by the analysis of dolphin sighting data and associated behavioural and physiographic characteristics (group size, depth, slope, distance to the coast and proximity to the different kinds of reefs), and the study of habitat and resource partitioning by the analysis of C and N stable isotopes from skin and blubber biopsies.

Material and Methods

Study area

The volcanic island of Mayotte (45°10'E, 12°50'S), which is part of the Comoros archipelago, is located in the northern Mozambique Channel (Indian Ocean) between Madagascar and Southeast Africa. Its surface area is 376 km 2 and it is composed of two main islands and about 30 islets scattered within and around a lagoon. Mayotte is surrounded by a large lagoon-reef complex, whose width varies from 3 to 15 km. Fringing reefs surround the archipelago, an inner doublereef is present off the south-west end of Mayotte, and the barrier reef, which is interrupted by numerous channels, separates the lagoon itself (maximum depth 80 m) from the external slope and more oceanic habitats.

The four species of interest, the Indo-Pacific bottlenose dolphin, the pantropical spotted dolphin, the spinner dolphin, and the melon-headed whale, range in size from about 200 cm and 90 kg for the spinner dolphin to 250 cm and 250 kg for the melon-headed whale (Perrin, 2002aand b, Perryman, 2002[START_REF] Wells | Bottlenose dolphins Tursiops truncatus and T. aduncus[END_REF].

Data and sample collection

Data were collected from 1997 to 2005, during small boat-based surveys dedicated to studying marine mammals (Figure 1). Several types of boats were used: a 7 m catamaran equipped with two, four-stroke, 60-hp outboard engines; a 7 m boat equipped with two, two-stroke, 40-hp outboard engines; a 6.4 m cabin boat equipped with an inboard four-stroke and 150-hp outboard engine. Surveys were conducted during daylight hours, i.e. between 0700 h and 1800 h, in sea conditions not exceeding Beaufort 3. The survey vessels did not follow pre-defined transects but sampling covered all habitats within the lagoon and over the external insular slope (Figure 1).

Effort varied according to month (Figure 2), with more effort being applied in the austral summer (November to January). When dolphins were encountered, preliminary information records included group size (maximum, minimum, best estimate), geographic position, activity (travelling, resting, foraging/feeding, socialising, milling, play), group classification on the basis of the relative size of individuals (adults, sub-adults, calves), research boat disturbance (bowride, approach, avoidance, no response) as well as group formation (tight, loose, dispersed, variable, convergent; [START_REF] Shane | Behaviour and ecology of the bottlenose dolphin at Sanibel Island, Florida[END_REF][START_REF] Würsig | Behaviour of cetaceans in the Northern Gulf of Mexico relative to survey ships and aircraft[END_REF]. This study is still on-going and, therefore, only the sighting locations and associated physiographic variables are analysed here.

When conditions were optimal (good weather and sea state, dolphins closely approaching the boat), biopsies were collected using a cross-bow (BARNETT Veloci-Speed® Class) with Finn Larsen bolts and tips (20-mm). The dolphins were hit below the dorsal fin, when close (3-10 meters) to the research boat. Sampling periods spanned all seasons but sample sizes did not allow seasonal comparisons (January, August and December for T. aduncus, N=4; January, February, March and October for S. attenuata, N=4; February, March, May and October for S. longirostris, N=5; March, July and December for P. electra, N=4). It was not possible to determine sex, size or age of the individuals biopsied. Blubber and skin biopsy samples were preserved separately in 90° ethanol before shipping and subsequent analysis. Biopsy sampling was conducted under scientific permit #78/DAF/2004.

Database

We constituted a database in which every dolphin observation was associated with the physiographic characteristics (distance to the coast, to the different reefs and to the closest channel, as well as depth and slope of seafloor and the variance of these two parameters) corresponding to the GPS (Global Positioning System) fixes of the observation. The distance data were obtained using GIS (Geographic Information System) software ArcView (ArcGIS 8.2) by ESRI (Environmental Systems Research Institute). Bathymetric data were obtained from Service Hydrographique et Océanographique de la Marine (SHOM). Interpolation of bathymetry data, needed to generate depth and slope data for each sighting, was undertaken with the extension Spatial Analyst by kriging transformation of the raster file into an interpolated data file. This was obtained by calculating the mean value of the twelve points closest to every bathymetric point in a 1 km 2 grid. This interpolated data file thus allowed us to generate depth and slope data over the whole study area and therefore to associate bathymetry data to any dolphin observation in the area.

Data analysis

The environmental data were first compared between species using basic methods (nonparametric analyses and ANOVA). Then we used multivariate statistical methods including discriminant linear and quadratic analyses to examine how well sightings were assigned to the correct species from the combination of associated physiographic variables. All methods were implemented with the software R (R-2.2.1, R Development Core Team, 2005).

Stable isotope analyses

Blubber and skin were separated for each biopsy. The ethanol they contained was evaporated at 45°C over 48 h and the samples were ground and freeze-dried [START_REF] Hobson | Preservation of blood and tissue samples for stable-carbon and stable-nitrogen isotope analysis[END_REF]. Lipids were extracted using cyclohexane (C 6 H 12 ) prior to analysis because they are depleted in 13 C; if they were not extracted, this would cause a bias in the isotopic signature of 13 C (De Niro and Epstein, 1978; Tieszen et al., 1983). Small sub-samples (0.35 to 0.45 mg + 0.001 mg) were prepared for analysis. Stable isotope measurements were performed with a continuous-flow isotope-ratio mass spectrometer (Isoprime, Micromass) coupled to an elemental analyser (Eurovector EA 3024).

