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Provisioning Strategies of Antarctic Fur Seals and Chinstrap Penguins Produce Different Responses to Distribution of Common Prey and Habitat

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Provisioning Strategies of Antarctic Fur Seals and Chinstrap Penguins Produce Different Responses to Distribution of Common Prey and Habitat University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Publications, Agencies and Staff of the U.S. Department of Commerce U.S. Department of Commerce 2007 Provisioning Strategies of Antarctic Fur Seals and Chinstrap Penguins Produce Different Responses to Distribution of Common Prey and Habitat Taro Ichii National Research Institute of Far Seas Fisheries. 2-12-4 Fukuura. Kanazawa. Yokohama 236-8648, Japan John Bengston National Marine Mammal Laboratory. Alaska Fisheries Science Center NOAA Peter Boveng National Marine Mammal Laboratory. Alaska Fisheries Science Center, NOAA Yoshimi Takao National Research Institute of Fisheries Engineering. 7620-7. Hasaki. Karnisu. Ibaraki 314-0408, Japan John Jansen National Marine Mammal Laboratory. Alaska Fisheries Science Center NOAA See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/usdeptcommercepub Part of the Environmental Sciences Commons Ichii, Taro; Bengston, John; Boveng, Peter; Takao, Yoshimi; Jansen, John; Hiruki-Raring, Lisa; Cameron, Michael; Okamura, Hiroshi; Hayashi, Tomonari; and Naganobu, Mikio, "Provisioning Strategies of Antarctic Fur Seals and Chinstrap Penguins Produce Different Responses to Distribution of Common Prey and Habitat" (2007). Publications, Agencies and Staff of the U.S. Department of Commerce. 149. https://digitalcommons.unl.edu/usdeptcommercepub/149 This Article is brought to you for free and open access by the U.S. Department of Commerce at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Publications, Agencies and Staff of the U.S. Department of Commerce by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Taro Ichii, John Bengston, Peter Boveng, Yoshimi Takao, John Jansen, Lisa Hiruki-Raring, Michael Cameron, Hiroshi Okamura, Tomonari Hayashi, and Mikio Naganobu This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/ usdeptcommercepub/149 Vol. 344: 277-297.2007 MARINE ECOLOGY PROGRESS SERIES Published August 23 doi: 10.3354/meps068?3 Mar Ecol Prog Ser Provisioning strategies of Antarctic fur seals and chinstrap penguins produce different responses to distribution of common prey and habitat Taro lchiilr*,John L. Bengtson2,Peter L. Boveng2,Yoshimi ~akao~,John K. an sen^, Lisa M. ~iruki-~aring~,Michael F. cameron2,Hiroshi Okamural, Tomonari ~ayashil,Mikio ~aganobul 'National Research Institute of Far Seas Fisheries. 2-12-4 Fukuura. Kanazawa. Yokohama 236-8648. Japan 'National Marine Mammal Laboratory. Alaska Fisheries Science Center1NOA.A. 7600 Sand Point Way NE. Bldg. 4. Seattle. Washington 98115. USA 3National Research Institute of Fisheries Engineering. 7620-7. Hasaki. Karnisu. Ibaraki 314-0408. Japan ABSTRACT: Central-place foragers that must return to a breeding site to deliver food to offspring are faced with trade-offs between prey patch quality and distance from the colony. Among colonial ani- mals, pinnipeds and seabirds may have different provisioning strategies, due to differences in their ability to travel and store energy. We compared the foraging areas of lactating Antarctic fur seals and chinstrap penguins breeding at Seal Island, Antarctica, to investigate whether they responded differ- ently to the distribution of their prey (Antarctic krill and myctophid fish) and spatial heterogeneity in their habitat. Dense krill concentrations occurred in the shelf region near the colony. However, only brooding penguins, which are expected to be time-minimizers because they must return frequently with whole food for their chicks, foraged mainly in this proximal shelf region. Lactating fur seals and incubating penguins, which can make longer trips to increase energy gain per trip, and so are expected to be energy-maximizers, foraged in the more distant (>20 km from the island) slope and oceanic regions. The shelf region was characterized by more abundant, but lower-energy-content immature krill, whereas the slope and oceanic regions had less abundant but higher-energy-content gravid krill, as well as high-energy-content myctophids. Furthermore, krill in the shelf region under- took diurnal vertical migration, whereas those in the slope and oceanic regions stayed near the sur- face throughout the day, which may enhance the capture rate for visual predators. Therefore, we sug- gest that the energy-maximizers foraged in distant, but potentially more profitable feeding regions, while the time-minimizers foraged in closer, but potentially less profitable regions. Thus, time and energy constraints derived from different provisioning strategies may result in sympatric