Abstract
Salmon sharks Lamna ditropis are highly migratory, upper trophic level predators in North Pacific ecosystems. We analysed a multi-year satellite tag dataset to investigate the habitat use of female salmon sharks across their broad range in the eastern North Pacific (NEP) and identified key environmental factors that influence vertical distribution. Salmon sharks displayed remarkable plasticity in habitat use across disparate oceanographic regions in the NEP and increased utilization of deeper waters in offshore habitats. Diel shifts in vertical distribution and behaviour were consistently observed across their range and likely reflect shifts in their foraging ecology. Salmon sharks utilized a broad thermal niche and exhibited submergence behaviour, possibly for thermal refuge, when encountering sea surface temperatures outside their preferred temperature distribution. Moreover, the vertical distribution of salmon sharks indicates they were able to exploit low dissolved oxygen environments (<1–3 ml l−1), occasionally for extended periods of time in offshore habitats. However, salmon sharks generally reduced their use of deeper waters when encountering the combination of cold temperatures (<6 °C) and low dissolved oxygen concentrations (<1–3 ml l−1). Combining vertical distribution with high-resolution horizontal movements furthers our understanding of the ecological and environmental drivers of movement across short (diel) and long-term (migratory) scales.
Highlights
Investigating patterns of habitat use and movements of top predators is fundamental to understanding their ecology and plays an important role in fostering effective management strategies[1,2,3]
Previous satellite tagging studies of salmon sharks in the eastern North Pacific (NEP) have only included female sharks due to the dramatic sexual segregation that occurs in the North Pacific[9], and have revealed that they are highly migratory throughout the California Current, Alaskan Gyre, and Subtropical Gyre[1, 6,7,8]
Incorporating 24-h archival data with 24-h and aggregated 24-h transmitted data sets resulted in 4,152 days of time-at-depth (TAD) histograms from 59 tags, 3,877 days of time-at-temperature (TAT) histograms from 58 tags, 4,209 days of profile of depth and temperature (PDT) data from 64 tags, 6,532 days of minimum and maximum depth from tags, and 6,860 days of sea surface temperatures (SST) from tags (Supplementary Table S1)
Summary
Investigating patterns of habitat use and movements of top predators is fundamental to understanding their ecology and plays an important role in fostering effective management strategies[1,2,3]. Weng et al.[7] described a shift in the vertical distribution of a tagged salmon shark as it migrated to the Subtropical Gyre, where it spent more time at greater depths, avoiding the surface waters, in the warmer, southern extent of its range. This is the only study to describe the vertical distribution of salmon sharks in pelagic habitats, yet it was based on four individuals and did not encompass their full geographic distribution.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have