Results are expressed in δ notation relative to PeeDee Belemnite and atmospheric N 2 for δ 13 C and δ 15 N, respectively, according to the equation δX = [(R sample /R standard ) -1] × 10 3 , 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 internal laboratory standards (acetanilide) indicated that measurement errors were <0.15‰ and <0.20‰ for δ 13 C and δ 15 N, respectively. Percent C and N elemental composition of tissues were obtained using the elemental analyzer and used to calculate the sample C:N ratio, indicating a good lipid removal efficiency when <4.

Results

General

Our cetacean sightings comprised 394 positional data for S. longirostris (n = 208), S. attenuata (n = 88), T. aduncus (n = 83) and P. electra (n = 15) in all sectors around Mayotte (Figure 2) and all seasons (Figure 3). Indo-Pacific bottlenose were mostly found within the lagoon, very often in the immediate proximity of the fringing reef, and to a lesser extent over the North West bank located outside the main barrier reef. The two Stenella species were observed all along the barrier reef on its outer side and made only a few incursions into the lagoon. Finally, the melon-headed whale was only seen outside the barrier reef.

Habitat use and niche partitioning

A preliminary Principal Component Analysis (PCA plot not shown) allowed us to select group size, distance to coast, depth and slope as the set of physiographic variables with least redundancy. Distances to the various reefs and to the nearest channel were heavily redundant relative to distance from coast and therefore not retained. A simple comparison of the distribution of these variables for the four focal species was performed using Kruskall-Wallis tests (Figure 4). T. aduncus is observed at short distances from the coast with shallow bathymetry and moderate slopes, whereas the other three species cannot be significantly differentiated in terms of habitat characteristics. In particular, the two Stenella species manifested similar characteristics in group size and environmental preferences. On the other hand, group size differed strongly between T. aduncus that lives in small groups (median = 6) and P. electra that is mostly found in groups of several hundred individuals (median = 300).

Linear discriminant analysis separated the species according to their environmental characteristics (Figure 5). The predictive power of the linear discriminant analysis was good only for T. aduncus which can be explained by its habitat preferences (Table 1, upper part). The other species' habitat characteristics were too similar to permit acceptable predictions. The good prediction for S. longirostris might be attributable only to the considerable number of sighting data for this species. Finally, the quadratic discriminant analysis provided slightly better predictive results, especially for P. electra (Table 1, lower part).

The different methods used to compare the preferred habitats of the four delphinid species under study all clearly showed that T. aduncus differs from the other species in its preferred environmental parameters. S. attenuata and S. longirostris share similar environmental characteristics. P. electra is characterised by a larger group size and deeper depth preference, but resembles Stenella in terms of the majority of its other environmental preferences (distance and slope).

Resource partitioning

Stable isotope ratios were lower in blubber than in skin but the pattern of differences observed between species was similar in both tissues (Figure 6). Skin and blubber of T. aduncus have the highest values of δ 13 C. The two Stenella species are not discernable from each other as shown by the extensive overlap in standard deviation for both δ 15 N and δ 13 C, and have the lowest values for δ 13 C. P. electra has the highest δ 15 N and a δ 13 C values that are intermediate between those for the two Stenella species and T. aduncus. The intra-specific variance is represented by the standard deviation, which is more important for the δ 13 C values than for the δ 15 N, except in the blubber samples of T. aduncus where intra-specific variance in the δ 15 N is prevalent.

Discussion

The present study comprises a preliminary analysis of habitat and resource use among an assemblage of co-existing tropical delphinids living around Mayotte in the southwest Indian Ocean. The principal finding is that, among the four species of interest, the Indo-Pacific bottlenose dolphin is clearly differentiated from the other species in terms of both habitat preference and stable isotope analyses. From the variables tested here, the other three species can hardly be separated in terms of their preferred habitats but stable isotope analysis revealed a dietary segregation between the melon-headed whale and the two species of the genus Stenella.

This was not initially evident in the sighting data analyses that described the dolphins' diurnal use of habitats. However, some limitations render these findings preliminary. The sightings constituted presence-only data as the observation effort could not be readily quantified and, hence, the data cannot provide significant information concerning dolphin absence. In this work, we tried to characterise the habitats where dolphins were found, not assess the overall distribution of each species around the island. Nevertheless, the field surveys comprehensively covered the study area such that all habitats were visited and the sighting data of the four focal species were considered representative of their habitat preference.

The Indo-Pacific bottlenose dolphin, Tursiops aduncus, occupies an ecological niche that clearly differs from those occupied by the other study species. T. aduncus was observed only inside the lagoon except in the northern part of the island where the reef system is in the form of an open bank outside the lagoon. This species is generally found close to the fringing reef which constitutes the ecosystem where prey of this coastal dolphin may be concentrated. The high δ 13 C value in its tissues indicates a benthic carbon source that dolphins more easily access in coastal habitats [START_REF] Hobson | Tracing origins and migration of wildlife using stable isotopes: a review[END_REF]. This species has indeed been observed feeding near mangroves, along the fringing reefs or over seagrass beds. Its isotopic signature of δ 15 N is similar to that of the two Stenella, but this cannot be interpreted as an indication of similar trophic levels as the δ 15 N values of the local primary producers versus those outside the lagoon have not been investigated at this stage.

T. aduncus lives and forages individually or in small groups inside the lagoon, where the water is shallow and large predators are absent, and probably feeds on prey that would not aggregate in large schools [START_REF] Mann | Cetacean Societies -Field Studies of Dolphins and Whales[END_REF]. Indo-Pacific bottlenose dolphins forage over reefs or soft bottom substrata and near the shore relatively close to the island of Mayotte and around Zanzibar (Tanzania) [START_REF] Amir | Feeding ecology of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) incidentally caught in the gillnet fisheries off Zanzibar, Tanzania[END_REF].

The pantropical spotted dolphin and the spinner dolphin share a barrier reef-associated habitat outside the lagoon. They are also found where the water depth rapidly attains a depth of 100 m.

