D-Impact of shark feeding

Impact of « shark feeding » activities on shark behaviour and ecology

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Figure: review of the existing shark and ray provisioning operations in the world (Brena et al. 2015)

The feeding of wildlife has become a popular means by which tourists and tourism operators can facilitate close observation and interaction with wildlife. Compared to marine pollution, coastal habitat degradation, over-exploitation and intensive fishery, the shark-feeding seems of little concern. However this practice is widespread throughout tropical and subtropical seas of the world and gives rise to controversy with little consensus on how it should be managed. Shark-feeding is probably one of the most impressive activity tourists can experience underwater. Deliberate and long-term shark feeding is suspected to alter natural behaviour patterns of shark populations, engender dependency and habituation, increasing aggression towards humans by conditioning them to associate humans with food, and to have adverse effects on surrounding communities. On the other hand, tour operators defend the practice as a mean to spread awareness and promote conservation. Despite this controversy, there are few comprehensive reports that consider the impacts of the shark-feeding while the practice is widespread and growing.

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Figure: Provisioning can have interacting and cascading effect on the behaviour, ecology and physiology on sharks at different scales (individual, group, community; Brena et al. 2015)

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In Moorea Island (French Polynesia), shark-feeding occurs since the 1990s in three localities on the outer slope off the north coast. One locality in the lagoon only feeds stingrays. Shark-feeding implicate several species but mainly the blacktip reef shark (Carcharhinus melanopterus), the grey reef shark (C. amblyrhynchos) and the sicklefin lemon shark (Negaprion acutidens).

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This study considers the potential impacts of shark-feeding practices in the wild on the behaviour and the ecology of shark populations.

The aims are to understand if the shark-feeding activity affects the natural behaviour of sharks (i.e. home range, scale of movements, habitat use and residency patterns, density and aggregation and shark population structrure).

Methods :

To evaluate impact of shark feeding activities on the behaviour of shark populations, we use 3 different methods in order to reply to the different questions:

1)Acoustic tracking

We use remote listening stations (Vemco acoustic receiver VR2)  to compare shark movements in areas where sharks are affected by shark-feeding activity and in areas where they are not affected.

2)Underwater observations

Underwater observations allow to quantify shark density in shark-feeding sites and non feeding sites. For each dive, I note the number of observed sharks to compare density of sharks on the different spots (Number of sharks per dive time). Sharks are identified individually by the photo-identification technique in order to count a shark only once.

3) Genetic approach

On sites where sharks aggregate unnaturally because of provisioning diving, naturally social interactions and group structure could be modified. By forming large groups in shark feeding area, this activity can favour intra-specific encounters between resident counterparts favouring a network of related sharks that could form family groups. This could lead sharks to mate with partners from the same family and thus increase locally the inbreeding rate compared with an area where shark feeding does not occur and where sharks would promote gene flow by moving and melting with different populations of unrelated sharks.

The aim is to detect the presence of kin-biased behavioural patterns, testing the hypothesis that sharks patrol with related conspecifics more often than with unrelated ones in “shark feeding” sites compared to “natural” sites.

In order to test this hypothesis, I use genetic parentage analysis and compare relatedness in different areas of the Island including area affected by shark feeding and other non-affected.

        4) Isotope analysis

We will compare isotope signatures of sharks between provisionning sites and natural sites in order to investigate potential impact of shark-feeding on shark trophic level. This study will be done in collaboration with Jeremy Kiszka and Mike Heithaus.

Main results:

At present, we published results on the sicklefin lemon shark population occuring on a shark-feeding site in Moorea.

During a 5-year monitoring, we visually recognised about 40 lemon sharks that regularly visit the feeding site by photo-identification (Buray et al. 2009). Each shark could be identified individually, which was the first step towards observing their behaviour with regard to feeding over a period of months or even years, as was the case from 2006–2010. By analysing 40 individual lemon sharks, it could be demonstrated that they became increasingly faithful to the feeding site as the years went by (Clua et al. 2010). From this long-term survey, we identified 5 different behavioural groups that we described as ‘new sharks’ (7), ‘missing sharks’ (4), ‘resident sharks’ (13), ‘unpredictable sharks’ (5) and ‘ghost sharks’ (7). In spite of movements in and out of the area by some males and females, which were probably related to mating, the general trend was that residency significantly increased during the study, particularly in males.

Example of the tendancy of increase residence for a shark social group on the feeding site (from Clua et al. 2010).

Number of different sharks contributing to the sightings during the course of the study.

Economic value of sharks through ecotourism

On Moorea, it was calculated that direct profits generated by shark diving provided a yearly revenue of USD 5.4 million and that one lemon shark contributed USD 2.3 million over its 20-year lifespan. By basing the study on separately identified individuals, it was possible to calculate individual yearly contributions that averaged USD 315,000 for each of the 13 resident sharks, which accounted for 73% of onsite observations. The most productive resident female alone contributed USD 475,000 (Clua et al. 2011).

Related published papers:

Brena PF, Mourier J, Planes S, Clua E (2015) Shark and ray provisioning : functional insights into behavioral, ecological and physiological responses across multiple scales. Marine Ecology Progress Series 538: 273-283.

Mourier J, Buray N, Schultz JK, Clua E, Planes S (2013) Genetic network and breeding patterns of a sicklefin lemon shark (Negaprion acutidens) population in the Society Islands, French Polynesia. PLoS ONE 8(8): e73899.

Clua E, Buray N, Legendre P, Mourier J, Planes S (2010) Effects of provisioning on shark behaviour: Reply to Brunnschweiler & McKenzie (2010). Marine Ecology Progress Series 420: 285-288.

Clua E, Buray N, Legendre P, Mourier J, Planes S (2010) Behavioural response of sicklefin lemon sharks Negaprion acutidens to underwater feeding for ecotourism purposes. Marine Ecology Progress Series 414:257–266.

Buray N, Mourier J, Planes S, Clua E (2009) Underwater photo-identification of sicklefin lemon shark, Negaprion acutidens, at Moorea (French Polynesia). Cybium 33(1): 21-27.

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