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Home , Abundance (ecology), Crabeater seal, King Haakon VII Sea, Leopard seal, Weddell seal

CCAMLR Science, Vol. 19 (2012): 49–74

A REVIEW OF DATA ON ABUNDANCE, TRENDS IN ABUNDANCE, USE AND DIET OF -BREEDING SEALS IN THE SOUTHERN

C. Southwell* Australian Division Department of the Environment, Water, Heritage and the Arts 203 Channel Highway Kingston, Tasmania 7050 Email – [email protected]

J. Bengtson National Marine Laboratory NOAA 7600 Sand Way Point, N.E. Seattle, WA 98115 USA

M. Bester Mammal Research Institute Department of Zoology and Entomology University of Pretoria Pretoria 0002 South

A.S. Blix Department of Biology University of Tromso N-9037, Tromso

H. Bornemann Alfred Wegener Institute Postfach 120161 D-27515 Bremerhaven Germany

P. Boveng and M. Cameron National Laboratory NOAA Fisheries 7600 Sand Way Point, N.E. Seattle, WA 98115 USA

J. Forcada High Cross, Madingley Road Cambridge CB3 0ET United Kingdom

J. Laake National Marine Mammal Laboratory NOAA Fisheries 7600 Sand Way Point, N.E. Seattle, WA 98115 USA

49 Southwell et al.

E. Nordøy Department of Arctic Biology University of Tromso N-9037, Tromso Norway

J. Plötz Alfred Wegener Institute Postfach 120161 D-27515 Bremerhaven Germany

T. Rogers School of Biological, and Environmental Sciences The University of New South Wales Sydney Australia

D. Southwell Australian Antarctic Division Department of the Environment, Water, Heritage and the Arts 203 Channel Highway Kingston, Tasmania 7050 Australia

D. Steinhage Mammal Research Institute Department of Zoology and Entomology University of Pretoria Pretoria 0002

B.S. Stewart Hubbs-SeaWorld Research Institute 2595 Ingraham Street San Diego, CA 92109 USA

P. Trathan British Antarctic Survey High Cross, Madingley Road Cambridge CB3 0ET UK

Abstract

The development of models of marine in the is becoming increasingly important as a means of understanding and managing impacts such as exploitation and . Collating data from disparate sources, and understanding biases or uncertainties inherent in those data, are important first steps for improving models. This review focuses on seals that breed in ice of the Southern Ocean (i.e. , Lobodon carcinophaga; , Ommatophoca rossii; seal, Hydrurga leptonyx; and , Leptonychotes weddellii). Data on populations (abundance and trends in abundance), distribution and habitat use (movement, key habitat and environmental features) and (diet) are summarised, and potential biases and uncertainties inherent in those data are identified and discussed. Spatial and temporal gaps in knowledge of the populations, habitats and diet of each are also identified.

50 Review of abundance, habitat use and diet data of ice-breeding seals

Introduction Abundance The development of ecosystem models is be- General survey methods coming more important as a means of understand- The general survey methods used to estimate ing and managing impacts (e.g. exploitation and abundance have been developed around the bio- climate change) in the Southern Ocean. Recently logical characteristics of the ice-breeding seals. the Scientific Committees of two Commissions Due to their dispersed distribution over very large responsible for managing biota in the Southern areas, ships and aircraft have been used as vehicles Ocean (i.e. the Commission for the Conservation to survey seals that are hauled out, using transects of Antarctic Marine Living Resources (CCAMLR) as sampling units, to first estimate densities of seals and the International Commission (IWC)) hauled out. Independent studies of haul-out behav- recognised the importance of ecosystem modelling iour are then needed to correct those estimates of by convening a joint workshop to coordinate and density to total density, which is then converted to improve the capacity of ecosystem modelling for an estimate of abundance taking into account the both Commissions. area of -ice. The focus of the workshop was on the data need- ed as input to ecosystem models rather than on the Survey reviews specifics of particular models. The data required for models of marine ecosystems cover many taxa, are The first regional and circumpolar estimates of scattered throughout the literature, and are likely to abundance of Antarctic seals were reported in the have many biases, uncertainties and gaps that could late 1940s and early 1950s (Table 1). Laws (1953) limit or affect the performances of those models. estimated the abundances of the four species in the Assimilating those data and understanding any Falkland Island Dependencies, though he cautioned biases or uncertainties inherent in them are impor- that those estimates were gross and largely guesses. tant first steps for improving ecosystem modelling. They were evidently not based on the use of rig- Identifying important gaps in knowledge can also orous survey methods. Scheffer (1958) later esti- focus data collection in the most needed areas. mated the circumpolar abundance of each species, but he did not describe the survey methods used to This review focuses on seals that breed in the derive them. The first estimates that describe meth- fast-ice and pack-ice habitats of the Southern Ocean ods were reported by Eklund and Atwood (1962) (crabeater seal, Lobodon carcinophaga; Ross seal, and Eklund (1964). They made sightings from Ommatophoca rossii; , Hydrurga lep- ships along transects in two relatively small areas tonyx; and Weddell seal, Leptonychotes weddellii). of pack-ice in the Pacific and sectors All four species of seal that breed in the sea-ice in December–January 1956/57 (Figure 1, methods habitats of the Southern Ocean have circumpolar summarised in Table 2). To derive circumpolar distributions and use the sea-ice as a platform to estimates of abundance, they applied the average haul out on when giving and . Breed- density of seals hauled out along sample transects ing occurs in late spring and early summer, and to the estimated area of pack-ice around moulting in mid- to late summer. For the rest of in January (Table 3), though they qualified this by the year, these species spend much of their time noting that the two regional samples were inade- foraging in the ocean, but continue to haul out peri- quate to represent the entire pack-ice. odically to rest, making them amenable to observe and count from the air or from ships. Crabeater, From the late 1960s to the early 1980s, Erickson Ross and leopard seals usually occur alone or in and colleagues made a series of shipboard and small groups when hauled out, whereas Weddell aerial surveys around the Antarctic seals often aggregate in larger groups in fast-ice (Figure 2), and then derived several estimates of habitats in early summer when breeding. Data on regional and circumpolar abundance for the four populations (abundance and trends in abundance), species (Tables 1, 2 and 3). distribution and habitat use (movement, key habitat and environmental features) and foraging (diet) are The earliest of those surveys were in the summarised, potential biases and uncertainties in- in the austral summers of 1967/68, herent in the data are identified and discussed, and 1968/69 and 1969/70. Erickson et al. (1969) and spatial and temporal gaps are identified. Siniff et al. (1970) computed densities of crabeater