In comparison to the Indo-Pacific bottlenose dolphin, their tissues had a lower δ 13 C , suggesting it was derived from an oceanic carbon source; oceanic phytoplankton is reported to be 13 C-depleted relative to marine phanerogams [START_REF] Hobson | Tracing origins and migration of wildlife using stable isotopes: a review[END_REF]. Their isotopic ratios suggested their diet comprised oceanic prey.

S. attenuata and S. longirostris can occasionally be observed inside the lagoon where they might take advantage of the safety it provides for resting. This kind of behaviour has been observed in Hawaiian spinner dolphin populations [START_REF] Norris | The Hawaiian Spinner Dolphin[END_REF]. S. longirostris generally lives in single-species groups from several dozens to several hundreds of individuals, e.g. around the main Hawai'i island [START_REF] Norris | The Hawaiian Spinner Dolphin[END_REF]. Their aggregation in large groups might offer some protection against predators but it might also facilitate feeding through communal hunting on large pelagic fish schools. In the present work, S. attenuata was rarely observed in single-species groups but was generally found in association with S. longirostris, forming important mixedspecies groups. Both species might take advantage of a larger group size for safety and foraging.

Nevertheless, a large group size increases the potential for intra-specific competition as well as inter-specific competition if the two species feed together. A study in the southwest Atlantic has shown that distributions of spotted dolphins and spinner dolphins may partially overlap [START_REF] Moreno | Distribution and habitat characteristics of dolphins of the genus Stenella (Cetacea: Delphinidae) in the southwest Atlantic Ocean[END_REF]. Associations of spotted dolphins and spinner dolphins are frequently found in Hawai'i, where the two species travel together while showing many aggressive interactions, but they do not seem to feed together [START_REF] Psarakos | Mixed-species associations between Pantropical spotted dolphins (Stenella attenuata) and Hawaiian spinner dolphins (Stenella longirostris) off Oahu, Hawaii[END_REF]. Conversely, in the Azores, common dolphins, Delphinus delphis, and Atlantic spotted dolphins, Stenella frontalis, associate and forage together [START_REF] Clua | Mixed-species feeding aggregation of dolphins, large tunas and seabirds in the Azores[END_REF]. As S. attenuata and S. longirostris have similar habitat preferences and similar isotopic signatures, both for carbon and nitrogen, there is no evidence of ecological niche differentiation in these two species. Two options could be investigated in the future: either the two dolphins share the same resources in the same habitats, presumably because food is not limiting there, or they segregate when feeding on different resources but their prey have similar isotopic signatures because they rely on the same carbon source at the same trophic level.

The melon-headed whale, Peponocephala electra, prefers steep slopes and slightly deeper water than the two Stenella species. Peponocephala electra forms large groups of several hundred individuals. As it was always observed in a habitat that overlaps with that of the spinner and spotted dolphins, analysis of its habitat characteristics failed to distinguish between it and the two Stenella species. This might be due to the fact that melon-headed whale sightings were only made on groups that occasionally approached the island, as the surveys were conducted in a limited area around Mayotte and groups living farther offshore in the open ocean would not have been observed. In this case, our understanding of the preferred habitat of this species remains marginal, being limited to its nearshore fringe. Stable isotope analysis, on the other hand, clearly showed that there is an ecological differentiation between P. electra and the two Stenella species. Values of δ 13 C for P. electra's were intermediate between those of the Stenella species and T. aduncus. This would suggest that carbon isotopic composition of P. electra is influenced more by benthic primary production than that of the two Stenella species. Peponocephala electra is known for its oceanic habitat [START_REF] Perryman | Melon-headed whale Peponocephala electra[END_REF], and possible interpretations for its δ 13 C include the possibility that it is a deep-diving species that feeds on prey derived from a detritus-based food web unlike the Stenella that feed on a phytoplankton-based food web. In addition, P. electra clearly differs in its δ 15 N, this being indicative of a higher trophic level, suggesting its diet includes more carnivorous fish and squid than the spotted and spinner dolphins. Again, as in T. aduncus, all sources of primary production should be investigated concerning their δ 15 N to adequately interpret the trophic levels.

If there is high inter-individual variance in the δ 15 N (versus δ 13 C) values within a species, the interpretation is that the species is composed of individuals that have varied feeding habits and prey on organisms at different trophic levels (δ 15 N) or are found in different habitats (δ 13 C). A low variance indicates that all the individuals are specialist feeders on similar prey or within the same habitat. Thus, stable isotope variance is sometimes considered a measure of niche width [START_REF] Bearhop | Determining trophic niche width: A novel approach using stable isotope analysis[END_REF] or at least the inter-individual measure of niche width. Results of our stable isotope analysis indicate that P. electra is a fairly specialized feeder, whereas S. attenuata, S. longirostris and especially T. aduncus would be more eclectic feeders, which, in the latter case, is in line with previous studies [START_REF] Mann | Cetacean Societies -Field Studies of Dolphins and Whales[END_REF].

Detectable differences between the standard deviations in the stable isotope composition in the skin and blubber samples might be attributable to their differential rates in tissue renewal: this takes a few days for epidermis but several months for the collagen matrix of the blubber [START_REF] Abend | Differences in ratios of stable isotopes of nitrogen in longfinned pilot whales (Globicephala melas) in the western and eastern North Atlantic[END_REF]. The residence time of elements in tissues depends on metabolic turnover rates (Rubenstein and [START_REF] Rubinstein | From birds to butterflies: animal movement patterns and stable isotopes[END_REF]. This enables tracking of an animal's foraging history as demonstrated by a study on pilot whales (Globicephala melas) in the North Atlantic [START_REF] Abend | Differences in ratios of stable isotopes of nitrogen in longfinned pilot whales (Globicephala melas) in the western and eastern North Atlantic[END_REF]. T. aduncus and the two Stenella species clearly differ in the respective isotopic carbon signatures in their skin and blubber, indicating that they feed on trophic webs with different carbon sources over the long term.

