Seasonal variation of sharks and large predatory fish in the Galapagos Marine Reserve

Anthropogenic pressures are driving elasmobranch populations around the world towards extinction. The islands of Darwin and Wolf in the far north of the Galapagos Marine Reserve are known to harbour an exceptionally large reef fish biomass, mostly composed of sharks, and therefore represent a conservation hotspot of international importance. Due to the dynamic oceanographic setting of the archipelago, the composition of sharks and large predatory fish is likely to change throughout the year. With the aim to investigate these potential changes, the current study combined multiple underwater sampling video techniques to assess the seasonal variation in sharks and large predatory fish assemblages at Darwin and Wolf Islands. The results provided evidence that the diversity and relative abundance of species was significantly higher during the cold season, and that seasonal variation in community composition was driven by large and highly mobile predators, including scalloped hammerhead sharks (Sphyrna lewini), silky sharks (Carcharhinus falciformis), and Carangids. As these species are of high conservation and commercial significance, the results on seasonal variation highlight the need for temporal management actions, such as higher restrictions and enforcement of fisheries at Darwin and Wolf Islands during the cold season.