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The Hidden Risks of Shark Feeding in French Polynesia
Sharks often carry the reputation of being indiscriminate eaters, consuming anything that fits in their jaws. However, recent research reveals a concerning reality in French Polynesia, where blacktip reef sharks are adversely affected by the low-quality scraps frequently thrown to them by tourists. This situation has led to negative impacts on their metabolic and reproductive health, as reported in the journal Animal Conservation on December 24.
Popular sites for shark tourism, particularly around Mo’orea—a small island near Tahiti—draw divers and snorkelers eager to observe these marine creatures. Unfortunately, many of these visitors contribute to the problem by tossing everything from frozen squid to leftover human food into the waters, attracting sharks and stingrays to areas inundated with low-nutritional value offerings.
During his time at the Island Research Center and Environmental Observatory in Mo’orea, marine behavioral ecologist Johann Mourier studied the movements and reproductive patterns of these sharks. The nature of blacktip reef sharks—Carcharhinus melanopterus—is largely to stay local, often remaining in the same reef for extended periods. Given this behavior, Mourier and his team were curious about how frequent human interaction and feeding might influence the sharks’ health and behavior.
Earlier investigations showed that female sharks near active feeding areas exhibited increased movement compared to those in less disturbed locations. Additionally, pregnant females were found to stray from their preferred warm, shallow lagoon waters. This raised the question of whether their observed behavioral shifts correlated with health-related indicators.
From May 2008 to May 2011, the research team captured 49 female and 68 male blacktip reef sharks across various sites. They differentiated between five feeding sites and twelve nonfeeding sites, collecting blood samples to analyze levels of various biochemicals and hormones linked to metabolism and reproduction.
Findings indicated that both male and female sharks at feeding locations had a lower ratio of red blood cells, suggesting a deteriorated health condition. Notably, during the breeding season, females found near feeding sites displayed decreased blood glucose levels, a sign that the quality of food they consumed was inadequate.
Mourier noted that the food scraps provided by humans resemble junk food, lacking the essential nutrients found in their natural diets. This shift towards poorer quality nourishment poses serious threats to the sharks’ health.
Additionally, the feeding dynamics appear to alter the reproductive hormones in males, who exhibited elevated testosterone levels due to increased competitive interactions among densely grouped sharks. Conversely, females at locations that did not involve feeding were consistently pregnant, with one specific form of estrogen being three times higher than that of females at feeding sites—where pregnancy was not guaranteed.
This inconsistent, low-quality diet could hinder female sharks from adequately investing in their future pups, suggesting potential long-term repercussions on reproduction and fitness across generations. Alarmingly, the blacktip reef shark is currently classified as “vulnerable” by the International Union for Conservation of Nature.
Natascha Wosnick, a biologist affiliated with the Cape Eleuthera Institute, emphasized the importance of these findings, stating, “This study represents a significant advancement in our understanding of shark health.” She pointed out that current feeding practices often lack regulations, which can lead to detrimental effects on shark behavior and welfare.
Given that blacktip reef sharks typically inhabit smaller ranges, they could be especially susceptible to the effects of consistently human-fed diets. In contrast, larger species such as tiger and lemon sharks, which travel farther distances, might be less vulnerable to such feeding practices.
Other shark species could also face adverse effects from human-induced feeding. Wosnick remarked on nurse sharks in the Bahamas, which have shown alterations in behavior and health due to dependency on fish scraps. These sharks tend to swim more actively during the day, leading to increased energy expenditure that may not be sufficiently met by the quality and quantity of food available to them.
The research team advocates for stricter regulations on the types of food provided to sharks in popular feeding areas, particularly during breeding seasons, to safeguard the sharks’ health. Mourier concluded, “Shark tourism is beneficial for conservation and public education, but it is essential to manage these activities more effectively.”
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