Shark research - Johann MOURIER

Low level of gene flow in Blacktip reef sharks accross Polynesian Archipelagos

johannmourier — Wed, 10 Apr 2013 08:44:30 +0000

Microsatellite Analyses of Blacktip Reef Sharks (Carcharhinus melanopterus) in a Fragmented Environment Show Structured Clusters

Abstract

The population dynamics of shark species are generally poorly described because highly mobile marine life is challenging to investigate. Here we investigate the genetic population structure of the blacktip reef shark (Carcharhinus melanopterus) in French Polynesia. Five demes were sampled from five islands with different inter-island distances (50–1500 km). Whether dispersal occurs between islands frequently enough to prevent moderate genetic structure is unknown. We used 11 microsatellites loci from 165 individuals and a strong genetic structure was found among demes with both F-statistics and Bayesian approaches. This differentiation is correlated with the geographic distance between islands. It is likely that the genetic structure seen is the result of all or some combination of the following: low gene flow, time since divergence, small effective population sizes, and the standard issues with the extent to which mutation models actually fit reality. We suggest low levels of gene flow as at least a partial explanation of the level of genetic structure seen among the sampled blacktip demes. This explanation is consistent with the ecological traits of blacktip reef sharks, and that the suitable habitat for blacktips in French Polynesia is highly fragmented. Evidence for spatial genetic structure of the blacktip demes we studied highlights that similar species may have populations with as yet undetected or underestimated structure. Shark biology and the market for their fins make them highly vulnerable and many species are in rapid decline. Our results add weight to the case that total bans on shark fishing are a better conservation approach for sharks than marine protected area networks.

Figure 1. Map of French Polynesia showing the 5 sample locations. Distances (in km) between the sample locations are shown in the matrix top right.

Figure 2. Bayesian approach results using the Discriminant Analysis of Principal Components to investigate genetic structure. The optimal number of principal components found for the analysis was 21 based on the trend in alpha scores (a). The BIC (Bayesian Information Criterion) values are shown in relation to the number of genetic clusters in (b). Each vertical bar represents an individual in the DAPC diagram (compoplot) shown as (c), and each color represents the probability of belonging to one of the genetic clusters. Some outliers have been noted on the top of the figure: M = male, F = female, followed by the total length of each shark in cm.

This study provides interesting additionnal informations to our previous paper in Molecular Ecology. Despite low levels of gene flow accross archipelagos (Figure 2 above), dispersal is likely made by males while at the same time some females could migrate for parturition accross islands (Mourier & Planes 2013).

The paper in Free-Access here:

Vignaud T, Clua E, Mourier J, Maynard J, Planes S (2013) Microsatellite Analyses of Blacktip Reef Sharks (Carcharhinus melanopterus) in a Fragmented Environment Show Structured Clusters. PLoS ONE 8(4): e61067.

Males blacktip reef sharks prefers the fore reef while females choose the lagoon at a tropical island.

johannmourier — Fri, 08 Feb 2013 17:18:11 +0000

My new paper recently published in Journal of Fish Biology described population characteristics of blacktip reef sharks at Moorea (French Polynesia).

This paper gathered capture data of this reef species during my PhD thesis to determinate some biological parameters such as mean size, growth and male size at maturity. It includes a review of the same existing parameters in previous studies at other locations and showed that Moorea’s sharks are bigger (on average) than those of other locations such as Australia, Aldabra (Indian Ocean) or Palmyra (Pacific Ocean). Indeed, maximum size of both males (139 cm) and females (157 cm) are higher, as well as size at maturity for males (111 cm) and size at birth (48 cm). Adult sharks grow an average 6 cm/year.

While this species have recently demonstrated that it was able to be social (see paper in Animal Behaviour), this paper show that at the island scale males and females have different habitat differences with males caught mainly on the fore reef while females caught in the lagoon. These informations have important implication for the evolutionary strategy of this species as well as for conservation.

Here is the abstract:

Mourier, J., Mills, S.C. & Planes, S. (in press). Population structure, spatial distribution and life history traits of blacktip reef sharks Carcharhinus melanopterus at Moorea, French Polynesia. Journal of Fish Biology.

During a survey of the population of blacktip reef shark Carcharhinus melanopterus in Moorea (French Polynesia) between 2007 and 2011, population structural characteristics were estimated from 268 individuals. Total length (L_T) ranged from 48 to 139 cm and 48 to 157 cm for males and females, respectively, demonstrating that the average L_T of females was larger than that of males. The C. melanopterus population at Moorea showed an apparent spatial sexual segregation with females preferentially frequenting lagoons and males the fore-reefs. Mean growth rate was c. 6 cm year⁻¹. Males reached sexual maturity at 111 cm L_T. This study reports on the population characteristics of this widespread carcharhinid shark species and makes comparisons with other locations, confirming high geographic variability in the population structure of the species.

