Abstract
Recovered archival satellite tags afford a rare opportunity to evaluate diving behavior relative to ocean conditions at fine spatiotemporal scales. Ocean temperature and mixed layer depth (MLD) were strongly related to daily and seasonal patterns in diving behavior of an adult female porbeagle shark Lamna nasus. The shark remained below MLD when waters were strongly stratified in summer or in the Gulf Stream; the daily timing of dives was associated with local sunrise and sunset. In the presence of a hurricane, diving activity abruptly increased, coincident with upwelling causing an abrupt decrease in surface temperature. Our first report of the behavioral response to a hurricane as well as the seasonal patterns in depths, occupied temperatures, and vertical speeds suggest environmental preferences of porbeagle are not static and individuals may use horizontal, as well as vertical, movement to take advantage of areas with specific characteristics.
Highlights
Understanding porbeagle Lamna nasus behavior in relation to ocean conditions is important to predict responses of this at-risk shark to climate change
The remarkable consistency in dive behavior exhibited at different periods for this female porbeagle shark Lamna nasus demonstrates a fine-tuned behavioral response to proximate ocean conditions (Pade et al 2009, Campana et al 2010, Francis et al 2015)
Dive depth was strongly related to the difference between sea surface temperature (SST) and bottom temperature (BT), as well as mixed layer depth (MLD) while on the continental shelf
Summary
Understanding porbeagle Lamna nasus behavior in relation to ocean conditions is important to predict responses of this at-risk shark to climate change. Their primary habitats in the Gulf of Maine (GOM) and Scotian Shelf (SS) (Fig. 1; Campana et al 2010) are in the confluence zone of the North Atlantic’s subtropical and subpolar gyres, an area that has undergone significant warming over the past half century (Greenan et al 2019). Recovered tags afford a rare opportunity to evaluate diving behavior at fine spatiotemporal scales, which could improve our understanding of habitat use and likely behavioral responses to ocean variation and may contribute to protection of this species
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