Blacktip reef sharks in French Polynesia are experiencing adverse effects on their health due to frequent exposure to low-quality food scraps from tourists. Reports indicate that these sharks, commonly found in the waters around Mo’orea, are being fed everything from frozen squid to human leftovers. This feeding practice has led to significant changes in their metabolism, movement, and reproductive patterns. Concerns have been raised regarding the long-term consequences on the species, classified as “vulnerable” by the International Union for Conservation of Nature.

Shark Feeding Practices Impact Metabolism

According to a study published in Animal Conservation, research conducted by marine behavioural ecologist Johann Mourier at the University of Montpellier and his team examined the metabolic and reproductive changes in these sharks. Over a three-year period, blood samples from 117 blacktip reef sharks across 17 sites—five of which were known for frequent tourist-driven feeding—were analysed. The results indicated that sharks at feeding sites displayed lower red blood cell levels, a marker of overall health. Blood glucose levels in females were also found to be lower, suggesting that the scraps provided lacked adequate nutritional value compared to their natural diet.

Reproductive Changes Observed in Feeding Site Sharks

Data from the study also highlighted notable shifts in reproductive hormone levels. Males at feeding sites exhibited increased testosterone levels, potentially due to heightened competition over food. Female sharks at non-feeding sites were consistently pregnant and exhibited triple the estrogen levels compared to those at feeding locations, where not all females carried pups. Scientists suggest that an unpredictable and nutritionally insufficient diet may be impacting reproductive success, ultimately affecting population sustainability.

Calls for Better Regulation of Shark Feeding

In an interview with Science News, Natascha Wosnick, a biologist at the Cape Eleuthera Institute, stated that unregulated shark feeding can alter natural behaviour and compromise welfare. Concerns extend beyond Mo’orea, as other species, such as nurse sharks in the Bahamas, may face similar risks due to increased energy expenditure linked to human-provided food. Experts suggest implementing regulations on the types of food offered to sharks, particularly during breeding seasons, to mitigate the negative impact on their health and reproduction.