We consider how Antarctic seals may respond to changes in climate, realizing that anthropogenic alteration of food webs will influence these responses. The species considered include the ice-obligate - crabeater (Lobodon carcinophaga), Weddell (Leptonychotes weddellii), Ross (Ommataphoca rossii) and leopard (Hydrurga leptonyx) seal - and the ice-tolerant Antarctic fur seal (Arctocephalus gazella) and southern elephant seal (Mirounga leonina). The data analysed are from long-term censuses of Weddell seals in McMurdo Sound (1997–2006), and of Weddell, fur and elephant seals at Arthur Harbour, Antarctic Peninsula (1974–2005). After considering their responses to recent changes in environmental features, as well as projected and current changes to their habitat our conclusions are that the distribution and abundance of 1) crabeater and Weddell seals will be negatively affected by changes in the extent, persistence and type of annual sea ice, 2) Ross and leopard seal will be the least negatively influenced by changes in pack ice characteristics, although, as may be the case for crabeater and Weddell, population size and distribution may be altered through changes in food web dynamics, and 3) southern elephant and fur seals will respond in ways opposite to the pack ice species, but could also be influenced most immediately by changes in their food resources due to factors other than climate.

Data on the response behaviour of seals (crabeater, leopard and Ross) and penguins (Adélie and emperor) to helicopter surveys over the pack ice off East Antarctica are presented. The surveys involved Sikorsky S76 helicopters flying at altitude 130 m and speed 90 knots along straight-line transects. The relative frequency of alert and movement behaviours by seal and penguin groups decreased with distance out to 800 m from the flight path. Penguin groups were more likely to show a movement response than seals at all distances. The perpendicular distances moved relative to the flight path were small (maximum 20 m, mean ≤ 3 m, for both seal and penguin groups) relative to the width of the area searched (800 m), and there was no evidence that response movement resulted in a spiked detection histogram. Observers were more likely to feel confident in identifying seal and penguin species if the animals responded to the helicopter by changing the body posture or moving. In this application of aerial survey, the response behaviour elicited by the passing helicopter was considered to be beneficial from a technical perspective, and the disturbance caused to the surveyed populations negligible from an ethical perspective.

Insights into the reproductive strategies of crabeater seals Lobodon carcinophagus were obtained from satellite-linked dive recorders deployed during the breeding season. All of the three females and seven males on which instruments were deployed hauled out continuously for extended periods of up to 24 days. The duration of extended haulout is consistent with a lactation period of around 3 weeks. In two cases where dive recorders were deployed on a male and female in the same group, the two animals stayed together on the ice continuously and entered the water at exactly the same time when extended haulout ceased. In both cases the male and female became geographically separated within a short time after entering the water, indicating that the association did not last beyond the period on the ice. Some males had multiple periods of extended haulout, suggesting they may try to find more than one female with which to mate. An optimal reproductive strategy with regard to the time spent on the ice may balance the conflicting needs of a short time imposed by the availability of breeding habitat and a long time to increase the reproductive success of males and females by finding more, or choosing between, mates.

As part of the multi-disciplinary project, Antarctic Marine Ecosystem Research at the Ice Edge Zone (AMERIEZ), habitat selection by marine mammals was investigated within the marginal ice zone in relation to measured ice variables and other environmental factors. Data were collected on three cruises to the southern Scotia and northern Weddell seas during spring 1983, autumn 1986, and winter 1988. During winter, Antarctic fur seals were significantly associated with drift, pancake, brash ice, icebergs, and areas of uneven floe distribution, all characteristic of the marginal ice zone. Fur seals were seen in open water close to the ice edge during autumn, but during spring, as the pack ice began to retreat rapidly, animals were seen more often away from the ice. Minke whales were also associated with pancake and new ice but were seen further into the pack ice during both winter and autumn. The largest groups of minke whales during winter were observed with a large krill swarm in new ice. Crabeater seal was exclusively a species of the deep pack ice during all seasons and was associated with ice cover of 7–8 oktas and evenly distributed ice floes.

From 15 December 1992–4 January 1993 aerial surveys of ice seals were undertaken by Puma helicopter across the pack ice off Dronning Maud Land. The 31 transects of 1/2 nautical mile (n.m.) width were flown at an elevation of 200 ft and a ground speed of 60 knots and covered 805.6 n.m.2 of pack ice. The overall species composition of the seals was 97.8% crabeater seals, 1.67% Ross seals, 0.34% leopard seals and 0.15% Weddell seals. The density abundance of seals was 2.47 n.m.−2 for crabeater, 0.01 n.m.−2 for leopard, 0.004 n.m.−2 for Weddell and 0.04 n.m.−2 for Ross seals. Leopard seals were largely found near the outer edge of the pack, Ross seals were absent only in the outer pack, whilst Weddell seals were virtually absent in the pack ice. Present throughout, crabeater seals and Ross seals showed a statistically significant preference for the inner pack, the reasons for this being unclear.

Apparent digestible efficiency (% DE) was studied by use of dietary Mn as an inert marker, in minke whales (Balaenoptera acutorostrata) and crabeater seals (Lobodon carcinophagus) which had been eating krill. Median % DE in minke whales (n 5) eating krill of the genus Thysanoessa sp. (energy density (ED) 23·8 kJ/g) was 93 (range 87–93). Median % DE in crabeater seals (n 6) eating krill of the species Euphausia superba (ED 20·8 kJ/g) was 84 (range 79–85), which is significantly lower than the % DE of krill in minke whales (P = 0·008). Since the chemical composition in E. superba and in Thysanoessa sp. is similar, it is suggested that the complex multi-stomached system of minke whales, which contains both chitinase (EC 3.2.1.14)-producing as well as several other types of bacteria, is superior to the single-stomached system of crabeater seals with regard to krill digestion. It is worth noting, however, that the % DE of krill in the crabeater seal is still very high.