Short-term movement patterns of the Pacific sleeper shark off California

Abstract

This study evaluated the movement patterns of four Pacific sleeper sharks (Somniosus pacificus) outfitted with satellite-based tags off the California coast, a region for which there is no reported tracking data. Pacific sleeper sharks (1.5–2.1 m) attained maximum individual depths ranging from 603–1,323 m, with an overall average depth of 424 ± 84 m. Depth distribution was relatively similar between day and night, remaining well below the thermocline throughout periods at liberty. A 180-cm individual tagged off central California exhibited a deeper but more consistent depth distribution throughout the day (µ = 528 ± 28 m) and night (µ = 545 ± 26 m), whereas a 221-cm shark tagged off southern California occurred deeper during the day (µ = 392 ± 43 m) than at night (µ = 352 ± 62 m) with continuous vertical oscillations between 300 and 500 m. Ambient water temperatures at depth ranged from 3.3–11.0°C, with a collective average temperature of 7.3°C. Despite extensive and continuous vertical movements, horizontal displacement was minimal over the 30-d tracks (µ = 1.7 km/d). Although the data presented here are temporally and spatially limited, findings support previous reports of consistent vertical oscillations within other regions in the Pacific. Insights into the movements and habitat use of this vulnerable elasmobranch provides a better understanding of the species within a previously undocumented portion of its range.