French Polynesia is now the biggest Shark Sanctuary in the World!

johannmourier — Thu, 06 Dec 2012 10:41:34 +0000

The Gouvernement has just listed the mako shark (Isurus oxyrinchus) as protected in French Polynesian waters (category B article A. 121-9). The mako was the only shark species which was not yet protected in this large territory since the protection of all other species in 2006. This propulse French Polynesia as a shark santuray reaching more than 5 million km2.

This is a good news, however a lot of work is still needed to improve the effectiveness of this conservation action.

French details:

Le Conseil des ministres de ce mercredi a intégré le requin mako (Isurus oxyrinchus) à la liste des espèces protégées de la catégorie B du code de l’environnement de la Polynésie française (article A. 121-9). Le mako était la seule espèce de requin non protégée à ce jour. Cette exception était justifiée par sa commercialisation sur le marché local et à l’export, pour la consommation de sa chair. Aujourd’hui, ce requin n’est pratiquement plus débarqué sur le port de pêche : le faible prix d’achat proposé aux pêcheurs ne permet pas de compenser le volume important que nécessite son stockage dans les cales des thoniers. Avec l’accord des professionnels du secteur, le régime dérogatoire accordé au mako a donc été supprimé.

Dorénavant, tous les requins bénéficient du même degré de protection, à savoir l’interdiction de transport, de détention, de collecte des œufs, de capture à terre ou en mer, de taxidermie, et de toute commercialisation, importation et exportation incluses (délibération 90-83 AT du 13 juillet 1990 modifiée, article A. 121-1- II du code de l’environnement de la Polynésie française).Toute infraction à ces interdictions est passible de sanctions pénales (peine d’emprisonnement et amende), assorties de la saisie-confiscation des moyens de transport et de pêche utilisés.

Direct genetic evidence for reproductive philopatry and associated fine-scale migrations in female blacktip reef sharks (Carcharhinus melanopterus) in French Polynesia

johannmourier — Wed, 07 Nov 2012 12:14:54 +0000

Here is my new paper on the reproductive migrations of females blacktip reef sharks to their nursery area inferred from parentage analysis.

Mourier, J.& Planes, S. (in press). Direct genetic evidence for reproductive philopatry and associated fine-scale migrations in female blacktip reef sharks (Carcharhinus melanopterus) in French Polynesia. Molecular Ecology. Doi: 10.1111/mec.12103

Figure 1: Migrations of female blacktip reef sharks from their site they are attached to, to their nursery area in Moorea. Note that some are going to the same nursery on multiple years to give birth. This was demontrated using genetic parentage analysis that assigned juveniles back to their parents within the population.

Figure 2: Reproductive migrations between Moorea and Tetiaroa, 2 islands separated by about 50 km and deep water (>2000 m).

Figure 3: An example of the monitoring of a female’s pregnancy. Its pup was found and sampled December 2009 in one of the nursery.

Abstract

Conservation of top predators has been emphasized as essential in an ecosystem due to their role in trophic chain regulation. Optimizing conservation strategies for these endangered marine top predators requires direct estimates of breeding patterns and connectivity as these are essential to understanding the population dynamics. There have been some attempts to investigate breeding patterns of reef sharks from litter reconstruction using molecular analyses. However, direct fine-scale migrations of female sharks for parturition as well as connectivity at a medium scale like between islands remain mostly unknown. We used microsatellite DNA markers and a likelihood-based parentage analysis to determine breeding patterns of female blacktip reef sharks in Moorea (Society Islands, French Polynesia). Most females gave birth at their home island but some migrated to specific nursery areas outside the area they are attached to, sometimes going to another island 50 km away across deep ocean. Our analysis also revealed that females migrated to the same nursery for every birthing event. Many offspring showed a high level of inbreeding indicating an overall reduced population size, restricted movements and dispersal, or specific mating behaviour. Females represent the vectors that transport the genes at nursery grounds, and their fidelity should thus define reproductive units. As females seem to be philopatric, males could be the ones dispersing genes between populations. These results highlight the need to conserve coastal zones where female reef sharks seem to exhibit philopatry during the breeding season.