Each species' habitat preference is presumably based on their prey distributions (Baumgartner et al., 2000) which, in turn, are related to water depth [START_REF] Hastie | Environmental models for predicting oceanic dolphin habitat in the Northeast Atlantic[END_REF] and, indirectly, bathymetric features that influence currents and productivity [START_REF] Fiedler | Ocean environment[END_REF]. Foraging behaviour seems to be closely related to submarine habitat characteristics [START_REF] Hastie | Functional mechanisms underlying cetacean distribution patterns: hotspots for bottlenose dolphins are linked to foraging[END_REF]. It has been demonstrated that a variable bathymetry contributes to global delphinid abundance, promoting the regional abundance of different species [START_REF] Gannier | Summer distribution and relative abundance of delphinids in the Mediterranean Sea[END_REF]. The rich marine biodiversity of Mayotte is possibly related to its variety of habitats and these provide numerous ecological niches for delphinid prey.

Conclusions

The present study provides preliminary ecological indications of niche differentiation and resource partitioning within the Mayotte delphinid communities. The only species that differs from the others in terms of habitat characteristics is the coastal-dwelling Indo-Pacific bottlenose dolphin, whereas pantropical spotted and spinner dolphins and the melon-headed whale share similar oceanic habitats immediately outside the lagoon. Stable isotope analysis confirmed the ecological specialisation of T. aduncus and, in addition to this, revealed a clear segregation of P. electra, from to the two Stenella species in terms of their feeding that was not apparent in the habitat analysis. This may reflect behavioural differences that were not detectable from diurnal surface observations. Further work should strengthen these conclusions through dedicated sampling of habitat preference and an expansion of the stable isotope studies. These should focus on seasonal changes in food partitioning and the isotopic composition of a series of putative prey species and primary producers characteristic of the inshore-offshore gradient of habitats found around Mayotte.

  Conservation Society). The other sightings were collected from November 2004 to August 2005 during a dolphin research project conducted by the Office National de la Chasse et de la Faune Sauvage (ONCFS) and the Agriculture and Forestry Office (Direction de l'Agriculture et de la Forêt). We thank Peter Ersts (American Museum of Natural History, Center for Biodiversity and Conservation) for providing the map showing tracks of the cetacean surveys conducted around Mayotte. We are particularly grateful to Gaël Guillou (Université de la Rochelle) for undertaking the mass spectrometer analyses. Funding for field work was provided by the Ministère de l'Energie, l'Ecologie, le Développement Durable et de l'Aménagement du Territoire (MEEDDAT) and the Collectivité Départementale de Mayotte (CDM). We thank Robin Rolland, Alban Jamon, Wilfrid Fousse, Ismaël Ousseni (DAF), Sarah Caceres, Franck Charlier, Denis Girou (ONCFS), Didier Fray (CDM) and the personnel of Brigade Nature (CDM) for assistance in the field in Mayotte.

Figure captions Figure 1 :

 captions1 Figure captions

Figure 2 :

 2 Figure 2: General locations of delphinid sightings around Mayotte and its reefs.

Figure 3 :

 3 Figure 3: Temporal distribution of effort expressed as number of sightings per three-month

Figure 4 :

 4 Figure 4: Delphinid sighting median values, 50, 75 percentiles and outliers of (a) group size, (b)

Figure 5 :

 5 Figure 5: Sighting density for melon-headed whale (dotted line), pan-tropical spotted (black

Figure 6 :

 6 Figure 6: Stable isotope (δ 13 C and δ 15 N in ‰) values in delphinid blubber (right-hand graph)

  Fig.2

Fig. 3

 3 Fig.3

  Fig. 5

Acknowledgements

Sightings were collected from 1997 to 2004 during the austral winter (July to October) as part of the humpback whale (Megaptera novaeangliae) surveys conducted by the Observatoire des Mammifères Marins de Mayotte (Direction de l'Agriculture et de la Forêt, DAF) and the Cetacean Conservation and Research Program (American Museum of Natural History-Wildlife

Table 1: Discriminant analysis: linear and quadratic predictions for the four species. Each sighting was assigned to one of the four study species on the basis of its associated physiographic characteristics. Only T. aduncus data were correctly assigned to the right species whereas all others were mostly assigned to S. longirostris as they all share similar habitat characteristics.

Linear discriminant analysis


J J Kiszka
email: jeremykiszka@wanadoo.fr

B Simon-Bouhet

F Charlier

C Pusineri

V Ridoux

Effect of biopsy sampling on small delphinids Individual and group behavioural reactions of small delphinids to remote biopsy sampling

Keywords: animal welfare, delphinids, group reactions, individual reactions, Indo-Pacific bottlenose dolphin, melon-headed whale, pantropical spotted dolphin, spinner dolphin, remote biopsy sampling

Biopsy sampling is an effective technique to collect cetacean skin and blubber samples for various biological studies. However, determining the impact of this research practice is important, as impact may vary among sites, species and gear used. We examined the shortterm behavioural reactions of four small (160-278 cm in length) delphinid species (Stenella longirostris, Stenella attenuata, Tursiops aduncus and Peponocephala electra) to remote biopsy sampling around the island of Mayotte (12 o 50'S, 45 o 10'E, SW Indian Ocean). Two scales of behavioural reactions were considered: 1-the behavioural reaction of the individual, and 2-the reaction of the focal group to which the targeted individual belonged. Three main categories of behavioural responses were defined on the basis of the character and duration of behavioural response: low, moderate and strong. This study underlines that biopsy sampling induces moderate reactions of individuals. No inter-specific variations of responses, at the scale of individuals or focal groups, were observed. In other words, smaller delphinids were not more reactive than larger ones. No effect of group size was observed on the strength of behavioural reactions. However, it was clear that biopsy success during sampling sessions was higher in species with large group size. Finally, in the spinner dolphin (S. longirostris), we investigated whether initial behavioural state affected the level of reaction. Resting and socialising groups showed a stronger response than milling and travelling groups. This study confirms the limited impact of remote biopsy sampling in small delphinids, especially in the spinner dolphin. However, as a precautionary approach, in situations where it is possible, biopsy sampling of milling and travelling dolphins may be preferred.

