Abstract
Development in foraging behaviour and dietary intake of many vertebrates are age-structured. Differences in feeding ecology may correlate with ontogenetic shifts in dispersal patterns, and therefore affect foraging habitat and resource utilization. Such life-history traits have important implications in interpreting tropho-dynamic linkages. Stable isotope ratios in the whiskers of sub-yearling southern elephant seals (Mirounga leonina; n = 12) were used, in conjunction with satellite telemetry and environmental data, to examine their foraging habitat and diet during their first foraging migration. The trophic position of seals from Macquarie Island (54°30′S, 158°57′E) was estimated using stable carbon (δ1 3C) and nitrogen (δ15N) ratios along the length of the whisker, which provided a temporal record of prey intake. Satellite-relayed data loggers provided details on seal movement patterns, which were related to isotopic concentrations along the whisker. Animals fed in waters south of the Polar Front (>60°S) or within Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Statistical Subareas 88.1 and 88.2, as indicated by both their depleted δ1 3C (<−20‰) values, and tracking data. They predominantly exploited varying proportions of mesopelagic fish and squid, and crustaceans, such as euphausiids, which have not been reported as a prey item for this species. Comparison of isotopic data between sub-yearlings, and 1, 2 and 3 yr olds indicated that sub-yearlings, limited by their size, dive capabilities and prey capture skills to feeding higher in the water column, fed at a lower trophic level than older seals. This is consistent with the consumption of euphausiids and most probably, Antarctic krill (Euphausia superba), which constitute an abundant, easily accessible source of prey in water masses used by this age class of seals. Isotopic assessment and concurrent tracking of seals are successfully used here to identify ontogenetic shifts in broad-scale foraging habitat use and diet preferences in a highly migratory predator.
Highlights
The interplay between the physical and biological regimes of the Southern Ocean [1] dictates the dispersal, foraging habitats and diet of higher order predators [2]
The foraging range and prey intake of air-breathing marine predators is largely dictated by their physiological capabilities, most often related to body size [77,78,79]
In southern elephant seals the dive durations and depth of newly weaned seals are known to be limited by their body size [20,40]
Summary
The interplay between the physical and biological regimes of the Southern Ocean [1] dictates the dispersal, foraging habitats and diet of higher order predators [2]. Information on diet is fundamental to better understand the diversity of linkages within Southern Ocean marine ecosystems and the response of higher order predators to large-scale ecosystem change and other anthropogenic activities such as commercial fishing [3]. Due to their marine existence, the dietary study of marine mammals is one of the most challenging of any vertebrate taxon [4]. Marine mammal species often exhibit ontogenetic shifts in dispersal patterns, foraging habitat and resource utilisation [5] Such life-history traits have important individual and population level implications and must be taken into account when assessing the diet and trophic interactions of a species within an ecosystem. The mechanism which governs this phenomenon is largely unknown [8], intra-specific competition for resources (e.g. food, space and mates) is one of the main hypothesises advanced to explain natal dispersal in the life history of most species [9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
