Salty seas and sharks from space: Combining satellite remote sensing and in situ data sets to understand elasmobranch movement ecology in relation to ocean salinity and other sea changes

Abstract:

Elasmobranchs, a subclass of cartilaginous fish that includes sharks, rays, and skates, have seen their populations decline significantly over the past 50 years [1]. One of the key questions in movement ecology of marine megafauna is the role of the physical oceanographic environment [2]. However, only four studies, to date, have investigated more than two environmental variables simultaneously to study how the ocean environment affects species’ movements. Especially glaring is that despite the likely importance of salinity in driving movement, only two studies have used SRS-derived salinity data previously [1]. As such, the influence of ocean environmental factors on elasmobranch behavior and movement patterns is still relatively poorly understood; in particular, . Here, we combine global datasets of seven remotely-sensed variables (sea surface salinity and temperature, wind speeds, precipitation, bathymetry, currents, and chlorophyll-a), to reconstruct trend and anomaly time series since 2011 on daily, weekly and monthly scales. As these are surface environmental variables, properties at depth will be acquired from global ECCO ocean state estimate reconstructions on the same temporal and spatial grid, enabling an investigation into the vertical variability of these properties in time. This 4D reconstruction (3D+time variable) is paired with available elasmobranch tag tracking data for 25+ species to characterize how environmental variables and their covariance drive elasmobranch movement; how elasmobranch species differ in their responses; and finally, given the rapid changes occurring in some areas on the planet, what regions are most likely to affect species behavior in the near future. With this research we aim to show how elasmobranch movement ecology relates to basin-scale oceanographic changes and end with a discussion of how this new remote sensing approach could be beneficial for conservation management strategies, for example, optimizing designs for marine protected areas.

[1]Williamson M. J., et al. (2019). Frontiers in Marine Science, 6, 135, doi: 10.3389/fmars.2019.00135; [2] Hays, G. C., et al. (2016) Trends Ecol. Evol. 31, 463–475. doi: 10.1016/j.tree.2016.02.015