51 Southwell et al. seals seen hauled out during shipboard strip tran- the time of day that the photographs were taken sects in the pack-ice of the Weddell Sea (Figure 2), was not indicated by Gilbert and Erickson (1977), but they did not estimate population sizes for the and it is not clear whether counts were adjusted for entire because the relationship between the haul-out patterns. Extrapolation of density in sam- number of seals counted on the ice and the number pled strips to 919 000 km2 of pack-ice (latitudinal actually present in the area was unknown (Siniff et and longitudinal bounds not specified) resulted in al., 1970). Erickson et al. (1971) later reported the an estimate of 48 750 seals (Gilbert and Erickson, results of observational studies of haul-out patterns 1977; estimate not shown in Table 1 because it was of crabeater seals relative to time of day during the not species-specific). 1968/69 surveys. They re-calculated crabeater seal densities, where appropriate, by adjusting counts of In the Amundsen–Bellingshausen and hauled-out seals upwards to the number expected Oates–George V coast surveys, counts were made at midday (i.e. 1100–1400 hr) peak haul-out time. and recorded directly from a helicopter flying at They then applied the adjusted densities to the total 152 m altitude along transects extending from the estimated area of pack-ice in the Weddell Sea that ice edge southward (Table 3, Figure 2). Because was typical of having been surveyed to obtain an most of the pack-ice habitats in the inner region approximate estimate of the abundance of crabeater of the area could not be reached by the helicop- seals in the Weddell Sea (8.25 million in 1967/68 ter (Figure 2), aerial photographic surveys from a and 10.60 million in 1968/69; Table 1). Erickson fixed-wing aircraft (similar to those in the western et al. (1971) cautioned about some potential , above) were also made along two tran- biases and errors in these approximate estimates sects through the interior of the pack-ice. In both (e.g. seals missed in surveys; the likely presence of the helicopter surveys were made between seals in unsampled habitat such as ice-free areas or 1100 and 1400 hr solar time when most crabeater consolidated ice; errors in estimation of ice habi- seals were expected to be hauled out, and one - tat), but nonetheless speculated about a circumpo- server counted seals within strips of 463 m width lar population of crabeater seals of between 50 and on each side of the helicopter. Densities of seals 75 million. The authors did not derive estimates of hauled out in the outer ice regions were calculated the abundances of Ross, leopard or Weddell seals, using strip transect methods, and densities were but noted that adjustments for haul-out would also adjusted for haul-out patterns using a half-hourly have to be made for these species. time adjustment factor derived from counts from both surveys. The adjustment factor was apparently From 1970 to 1974, Erickson and his colleagues not species-specific. In the Oates–George V coast surveyed several other regions around Antarc- region, densities of seals in the interior of the pack- tica (Tables 2 and 3 and Figure 2), including the ice were derived from helicopter counts > 93 km western Ross Sea region in 1970/71 (briefly men- south from the northern ice edge on the assumption tioned by Erickson et al., 1971), the Amundsen– that the nature of pack-ice was relatively constant Bellingshausen Seas region (135°W–80°W) from this point southward to the continent. In the in 1971/72 (unadjusted or hauled-out densities Amundsen–Bellingshausen Seas region, densities reported in Erickson et al., 1972), the Oates and of seals in the interior of the pack-ice were derived George V coast region (145°E–170°E) in 1972/73 from a combination of helicopter counts > 130 km (densities of seals hauled out and a minimum south from the northern ice edge and the aerial population estimate reported in Erickson et al., photography counts throughout the interior of the 1973), and the Adélie, Claire and BANZARE coast pack-ice. Separate estimates of abundance were region (120°E–137°E) in 1973/74 (densities of calculated for outer and interior regions by ex- seals hauled out reported in Erickson et al., 1974). trapolating adjusted estimates of density across the All but the last of those surveys were analysed and estimated areas of pack-ice, and estimates for outer presented in more detail in Gilbert and Erickson and interior regions were then summed to derive an (1977), as summarised below. estimated total for each species in each region (Table 1). In the western Ross Sea survey, seals were counted from vertical photographs taken from a fixed-wing Collectively, Erickson’s surveys from 1967/68 aircraft flying along transects in November 1970 to 1973/74 between 25°W and 120°E covered (Figure 2). Seals were not distinguished by species, slightly more than half the circumpolar pack-ice

52 Review of abundance, habitat use and diet data of ice-breeding seals region (Figure 2). A final effort during a circum- was applied to counts of each species over the polar voyage around Antarctica in the summer months of January to March. The revised estimates of 1982/83 (Erickson et al., 1983) was made to are shown in Table 1. The estimates of abundance sample the sea-ice off the other half of the conti- from the reanalysis were generally lower than the nent to allow estimates of circumpolar population original estimates, and substantially and surprising- abundance for each species to be made (Erickson ly lower in some regions (e.g. 8.2–10.6 million for and Hanson, 1990). The survey effort in 1982/83 original estimates vs. 2.2 million for the reanalysis involved both aerial and shipboard surveys (only in the western Weddell Sea region; 1.19 million for aerial transects are shown in Figure 2 as shipboard original vs. 0.63 million for the reanalysis in the transects were not described by Erickson et al. Amundsen–Bellingshausen Seas region). Based (1983)). As in previous aerial surveys, transects on the revised regional estimates, Erickson and were flown directly southward from the outer ice Hanson (1990) estimated the circumpolar popula- edge and seals were counted by one observer within tion of crabeater seals in unconsolidated pack-ice to 463 m wide strips on each side of the helicopter. be at least 7 million, though they stressed that this The surveys in 1982/83 were, however, flown at a did not include the potentially significant number substantially lower altitude (76 m vs. 152 m in ear- of seals that might be in ice-free areas of the South- lier surveys). Shipboard survey methods were the ern Ocean in summer, nor the number of seals that same as those used in previous years. The area of did not haul out during the peak haul-out period. interior ice that was covered by aerial surveys, and From those considerations, they thought that a the location and distribution of shipboard transects circumpolar population of 11–12 million crab­ in the pack-ice, were not described by Erickson eater seals was reasonable. Laws (1984) had earlier et al. (1983). Only raw counts were presented by derived an estimate of around 15 million crabeater Erickson et al. (1983); analysis and synthesis of seals from the Erickson surveys from 1967/68 to these data with all the data collected in previous 1972/73 (Table 1), but noted that this might have years appears in Erickson and Hanson (1990), as been conservative and had further speculated that a summarised below. population of 30–40 million crabeater seals might not be unlikely. The main features of the synthesis and revised analysis by Erickson and Hanson (1990) were Ainley (1985) carried out shipboard sighting the collection of additional data on haul-out pat- surveys of and marine in the terns and the development and testing of a model Ross Sea in December and January in the austral to account for diurnal variation in counts of seals summers of 1976/77, 1977/78 and 1979/80 (Table 2, hauled out (Erickson et al., 1989). During the final Figure 3). The densities of seals hauled out in sam- circumpolar survey in 1982/83, crabeater seals pled areas were estimated using strip transect meth- hauled out on the ice were counted throughout ods and then adjusted to the densities expected at the day from a relatively stationary position in the time of peak haul out in a manner similar to the pack-ice at five locations around Antarctica in Erickson et al. (1971). Abundances were estimated February (at one of these sites counts of Weddell for each of the four seal species in the surveyed seals were also made, and crabeater counts in 1969 region by constructing strata based on ice and were also available from a sixth location). Regres- physical attributes, calculating abundance in each sion analysis indicated a unimodal distribution strata as the product of average-adjusted density for of counts that peaked around midday at all sites. each species and strata area, and finally summing A predictive model was then developed to adjust the strata estimates for each species. The resulting counts at any time of day to those expected at the estimates of abundance were 204 000 crab­eater time of peak haul-out. Erickson and Hanson (1990) seals, 5 000 Ross seals, 8 000 leopard seals and applied this model to all counts made during the 32 000 Weddell seals (Table 1). surveys from 1967/68 to 1982/83 and derived esti- mates of abundance for five oceanographic regions The Antarctic Pack-Ice Seals (APIS) program (Amundsen–Bellingshausen Seas (60°W–130°W), was initiated by the Scientific Committee on Ant- Ross Sea (130°W–160°W), south arctic Research (SCAR) Group of Specialists on (90°E–160°E), south Indian Ocean (20°E–90°E) Seals. A key aim of the APIS program was to co- and Weddell Sea (20°E–60°W)). The haul-out ordinate multiple ship and aerial operations to ob- model developed for crabeater seals in February tain a synoptic circumpolar survey effort. The APIS