colonial predator species using different foraging areas, and as a result, some central-place foragers use sub- optimal foraging habitats, in terms of the quality or quantity of available prey. KEY WORDS: Habitat selection - Antarctic fur seals - Chinstrap penguins - Antarctic krill - Myctophid fishes . Provisioning offspring . Energy-maximizer - Time-minimizer Resale or republication not permitted without written consent of the publisher INTRODUCTION of energy intake (energyhme,Pyke et al. 1977).There are 2 simple strategies to accomplish this. The energy- Foraging is clearly related to an animal's fitness so maximizer tries to maximize the energy intake, while that animals are likely to be under natural selection to the time-minimizer tries to minimize the time spent be efficient foragers. Optimal foraging theory assumes foraging to meet nutritional requirements (Stephens & that animals feed in a way that maximizes their net rate Krebs 1986). These 2 approaches represent the end- 8 Inter-Research 2007 - www.int.-res.com Mar Ecol Prog Ser 344: 277-297,2007 points of a continuum of foraging behaviors which are provision their offspring. Normal foraging trip duration constrained by environmental and life history factors is about 4 to 5 d, alternating with shore-based pup- (for example, patchiness of food availability or time of suckling bouts of 1 to 2 d (Walker and Boveng 1995). year in the life history cycle). Pups depart rookeries when they are weaned in late During the breeding season, most animals face the March and April. Chinstraps establish nests and typi- problem of obtaining food for themselves and for their cally lay a 2-egg clutch in early November (Jansen offspring. Colonial animals face the additional con- 1996).Both parents undertake long incubation shifts (5 straint of having to return from feeding areas to a to 10 d) followed by foraging trips of similar duration breeding site to deliver food to offspring. These ani- (Williams 1995). Upon hatching 1 or 2 chicks in late mals, which are called central-place foragers since December, parents begin making daily foraging trips they carry food back to a central place, have restricted while alternating brooding duties with their mates. foraging ranges (in comparison to non-breeding indi- During late January chicks are left unattended (crhche viduals) to avoid offspring starvation. Central-place phase), and adults continue daily feedings until chicks foragers are predicted to choose the closest suitable fledge in mid-February (Jansen et al. 2002). Thus, the foraging area to the colony (Orians & Pearson 1979). breeding seasons of these 2 species are highly syn- Among central-place foragers, breeding penguins chronous. and lactating fur seals have different constraints on The purpose of this study was to determine provisioning offspring (Costa 1991). During the incu- whether provisioning constraints of Antarctic fur seals bation period penguins need energy primarily to and chinstrap penguins produce different responses restore their body reserves lost during fasting. Because to shifts in the distribution of their common prey and incubation shifts can span several days, penguins have the spatial heterogeneity of the marine habitat. We a relatively long time to do this, and hence they have identified and described the ecological characteristics the potential to make long trips at sea. Thus, they can of the foraging areas of lactating Antarctic fur seals be expected to use strategies that maximize the energy and chinstrap penguins breeding at Seal Island, acquired in a foraging trip. In contrast, during the South Shetland Islands (Fig. la). Since these preda- chick-brooding period, they must replenish their tors feed not only on krill, but also on myctophids reserves and provide food to their chicks. They store (Jansen et al. 1998, Casaux et al. 1998, Osman et al. prey in the stomach and later feed the chicks by regur- 2004), both prey species were studied. We analyzed gitation. They cannot increase the food delivery to off- the diets and foraging area (habitat) selection of fur spring beyond the stomach capacity, and so they must seals and penguins during mid-breeding season to increase the rate of energy delivery to chicks by mini- compare their responses. mizing their time at sea. Thus, chick-brooding pen- guins can be expected to use strategies that minimize the time required to return sufficient resources to their MATERIALS AND METHODS offspring. Fur seals use lactation as a method to con- centrate and deliver energy to their offspring. They The specific procedures of this study were (1) follow- store energy as fat when at sea and convert this to milk ing the predators during their feeding trips to sea in for delivery to the pups. Thus, fur seals, as compared order to locate important foraging areas using ship- with chick-brooding
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