Introduction

In wildlife studies, some invasive techniques may be used to collect biological samples to answer a variety of questions which may be of particular relevance for management and conservation purposes. It is critical that the impact of such research practices is quantitatively assessed and managed, as the process of sample collection may negatively impact individuals and/or populations over a range of scales (e.g. injuries, individual stress, individual/group displacement, change of behaviour, etc.).

The use of skin and blubber biopsy samples from free-ranging cetaceans is a widespread and powerful technique to answer many questions, including population genetics (stock identity, social organization, population size, phylopatry, genetic connectivity, Amos [START_REF] Hoelzel | DNA fingerprinting cetacean biopsy samples for individual identification[END_REF][START_REF] Bérubé | Population genetic structure of North Atlantic, Mediterranean and Sea of Cortez fin whales, Balaenoptera physalus (Linnaeus 1758): analysis of mitochondrial and nuclear loci[END_REF], feeding ecology and trophic relationships using stable isotope and fatty acid analyses (Herman et al 2005;de Stephanis et al 2008;Gross et al 2009), and pollutant analysis (Godard et al 2004). In order to collect samples, modified crossbows, rifles and hand held biopsy poles have been used, both for large and small cetaceans, including delphinids (Weinrich et al 1991;Barrett-Lennard et al 1996;Krützen et al 2002;[START_REF] Bilgmann | A biopsy pole system for bowriding dolphins: sampling success, behavioral responses, and test for sampling bias[END_REF].

The behavioural effect of biopsy sampling has been investigated in large whales, such as right whales (Eubalaena glacialis and E. australis, [START_REF] Brown | Reaction of north Atlantic right whales (Eubalaena glacialis) to skin biopsy sampling for genetic and pollutant analysis[END_REF][START_REF] Best | Biopsying southern right whales: their reactions and effect on reproduction[END_REF] The International Whaling Commission considers biopsy sampling to be acceptable, since no long-term effects (change of behaviour) have been shown on individuals and populations (International Whaling Commission 1991). Levels of short-term reactions to biopsy sampling could potentially vary among species, populations and individuals. However, for both small and large cetaceans, the behavioural impact of biopsy sampling is generally considered to be low. Responses from the animals can be typified as reactions to a noxious stimulus of brief duration and low-to-moderate amplitude (Weinrich et al 1992;[START_REF] Best | Biopsying southern right whales: their reactions and effect on reproduction[END_REF][START_REF] Bilgmann | A biopsy pole system for bowriding dolphins: sampling success, behavioral responses, and test for sampling bias[END_REF]Jefferson & Hung 2008). In small cetaceans, a case of death has been reported in a short-beaked common dolphin, underlining that remote biopsy sampling is not without risk [START_REF] Bearzi | First report of a common dolphin (Delphinus delphis) death following penetration of a biopsy dart[END_REF]. Consequently, the use of less invasive sampling techniques may be preferred.

Other methods include skin swabbing and faecal sampling (Harlin et al 1999;Parsons et al 1999). However, these techniques provide a limited amount of material, and DNA may not be of sufficient quality to undertake multiple markers analyses and other analyses (such as pollutant analyses, for example). Biopsy sampling is generally preferred for molecular genetic studies (Parsons et al 2003) and other analyses such as those of stable isotopes (Gross et al 2009). In addition, the use of remote techniques, using a gun or a crossbow, is more effective than a pole system for studies of population structure and parentage because animals can be sampled even if they do not bowride. Remote sampling also allows the individual identification of targeted dolphins [START_REF] Bilgmann | A biopsy pole system for bowriding dolphins: sampling success, behavioral responses, and test for sampling bias[END_REF]. Proper identification of bowriding animals is generally not possible (good photograph angle).

The objective of this study is to characterize short-term reactions of four small delphinid species to remote biopsy sampling: the spinner dolphin (Stenella longirostris, 160-208 cm), the pantropical spotted dolphin (Stenella attenuata, 160-260 cm), one of the smallest delphinids, the Indo-Pacific bottlenose dolphin (Tursiops aduncus, 230-270 cm) and the melon-headed whale (Peponocephala electra, 240-278 cm), one of the least known delphinids. This study provides, to the best of our knowledge, the first information on the effect of biopsy sampling on these species.

Effect of biopsy sampling on small delphinids In order to collect skin and blubber samples for stable isotope, genetic and histopathological investigations, remote biopsy sampling was conducted from December 2004 to October 2008. Levels of behavioural reactions were recorded at two different scales: 1-the individual reaction of the sampled dolphin and 2-the behavioural reaction of the focal group to which the targeted animal belonged. The latter component of the study has not been investigated in previous studies for any other cetacean, as far as we are aware, and allows understanding the impact of remote biopsy sampling at a broader scale, i.e. groups and not only targeted individuals.

Materials and methods

Study area

The island of Mayotte (45°10'E, 12°50'S), which is part of the Comoros archipelago, is located in the northern Mozambique Channel (western Indian Ocean) between Madagascar and Southeast Africa (Figure 1). Its surface area is 376 km 2 . This territory is composed of two main islands: the main inhabited island, on the east and on the barrier reef, a smaller inhabited island. The other islands are small islets dispatched all over the lagoon. The island of Mayotte is characterized by the presence of high marine mammal diversity (22 species including 12 delphinids; Kiszka et al 2007). The most common species are the spinner dolphin, the pantropical spotted dolphin, the Indo-Pacific bottlenose dolphin and the melon-headed whale; these are resident year-round (Kiszka et al 2007).