53 Southwell et al. surveys also planned to implement improvements rather than assuming similar haul-out behaviour for in methods to address some of the known or poten- all species, and third by estimating probability of tial biases in earlier surveys. haul-out specific to the time of year that each sight- ing survey was done. It was not logistically possible to sample all areas of the Antarctic pack-ice in one year, but the Although the spatial coverage of pack-ice habi- resulting spatial coverage of the coordinated APIS tat by the APIS transects was more comprehensive program was substantially better in its geographic than for previous surveys, the practical constraints scope (both longitudinally and latitudinally) than on ship and aircraft operation in the pack-ice meant all previous surveys (compare Erickson surveys that true random or representative placement of in Figure 2 with the APIS surveys in Figure 4). transects was not possible. To address and mini- Shipboard and aerial sighting surveys undertaken mise bias in extrapolating from densities of seals in the summer of 1999/2000 were contiguous and sampled along the potentially non-representative extended around half the continent from 100°W to transects to the entire area of pack-ice, analysis of 64°E (Figure 4). In the three previous summers, the APIS data used spatial modelling and predic- aerial surveys were carried out along the Antarc- tive methods (Bengtson et al., 2011; Forcada and tic Peninsula (1998/99) and eastern Weddell Sea Trathan, 2008; Southwell et al., 2008a, 2008b, coasts (1996/97 and 1997/98), and aerial photo- 2008c). graphic surveys were carried out over the pack-ice of the eastern Weddell Sea during five consecutive Analysis of the APIS data has addressed the summers from 1996/97 to 2000/01 (Figure 4). The major sources of uncertainty in estimating abun- use of ship-based helicopters improved the north to dance. Bootstrap and jack-knife methods were used south coverage of pack-ice. to include uncertainty related to the estimation of probabilities of detection and haul-out, and uncer- In contrast to Erickson’s aerial sighting surveys, tainty in predicting abundance across the survey where one observer counted in 463 m strips on each region using spatial models (Bengtson et al., 2011; side of the aircraft and did not record distance data, Forcada and Trathan, 2008; Southwell, 2008a, observers in the APIS aerial surveys counted seals 2008b, 2008c). Model uncertainty was considered on only one side of the aircraft and recorded dis- by deriving estimates based on several plausible tance data to allow estimates of densities of seals predictive models, and uncertainty related to spe- hauled out to be made with line transect methods. cies identification was addressed by estimating Some aerial surveys also used additional observ- abundance from both definite only and definite ers to allow density to be estimated from mark- plus probable species sightings. The problem of recapture line transect methods and testing of the dynamic sea-ice distribution was addressed by line transect assumption of perfect detection on the deriving a survey region that represented the local transect line (Table 3). Line transect methods were sea-ice extent and concentration at the time that also used during shipboard surveys (Table 2). surveys were conducted (Bengtson et al., 2011).

An integral component of the APIS work was Most regional analyses of APIS data have been the deployment of satellite-linked dive recorders on completed. The most plausible estimates of crab­ a sample of seals around the continent to estimate eater seal abundance were 1 736 000 (95% CI the probability of seals being hauled out at any time 1 219 000–2 472 000) for the longitudinal sec- of day or year. Dive recorders were attached to tor from 150°E to 100°W, 3 187 000 (1 754 000– seals of all four species and provided haul-out data 4 748 000) from 90°W to 30°W, and 946 000 throughout each day for several months or more (726 000–1 397 000) from 64°E to 150°E. The (Bengtson and Cameron, 2004; Southwell, 2003, crabeater seal abundance estimate of 3 564 000 2005; Blix and Nordøy, 2007; Nordøy and Blix, reported by Bester and Odendaal (2000) for the 2009). Those data allowed improved adjustment area from 26°W to 7°W was only a simple prelimi- of counts of seals hauled out during the surveys nary estimate and is likely to be an overestimate. relative to diel haul-out patterns, first by estimat- Regional abundance estimates for Ross, leopard ing the previously unknown proportion of seals in and Weddell seals were highly uncertain (150°E– the water at the time of peak haul-out, second by 100°W sector: Ross seals 22 600 (11 700–43 700); estimating species-specific haul-out probabilities leopard seals 15 000 (3 500–65 000); Weddell seals

54 Review of abundance, habitat use and diet data of ice-breeding seals

331 000 (144 000–759 000); 90°W–30°W sector: recorders indicate that, for crabeater seals, no estimate for Ross seals, only one seen; leop- the proportion of seals underwater around so- ard seals 13 200 (3 700–23 100); Weddell seals lar midday in the summer months is between 302 000 (77 000–576 000); 64°E–150°E sector: 20% and 40% (Bengtson and Cameron, 2004; Ross seals 55 900 (27 700–187 500); leopard seals Bengtson et al., 2011; Southwell, 2005). Some 7 300 (3 700–14 500); no estimate for Weddell more subtle biases in Erickson and Hanson’s seals because virtually no fast-ice was surveyed). (1990) estimates may have arisen due to their use of haul-out adjustments developed only, or predominantly, for crabeater seals in Feb- Potential biases and uncertainties ruary being applied to counts of all four spe- in abundance estimates cies across the months of January to March. Substantial biases and uncertainties were un- More recent studies have shown that haul-out doubtedly present in the early estimates of popu- behaviour varies among species and months lation size. Indeed the authors were very direct in (e.g. Bengtson and Cameron, 2004; Blix and stating the uncertainties known or suspected by Nordøy, 2007). them. The densities of seals hauled out reported by Eklund and Atwood (1962) would have underes- (iii) Transect placement and extrapolation from timated true densities because no adjustment was sampled to unsampled areas. An ideal survey made for the number of seals in the water at the time design would have multiple randomly or regu- of the survey. The early circumpolar estimates were larly spaced transects extending in a north– based on very limited sampling in two small regions south direction from the Antarctic continent of the circumpolar pack-ice, and there would be to the ice edge to allow application of design- substantial uncertainty associated with extrapolat- based inference methods for extrapolating ing from the sampled regions to the entire pack-ice. densities estimated for the sampled transects to Given these issues, the acknowledged guesswork the entire region. Clearly this ideal design was underlying Laws’ (1953) estimates, and the lack not achieved in the shipboard sighting surveys of information on survey methods for Scheffer’s in the Weddell Sea (Figure 2), and while aerial (1958) estimates, it is strongly recommended that sighting surveys aspired to this design, the all of these early estimates be treated only as the range of helicopters was insufficient to cover good-faith guesses that they were offered as. the full extent of ice, leaving the interior ice largely unsampled. With very limited sampling The methods used during the Erickson surveys of the interior ice (some aerial photographic were an improvement over the early surveys. Nev- transects were flown), the estimates of abun- ertheless, there were several sources of actual or dance there were largely based on untested potential bias and uncertainty underlying the esti- assumptions about seal distribution across mates derived from the Erickson surveys. the ice gradient. Estimates of Weddell seal abundance would be particularly prone to bias (i) Detectability. Use of strip transects would because their favoured fast-ice habitat received have resulted in a negative bias in estimates very little sampling. The magnitude, and even of densities of seals hauled out if some seals the direction, of bias relating to this issue is within the strips were undetected. This is very unclear. likely to have occurred during aerial surveys where a single observer searched across strips (iv) Uncertainty or precision. Large-scale surveys of 463 m width on both sides of the aircraft, of wildlife abundance often have low preci- but is unlikely in shipboard surveys using sion (= high uncertainty). None of the regional 200 m strips. or circumpolar estimates derived from the Erickson surveys and listed in Table 1 were (ii) Correction for haul-out. Because correction qualified with estimates of uncertainty or pre- of counts to peak haul-out was based only on cision. counts of seals hauled out, the proportion of seals in the water at the time of peak haul-out (v) Availability. One potential source of bias noted could not be assessed and so was not account- by Erickson and Hanson (1990) is the lack of ed for. Recent studies using electronic dive accounting for seals in ice-free areas of the