Trophic interactions at the top of the coral reef food chain

johannmourier — Wed, 31 Oct 2012 21:59:29 +0000

Here is our new paper describing a rare and extraordinary observation of both social and predator-prey interaction:

Mourier J., N. Buray & S. Planes (in press). Trophic interactions at the top of the coral reef food chain. Coral Reefs.

Sharks, as apex predators, play a fundamental role in most coral reef ecosystems by influencing communities directly via predation or via behaviourally mediated trophic interactions (Heithaus et al. 2008). Healthy coral reefs are generally regulated by small sharks, such as grey reef sharks (Carcharhinus amblyrhynchos). Although small sharks have been found in the stomachs of the great hammerhead shark (Sphyrna mokarran) (Cliff 1995), direct observations of predation on free-living reef sharks are absent. Here, we report upon a great hammerhead shark preying on a grey reef shark at the World Heritage atoll of Fakarava (French Polynesia).

At sunset on 9 May 2011, a large female great hammerhead shark (~ 4.5–5 m TL) was observed to attack a school of approximately 100 grey reef sharks at a depth of 20–30 m in the pass ‘Garuae’. The hammerhead charged a grey reef shark (~ 1 m TL) from the deep. Its approach was very fast and deliberate. The predator then moved to the middle of the pass holding its prey motionless in its jaws (Fig. 1). The hammerhead disappeared slowly into the lagoon pursued by the entire school of grey reef sharks.

Fig. 1 a, b Predation of a free-living Carcharhinus amblyrhynchos by a large female Sphyrna mokarran in the atoll of Fakarava, French Polynesia. (Photograph: a Christian Hornecker and b Ludovic Jego)

Schools of grey reef sharks have often been observed to be frightened by great hammerhead sharks and to pursue their assailant. Several hypotheses may explain the response of the other grey reef sharks: a collective mobbing as found in dolphins or seals (Kirwood and Dickie 2005) or simply an attempt to feed opportunistically on the carcass. Although sharks may not be a major component of the great hammerhead shark’s diet, this rare field observation confirms previous data from stomach contents, further documents this predator–prey interaction and highlights the complexity of the trophic food chain in healthy coral reef ecosystems.

Acknowledgments

We are grateful to TOPDIVE, especially to Sébastien Jolivet, for their contribution to the description of the event. We are grateful to Ludovic Jego and Christian Hornecker for providing the photographs.

First record of M. birostris in French Polynesia and most easterly record of M. alfredi in the Pacific

johannmourier — Wed, 24 Oct 2012 22:42:34 +0000

During a recent oceanographic expedition Pakaihi i te Moana (Respect the Ocean) to Marquesas Islands in French Polynesia between October 2011 and February 2012, I recorded every sightings of manta rays among a hundred of dives. I reported the first sighting of Manta birostris in French Polynesia and reported the presence of its sister species, the reef manta ray Manta alfredi, at the most easterly location in the Pacific Ocean. Manta rays were sighted at seven of the 10 islands surveyed. No manta rays were sighted at seamounts nor around oceanic rocks. Individuals of M. alfredi were observed at seven islands and individuals of M. birostris were observed at four islands. Occurrence of both species was observed on four islands, but a mixed aggregation was observed on only one occasion in Nuku-Hiva. As described by Kashawagi et al. (2011), this suggests that the two species occur in microsympatry (record of co-occurrence at the same dive site) at least in Nuku-Hiva. The occurrence of the two species, however, generally appears to be spatially segregated.

Prior to this study, the most easterly known record of M. alfredi in the Pacific Ocean was at Keauhou, Hawaii (19◦ 33_ N; 155◦ 57_ W; Kashawagi et al., 2011). The observations in the Marquesas Islands, reported here, extend its eastern range in the Pacific Ocean to Fatu Hiva (10◦ 29_ S; 138◦ 37_ W). The present surveys also documented the first record of M. birostris in French Polynesia.

This study was published in Journal of Fish Biology:

Mourier J. (2012). Manta rays in the Marquesas Islands: first records of Manta birostris in French Polynesia and most easterly location of Manta alfredi in the Pacific, with notes on their distribution. Journal of Fish Biology. DOI: 10.1111/j.1095-8649.2012.03449.x

New Association for Shark & Rays in French Polynesia

johannmourier — Fri, 16 Mar 2012 03:11:55 +0000

With colleagues we recently created a new association on Shark & Rays in French Polynesia.

It is devoted to the observatory of shark and rays in Polynesian water and to gather records of elasmobranchs in all French Polynesian territory.

It is actually only developped in French but futur update will allow to make an English version of the website.