Biopsy collection

From December 2004 to September 2008, small-boat-based cetacean surveys were conducted throughout the year in Mayotte waters in sea conditions not exceeding Beaufort 3.

Observation effort concentrated mostly on the lagoon and over the insular slope in adjacent waters of the barrier reef. Biopsy attempts were made opportunistically, when groups and individuals were easily approachable and when conditions were optimal (Beaufort < 2, dolphins closely approaching the boat). Optimal weather conditions allowed stability of the research boat and better chances to sample the animals successfully and safely. Several types of boats were used: a 7-m catamaran equipped with two, four-stroke, 60-hp outboard engines; a 7-m mono hull boat equipped with two, two-stroke, 40-hp outboard engines; a 6.4-m cabin cruiser equipped with one, four-stroke, and 150-hp outboard engine; and a 10.8-m cabin cruiser equipped with two, four-stroke, 115-hp outboard engines. Biopsies were collected by using a crossbow (BARNETT Veloci-Speed® Class, 68-kg draw weight) with Finn Larsen (Ceta-Dart, Copenhagen, Denmark) bolts and tips (dart 25-mm long, 5-mm-diameter). A conical plastic stopper caused the bolt to rebound after the impact with the dolphin. The dolphins were hit below the dorsal fin when sufficiently close (3-10 m) to the research boat.

Focal groups/individuals were approached under power at speeds of 1-4 knots. Blubber and skin biopsy samples were preserved individually in 90% ethanol before shipping and subsequent analysis. Biopsy sampling was conducted under French scientific permit #78/DAF/2004 (September 10, 2004) and permit #032/DAF/SEF/2008 (May 16, 2008) after examination of the project by Conseil National de Protection de la Nature.

Behavioural observations

During biopsy sampling sessions, an observer recorded behavioural reactions of dolphins at two different scales: the targeted individual and the focal group with which the targeted individual was associated. The focal group was defined as a group of dolphins engaged in the same activity and travelling in the same direction (Shane 1990). Three levels of behavioural reaction were defined for individuals and focal groups. These reactions followed Hooker et al (2000) and were adapted for the species investigated in this study:

Data analysis

We investigated the occurrence (events and their proportions) of reactions described above and factors responsible for the variability of reactions (group size, species, activity), at the scale of hit/targeted individuals as well as focal groups. Group size was defined prior to biopsy sampling as the number of animals at the surface within five body lengths of each other (Smolker et al 1992). The estimates of group size were more stochastic for spinner dolphins, pantropical spotted dolphins and melon-headed whales, as group size for these species was important (mostly > 50 individuals). Determining absolute group size was not possible for large groups of delphinids. The predominant behaviour was recorded as the activity displayed by the majority of the animals of the group during the first 10 minutes. These data were collected during scan sampling of the group (Mann 1999) using six different behavioural categories: travelling, milling, resting, feeding/foraging, playing and socializing (Shane 1990).

Effect of biopsy sampling on small delphinids Analysis of individual behavioural reactions were differentiated when the animal was missed (the bolt did not reach the animal) or hit. An individual is considered as hit when the bolt reached the body. There was no differentiation between biopsy hit providing or not providing a sample. We tested how group size may affect individual behavioural reactions, especially for the most frequently sampled species, the spinner dolphin. For this species, we also investigated the effect of initial behavioural state on the levels of reaction and the long term effect of biopsy sampling. In this later case, we hypothesised that avoidance behaviour would increase across the study period. Significance of this increase has been tested using a Pearson's correlation. For comparisons, Fisher exact tests, Kruskal Wallis tests and contingency table analyses were performed using Rv2.10.0 (R Development Core Team, 2009).

Results

Biopsy sampling was undertaken from December 2004 to September 2008 (n = 271 attempts, n = 193 samples). Four species (spinner dolphin, pantropical spotted dolphin, melon-headed whale and Indo-Pacific bottlenose dolphin) constituted 96% of the biopsies sampled (n = 259 attempts, n = 181 samples). Other species included the Fraser's dolphin (Lagenodelphis hosei, n = 7), the common bottlenose dolphin (Tursiops truncatus, n = 2), the Indo-Pacific humpback dolphin (n = 2) and the short-finned pilot whale (Globicephala macrorhynchus, n = 1), but this data was not been included in this study. We used three types of vessels to undertake biopsy sampling, but no significant differences of individual behavioural reactions were found between boat types (all species combined, χ² = 3.7, df = 6; P = 0.391).

Among the four species, no significant inter-specific differences in reactions were recorded, both at the scales of individuals (Fisher exact test; P = 0.9) and groups (P = 0.643). Sampling success (a hit) varied between species from 65 to 78% (Table 1). On 34 occasions overall, the hit was successful but no sample was retained in the biopsy tip. Individual behavioural reactions to remote biopsy sampling were recorded on 252 occasions (180 hits, 72 misses), while focal group behavioural reactions were recorded on 271 occasions (193 hits, 78 misses).

There were no statistical differences between individual behavioural reactions between biopsy hits and misses (all species combined, Fisher exact test, P = 0.068). Similarly, at the scale of focal groups, no significant differences between biopsy hits and misses were found (all species combined, KW test; H = 0.702; df = 1; P = 0.402).

At the individual scale, 94% of individual reactions were moderate, i.e. twitch and immediate dive, and simple immediate dive (Figure 2, Table 2). Strong reactions (tail slap, leaping, successive breaches and escape) only represented 2% of behavioural responses of individual dolphins. Escape and leaping was only observed in spinner and spotted dolphins. Increase of speed was observed once in a bottlenose dolphin group (Table 2).

Group behavioural reactions were frequent (54% of sampling sessions), with dive being the commonest moderate reaction (45%, Figure 3, Table 2). Strong reactions of focal groups were rare, representing only 4% of responses. These strong reactions consisted of increased swimming speed or escape (Table 2, Figures 2 and3).