55 Southwell et al.

Southern Ocean. As seals that do not haul out detectability (e.g. distance data) were not recorded on the pack-ice, they are completely unavail- in most of the early surveys (this would be espe- able to estimation with the methods applied in cially important for aerial sighting data). Finally, the Erickson surveys, some alternate method recent analyses have shown that uncertainty about would be needed to assess their status and im- abundance estimates is substantial, and this will portance. make detection of anything but relatively large changes difficult. Most of the above comments for the Erickson surveys apply to the Ross Sea surveys. The stratified analysis used by Ainley (1985) to estimate abun- Distribution and habitat use dance should have minimised any bias that could As discussed above, sighting surveys to estimate otherwise have resulted from non-representative abundance have capitalised on the dependence of sampling. Antarctic phocid seals on sea-ice as a substrate to haul out on to breed and moult in the late spring Improved coordination of the APIS survey and summer months. Much of the available data efforts and the application of state-of-the-art survey and interpretations of distribution and habitat use and analytical methods should have reduced many of seals are based on observations made during of the biases associated with the Erickson surveys those population surveys. Consequently, there has and arguably provided a more realistic assessment been a bias towards the use of haul-out habitat. The of the uncertainty surrounding abundance esti- relatively recent development of satellite-linked mates. Nevertheless, some biases are still likely dive recorders has allowed data on both haul-out to be inherent in estimates derived from the APIS and foraging habitat (both geographical and verti- surveys. The main bias that remains unresolved cal) to be collected, and consequently, knowledge concerns the availability of seals to conventional of habitat use has been increasing (summarised survey methods that involve counting and cap- ture. Southwell et al. (2008c) considered that this below). problem was likely to be greatest for leopard seals and least for crabeater seals, and recent studies of Species reviews haul-out patterns and movement using satellite- linked dive recorders (e.g. Blix and Nordøy, 2007; Crabeater seals Nordøy and Blix, 2009) highlight the importance Most satellite telemetry studies have found that of this concern for both Ross and leopard seals. crabeater seals are largely confined to the pack-ice Abundance estimates for these species could be (Bengtson et al., 1993; Nordøy et al., 1995; Burns significantly negatively biased because a large pro- et al., 2004). In the longest study through winter, portion of the population is pelagic for much of the Nordøy et al. (1995) noted that the only crabeater time and hence not available for estimation. seal that left the pack-ice crossed a large bay of open water in about three days and then settled in the outer pack on the other side. Wall et al. (2007) Trends in abundance found that association with pack-ice was not It is difficult to reliably estimate population complete however, as seals spent around 14% of trends from the abundance estimates reported by their time in open water after the breeding season. the various surveys for several reasons. Firstly, Satellite telemetry studies have also shown that very few repeat surveys have been undertaken in when crabeater seals do haul out during spring and the same or similar regions. Secondly, a reanalysis summer, they are mostly hauled out around solar of all data from previous surveys would be needed midday (Bengtson and Cameron, 2004; Southwell, to make estimates of abundance from those sur- 2005), indicating that sighting surveys of hauled- veys comparable with recent surveys from which out crabeater seals can provide reasonably unbiased abundance was estimated with newer analytical broad inferences on both haul-out and foraging methods. This might not be possible if the original habitats at these times of year. In spring, when data from early surveys are not now available. Even crabeater seals are breeding, shipboard surveys if the original data were available, a reanalysis have found that breeding crabeater seals in East might not provide comparable results because the Antarctica were most likely to be present in a zone covariate data required to estimate and correct for between the continental shelf break in the south and

56 Review of abundance, habitat use and diet data of ice-breeding seals extending northward about 1.5 to 5° latitude, while The diving behaviour of crabeater seals has been non-breeders ranged further north (Southwell et al., examined in most areas of the Southern Ocean from 2005). Those areas are coincident with the known summer to winter (Table 4), including the Weddell distribution of the crabeater seals’ primary food Sea (Bengtson and Stewart, 1992), Queen Maud source (Antarctic (Euphausia superba)), and Land (Nordøy et al., 1995), the also coincide with oceanographic fronts (e.g. the (Burns et al., 2004, 2008), the Ross Sea (Ackley et Antarctic Slope Front and the southern bound- al., 2003) and (Gales et al., 2004; ary of the Antarctic Circumpolar Current) which Wall et al., 2007). The mean dive depth by crabeater are thought to be areas of enhanced primary and seals in these studies ranged from 40 to 140 m, but secondary . Ainley (1985) and Ackley dives as deep as 713 m have been recorded (Burns et al. (2003) also reported greater densities of crab­ et al., 2004). Diving patterns vary seasonally, with eater seals near the continental shelf break and the a clear preference for diving during darkness and Antarctic Slope Front during early summer. hauling out during daylight during summer and autumn and a reverse pattern in winter. Nordøy et The retreating ice edge is also thought to be a al. (1995) reported that seals made deeper dives zone of enhanced productivity in summer, but evi- in February and shallower dives in June, whereas dence of crabeater seals preferentially using the Hofmann et al. (2002) noted deepest dives occur- ring in May and shallowest dives in September. ice edge is equivocal. For example, Gilbert and Most studies have reported diurnal or diel patterns Erickson (1977) and Laws (1984) reported that in the diving behaviour of crabeater seals, perhaps densities of crabeater seals were greater near the in response to diel vertical migrations of prey. ice edge than farther south, whereas van Franeker (1992), Bester et al. (1995, 2002) and Flores et al. (2008) did not find any differences. Ross seals

Some studies suggest that crabeater seals pre- In contrast to crabeater seals, Ross seals have fer ice floes of particular sizes, concentrations or been found to make long foraging trips north of thicknesses to haul out on (Condy, 1977; Bester the pack-ice into pelagic areas of the Southern et al., 2002; McMahon et al., 2002; Flores et al., Ocean for most of the year and return to the pack- 2008), whereas other studies found no evidence ice only for short periods to breed and moult (Blix and Nordøy, 2007). This finding has changed the for preferences (Bester et al., 1995). Burns et al. dogmatic view of Ross seal habitat use, which had (2004) concluded that the use of particular types previously concluded, based on sparse observa- of sea-ice habitat by crabeater seals along the Ant- tions from sighting surveys, that Ross seals prefer arctic Peninsula in winter reflected the interaction dense concentrations of interior pack-ice (Wilson, between the reliance of seals on regions of high 1975; Condy, 1976; Gilbert and Erickson, 1977). zooplankton abundance (e.g. near the bottom, at Clearly, for this species sighting surveys provide a water mass boundaries, over varied topography, very biased view of overall habitat use. and perhaps under stable sea-ice) and their need to access air to breath and ice to rest. Based on Satellite telemetry studies have shown that shipboard surveys undertaken in the northeastern Ross seals forage to greater depths than crabeater Weddell Sea pack-ice in winter, Plötz et al. (1991b) seals, commonly diving to depths of 100–300 m reported that crabeater seals were more abundant and occasionally reaching depths of close to 800 m near the submarine Maud Rise (about 700 km north (Bengston and Stewart, 1997; Southwell, 2005; of the continental margin) than in other areas where Blix and Nordøy, 2007) (Table 4). ice coverage was more substantial. The distribution pattern of crabeater seals and other krill predators during those surveys coincided with the course of Leopard seals a warm water belt upwelling near Maud Rise. That Satellite telemetry is also starting to shape a upwelling evidently caused surface ice to melt, more complete view of leopard seal habitat use. which then might have resulted in the release of Sighting surveys have provided few insights into large amounts of sea-ice algae and nutrients, and leopard seal habitat use because very few sightings subsequently in large concentrations of krill, be- have ever been obtained from sighting surveys, neath the new sea-ice in winter. and as for Ross seals, the potential for biased

57 Southwell et al. interpretation of sighting data exists if they spend out. Observations of Weddell seals during ship- long periods in the water and consequently are board sighting surveys in the pack-ice occur but are difficult to observe. Nordøy and Blix (2009) moni- uncommon compared with the other species. tored two leopard seals from summer to winter near . The seals moved north as the Weddell seal diving behaviour has been well pack-ice expanded and one eventually passed by studied (Table 4), reflecting the relative ease of the South Shetland Islands to as far north as 57°S, access to this species for study when hauled out on where it stayed in open water for a considerable fast-ice in several areas. They dive deeply, feeding time before moving south back to the ice edge. primarily in the mid-water regions of the water col- umn at depths of around 100–300 m. Some authors Northward movement of this scale is consistent suggest that Weddell seals exhibit diurnal feeding with numerous observations over the last century patterns within two depth layers (0–160 m and of leopard seals hauling out at sub-Antarctic is- 340–450 m) as a response to vertically migrating lands in winter, and year-round on some islands in prey. Much effort has been devoted to classifying close proximity to the south of the Antarctic Po- dives into behavioural classes such as pelagic for- lar Front such as at South Georgia (Jessopp et al., aging, benthic foraging, exploration and travelling 2004), Îles Kerguelen (Bester and Roux, 1986) and using multivariate statistics. Between three and Heard Island (Gwynn, 1953). In contrast, Rogers nine dive types have been classified depending et al. (2005) reported that leopard seals tagged at on the method and type of data collected. Recent the fast-ice edge in Prydz Bay remained close to advances in dive-depth recording technology and their tagging site with no evidence of pronounced the inclusion of cameras to record prey capture north–south movement. While these studies are have also allowed the three-dimensional diving significant advances, our understanding of leopard behaviour and presence of prey within the water seal habitat use is still limited and further study is column to be examined (e.g. Fuiman et al., 2007). required.

