Inter‐ and intrasex habitat partitioning in the highly dimorphic southern elephant seal

Abstract

Partitioning resources is a key mechanism for avoiding intraspecific competition and maximizing individual energy gain. However, in sexually dimorphic species it is difficult to discern if partitioning is due to competition or the different resource needs of morphologically distinct individuals. In the highly dimorphic southern elephant seal, there are intersexual differences in habitat use; at Iles Kerguelen, males predominantly use shelf waters, while females use deeper oceanic waters. There are equally marked intrasexual differences, with some males using the nearby Kerguelen Plateau, and others using the much more distant Antarctic continental shelf (~2,000 km away). We used this combination of inter and intrasexual behavior to test two hypotheses regarding habitat partitioning in highly dimorphic species. (a) that intersexual differences in habitat use will not appear until the seals diverge in body size and (b) that some habitats have higher rates of energy return than others. In particular, that the Antarctic shelf would provide higher energy returns than the Kerguelen Shelf, to offset the greater cost of travel. We quantified the habitat use of 187 southern elephant seals (102 adult females and 85 subadult males). The seals in the two groups were the same size (~2.4 m) removing the confounding effect of body size. We found that the intersexual differences in habitat use existed before the divergence in body size. Also, we found that the amount of energy gained was the same in all of the major habitats. This suggests that the use of shelf habitats by males is innate, and a trade‐off between the need to access the large benthic prey available on shelf waters, against the higher risk of predation there. Intrasexual differences in habitat use are another trade‐off; although there are fewer predators on the Antarctic shelf, it is subject to considerable interannual fluctuations in sea‐ice extent. In contrast, the Kerguelen Plateau presents more consistent foraging opportunities, but contains higher levels of predation. Habitat partitioning in this highly dimorphic species is therefore the result of complex interplay of life history strategies, environmental conditions and predation pressure.

Trade-offs between foraging reward and mortality risk drive sex-specific foraging strategies in sexually dimorphic northern elephant seals

“…These foraging behaviours are largely consistent with previous work [27][28][29]31,40]. Southern elephant seals (Mirounga leonina), the sister taxa to northern elephant seals, also show similar sexual segregation in foraging behaviours [42][43][44][45].…”

Regional Variation in Winter Foraging Strategies by Weddell Seals in Eastern Antarctica and the Ross Sea

“…First, we calculated the area (km 2 ) of each UDi by counting the number of 5 × 5 km cells visited by each seal and compared these among the three deployment locations using a GLMM which included deployment duration as a random term to account for animals with longer durations potentially having larger UD areas. Seal standard length (m) was included in the model to account for animal size potentially being an important source of individual variation in space use (Hindell et al, 2021). We used length as it was the only morphometric measure common to all studies.…”

“…Photopoulou et al (2020) reported that male Weddell seals spent more time in highsalinity shelf water masses at depth, benthically diving, while females ventured off the continental shelf and visited warmer, shallower water masses while undertaking a mix of benthic and pelagic dives. Our sample did not include sub-adults or juveniles, age classes which have very different distributions in other Southern Ocean pinnipeds (e.g., elephant seals, Hindell et al, 2021). Burns et al (1999) reported that some weaned Weddell seal pups from McMurdo Sound in the southern Ross Sea dispersed widely, others did not, but all stayed relatively close to the Antarctic coastline.…”

Animal Borne Ocean Sensors – AniBOS – An Essential Component of the Global Ocean Observing System

“…Animalborne sensors also provide data on animal behavior in relation to in situ environmental conditions undertaking adaptive sampling by seeking areas of both physical and biological interest (Guinet et al, 2014;Labrousse et al, 2017aLabrousse et al, ,b, 2018Nachtsheim et al, 2019). Linking physical and biological data in this way allows us to quantify the differences in environmentally mediated behavior at the population, species and community levels (Chambault et al, 2016;Hindell et al, 2016Hindell et al, , 2017Hindell et al, , 2021McMahon et al, 2017;Bestley et al, 2020;Citta et al, 2020).…”