Distribution and Habitat Suitability of Ross Seals in a Warming Ocean

Horst Bornemann,Marthán Nieuwoudt Bester,Louise Biddle,Mia Wege,Erling Sverre Nordøy,Arnoldus Schytte Blix

doi:10.3389/fmars.2021.659430

Abstract

Understanding the determinants of poorly studied species’ spatial ecology is fundamental to understanding climate change impacts on those species and how to effectively prioritise their conservation. Ross seals (Ommatophoca rossii) are the least studied of the Antarctic pinnipeds with a limited knowledge of their spatial ecology. We present the largest tracking study for this species to date, create the first habitat models, and discuss the potential impacts of climate change on their preferred habitat and the implications for conservation. We combined newly collected satellite tracking data (2016–2019: n = 11) with previously published data (2001: n = 8) from the Weddell, King Haakon VII and Lazarev seas, Antarctica, and used 16 remotely sensed environmental variables to model Ross seal habitat suitability by means of boosted regression trees for summer and winter, respectively. Five of the top environmental predictors were relevant in both summer and winter (sea-surface temperature, distance to the ice edge, ice concentration standard deviation, mixed-layer depth, and sea-surface height anomalies). Ross seals preferred to forage in waters ranging between −1 and 2°C, where the mixed-layer depth was shallower in summer and deeper in winter, where current speeds were slower, and away from the ice edge in the open ocean. Receding ice edge and shoaling of the mixed layer induced by climate change may reduce swimming distances and diving depths, thereby reducing foraging costs. However, predicted increased current speeds and sea-surface temperatures may reduce habitat suitability in these regions. We suggest that the response of Ross seals to climate change will be regionally specific, their future success will ultimately depend on how their prey responds to regional climate effects and their own behavioural plasticity.

Highlights

Climate change and extreme weather events are increasing and as a consequence are influencing the distribution and movements of species globally (Karl and Trenberth, 2003; Meehl et al, 2007)
In the Southern Ocean, rapid climate change is expressed through various pathways (Meredith et al, 2019; Rogers et al, 2020); e.g., sea-surface temperatures are increasing and sea-surface temperature isotherms previously associated with oceanic fronts, are shifting toward the pole, the sea-ice extent is decreasing, and the Southern Annular Mode has a tendency toward a positive phase, which coincides with the poleward shift and strengthening of the westerlies (White and Peterson, 1996; de la Mare, 1997; Tynan, 1998; Sallée et al, 2010; Young et al, 2011; Bracegirdle et al, 2013; Meijers et al, 2019; Hindell et al, 2020)
Hereafter we refer to the King Haakon VII Sea, Lazarev Sea, Weddell Sea, and the rest of the area bounded by 40◦S to 80◦S; 80◦W to 80◦E as “the Weddell Sea and adjoining areas.”

Summary

Introduction

Climate change and extreme weather events are increasing and as a consequence are influencing the distribution and movements of species globally (Karl and Trenberth, 2003; Meehl et al, 2007). Whereas decreasing ice extent in the Ross Sea, causes females that forage in this region to increase the distances travelled between breeding and feeding sites Both scenarios of changing sea-ice conditions likely forces southern elephant seals to leave their foraging grounds earlier (Van den Hoff et al, 2014; Hindell et al, 2016, 2017; Younger et al, 2016)

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Conclusion