Satellite telemetry studies have reported that Diet leopard seals are primarily shallow divers, with Methods used to measure or infer the diet of most dives to depths of 10–50 m and only occa- ice-breeding seals have included examination of sionally as deep as, or deeper than, 200 m (Kuhn et stomach contents or faeces (scats), stable isotope al., 2006; Nordøy and Blix, 2009). analysis and indirect inference from studies of div- ing behaviour and habitat use. Weddell seals Satellite telemetry studies and sighting surveys Species reviews have suggested that Weddell seals primarily use Crabeater seal fast-ice and nearby pack-ice habitats close to the Quantitative information on crabeater seal diet coast. Testa (1994) found adult Weddell seals were is available from analyses of stomach contents reluctant to leave the fast-ice in McMurdo Sound (Øritsland, 1977; Bengston, 1982; Lowry et al., where they had bred until March or April and then 1988; Dzhamanov, 1990) and faeces (Green and mostly remained within 50–100 km of their sum- Williams, 1986; Burns et al., 2004, 2008). Indirect mer breeding colonies, although some seals moved inferences about diet have been made from mor- longer distances and spent long periods in heavy phology of teeth and mandibles (King, 1961), from winter pack-ice. Burns et al. (1999) found that observations of captive individuals (Klages and Weddell seal pups from the McMurdo region trav- Cockcroft, 1990) and from data on seal movements elled along the Antarctic continental coastline into and diving behaviour (Nordøy et al., 1995; Burns pack-ice after leaving their natal area, but preferred et al., 2004, 2008). Crabeater seals are believed to to remain closer to the coast than adults. Lake et feed primarily on (>90%), but also al. (2006) inferred from satellite telemetry studies evidently eat and when krill is not that Weddell seals in East Antarctica foraged off- available (Øritsland, 1977). The information cur- shore within pack-ice in winter for periods of up to rently available is insufficient to assess geographic 30 days, but returned to the stable fast-ice to haul or temporal variability in diet.

58 Review of abundance, habitat use and diet data of ice-breeding seals

Ross seal Walker et al., 1998), Antarctic seals and pen- guins are important prey (Forcada et al., 2009) Diet of Ross seals has been determined by anal- though rare sightings suggest that opportunistic ysis of stomach contents (King, 1969; Øritsland, prey can be variable (Edwards et al., 2009). 1977; Dzhamanov, 1990; Skinner and Klages, 1994) and ratios of stable isotopes in tissues (Rau et al., 1992). Diet has also been inferred from patterns Weddell seal of movement and diving behaviour (Bengtson and Stewart, 1997; Southwell, 2005; Blix and Nordøy, Quantitative data on Weddell seal diet have 2007). Those data indicate that Ross seals most- been obtained from analyses of stomach contents ly eat squid (Moroteuthidae, Onychoteuthidae, (Øritsland, 1977; Weiner et al., 1981; Plötz, 1986, Oegopsidae; ~60%) and fish (e.g. Myctophidae, Plötz et al., 1991a), scats (Øritsland, 1977; Green Bathydraconidae; ~20% of the diet), and occasion- and Burton, 1987; Burns et al., 1998, Casaux et al., ally (~10%) and benthic invertebrates 1997, 2006) and ratios of stable isotopes (Burns (<10%) (Øritsland, 1977). There have been no stud- et al., 1998), and indirect inferences made from ies of Ross seal diet in the Pacific or Indian sectors. three-dimensional movements and diving patterns There are insufficient data to assess geographic or (Testa et al., 1989; Testa, 1994; Schreer and Testa, 1996; Plötz et al., 2001; Sato et al., 2002; Hindell temporal variability. et al., 2002; Davis et al., 2003; Watanabe et al., 2003; Fuiman et al., 2007). Most studies report Leopard seal that fish (mainly P. antarcticum) are the primary prey, followed by cephalopods and crustaceans, al- Quantitative information on leopard seal diet though there appears to be substantial geographic is available from examination of stomach contents variability: for example, benthic fish, pelagic fish (Øritsland, 1977; Stone and Meier, 1981; Siniff and and crustaceans dominated the diet at the Vestfold Stone, 1985; Dzhamanov, 1990), faeces (Øritsland, Hills in East Antarctica (Green and Burton, 1987; 1977; Green and Williams, 1986; Lowry et al., Green et al., 1995), whereas pelagic fish domi- 1988; Walker et al., 1998; Hall-Apsland and nated at McMurdo Sound (Burns et al., 1998), Rogers, 2004; Casaux et al., 2009), direct observa- and cephalopods were the main prey at the South tions of predatory behaviour (Hunt, 1973; Bester Shetland Islands and near Mawson (Lipinski and and Roux, 1986; Borsa, 1990; Kooyman et al., Woyciechowski, 1981; Clarke and McLeod, 1982; 1990), and inferences have been made from data Green and Burton, 1987; Casaux et al., 1997). Stud- on movement and diving behaviour (Kuhn et al., ies have also found considerable variability within 2006; Nordøy and Blix, 2009). Those data indicate areas and seasons (Table 5). that leopard seals eat a variety of prey including fish, cephalopods, crustaceans, and other seals (e.g. Green and Williams, 1986; Costa and Potential biases and uncertainties in diet data Crocker, 1996), and that diet composition varies Each of the diet methods has some potential between seasons and regions. Green and Williams biases and limitations. Analysis of stomach con- (1986) reported that fish (Pleuragramma antarcti- tents and scats can provide detailed quantitative, cum), followed by demersal species, were primary taxonomic dietary information, but the recovered prey in winter and spring. Newly weaned crabeater remains of prey are generally only from the most seals appear to be important prey in December and recent meals. Differential rates of digestion of dif- January (Siniff and Stone, 1985; Siniff, 1991), and ferent prey can also result in biases toward prey penguins are the primary prey in late January and with robust hard parts that can be identified. Stable February (Siniff and Stone, 1985), although analy- isotopes in seal tissues can be used to infer general ses of scats and stomach contents from Prydz Bay diets of seals over longer time periods (e.g. over in East Antarctica suggested that Adélie penguins several years for bone collagen), but fine-scale (Pygoscelis adeliae) were eaten throughout the taxonomic detail is not possible. Inferring diet from year at some locations (Rogers and Bryden, 1995; diving behaviour and habitat use is indirect and cir- Hall-Apsland and Rogers, 2004). Krill is believed cumstantial. to be the most important prey in winter (Lowry et al., 1988; Siniff and Stone, 1985; Nordøy and Blix, Diet studies are often based on small sample 2009). In some areas (e.g. sub-Antarctic islands; sizes (numbers of ) leading to questions of

