Over 50 000 individual dive records collected by time-depth recorders were analysed with respect to sex of the seal, time of year and the approximate geographic location of the dive. Six distinct dive types were described on the basis of parameters such as the amount of time spent at the maximum depth of the dive, the rate of ascent and descent, and the general form of the dive profile. These dive types were 'rest' dives, 'travel' dives, 'surface' dives, 'general non-foraging' dives, 'pelagic foraging' dives and 'benthic foraging' dives. The seals spent 90% of their time at sea submerged. Less than 2% of the time was spent on the surface in intervals of more than 10 min. A further 20-30% of the time was spent on the various non-foraging types of dives. Most females performed only 'pelagic foraging' dives, while males performed both 'pelagic' and 'benthic foraging' dives. All the 'benthic foraging' dives occurred in Area 3 (defined by water-temperature data as lying over the Antarctic Continental Shelf) and were 400-500 m deep. 'Pelagic foraging' dives occurred in all three foraging areas and ranged in depth from 200 to 1100 m. These types of dives also exhibited marked diurnal variations in depth, unlike 'benthic foraging' dives. The seals spent 10-20 min at the bottom of each 'foraging' dive, where they generally displayed a series of small changes in depth (wiggles). The size of these 'wiggles' tended to be larger in 'pelagic foraging' dives than in 'benthic foraging' dives. The diving behaviour of southern elephant seals is related to the possible prey they exploit in the Southern Ocean.

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Ultrasound measurements of subcutaneous fat at 18 body sites on each of 23 southern elephant seals Mirounga leonina (Linn.), together with circumference and length measurements, were used to estimate the total subcutaneous blubber weight on each animal. Twelve cows (including animals that were pregnant and others at early, mid-, late and post-lactation), 10 males and one male pup were anaesthetised for these measurements, made at Heard I. (53�01'S.,73�23'E.) on various dates in October and November 1985. Comparison of the estimates of blubber weight from cows at various stages of lactation allowed a mean blubber loss of 62.8 kg per cow per lactation to be calculated. It is suggested that measuring variations in the subcutaneous fat reserves of cows coming ashore to pup at Heard I. may be one relevant approach in any future research that attempts to explain the 60% drop in pup production at that island between 1949 and 1985. The use of ultrasound to estimate the subcutaneous fat reserves of seals was shown to be a safe, non-invasive and logistically practical technique.

Abstract:Between September 1987 and February 1988, Antarctic fur seals Arctocephalus gazella (Peters) at Heard Island fed mainly on fish with an average 95.2% of scats in monthly collections containing fish remains. Pelagic myctophids constituted more than 50% of fish taken by fur seals at the beginning of the summer season and again at the end when there was an influx of non-breeding male seals. During the middle period from October to December, fish from the surrounding shelf area comprised the bulk of the diet. These included various benthic nototheniid species, the bentho-pelagic ice fish Champsocephalus gunnari Lonnberg and skate (Bathyraja spp.), the latter being found in over 60% of scats in October and November. The population of Antarctic fur seals at Heard Island is increasing at about the same rate as at South Georgia. There the increase is thought to be due to the high availability of krill E. superba, but in the present study no euphausiid remains were found, so the increasing population at Heard Island has been supported on a diet of fish. Whether this population increase can be sustained in future on a diet of fish is arguable. Trial fishing around Heard Island indicates that one of the major dietary items of the seals (C. gunnari) is of probable commercial importance and therefore any plans for the establishment of a fishery on Heard Island grounds must be considered in this light.