We did not find any correlation between group size and behavioural reactions (Fisher exact test; P = 0.431). However, there is a clear relationship between the mean specific group size and the mean number of biopsies collected per biopsy session (Table 1). The average number of biopsies collected during each session was the lowest for the Indo-Pacific bottlenose dolphin, which had the lowest mean group size (Table 1).

On six occasions, hit dolphins were observed bow-riding just after being sampled (fresh wound of the biopsy hit observed below the dorsal fin or in adjacent areas). These cases were observed in the pantropical spotted dolphin (n = 2 events), spinner dolphin (n = 2) and Indo-Pacific bottlenose dolphin (n = 2). During sampling sessions, significant signs of avoidance of the research vessel by groups were observed on few occasions: in spinner dolphins (n = 2, after one and four biopsy attempts) and in melon-headed whales (n = 2, after one and six biopsy attempts).

We hypothesized that group reactions to biopsy sampling would differ according to activity (milling/travelling, resting, socializing, and playing). We tested this for spinner dolphins, as the dataset for that species was the largest. A statistical difference was found between group reactions and initial behavioural states in which spinner dolphin groups were engaged (Fisher exact test; P = 0.041). Spinner dolphins predominantly showed a stronger response to biopsy sampling when resting and socialising. When milling and travelling, reactions were moderate.

We did not observe changes of dolphin reactions (increase of avoidance behaviour) to the research vessel prior to biopsy sampling over the study period (nearly four years; Pearson's correlation, r = 0.324, P > 0.05).

Discussion

In this study, we observed behavioural reactions of four delphinid species to remote biopsy sampling. The biopsy success reached 65-78%, which is consistent with previous studies. This was mostly due to the high accessibility of the targeted species. They generally came close to the research vessel, especially dolphins of the genus Stenella, often coming to ride waves created by the bow of the boat. No significant inter-species differences were found in reactions to remote biopsy sampling. Indeed, the smallest species (spinner and pantropical spotted dolphins) did not have a higher occurrence of moderate reactions than larger ones (Indo-Pacific bottlenose dolphin and melon-headed whale), as might have been expected. However, the strongest reactions, such as breaches and escape, occurred (but were very rare).

Effect of biopsy sampling on small delphinids Such extreme reactions were only observed in the smaller species, especially spinner and pantropical spotted dolphins. However, due to the small sample size for Indo-Pacific bottlenose dolphins and melon-headed whales, we can not exclude that these species could also react strongly, like spinner and spotted dolphins do.

The mean number of biopsies per session was greater for species with a larger mean group size, i.e. melon-headed whales, spinner and pantropical spotted dolphins. In larger groups, animals are more accessible for biopsying, as there are more individuals to choose from. This is likely to be not just a function of the behaviour or the group reaction, but also because of the higher number of individuals.

Despite the fact that we used three different types of boats, no differences in reactions were found among boats. These differences have been documented in other studies, with generally stronger reactions when smaller boats were used [START_REF] Bilgmann | A biopsy pole system for bowriding dolphins: sampling success, behavioral responses, and test for sampling bias[END_REF]. However, in this later study, sampling was done on bowriding dolphins, and the boat types and length differed to a much larger extent than in the study presented here.

Delphinids around Mayotte exhibited short-term behavioural reactions to biopsy attempts, characterized by acceleration, twitch and immediate dive and simple immediate dive. Strong reactions to biopsy sampling were previously recorded in common bottlenose dolphins (Parsons et al 2003). Conversely, reactions of common bottlenose dolphins appear to be minimal in other areas such as in eastern US (Gorgone et al 2008). Dolphins of all species sampled react in a similar fashion to biopsy hits and misses. This has been previously documented for other species such as the Indo-Pacific humpback dolphin (Jefferson & Kung 2008), meaning that the hit of the bolt on the water has a significant effect on the reactions of dolphins at the proximity of the impact. In the study presented here, focal groups were frequently impacted by biopsy sampling, meaning that remote biopsy sampling does have a broader effect on small cetaceans, i.e. on adjacent individuals belonging to the group. This effect was also greater on species constituting small groups, i.e. Indo-Pacific bottlenose dolphins, as the biopsy success decreased during sampling sessions for such species. The group behavioural reactions of spinner and pantropical spotted dolphins were relatively low, apparently because they formed larger aggregations. However, results underlined that there is a variability of reactions according to initial behavioural state. Indeed, for the spinner dolphin, we observed that the animals had stronger reactions to remote biopsy sampling when resting and socialising. When milling and travelling, reactions were more moderate. This suggests that remote biopsy sampling should be preferably conducted during travelling and milling activities.

Animal welfare implications

Overall, conducting remote biopsy sampling is effective on small delphinids and induces a limited short-term (less than 5 minutes) behavioural impact on hit and missed individuals, including in the smallest delphinid species (especially dolphins of the genus Stenella). However, we observed that biopsy sampling does not only impact hit individuals, but groups to which the targeted individual belongs. No long-term effect of biopsy sampling was observed, such as an increase of avoidance of the research vessel of the animals. This confirms that the method has no long term impact on the animals. However, as a precautionary approach, our findings suggest that biopsy sampling may preferably be conducted when the animals are milling or travelling. However, it is critical to reconsider practicing biopsy sampling to answer scientific questions.

  , humpback whales (Megaptera novaeangliae, Weinrich et al 1991; Clapham & Mattila 1993), other large balaenopterid whales (Gauthier & Sears 1999), and delphinids such as short-beaked common (Delphinus delphis, Bearzi 2000), bottlenose dolphin (Tursiops spp., Krützen et al 2002; Bilgmann et al 2007; Gorgone et al 2008) and Indo-Pacific humpback dolphin (Sousa chinensis, Jefferson & Hung 2008).