59 Southwell et al. how representative the samples are to the broader Acknowledgements population. The patchy nature of diet data in both space and time, and the limited number of diet We thank David Smith from the Australian Ant- studies, also makes it difficult to make broader arctic Division for producing the maps. generalisations beyond the individual studies with any certainty, such as whether or how diet changes regionally, seasonally, or over the long term. Dis- References tilling these broad generalisations from the detailed Ackley, S.F., J.L. Bengtson, P. Boveng, M. Castellini, diet studies, and attributing some level of certainty K.L. Daly, S. Jacobs, G.L. Kooyman, J. Laake, to them, are necessary and challenging steps before L. Quetin, R. Ross, D.B. Siniff, B.S. Stewart, the available data can be incorporated into food- I. Stirling, J.J. Torres and P.K. Yochem. 2003. A web models. top-down, multidisciplinary study of the struc- ture and function of the pack-ice ecosystem in Concluding remarks the eastern Ross Sea, Antarctica. Polar Rec., The data reviewed here are critical initial 39: 219–230. blocks for building food-web models. With regard to abundance, the relatively recent APIS surveys Ainley, D.G. 1985. of birds and mammals provide the best regional-scale estimates of abun- in the Ross Sea. In: Siegfried, W.R., P.R. Condy dance possible with existing methods. Past trends and R.M. Laws (Eds). Antarctic Nutrient Cy- in abundance cannot be estimated with any confi- cles and Food Webs. Springer-Verlag, Berlin: dence because of biases and differences in earlier 498–515. methodology. Repeating the APIS surveys in the future may allow estimation of future trends, but Bengtson, J.L. 1982. Reproductive of the power to assess change would not be high, crab­eater and leopard seals along the Antarctic only large changes might be detected, and future Peninsula. Antarct. J. US, 17: p. 185. surveys on the scale of APIS would be expensive. Knowledge of three-dimensional foraging habitat Bengtson, J.L. and B.S. Stewart. 1992. Diving and use is currently sufficient for characterisation at a haul-out behavior of crabeater seals in the Wed- very broad level (e.g. ice-dependent/independent, dell Sea, Antarctica, during March 1986. Polar shelf/slope, shallow/deep), which may be sufficient for food-web modelling over large scales. Fur- Biol., 12: 635–644. ther knowledge of habitat use that would benefit food-web modelling is most likely to come from Bengtson, J.L. and B.S. Stewart. 1997. Diving pat- satellite telemetry work, especially on leopard and terns of a Ross seal (Ommatophoca rossii) near Ross seals, in regions and seasons where few data the eastern coast of the Antarctic peninsula. Po- currently exist. Diet studies are not yet sufficient lar Biol., 18: 214–218. to characterise temporal or regional variation to inform spatially explicit food-web models, and Bengtson, J.L. and M.F. Cameron. 2004. Seasonal this deficiency is a major constraint for food-web haul-out patterns of crabeater seals (Lobodon modelling. carcinophaga). Polar Biol., 27: 344–349.

Finally, food-web models are validated by or fit- Bengtson, J.L., R.D. Hill and S.E. Hill. 1993. Using ted to estimates of food consumption by the various satellite telemetry to study the ecology and be- ecosystem components. While abundance and diet havior of Antarctic seals. Kor. J. Polar Res., 4: are primary inputs to estimating food consumption, 109–115. energetics models are needed to synthesise these with additional physiological and life-history pa- Bengtson, J.L., J.L. Laake, P. Boveng, M.F. rameters. A priority for future work should be the development of energetics models for ice-breeding Cameron and B.S. Stewart. 2011. Distribution seals so that the data reviewed here can be used to and abundance of Weddell, Ross, crabeater, and estimate food consumption and ultimately used to leopard seals in the Amundsen and Ross Seas, facilitate the building of food-web models. Antarctica. Deep-Sea Res., 58: 1261–1276.

60 Review of abundance, habitat use and diet data of ice-breeding seals

Bester, M.N. and J.-P. Roux. 1986. Summer pres- Casaux, R., A. Baroni and A. Carlini. 1997. The ence of leopard seals Hydrurga leptonyx at the diet of the Weddell seal Leptonychotes wed- Courbet Peninsula, Iles Kerguelen. S. Afr. J. delli at Harmony Point, South Shetland Islands. Antarct. Res., 16: 29–32. Polar Biol., 18: 371–375.

Bester, M.N. and P.N. Odendaal. 2000. Abundance Casaux, R., A. Baroni and A. Ramon. 2006. The and distribution of Antarctic pack ice seals in diet of the Weddell Seal Leptonychotes wed- the Weddell Sea. In: Davison, W., C. Howard- dellii at the Danco Coast, Antarctic Peninsula. Williams and P. Broady (Eds). Antarctic Eco- Polar Biol., 29: 257–262. systems: Models for Wider Ecological Under- standing. Caxton Press, Christchurch: 51–55. Casaux, R., A. Baroni, A. Ramón, A. Carlini, M. Bertolin and C.Y. DiPrinzio. 2009. Diet Bester, M.N., A.W. Erickson and W.H. Ferguson. of the leopard seal Hydrurga leptonyx at the 1995. Seasonal change in the distribution and Danco Coast, Antarctic Peninsula. Polar Biol., density of seals in the pack ice off Princess 32: 307–310. Martha Coast, Antarctica. Ant. Sci., 7: 357–364. Clarke, M.R. and M. McLeod. 1982. Bester, M.N., J.W.H. Ferguson and F.C. Jonker. remains in the stomachs of eight Weddell seals. 2002. Population densities of pack ice seals Br. Antarct. Surv. Sci. Rep., 57: 33–40. in the Lasarev Sea, Antarctica. Ant. Sci., 14: 123–127. Condy, P.R. 1976. Results of the third seal survey in the King Haakon VII Sea, Antarctica. S. Afr. Blix, A.S. and E.S. Nordøy. 2007. Ross seal (Om- J. Antarct. Res., 6: 2–8. matophoca rossii) annual distribution, div- ing behaviour, breeding and moulting, off Condy, P.R. 1977. Results of the fourth seal survey Queen Maud Land, Antarctica. Polar Biol., 30: in the King Haakon VII Sea, Antarctica. S. Afr. 1449–1458. J. Antarct. Res., 7: 10–13. Borsa, P. 1990. Seasonal occurrence of the leopard Costa, D.P. and D.E. Crocker. 1996. Marine Mam- seal (Hydrurga leptonyx) in the Kerguelen Is- mals of the Southern Ocean. Foundations for lands. Can. J. Zool., 68: 405–408. Ecological Research West of the Antarctic Pen- Burns, J.M., S.J. Trumble, M.A. Castellini and insula. Antarct. Res. Ser., 70: 287–301. J.W. Testa. 1998. The diet of Weddell seals in Davis, R.W., M. Castellini, M. Horning, M. Davis McMurdo Sound, Antarctica as determined from scat collections and stable isotope analy- and G. Kooyman. 1982. Winter ecology of sis. Polar Biol., 19: 272–282. Weddell seals at White Island. Antarct. J. US, 17: 183–184. Burns, J.M., M.A. Castellini and J.W. Testa. 1999. Movements and diving behavior of weaned Davis, R.W., L.A. Fuiman, T.M. Williams, Weddell seal (Leptonychotes weddelli) pups. M. Horning and W. Hagey. 2003. Classification Polar Biol., 21: 23–36. of Weddell seal dives based on 3-dimensional movements and video-recorded observations. Burns, J.M., D.P. Costa, M.A. Fedak, M.A. Hindell, Mar. Ecol. Prog. Ser., 263: 109–122. C.J.A. Bradshaw, N.J. Gales, B. McDonald, S.J. Trumble and D.E. Crocker. 2004. Winter habi- Dearborn, J.H. 1965. Food of Weddell seals at tat use and foraging behavior of crabeater seals McMurdo Sound, Antarctica. J. Mammal., 46: along the Western Antarctic Peninsula. Deep- 37–43. Sea Res. II, 51: 2279–2303. Dzhamanov, G.K. 1990. Some aspects of the biol- Burns, J.M., M.A. Hindell, C.J.A. Bradshaw and ogy and distribution of ice-inhabiting seals near D.P. Costa. 2008. Fine-scale habitat selection of the Balleny Islands and east of the d’Urville crabeater seals as determined by diving behav- Sea in 1986–87. Morskie Mlekopitayushchie, ior. Deep-Sea Res. II, 55: 500–514. 112–129.

61 Southwell et al.

Edwards, E.W.J., J. Forcada and G.T. Crossin. Erickson, A.W., L.J. Bledsoe and M.B. Hanson. 2009. First documentation of leopard seal pre- 1989. Bootstrap correction for diurnal activity dation of duck. Polar cycle in census data for Antarctic seals. Mar. Biol., 33: 403–405. Mammal Sci., 5: 29–56.

