Sexual segregation of seasonal foraging habitats in a non-migratory marine mammal

Abstract

Many animal species segregate by sex. Such segregation may be social in nature, or ecological, or both. Grey seals (Halichoerus grypus), like many large mammals, are sexually size dimorphic. In size dimorphic species, allometric differences in morphology, metabolic rate and reproductive costs are likely. Such differences may require the sexes to use different foraging strategies or different habitats. To investigate sexual segregation of habitat in grey seals, we used satellite tracks from 95 (male 46; female 49) adults breeding at Sable Island, Nova Scotia (44 degrees N, 60 degrees W) collected from 1995 to 2005. Location estimates were made from satellite fixes using a state-space movement model to estimate true locations and regularize them in time. Location estimates were used to calculate home range kernels of male and female habitat use each month. Month by sex kernel home ranges revealed striking differences and dynamics in habitat use between males and females on spatial scales broader than most terrestrial examples and at temporal and spatial resolutions rarely available for marine species. Differences were most pronounced just before (October-December) and immediately after breeding (February-March). During both periods, males primarily used areas along the continental shelf break, while females mainly used mid-shelf regions. Coupled with previously identified sex-specific seasonal patterns of energy storage, diving and diet, our findings suggest that males and females differ profoundly in their spatial foraging strategies. These differences may serve to maximize fitness by reducing intersexual competition during key foraging periods.

O' mother where wert thou? Maternal strategies in the southern elephant seal: a stable isotope investigation

“…Male harassment may also explain this pattern [38]. Isotopic analysis of archival tissues, such as whiskers or teeth, may prove useful to shed light on the ontogeny of this putative sexual segregation, a pattern documented in other seal species [57] and between juveniles of both sexes and adult females in southern elephant seals [58].…”

Individual-level Variation and Higher-level Interpretations of Space Use in Wide-ranging Species: An Albatross Case Study of Sampling Effects

“…Our approach is similar to previous studies (Wood et al, 2000;Hindell et al, 2003;Taylor et al, 2004;Breed et al, 2006;Soanes et al, 2013;Orben et al, 2015) but our focus is not identifying the presence of an asymptote but rather the range in output at each sample size. For each dataset, we randomly sub-sampled n individuals (without replacement) beginning with n = 3 and increasing in increments of two, up to three less than the maximum number available.…”

“…This approach most accurately simulates having only the data in the sub-sample from which to estimate the range and distribution of the represented group (i.e., the species and colony in a given period of the annual cycle). This differs from past studies, where a pre-determined fixed value of h was applied to all KDE iterations (e.g., Breed et al, 2006;Orben et al, 2015). Here we are interested in the degree of variation among KDE outputs given the "available" data set, and therefore a data-based selection method for each independent KDE is most appropriate.…”

“…The assumption of representativeness is sometimes briefly conceded, but implications for the biological interpretations of the results generally are not formally evaluated. A number of marine vertebrate studies have illustrated an asymptotic saturation effect of increasing the number of tracked individuals or number of foraging trips per individual on estimates of the size of the area occupied by a sample of tracked animals in a pooled analysis (e.g., Wood et al, 2000;Hindell et al, 2003;Taylor et al, 2004;Breed et al, 2006;Soanes et al, 2013;Orben et al, 2015). These studies suggest that a sample of individuals may be representative of their respective group if the estimated occupied areas reach an asymptote before the maximum sample size is included in the analysis.…”

“…These studies suggest that a sample of individuals may be representative of their respective group if the estimated occupied areas reach an asymptote before the maximum sample size is included in the analysis. In addition to the estimated size of the area occupied by a group, it has also been demonstrated that the geographic locations of contours resulting from pooled analyses of different individuals can vary depending on the degree of individual variation within the sample (Taylor et al, 2004;Breed et al, 2006;Orben et al, 2015). Beyond these few examples which directly address assumptions of group-level representativeness of a sample, consistencies in movements among individuals comprising a dataset and among members of the higher-level group they represent remain un-tested assumptions, especially in seabird studies with small sample sizes (Soanes et al, 2013).…”