An echogram from (A) an anticyclonic eddy, (B) a cyclonic eddy. White sharks seem to prefer the core of the former (courtesy A. Della Penna)

An echogram from (A) an anticyclonic eddy, (B) a cyclonic eddy. White sharks seem to prefer the core of the former (courtesy A. Della Penna)

During last MESOPP workshop (see report), several use cases were demonstrated over different areas (not all of them over Southern Ocean, but on similarly dynamical regions), providing an overview of the possible outputs and developments of the project. Among those, A. Della Penna showed her work on the mesoscale variability of zooplankton and micronekton in the North Atlantic, with a link to a study by [Gaube et al 2018] on white shark behaviour with respect to the ocean eddies and meanders. Such predators are indeed good indicators of the food chain in the ocean, and so studying them provide with a better knowledge of the environment.

Data collected across fourteen eddies in the North Atlantic during the North Atlantic Aerosol and Ecosystem Study (NAAMES)  suggest that acoustic backscattering is particularly intense in the mesopelagic layer in anticyclonic eddies and is positively correlated with Sea Level Anomaly (positive in anticyclones). Surprisingly, there is no or even anti-correlation between surface primary production and acoustic backscattering at depth. The possibly higher concentration of mesopelagic organisms in anticyclonic eddies suggested by acoustic data could partially explain why this white shark spend time in anticyclonic eddies, either to feed on them or on larger animals that are predators of mesopelagics.

The track of the white shark superimposed on the predicted mesopelagic micronekton biomass (see animation) shows that mesoscale eddies and fronts create patches of higher concentrations that seem to influence the behaviour of this top predator.

Shark track animation overlaid on micronekton (all layers) from Seapodym model. Tracking data courtesy of Ocearch

Links:

References:

  • Peter Gaube, Camrin D. Braun, Gareth L. Lawson, Dennis J. McGillicuddy Jr, Alice Della Penna, Gregory B. Skomal, Chris Fischer & Simon R. Thorrold, 2018: Mesoscale eddies influence the movements of mature female white sharks in the Gulf Stream and Sargasso Sea, https://doi.org/10.1038/s41598-018-25565-8