  Effect of biopsy sampling on small delphinids 1. No reaction: the individual and focal group continued to show the same behaviour as before the biopsy attempt; 2. Moderate reaction: the individual or the focal group modified its behaviour but gave no prolonged (>5 min) evidence of behavioural disturbance; reactions included e.g. acceleration, twitch and immediate dive and simple immediate dive. A dive was considered as a behavioural response to biopsy sampling when it lasted more than 5 minutes; 3. Strong reaction: the individual or the focal group modified its behaviour in a succession of percussive behaviours (strong and short-lived reactions), including escape from the research boat of the individual or/and focal group (leaping, breaches, tail slaps).

  AE and Donovan GP (eds) Genetic ecology of whales and dolphins pp 81-89. The International Whaling Commission: Cambridge, UK Clapham PJ and Mattila DK 1993 Reactions of humpback whales to skin biopsy sampling on a West Indies breeding ground. Marine Mammal Science 9: 382-391 De Stephanis R, Garcia-Tíscar S, Verborgh P, Esteban-Pavo R, Pérez S, Minvielle-Sebastia L and Guinet C 2008 Diet of social groups of long-finned pilot whales (Globicephala melas) in the Strait of Gibraltar. Marine Biology 154: 603-612 Gauthier J and Sears R 1999 Behavioral response of four species of balaenopterid whales to biopsy sampling. Marine Mammal Science 15: 85-101 Godard CAG, Smolowitz RM, Wilson JY, Payne RS and Stegeman JJ 2004 Induction of cetacean cytochrome P4501A1 by ß-Naphthoflavone exposure of biopsy slices. Toxicological Sciences 80: 268-275 Gorgone AM, Haase PA, Griffith ES and Hohn A 2008 Modelling response of target and nontarget dolphins to biopsy darting. Journal of Wildlife Management 72: 926-932 Gross A, Kiszka J, Van Canneyt O, Richard P and Ridoux V 2009 A preliminary study of habitat and resource partitioning among co-occurring tropical dolphins around Mayotte, southwest Indian Ocean. Estuarine, Coastal and Shelf Science 84: 367-374 Harlin AD, Würsig B, Baker CS and Markowitz TM 1999 Skin swabbing for genetic analysis: application to Dusky dolphins (Lagenorhynchus obscurus). Marine Mammal Science 15: 409-425 Herman DP, Burrows DG, Wade PR, Durban JW, Matkin CO, LeDuc RG, Barret-Lennard LG and Krahn MM 2005 Feeding ecology of eastern North Pacific killer whales Orcinus orca from fatty acid, stable isotope, and organochlorine analyses from blubber biopsies. Marine Ecology Progress Series 302: 275-291 Effect of biopsy sampling on small delphinids Shane SH 1990 Comparison of bottlenose dolphin behavior in Texas and Florida, with a critique of methods for studying dolphin behavior In Leatherwood S and Reeves RR (eds) The bottlenose dolphin pp 245-265. Academic Press: San Diego, USA Smolker RA, Richards AF, Connor RC and Pepper JW 1992 Sex differences in patterns of association among Indian Ocean bottlenose dolphins. Behaviour 123: 38-69 Weinrich MT, Lambertsen RH, Baker CS, Schilling MR and Belt CR 1991 Behavioral responses of humpback whales Megaptera novaeangliae in the southern Gulf of Maine to biopsy sampling. In Hoelzel AR and Donovan GP (eds) Genetic ecology of whales and dolphins pp 91-98. International Whaling Commission: Cambridge, UK Weinrich MT, Lambertsen RH, Belt CR, Shilling MR, Iken JH and Syrjala SE 1992 Behavioral responses of humpback whales Megaptera novaeangliae to biopsy procedures. Fishery Bulletin 90: 588-598 Weller DW, Cockcroft VG, Würsig B, Lynn SK and Fertl D 1997 Behavioral responses of bottlenose dolphins to remote biopsy sampling and observations of surgical biopsy healing. Aquatic Mammals 23: 49-58 Effect of biopsy sampling on small delphinids

Figure 1 :

 1 Figure captions

Figure 2 :

 2 Figure 2: Individual behavioural reactions of delphinids (Stenella longirostris, Stenella

Figure 3 :

 3 Figure 3: Focal group behavioural reactions of delphinids (Stenella longirostris, Stenella

Figure 2 Figure 3

 23 Figure 2

Table 1 :

 1 Number of attempts, biopsy samples collected and sampling success in delphinids sampled around the island of Mayotte from December 2004 to September 2008.

	Species	n attempts	n samples	% success	Number of biopsy sessions	Mean group size	Average n biopsies/ session
	Stenella longirostris	137	96	70	30	70.5	3.2
	Stenella attenuata	77	50	65	20	78.5	2.5
	Peponocephala electra	23	18	78	5	310	3.6
	Tursiops aduncus	22	17	77	15	6.3	1.1

Table 2 :

 2 Individual and focal group behavioural reactions of Stenella longirostris, Stenella attenuata, Peponocephala electra and Tursiops aduncus to remote biopsy sampling (numbers represents events).

Acknowledgements

This research has been funded by the Collectivité Départementale de Mayotte and the Ministère de l'Ecologie et du Développement Durable (French Ministry of Environment). We Effect of biopsy sampling on small delphinids thank Robin Rolland, Alban Jamon, Wilfrid Fousse, Ismaël Ousseni (DAF), Claire Pusineri (ONCFS) and the personnel of Brigade Nature (CDM/ONCFS) for assistance in the field in Mayotte. Special thanks are addressed to Didier Fray (CDM), our main boat pilot, for his patience and perseverance in the field. We warmly thank Tom Jefferson and William Perrin (NOAA Fisheries) for their helpful comments on the early version of the manuscript, and the two anonymous reviewers for their constructing comments and corrections.