At Cape Gantheaume, Kangaroo Island (South Australia), adult male, lactating female
and juvenile New Zealand (NZ) and Australian fur seals regularly return to the same
colony, creating the potential for intra- and inter-specific foraging competition in nearby
waters. I hypothesised that these demographic groups would exhibit distinct foraging
strategies, which reduce competition and facilitate their coexistence. I analysed the diet
of adult male, adult female and juvenile NZ fur seals and adult male Australian fur seals
and studied the diving behaviour of adult male and lactating female NZ fur seals and the
at-sea movements of juvenile, adult male and lactating female NZ fur seals. Female diet
reflected that of a generalist predator, influenced by prey availability and their
dependant pups� fasting abilities. In contrast, adult male NZ and Australian fur seals
used larger and more energy-rich prey, most likely because they could more efficiently
access and handle such prey. Juvenile fur seals primarily utilised small lantern fish,
which occur south of the shelf break, in pelagic waters. Juveniles undertook the longest
foraging trips and adult males conducted more lengthy trips than lactating females,
which perform relatively brief trips in order to regularly nurse their pups. Unlike lactating
females, some adult males appeared to rest underwater by performing dives that were
characterised by a period of passive drifting through the water column. The large body
sizes of adult males and lactating females facilitated the use of both benthic and pelagic
habitats, but adult males dived deeper and for longer than lactating females, facilitating
vertical separation of their foraging habitats. Spatial overlap in foraging habitats among
the age/sex groups was minimal, because lactating females typically utilised continental
shelf waters and males used deeper water over the shelf break, beyond female foraging
grounds. Furthermore, juveniles used pelagic waters, up to 1000 km south of the
regions used by lactating females and adult males. The age and sex groups in this
study employed dramatically different strategies to maximise their survival and
reproductive success. Their prey and foraging habitats are likely to be shaped by body
size differences, which determine their different physiological constraints and metabolic
requirements. I suggest that these physiological constraints and the lactation
constraints on females are the primary factors that reduce competition, thereby
facilitating niche partitioning.
| Identifer | oai:union.ndltd.org:ADTP/236012 |
| Date | January 2005 |
| Creators | Page, Brad, page.bradley@saugov.sa.gov.au |
| Publisher | La Trobe University. Zoology Department, School of Life Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.latrobe.edu.au/copyright/disclaimer.html), Copyright Brad Page |
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