What can we learn about the open ocean from tracking white sharks? In this short video I provide an overview of some of the results of our work that investigates the use of mesoscale eddies by large pelagic fish.
In the coming week, we will again venture into the North Atlantic to continue our investigation of the role of eddies in structuring pelagic ecosystems. Even though it feels like we just returned from our first cruise (November-December, 2015), we have had a bit of time to digest some of the observations made during NAAMES-1. During our first expedition, we discovered that eddies indeed have a significant influence on mesopelagic fish. Eddies affected not only the depth at which these organism live, but also their abundance.
Using our custom-built deep-water echosounder (the RUMP), we observed that deep scattering layers, the acoustic signature of these mesopelagic ecosystems, are not only deeper in anticyclones, but also have stronger back scattering, when compared to cyclones (Fig. 5). This suggests that the observed pattern of white sharks preferentially using anticyclone eddies may be the result of these eddies affecting their prey. In the weeks to come, we will expand on these observations and surely gain more insight into the roles of eddies in structuring pelagic ecosystems.
Two days ago I reported that Lydia swam towards a large anticyclonic (clockwise rotating) eddy or meanders (see post here). She approached this anticyclone and swam northeast along its periphery. In the past 24 hours, Lydia has turned southeast of the previous anticyclone and has entered into the center of an adjacent anticyclonic eddy! Analysis of her interaction with eddies during her trip offshore in the summer and fall of 2013 (find more info here) suggests that she prefers the cores of anticyclones over cyclones and makes repetitive deep dives (often over 800 meters) while in the cores of anticyclones. Her activity in the past few days suggest that she might be honing in on some cues, be they potential prey, mates, or other, and is occupying the core of yet another anticyclonic eddy.
Lydia’s track overlaid on a map of sea level anomaly. Anticyclonic eddies and meanders are shown as orange and red features, cyclonic eddies and meanders are blue and purple features.
This begs the questions: Do white sharks seek out anticyclonic eddies because they are areas that concentrate prey and/or potential mates, or do they prefer the warm water found in anticyclones while swimming elsewhere? We’ll keep a close eye on where Lydia goes from here and hope to be able to address these questions in the future.