Selection of diving strategy by Antarctic fur seals depends on where and when foraging takes place

Abstract

We investigated the spatial and temporal distribution of foraging effort by lactating Antarctic fur seals Arctocephalus gazella at Heard Island using satellite telemetry and time-depth recorders. Two principal diving types were identified: 'deep' dives averaging 48.6 m, and 'shallow' dives averaging 8.6 m. Discriminant function analyses were used to assign dives based on their depth and duration. Generalised linear mixed-effects models of night dives (> 80% of all dives) indicated both spatial and temporal effects on the distribution of deep and shallow dives. Deep dives were more common in the deeper shelf waters of the Kerguelen Plateau, and these dives predominantly occurred after sunset and before sunrise. In contrast, shallow dives were more common in slope waters on the southeastern margin of the Kerguelen Plateau in the hours either side of local midnight. We suggest that these 2 distinct diving types reflect the targeting of channichthyid (deep dives) and myctophid (shallow dives) fish, and are indicative of spatial and temporal differences in the availability of these 2 important prey groups. We also identified 3 distinct behavioural dive groups (based on multidimensional scaling of 19 diving and foraging trip parameters) that also differed in their spatial distribution and in their relative importance of deep and shallow dives. The present study provides some of the first evidence that diving strategies are not only influenced by where foraging takes pace, but also when.

Challenges in marine mammal habitat modelling: evidence of multiple foraging habitats from the identification of feeding events in blue whales

“…Moreover, feeding behaviour can depend on when and where foraging is taking place (e.g. Goldsworthy et al 2010). Indeed, humpback whales have been shown to change feeding strategies over the diurnal cycle (Friedlaender et al 2009).…”

Cross-seasonal foraging site fidelity of subantarctic fur seals: implications for marine conservation areas

“…Some indicators include coastline orientation (Lea et al 2008, Goldsworthy et al 2010, local competition (Bonadonna et al 2001), direction and distance to physical oceanographic features such as fronts (Georges et al 2000) or continental shelf edges or ridges (Baylis et al 2012) Furthermore, the large number of avian predators breeding on Marion Island during the summer, results in large quantities of nutrient run-off, which is later associated with phytoplankton blooms and higher productivity downstream close to the islands (Smith & Fronemann 2008). In winter, the Subantarctic Front moves northwards and is located further away from the island (Pakhomov & Froneman 1999).…”

South for the winter? Within‐dive foraging effort reveals the trade‐offs between divergent foraging strategies in a free‐ranging predator

“…; Goldsworthy et al . ) varies with region and foraging habitat. Differences in prey, metabolic requirements and foraging experience can also alter the diving behaviour of marine predators including penguins (Miller & Trivelpiece ; Scheffer, Bost & Trathan ), cetaceans (Baird, Hanson & Dill ), turtles (Sale et al .…”

“…These mechanisms include experience, target prey type, capture techniques, morphological differences and habitat selection. For example, the diving behaviour of several species of pinnipeds including northern fur seals, Callorhinus ursinus (Nordstrom et al 2013), southern elephant seals, Mirounga leonina (Hindell, Slip & Burton 1991;James et al 2012) and Antarctic fur seals, Arctocephalus gazella (Staniland, Reid & Boyd 2004;Lea et al 2008;Goldsworthy et al 2010) varies with region and foraging habitat. Differences in prey, metabolic requirements and foraging experience can also alter the diving behaviour of marine predators including penguins (Miller & Trivelpiece 2008;Scheffer, Bost & Trathan 2012), cetaceans (Baird, Hanson & Dill 2005), turtles (Sale et al 2006) and pinnipeds (Lea et al 2002b).…”