Eklund, C.R. 1964. Population studies of Antarc- Flores, H., C. Haas, J.A. van Franeker and tic seals and birds. In: Carrick, R., M. Holdgate E. Meesters. 2008. Density of pack-ice seals and J. Prevost (Eds). Biologie Antarctique. Her- and penguins in the western Weddell Sea in re- mann, Paris: 415–419. lation to ice thickness and ocean depth. Deep- Sea Res. II, 55: 1068–1074. Eklund, C.R. and E.L. Atwood. 1962. A popula- tion study of Antarctic seals. J. Mammal., 43: Forcada, J. and P.N. Trathan. 2008. Abundance es- 229–238. timates for crabeater, Weddell and leopard seals at the Antarctic Peninsula and in the western Erickson, A.W. 1984. Aerial census of seals, Weddell Sea (90°–30°W, 60°–80°S). Document and penguins in the pack ice of the northwestern WG-EMM-PSW-08/6. CCAMLR, Hobart, Weddell Sea, November 1983. Antarct. J. US, Australia: 9 pp. 19: 121–124. Forcada, J., D. Malone, J.A. Royle and I.J. Stani- Erickson, A.W. and M.B. Hanson. 1990. Continen- land. 2009. Modelling by transient tal estimates and population trends of Antarc- leopard seals for an ecosystem-based manage- tic seals. In: Kerry, K.R. and G. Hempel (Eds). ment of Southern Ocean fisheries.Ecol. Model., Antarctic Ecosystems: Ecological Change 220: 1513–1521. and Conservation. Springer-Verlag, Berlin: 253–264. Fuiman, L.A., R.W. Davis and T.M. Williams. 2002. Behavior of midwater under the Erickson, A.W., D.R. Cline and R.J. Hoffman. Antarctic ice: observations by a predator. Mar. 1969. Population study of seals in the Weddell Biol., 140: 815–822. Sea. Antarct. J. US, 4: 99–100. Fuiman, L.A., K.M. Madden, T.M. Williams and Erickson, A.W., R.J. Hofman, R.J. Oehlenschlager, R.W. Davis. 2007. Structure of foraging dives J. Otis and D. Kuehn. 1971. Seal population by Weddell seals at an offshore isolated hole in studies in the Ross Sea. Antarct. J. US, 6: 98–99. the Antarctic fast-ice environment. Deep-Sea Res. II, 54: 270–289. Erickson, J.R., J.R. Gilbert, G.A. Petrides, R.J. Oehlenschlager, A.A. Sinha and J. Otis. 1972. Gales, N.J., W.R. Fraser, D.P. Costa and C. South- Populations of seals, whales, and birds in the well. 2004. Do crabeater seals forage coopera- Bellinghausen and Amundsen Seas. Antarct. J. tively? Deep-Sea Res. II, 51: 2305–2310. US, 6: 98–99. Gilbert, J.R. and A.W. Erickson. 1977. Distribution Erickson, A.W., J.R. Gilbert and J. Otis. 1973. Cen- and abundance of seals in the pack ice of the sus of pelagic seals off the Oates and George V Pacific sector of the Southern Ocean. In: Llano, coasts, Antarctica. Antarct. J. US, 8: 191–194. L. (Ed.). Adaptations within Antarctic Ecosys- tems. Smithsonian Institute, Washington DC: Erickson, A.W., R.N. Denney, J.J. Brueggeman, 703–740. A.A. Sinha, M.M. Bryden and J. Otis. 1974. Seal and bird populations off Adelie, Claire, Green, K. and R. Williams. 1986. Observations on and Banzare coasts. Antarct. J. US, 9: 292–296. food remains in faeces of elephant, leopard and crabeater seals. Polar Biol., 6: 43–45. Erickson, A.W., M.B. Hanson and D.M. Kehoe. 1983. Population densities of seals and whales Green, K. and H.R. Burton. 1987. Seasonal and observed during the 1983 circumnavigation of geographical variation in the food of Weddell Antarctica by the USCGC Polar Star. Antarct. seals, Leptonychotes weddellii, in Antarctica. J. US, 18: 163–166. Aust. Wildl. Res., 14: 475–489.

62 Review of abundance, habitat use and diet data of ice-breeding seals

Green, K., H.R. Burton and D.J. Watts. 1995. Stud- Kooyman, G.L., D. Croll, S. Stone and S. Smith. ies of the Weddell seal in the Vestfold Hills, 1990. Emperor colony at Cape Wash- East Antarctica. ANARE Res. Notes, 93: 64 pp. ington, Antarctica. Polar Rec., 26: 103–108.

Gwynn, A.M. 1953. The status of the leopard seal Kuhn, C.E., B.I. McDonald, S.A. Shaffer, J. Barnes, at Heard Island and Macquarie Island, 1948– D.E. Crocker, J. Burns and D.P. Costa. 2006. 1950. ANARE Research Expedition Interim Re- Diving physiology and winter foraging behavior of a juvenile leopard seal (Hydrurga leptonyx). port No. 3. Antarctic Division, Department of Polar Biol., 29: 303–307. External Affairs, Melbourne: 33 pp. Lake, S., H. Burton and J. van den Hoff. 2003. Re- Hall-Apsland, S.A. and T.L. Rogers. 2004. Sum- gional, temporal and fine-scale spatial variation mer diet of leopard seals (Hydrurga leptonyx) in Weddell seal diet at four coastal locations in Prydz Bay, Eastern Antarctica. Polar Biol., in east Antarctica. Mar. Ecol. Prog. Ser., 254: 27: 729–734. 293–305.

Harcourt, R.G., M.A. Hindell, D.G. Bell and J.R. Lake, S.E., H. Burton and S. Wotherspoon. 2006. Waas. 2000. Three-dimensional dive profiles Movements of adult female Weddell seals dur- of free-ranging Weddell seals. Polar Biol., 23: ing the winter months. Polar Biol., 29: 270–279. 479–487. Laws, R.M. 1953. The seals of the Falkland Islands Hindell, M.A., R. Harcourt, J.R. Waas and and dependencies. Oryx, 2: 87–97. D. Thompson. 2002. Fine-scale three-dimen- Laws, R.M. 1984. Seals. In: Laws, R.M. (Ed.). Ant- sional spatial use by diving, lactating female arctic Ecology. Vol. 2. Academic Press, Lon- Weddell seals Leptonychotes weddellii. Mar. don: 621–715. Ecol. Prog. Ser., 242: 275–284. Lipinski, M. and M. Woyciechowski. 1981. Hofmann E.E., J.M. Klinck, D.P. Costa, K.L. Daly, Cephalopods in the food of Weddell seals J.J. Torres and W.R. Fraser. 2002. U.S. Southern from the Admiralty Bay (King George Island, Ocean Global Ecosystems Dynamics Program. South Shetland Islands). Polish Polar Res.. 2: Oceanography, 15: 64–74. 163–167.

Hunt, J.F. 1973. Observations on the seals of Ele- Lowry, L.F., J.W. Testa and W. Calvert. 1988. Notes phant Island, South Shetland Islands, 1970–71. on winter feeding of crabeater and leopard seals Br. Antarct. Surv. Sci. Rep., 36: 99–104. near the Antarctic Peninsula. Polar Biol., 8: 475–478. Jessopp, M.J., J. Forcada, K. Reid, P.N. Trathan, and E.J. Murphy. 2004. Winter dispersal of McMahon, C., M. Hindell, T. Dorr and R.A. leopard seals (Hydrurga leptonix) environmen- Massom. 2002. Winter distribution and abun- dance of crabeater seals off George V Land, tal factors influencing demographics and - sea East Antarctica. Antarct. Sci., 14: 128–133. sonal abundance. J. Zool., 263: 251–258. Mitani, Y., K. Sato, S. Ito, M.F. Cameron, D.B. King, J.E. 1961. The feeding mechanism and jaws Siniff and Y. Naito. 2003. A method for recon- of the crabeater seal. Mammalia, 25: 462–466. structing three-dimensional dive profiles of marine mammals using geomagnetic intensity King, J.E. 1969. Some aspects of the anatomy of data: results from two lactating Weddell seals. the Ross seal Ommatophoca rossii (Pinnipedia: Polar Biol., 26: 311–317. Phocidae). Br. Antarct. Surv. Sci. Rep., 63: 1–54. Mitani, Y., Y. Watanabe, K. Sato, M.F. Cameron Klages, N.T.W. and V.G. Cockcroft. 1990. Feed- and Y. Naito. 2004. 3D diving behavior of Wed- ing behaviour of a captive crabeater seal. Polar dell seals with respect to prey accessibility and Biol., 10: 403–404. abundance. Mar. Ecol. Prog. Ser., 281: 275–281.