Our project is to analyse spatial and temporal trends in French Polynesian shark & rays by involving observators through the territory. Futur project will arise from ORP in many topics such as Conservation, Research and Education.

Here is a link:

Sharks are more social animals than previously believed

johannmourier — Tue, 27 Dec 2011 00:16:28 +0000

Sharks are usually viewed as solitary predators… However, my last study that has just been published in the journal Animal Behaviour shows the contrary: sharks can have preferred companions and a complex social structure, even at a small scale (10km coastline).

Here is the Abstract of the scientific article (you can find it here).

Here are also selected press related articles:

http://blogs.scientificamerican.com/thoughtful-animal/2012/01/23/sharks-with-friends/

http://news.discovery.com/animals/blacktip-reef-sharks-122002.html

http://wendyzukerman.com/2012/02/sharks-like-hanging-out-with-buddies/

http://www.foxnews.com/scitech/2012/02/21/even-sharks-make-friends-scientists-say/

Evidence of social communities in a spatially structured network of a free-ranging shark species

Johann Mourier ^,, Julie Vercelloni, Serge Planes

Laboratoire d’Excellence « CORAIL » and USR 3278 CNRS-EPHE, Centre de Recherche Insulaire et Observatoire de l’Environnement (CRIOBE) and Centre de Biologie et d’Ecologie Tropicale et Méditerranéenne, France

Received 5 April 2011; revised 30 June 2011; Accepted 14 October 2011. MS. number: 11-00283. Available online 19 December 2011.

Large, solitary, marine predators such as sharks have been observed to aggregate at specific areas. Such aggregations are almost certainly driven by foraging and behavioural strategies making space for diverse spatial organizations. Reef-associated shark species often show strong patterns of site fidelity that could be viewed as a prerequisite for sociality. However, there is limited empirical evidence that such aggregations are driven by intrinsic social factors. Association data for blacktip reef sharks, Carcharhinus melanopterus, were obtained from photoidentification surveys conducted in Moorea coral reefs (French Polynesia). We adapted a social network approach to demonstrate evidence of four main communities and two subcommunities within the population. We confronted the resulting structure with candidate explanatory variables. Sharks formed spatial groups characterized by nonrandom and long-term associations, despite opportunities for social relationships to develop between communities. Sex and length of sharks tended to influence assortment at the population and community levels. Individual space use also explained community structure, although spatial assortment was globally weaker than random expectations, suggesting that observed associations were not an artefact of the sampling design or spatial distribution of individuals. We conclude that the observed grouping patterns not only resulted from passive aggregations for specific resources, but rather the communities developed from an active choice of individuals as a sign of sociability. Individual preferences and adaptation to local conditions, as well as demographic, ecological and anthropogenic factors, may explain the social variability between communities. This suggests that a stable grouping strategy may confer substantial benefits in this marine predator.

Adventure Ocean Quest “Shark paradise of Polynesia”

johannmourier — Wed, 28 Sep 2011 14:24:56 +0000

Release of ADVENTURE OCEAN QUEST (PART 4)
About sharks of French Polynesia including sicklefin lemon sharks (juveniles and adults) of Moorea and Great hammerheads of Rangiroa.

Here is the documentary:

52 minutes, produced by Christian Pétron and Boris Raim, with Frédéric Buyle (World Champion ship of Free Diving)
Production: Sound & Vision GMBH et Cinemarine pour ZDF Entreprise.

A film with Frédéric BUYLE, William WINRAM, and Dr Johann MOURIER
Film supported by Polynesian Gouvernment (APAC) and the NRW Bank
Directed by Boris RAIM and Christian PETRON
Camera: Sascha Schöberl
Underwater camera: Christian PETRON

Expedition 2011_Spawning Camouflage Groupers (Epinephelus polyphekadion)

johannmourier — Wed, 27 Jul 2011 07:39:40 +0000

After my PhD defence on blacktip reef shark’s behavioural ecology, I was part of an expedition and started a new CRIOBE project in collaboration with Michael Domeier and other scientists in a special place in French Polynesia were Camouflage Groupers (Epinephelus polyphekadion) aggregate a month a year for spawning. The place is also characterized by the presence of undreds of grey reef sharks as well as tenth of blacktip sharks (Carcharhinus limbatus). We started to study this almost pristine ecosystem from sharks to fish.

During the spawning aggregation of groupers, plenty of grey reef sharks enter in feeding frenzy and predate on groupers.

Check out this video I made, begining with the shark wall, then with the begining of grouper aggregation and finishing with spawning and predations (predation at 08:18).