Discovery of a putative scalloped hammerhead shark Sphyrna lewini (Carcharhiniformes: Sphyrnidae) nursery site at the Galapagos Islands, Eastern Tropical Pacific

Sphyrna lewini is a viviparous shark that pups in shallow coastal waters. Given dramatic declines in the S. lewini Eastern Pacific population, it is essential to identify nursery grounds that could potentially increase the resilience of adult populations. Here, we provide evidence of a putative nursery ground for S. lewini at an oceanic island in the Galapagos Marine Reserve. A fortuitous finding of hammerhead shark pups in 2017 led to a series of focused surveys from 2018 onwards, using experimental fishing, baited remote underwater videos stations (BRUVS), and acoustic telemetry, to assess presence and residency patterns of this species at Puerto Grande: a shallow bay at the island of San Cristobal. We caught 66 individuals, of which we measured 54 (mean TL = 52.13 cm). Four individuals were fitted with ultrasonic tags and were detected on an array of 14 receivers in the bay for up to 93 days, showing a high residency index of at least 89%. We actively tracked a single individual for 3 h at night and a further hour a week later. Our results suggest that Puerto Grande is a key habitat for the development of the critically endangered S. lewini.