Abstract
AbstractThe population of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea is in a unique position on the continental shelf edge, with vast shelf waters to the south, and deep Southern Ocean to the north. We describe sex‐related differences in the winter distribution of this population, from data collected by 20 conductivity‐temperature‐depth satellite relay data loggers deployed in February 2011 at the end of the annual molt. The regional daily speed was calculated, and a state‐space model was used to estimate behavioral states to positions along individuals’ tracks. GLMMs estimated that males and smaller individuals, diving in shallower water, traveled less far per day of deployment (males 14.6 ± 2.26 km/d, females 18.9 ± 2.42 km/d), and males were estimated to dive in shallower water (males 604 ± 382 m, females 1,875 ± 1,458 m). Males and smaller individuals were also estimated to be more resident; males spent an average 83.4% ± 7.7% of their time in a resident behavioral state, compared to females at 74.1% ± 7.1%. This evidence that male and female Weddell seals in the southern Weddell Sea are adopting different strategies has not been shown elsewhere along their circumpolar distribution.
Highlights
The distribution of predators within the Southern Ocean is driven by the availability of resources important for growth, reproduction and survivorship (Stephens and Krebs 1986)
The population of Weddell seals in the southern Weddell Sea is unique in its proximity to the continental shelf edge, with water depths ranging from 500 m to >4,000 m off the continental shelf (Schenke et al 1997)
Despite the sample in this study being reduced to 13 individuals, due to tag failure and the lack of morphometric data for all tagged seals, our findings provide evidence for sex-related differences in the postmolt distribution of Weddell seals in the southern Weddell Sea
Summary
The distribution of predators within the Southern Ocean is driven by the availability of resources important for growth, reproduction and survivorship (Stephens and Krebs 1986). In the Southern Ocean, sexual differences have been described in the southern elephant seal (Mirounga leonina; McConnell and Fedak 1996) and the Antarctic fur seal (Arctocephalus gazella; Staniland and Robinson 2008) Both of these species display dramatic sexual size dimorphism, with males weighing almost three times as much as females (Ruckstuhl and Neuhaus 2002, Staniland 2005). The Weddell seal (Leptonychotes weddellii) is not dramatically sexually dimorphic, with some studies finding no difference in size at all (Staniland 2005) and others finding females to be slightly larger (Bryden et al 1984) Despite their circumpolar distribution, previous studies have focused on populations in both McMurdo Sound and towards the east of Antarctica (Kooyman 1967, Andrews-Goff et al 2010, Heerah et al 2013). This results in a time series of data that uses its spatial and temporal autocorrelation to predict future behavioral states (Patterson et al 2008)
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