The Behavioral Basis for Nonlinear Functional Responses and Optimal Foraging in Antarctic Fur Seals

Mori, Yoshihito; Boyd, Ian L.

doi:10.1890/03-4005

Cited by 85 publications

(73 citation statements)

References 45 publications

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“…There were no synoptic data for this distribution from hydroacoustic surveys that coincided with this study; therefore we used the vertical profile of the estimated IPQ of Antarctic fur seals Actocephalus gazella that were foraging in the same region and at the same time as our study birds, to represent the vertical distribution of prey. The IPQ measured for fur seals has previously been shown to be closely related to the abundance of krill measured by ship-based hydroacoustic surveys (Mori & Boyd 2004).…”

Section: Methodsmentioning

confidence: 86%

“…This also assumed that fur seals adjusted their dive cycle optimally as rate-maximisers, probably at the scale of the dive cycle (see Boyd et al 1995). In addition, inter-annual variation in estimates of patch quality based on the diving behaviour of Antarctic fur seals at Bird Island was positively correlated with that of krill density measured in ship-based hydroacoustic surveys around Bird Island (Mori & Boyd 2004). Also, the effect of krill density on reproductive success was similar between Antarctic fur seals and the 2 penguin species at Bird Island (Boyd & Murray 2001).…”

Section: Discusssion Assumptions Used In Modelmentioning

confidence: 99%

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Segregation of foraging between two sympatric penguin species: does rate maximisation make the difference?

Mori

Boyd²

2004

Mar. Ecol. Prog. Ser.

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Macaroni Eudyptes chrysolophus and gentoo Pygoscelis papua penguins occur sympatrically at Bird Island (54°00' S, 38°02' W), South Georgia, and have a similar diet. Macaroni penguins forage at shallower depths and further from the island than gentoo penguins. We tested the hypothesis that differences in the optimal foraging behaviour at the level of individual dives help to explain this ecological foraging segregation. Using a rate maximising diving model, we predicted that macaroni penguins would obtain more energy per dive cycle than gentoo penguins only when they used patches shallower than 30 to 40 m. This prediction was supported by observations of actual dive depths. We conclude that different foraging efficiencies at different depths results in each species being differentially sensitive to the vertical distribution of prey in the water column. We suggest that differing capacities to exploit natural heterogeneity in the distribution of prey has an important role in maintaining these 2 species as sympatric predators of a common resource. KEY WORDS: Optimal foraging · Segregation of foraging area · Macaroni penguins · Gentoo penguinsResale or republication not permitted without written consent of the publisher

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Section: Methodsmentioning

confidence: 86%

Section: Discusssion Assumptions Used In Modelmentioning

confidence: 99%

Segregation of foraging between two sympatric penguin species: does rate maximisation make the difference?

Mori

Boyd²

2004

Mar. Ecol. Prog. Ser.

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“…However, alternative hypotheses might explain the effect of prey patch quality or increased body size on bottom duration of dives. For example, higher prey patch quality may lead to decreased bottom duration depending on timescales [54,55], suggesting diving animals should stay longer at foraging depth as the patch quality declines [56,57]. In addition, increased body size may lead to decreased bottom duration by increasing swimming costs owing to increased drag force (i.e.…”

Section: Discussion (A) Buoyancy Determines Locomotor Costs Of Swimmingmentioning

confidence: 99%

The foraging benefits of being fat in a highly migratory marine mammal

et al. 2014

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Foraging theory predicts that breath-hold divers adjust the time spent foraging at depth relative to the energetic cost of swimming, which varies with buoyancy (body density). However, the buoyancy of diving animals varies as a function of their body condition, and the effects of these changes on swimming costs and foraging behaviour have been poorly examined. A novel animalborne accelerometer was developed that recorded the number of flipper strokes, which allowed us to monitor the number of strokes per metre swam (hereafter, referred to as strokes-per-metre) by female northern elephant seals over their months-long, oceanic foraging migrations. As negatively buoyant seals increased their fat stores and buoyancy, the strokes-per-metre increased slightly in the buoyancy-aided direction (descending), but decreased significantly in the buoyancy-hindered direction (ascending), with associated changes in swim speed and gliding duration. Overall, the round-trip strokes-per-metre decreased and reached a minimum value when seals achieved neutral buoyancy. Consistent with foraging theory, seals stayed longer at foraging depths when their round-trip strokes-per-metre was less. Therefore, neutrally buoyant divers gained an energetic advantage via reduced swimming costs, which resulted in an increase in time spent foraging at depth, suggesting a foraging benefit of being fat.

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“…Time spent in the bottom phase of dives has been used as an indication of patch quality, with longer durations correlated with a higher net rate of energy intake (Thompson & Fedak 2001, Mori & Boyd 2004). Seals showed increased activity around 70 to 80 km from the 2 breeding beaches, which equates to the shelf break region.…”

Section: Discussionmentioning

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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The Behavioral Basis for Nonlinear Functional Responses and Optimal Foraging in Antarctic Fur Seals

Cited by 85 publications

References 45 publications

Segregation of foraging between two sympatric penguin species: does rate maximisation make the difference?

Segregation of foraging between two sympatric penguin species: does rate maximisation make the difference?

The foraging benefits of being fat in a highly migratory marine mammal

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

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