Shark feeding affects health and female reproductive investment in blacktip reef sharks from French Polynesia

Ecotourism is branded as transforming wildlife biodiversity conservation; yet, its positive and negative effects are not always assessed in wild populations. Wildlife viewing with feeding is a popular form of ecotourism, but its potential health impacts on wildlife are becoming increasingly evident. Shark feeding is a global phenomenon; however, impact studies on species' persistence (i.e. survival and reproduction) are lacking. In this study, we expand upon previous work on shark tourism and use physiological indicators to assess the sub-lethal health and fitness consequences of shark feeding. Blood cellular, biochemical and endocrinological parameters were sampled from 117 adult wild blacktip reef sharks, Carcharhinus melanopterus, at feeding and non-feeding sites around Mo'orea, French Polynesia, to compare general condition, nutritional status, a metabolism proxy and reproductive investment on the respective sites. In addition to sex- and season-specific differences observed in multiple physiological parameters, we found lower haematocrit levels (condition) at feeding sites for both sexes, as well as lower insulin levels (metabolism proxy) in male sharks at feeding sites. Further impacts of feeding on physiology were found in interaction with the breeding season: adult females using feeding sites had lower glucose levels (nutritional status), as well as lower 17β-oestradiol levels during the breeding season (reproductive investment) compared to non-feeding sites. Male sharks using feeding sites during the breeding season exhibited higher levels of testosterone compared to non-feeding sites. Our results suggest that tourism feeding activity in Mo'orea provides poor nutrition and/or unpredictable food, especially for site-attached females during the energy-intensive breeding season. We highlight how physiological indicators reveal negative health and fitness impacts of shark feeding, with the reproductive impacts potentially having longer-lasting consequences for population dynamics, making feeding an ecological trap. Animal sex and season should be considered when evaluating feeding impacts, and stricter regulations for the nutritional content of the food given to sharks are needed in ecotourism management.