Have you ever seen a shark being fed while on vacation to attract it to tourists? If so, did you wonder about the impact of the food reward on the shark? It may not have occurred to you in the moment, but food rewards provided through wildlife tourism contribute to the energy requirements of many species. However, the exact contributions to conservation, animal behavior, and animal health that provisioning activities make have largely been unexplored, especially for shark species.
Brunnschweiler, an independent researcher, and his colleagues, Payne and Barnett, from the University of Roehampton and James Cook University, respectively, published an article in the journal, Animal Conservation, addressing this gap in knowledge. In their study, they examined the contributions of hand-fed tuna heads to the daily energy requirements of Carcharhinus leucas, or bull sharks, a popular target of provisioning in Fiji, the Bahamas, and Mexico. Using bioenergetics modelling, they found that the energy requirements of some sharks are periodically met through provisioning.
Data were collected from 36 commercial shark watching dives in Fiji’s Shark Reef Marine Reserve (SRMR) between January and March of 2008 and 2009. On each dive, the following was recorded: (1) feeding duration; (2) tuna heads taken total and by individuals; and (3) presence and identification of individual sharks. Sharks that were present for 10 or more of the 36 dives were declared focal individuals.
It was estimated that 1087 kcal of energy per day was needed for wild bull sharks at the SRMR to have similar growth rates as captive ones. Using the average mass (2.4 kg) and bomb calorimetry estimate of tuna head energy content (1.92 kcal of energy per gram), it was determined that 2.3 tuna heads are required per shark per week to fulfill energy requirements. Using the provisioning frequency (3-4 times per week) and average number of tuna heads consumed per provisioning day (0.74 tuna heads), it was also determined that 2.6 tuna heads were consumed per focal individual per week—more than enough to meet the weekly energy budget.
However, these data are only representative of 10 focal individuals and 36 dives. To be sure that this limitation did not heavily affect the findings of the study, I contacted the paper’s first author, Brunnschweiler, who stated, “We have been observing these sharks for 15 years and really know what is going on. The general findings would likely be the same, even if we had a bigger sample size.”
The authors also acknowledge several other aspects of the study that could not be accounted for. For example, encounter rates varied between individuals and months, feeding rates were inconsistent, individual sharks may have different energy expenditures, tuna heads are not completely representative of the natural prey of bull sharks, and focal individuals may be more bold than other bull sharks and thus, take more food. Therefore, it is important to note that the study’s findings are more of a generalization than anything and cannot definitively prove that wildlife tourism consistently fuels the energy requirements of all bull sharks.
Still, we can conclude that despite intraspecific variability, hand feeding tuna heads to bull sharks in Fiji’s SRMR periodically fuels energy requirements for some sharks. This finding is substantial, as Brunnschweiler notes, because “Feeding sharks is controversial, and I think a lot of critics think that if you offer food to sharks, individuals take as much as they can. This is not the case.” So the next time you see a shark being fed as a result of wildlife tourism, think about how your visit is contributing to the health and conservation of sharks!
Brunnschweiler, J.M., Payne, N.L. & Barnett, A. (2017). Hand feeding can periodically fuel a major portion of bull shark energy requirements at a provisioning site in Fiji. Animal Conservation. doi:10.1111/acv.12370