Andrea Asunsolo Rivera
Overfishing is currently the biggest threat to sharks. Pelagic sharks account for 52% of all identified global catch. Reducing shark mortality by enforcing management and fishing regulations is challenging due to the extensive migrations of pelagic sharks, which frequently cross international borders and into the high seas. A tool promoted to reduce shark mortality and help shark populations recover is Marine Protected Areas (MPAs), where extractive activities such as fishing are prohibited or regulated. Yet, their effectiveness in protecting sharks is under debate, particularly for highly mobile species such as pelagic sharks. Very large MPAs (>100 km²) have been proposed to protect these species and while these sharks might benefit from large MPAs, it is impossible to cover their large-scale movements. A suggested solution for effective MPAs offering spatial protection for wide-ranging sharks is the protection of one or multiple essential habitats, such as important foraging areas and nursery and mating grounds.
Foraging grounds are essential for a species’ survival, and when effectively protected, can greatly reduce mortality. Stable isotope analysis (SIA) is an effective method to study food webs and help predict how impacts, such as fishing, will affect communities within an ecosystem. Different primary producers, habitats, and dietary sources can have different stable isotope compositions (SIC). These SIC change in a predictable way through trophic links, so that the diet is reflected in the consumer’s tissue. This technique can thus provide insights into dietary sources, trophic position, and movement. I will use bulk and compound-specific SIA in combination with movement data to identify blue sharks' foraging grounds in the Galapagos Marine Reserve (GMR), Hermandad Marine Reserve (HMR), and surrounding waters. Identifying and assessing the level of protection granted to these foraging grounds and the overlap with fishing threats is essential to reduce blue shark mortality in the region.
Blue sharks are the highest caught shark species in Ecuador, yet little is known about their population in the Eastern Tropical and Ecuadorian Pacific. Demographic, seasonality, trophic, and diet information come from fishery-dependent studies and movement studies are lacking. Unravelling the movement ecology, habitat use, and trophic ecology of blue sharks in Ecuadorian waters, particularly around the GMR and HMR, will allow for science-based recommendations for effective fisheries regulation and management in Ecuador.