Swimming speed and allocation of time during the dive cycle in Antarctic fur seals

Boyd, Ian L.; Reid, Keith; Bevan, R. M.

doi:10.1016/0003-3472(95)80137-5

Cited by 90 publications

(68 citation statements)

References 29 publications

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“…Bottom time was defined as the time between the end of the descent and the beginning of the ascent. These points were taken to be when, within 35% of the maximum depth, the instantaneous rate of vertical movement decreased below the mean rate, which was measured between the surface and the maximum depth (Boyd et al 1995).…”

Section: Methodsmentioning

confidence: 99%

Foraging behaviour in two Antarctic fur seal colonies with differing population recoveries

Staniland

Morton²,

Robinson³

et al. 2011

Mar. Ecol. Prog. Ser.

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We compared Antarctic fur seals Arctocephalus gazella breeding at 2 contrasting sites on South Georgia: one high density colony at Bird Island and one lower density colony at Cooper Bay. The population at Cooper Bay was considerably smaller than that at Bird Island despite ample suitable breeding area being available. At Cooper Bay, female seals were longer but weighed less than those breeding at Bird Island and, whilst both maintained the same rate of female pup growth, male pups grew faster at Cooper Bay. Although Bird Island seals dived deeper, they dived less often than Cooper Bay seals so that both populations spent comparable amounts of time in the bottom phase of dives actively foraging. Longer distance oceanic foraging trips that were observed at Bird Island were almost entirely absent from Cooper Bay. Both populations fed on Antarctic krill, but there was an absence of myctophid prey in the diet of seals at Cooper Bay. Evidence suggests that the favoured myctophid prey of fur seals at South Georgia, Protomyctophum choriodon, are absent from the colder waters around the south-east of the island. We propose that, if these energy-rich prey are unavailable in this region then seals at Cooper Bay may find it hard to offset the increased costs of foraging trips with longer duration and distance. This potentially reduced niche width means that the Cooper Bay population may be less buffered against environmental variability. Although food resources appeared to be sufficient during the period of our study, the south-eastern region of South Georgia has increased variability in food resources that, coupled with a smaller area in which to forage, might explain the reduced population size compared to the north-eastern end of the island.

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Section: Methodsmentioning

confidence: 99%

Foraging behaviour in two Antarctic fur seal colonies with differing population recoveries

Staniland

Morton²,

Robinson³

et al. 2011

Mar. Ecol. Prog. Ser.

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show abstract

“…A filter was applied to the satellite-recorded locations to exclude outliers, defined as locations that required the animal to swim at > 2.5 m s -1 to reach the location from the previous plausible track or to return to the subsequent plausible track. This speed is slightly greater than the maximum sustained swimming speed (Boyd et al 1995, Boyd et al 1997. During 1995 and 1996, PTTs were deployed on individuals for 2 foraging trips, but for the purpose of statistical analyses, these were considered as a single trip.…”

Section: Methodsmentioning

confidence: 99%

Distribution of foraging by female Antarctic fur seals

Boyd

Staniland²,

Martin³

2002

Mar. Ecol. Prog. Ser.

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The study examined the distribution of critical habitat for foraging by female Antarctic fur seals breeding at the island of South Georgia. Bathymetric features of the continental shelf around the island of South Georgia were an important indicator for the localisation of foraging. This pattern was consistent among years of different prey availability. Lactating females were constrained to forage mainly within 100 km of the location at which the offspring was being raised. When this constraint was removed at the end of lactation, females foraged to much greater ranges and dispersed to specific regions of the continental shelf east of Patagonia (>1000 km) and to the northern edge of the Antarctic pack ice (500 km). The empirical distribution of foraging during the breeding season was used to develop a function that described the foraging distribution for the whole breeding population of females. The result was consistent with past observations from ship-based surveys and it allowed estimation of the spatial impact of breeding female fur seals on krill at South Georgia. This suggested that, in extreme cases and assuming that krill influx is limited, female fur seals could eat most of the krill present in some regions where they forage intensively. However, mean consumption was about one-tenth of the mean density of krill.

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“…Assuming that such animals rely principally on aerobic respiration (e.g. Butler 2004), an individual's dive duration will be primarily limited by the rate of oxygen use, this itself being closely linked to the mechanical power used underwater (Boyd et al 1995, Butler & Jones 1997. In benthicforaging diving birds, power requirements for the descent and ascent phases of the dive are a remarkably constant function of dive depth (Watanuki et al 2005, Wilson et al 2006 Fig.…”

Section: Introductionmentioning

confidence: 99%

“…High speeds, including those characteristic of prey pursuit, are therefore particularly energetically costly, and use of such speeds causes substantial depletion of oxygen reserves, compromising dive duration accordingly (Wilson et al 2002a). Therefore, there is likely to be strong pressure for the conservative use of power during the dive, with animals selecting search speeds that will maximise their prey search time, increasing their speed only where, and as much as, necessary to pursue and capture prey items (Boyd et al 1995, Wilson et al 2002a. As air-breathing divers can catch multiple prey items in one dive (e.g.…”

Section: Introductionmentioning

confidence: 99%