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Pros and Cons of shark feeding
The use of fresh soybeans as an attractant in fishing has been altering the diet of the characiform Brycon falcatus, which are thriving at fishing spots. This has subsequently affected the amount of abdominal fat in the species from the Tapajós River basin, Southern Amazon. In the Teles Pires River basin region, one of the most common capture techniques employed by fishermen is the use of attractant feeds (soybeans, corn, cassava) at certain locations to attract mostly omnivorous fish. Tourists also feed fish chips and breadcrumbs. In the experimental design, rivers were mapped according to attractant availability to develop an attractant-density classification system comprising four rivers with different attractant densities (low, medium, and high), plus a river serving as control (no attractants). Monthly collections were carried out during the 2012 and 2013 dry seasons. For diet analyses, methods of frequency of occurrence and relative volume were used to calculate the feeding index (IAi) of 97 specimens. For analyses of abdominal fat, an index was calculated by dividing the wet weight of the abdominal fat by the total wet weight of each individual. Standard length ranged from 15.0 to 48.5 cm, and weight between 0.18 and 4.40 kg. Composition and diversity of diet items changed with the increasing density of attractants. In the river with a high attractant density, fresh soybeans and corn were dominant diet items; in the control river, the diet was natural (e.g. seeds, fruits, leaves, and insects) and therefore similar to those described for B. falcatus in undisturbed environments. Fish collected from rivers with high attractant densities were in better condition than those from the river with no attractants. Although use of attractants is prohibited by State legislation, there are no inspections. This study clearly shows an alteration in the natural diet and abdominal fat of B. falcatus resulting from an imbalanced, high-calorie feed via an attractant. It is recommended that these areas be monitored for the preservation of B. falcatus.
The feeding of marine predators is a popular means by which tourists and tour operators can facilitate close observation and interaction with wildlife. Shark-feeding has become the most developed provisioning activity around the world, despite its controversial nature. Amongst other detrimental effects, the long-term aggregation of sharks can modify the natural behaviour of the animals, potentially increase their aggression toward humans, and favour inbreeding. During 949 diving surveys conducted over 44 mo, we investigated the ecology and residence patterns of 36 photo-identified adult sicklefin lemon sharks Negaprion acutidens. The group contained 20 females and 16 males. 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, showing a risk of inbreeding due to the reduction of shark mobility. Intra- and interspecific aggression was also witnessed, leading to an increased risk of potentially severe bites to humans. Our findings suggest the need for a revision of the legal framework of the provisioning activity in French Polynesia, which could include a yearly closure period to decrease shark behavioural modifications due to long-term shark-feeding activities.
Despite growing concerns about overexploitation of sharks, lack of accurate, species-specific harvest data often hampers quantitative stock assessment. In such cases, trade studies can provide insights into exploitation unavailable from traditional monitoring. We applied Bayesian statistical methods to trade data in combination with genetic identification to estimate by species, the annual number of globally traded shark fins, the most commercially valuable product from a group of species often unrecorded in harvest statistics. Our results provide the first fishery-independent estimate of the scale of shark catches worldwide and indicate that shark biomass in the fin trade is three to four times higher than shark catch figures reported in the only global data base. Comparison of our estimates to approximated stock assessment reference points for one of the most commonly traded species, blue shark, suggests that current trade volumes in numbers of sharks are close to or possibly exceeding the maximum sustainable yield levels.
Most arguments invoked so far by the scientific community in favour of shark conservation rely on the ecological importance of sharks, and have little impact on management policies. During a 57-month study, we were able to individually recognise 39 sicklefin lemon sharks that support a shark-feeding ecotourism activity in Moorea Island, French Polynesia. We calculated the direct global revenue generated by the provisioning site, based on the expenses of local and international divers. The total yearly revenue was around USD5.4 million and the 13 sharks most often observed at the site had an average contribution each of around USD316 699. Any one of these sharks represents a potential contribution of USD2.64 million during its life span. We argue that publicising economic values per individual will be more effective than general declarations about their ecological importance for convincing policy makers and fishers that a live shark is more valuable than a dead shark for the local economy. Studies monitoring the potential negative ecological effects of long-term feeding of sharks should, however, be conducted to ensure these are also considered. Besides declarations about the non-consumptive direct-use value of sharks, as promoted by ecotourism, the calculation of their other economic values should also benefit shark conservation.
Shark feeding is a controversial recreational activity that may alter shark behaviour. In order to investigate possible behavioural changes at the level of the individual, it is necessary to recognise each shark underwater and in a nonintrusive way. In this study, we tested a protocol based on natural marks on fins, and coloured spots and scars on the body to differentiate individual sicklefin lemon sharks. We found that a feeding group, aggregated for 26 months at a northern location off Moorea Island, comprised 32 animals (19 females and 13 males), identified from 2589 observations made over 541 dives. Post-dive photo-identification of individual sharks was a reliable technique, whereas a high level of skill was required to ensure an instantaneous identification underwater. However, direct underwater identification of individual sharks can be of potential use in shark behavioural studies.