Habitat use and movement patterns of adult male and juvenile scalloped hammerhead sharks Sphyrna lewini throughout the Hawaiian archipelago

Abstract

Scalloped hammerhead sharks Sphyrna lewini are a circumglobal species found in tropical and subtropical waters. Globally, populations of S. lewini have undergone dramatic declines in recent decades, and 4 of 6 distinct population segments are at risk of extinction and listed under the United States Endangered Species Act. Despite this, limited data exist on movement behavior or habitat use requirements of S. lewini, especially in the Central Pacific region. In this long-term (2009-2020) telemetry study, 27 S. lewini (24 males [22 adults, 2 juveniles], and 3 juvenile females) ranging in size from 106 to 310 cm (total length) were tagged with a combination of acoustic and/or satellite tags in a known nursery area, Kāne‘ohe Bay, Hawai‘i. Acoustic data revealed repeated movements of adult male S. lewini to Kāne‘ohe Bay between May and September across multiple years. Horizontal movements away from the Bay indicate these individuals are highly associated with the Hawaiian Archipelago (i.e. Northwestern and main Hawaiian Islands), while vertical movements were dynamic, with repeated, nocturnal deep dives to depths beyond 800 m and temperatures as low as 5.0°C. We conclude that adult male and juvenile S. lewini tagged in Kāne‘ohe Bay exhibit fairly restricted movements throughout the Hawaiian Archipelago, and mature males specifically exhibit strong seasonal site fidelity to Kāne‘ohe Bay. These data add crucial baseline information on habitat preferences of S. lewini around the Hawaiian Islands, and can be used to help structure conservation strategies for a portion of the Central Pacific population.