63 Southwell et al.

Nordøy, E.S. and A.S. Blix. 2009. Movements and Rau, G.H., D.G. Ainley, J.L. Bengtson, J.J. Torres dive behaviour of two leopard seals (Hydrurga and T.L. Hopkins. 1992. 15N/14N and 13C/12C leptonix) off Queen Maud Land, Antarctica. in Weddell Sea birds, seals, and fish: implica- Polar Biol., 32: 263–270. tions for diet and trophic structure. Mar. Ecol. Prog. Ser., 84: 1–8. Nordøy, E.S., L. Folkow and A.S. Blix. 1995. Dis- tribution and diving behaviour of crabeater­ Rogers, T. and M.M. Bryden. 1995. Predation of seals (Lobodon carcinophagus) off Queen Adelie penguins (Pygoscelis adeliae) by leop- Maud Land. Polar Biol., 15: 261–268. ard seals (Hydrurga leptonyx) in Prydz Bay, Antarctica. Can. J. Zool., 73: 1001–1004. Øritsland, T. 1977. Food consumption of seals in the Antarctic pack ice. In: Llano, G.A. (Ed.). Adap- Rogers, T.L., C.J. Hogg and A. Irvine. 2005. Spatial tations Within Antarctic Ecosystems. Smithso- movement of adult leopard seals (Hydrurga lep- nian Institute, Washington DC: 749–768. tonyx) in Prydz Bay, Eastern Antarctica. Polar Biol., 28: 456–463. Plötz, J. 1986. Summer diet of Weddell seals (Lep- tonychotes weddelli) in the eastern and southern Sato, K., Y. Mitani, M.F. Cameron, D.B. Siniff, Weddell Sea, Antarctica. Polar Biol., 6: 97–102. Y. Watanabe, and Y. Naito. 2002. Deep forag- ing dives in relation to the energy depletion of Plötz, J., W. Ekau and P.J.H. Reijnders. 1991a. Weddell seal (Leptonychotes weddellii) mothers Diet of Weddell seals Leptonychotes weddellii during lactation. Polar Biol., 25: 696–702. at Vestkapp, eastern Weddell Sea (Antarctica), in relation to local food supply. Mar. Mammal Scheffer, V.B. 1958. Seals, Sea and Wal- Sci., 7: 136–144. ruses: A Review of the Pinnipedia. Stanford University Press, California: 179 pp. Plötz, J. , H. Weidel and M. Bersch. 1991b.Winter aggregations of marine mammals and birds in Schreer, J.F. and J.W. Testa. 1995. Statistical classi- the north-eastern Weddell Sea pack ice, Polar fication of diving behavior. Mar. Mammal Sci., Biol., 11: 305–309. 11 (1): 85–93.

Plötz, J., H. Bornemann, R. Knust, A. Schroder and Schreer, J.F. and J.W. Testa. 1996. Classification M.N. Bester. 2001. Foraging behaviour of Wed- of Weddell seal diving behavior. Mar. Mammal dell seals, and its ecological implications. Polar Sci., 12: 227–250. Biol., 24: 901–909. Siniff, D.B. 1991. An overview of the ecology of Plötz, J., D. Steinhage and H. Bornemann. Antarctic seals. Amer. Zool., 31: 143–149. 2011a. Seal census raw data during campaign EMAGE-I, doi:10.1594/PANGAEA.760097. Siniff, D.B. and S. Stone. 1985. The role of the leopard seal in the tropho-dynamics of the Ant- Plötz, J., D. Steinhage and H. Bornemann. arctic . In: Siegfried, W.R., 2011b. Seal census raw data during campaign P.R. Condy and R.M. Laws (Eds). Antarctic Nu- EMAGE-II, doi:10.1594/PANGAEA.760098. trient Cycles and Food Webs. Springer-Verlag: 555–559. Plötz, J., D. Steinhage and H. Bornemann. 2011c. Seal census raw data during campaign Siniff, D.B., D.R. Cline and A.W. Erickson. 1970. EMAGE-III, doi:10.1594/PANGAEA.760099. Population densities of seals in the Weddell Sea, Antarctica, in 1968. In: Holdgate, M.W. Plötz, J., D. Steinhage and H. Bornemann. (Ed.). Antarctic Ecology. Academic Press, Lon- 2011d. Seal census raw data during campaign don: 377–394. EMAGE-IV, doi:10.1594/PANGAEA.760100. Skinner, J.D. and N.T.W. Klages. 1994. On some Plötz, J., D. Steinhage and H. Bornemann. aspects of the biology of the Ross seal Om- 2011e. Seal census raw data during campaign matophoca rossii from King Haakon VII Sea, EMAGE-V, doi:10.1594/PANGAEA.760101. Antarctica. Polar Biol., 14: 467–472.

64 Review of abundance, habitat use and diet data of ice-breeding seals

Southwell, C. 2003. Haul-out behaviour of two (Leptonychotes weddelli) in the southwest- Ross seals off eastern Antarctica. Antarct. Sci., ern Ross Sea, Antarctica. Can. J. Zool., 72: 15: 257–258. 1700–1710.

Southwell, C. 2005. Optimising the timing of visu- Testa, J.W., S.E.B. Hill and D.B. Siniff. 1989. al surveys of crabeater seal abundance: haulout Diving behavior and maternal investment in behaviour as a consideration. Wildl. Res., 32: Weddell seals (Leptonychotes weddellii). Mar. 333–338. Mammal Sci., 5: 399–405.

Southwell, C.J., K.R. Kerry and P.H. Ensor. 2005. van Franeker, J.A. 1992. Top predators as indica- Predicting the distribution of crabeater seals off tors for ecosystem events in the confluence zone east Antarctica during the breeding season. Mar. and marginal ice zone of the Weddell and Sco- Ecol. Prog. Ser., 299: 297–309. tia Seas, Antarctica, November 1988 to January 1989 (EPOS Leg 2). Polar Biol., 12: 93–102. Southwell, C., C.G.M. Paxton, D. Borchers, P. Boveng, E.S. Nordøy and A.S. Blix. 2008a. Walker, T.R., I.L. Boyd, D.J. McCafferty, N. Huin, Estimating population status under conditions R.I. Taylor, and K. Reid. 1998. Seasonal occur- rence and diet of leopard seals (Hydrurga lep- of uncertainty: the Ross seal in east Antarctica. tonyx) at Bird Island, South Georgia. Antarct. Antarct. Sci., 20: 123–133. Sci., 10: 75–81. Southwell, C., C.G.M. Paxton, D.L. Borchers, Wall, S.M., C.J.A. Bradshaw, C.J. Southwell, N.J. P. Boveng and W.K. de la Mare. 2008b. Taking Gales and M.A. Hindell. 2007. Crabeater seal account of dependent species in management diving behaviour in eastern Antarctica. Mar. of the Southern Ocean krill : estimating Ecol. Prog. Ser., 337: 265–277. crabeater seal abundance off east Antarctica. J. Appl. Ecol., 45: 622–631. Watanabe, Y., Y. Mitani, K. Sato, M.F. Cameron and Y. Naito. 2003. Dive depths of Weddell Southwell, C., C.G.M. Paxton, T. Rogers, D.L. seals in relation to vertical prey distribution as Borchers, P. Boveng and W.K. de la Mare. estimated by image data. Mar. Ecol. Prog. Ser., 2008c. Uncommon or cryptic? Challenges in 252: 283–288. estimating leopard seal abundance by conven- tional but state-of-the-art methods. Deep-Sea Weiner, J., M. Woyciechowski and J. Zieliński. Res. I, 55: 519–531. 1981. An attempt to determine the digestibility of natural food in Antarctic seals using tracer Stone, S. and T. Meier. 1981. Summer leopard seal method: a preliminary study. Pol. Polar Res., ecology along the Antarctic Peninsula. Antarct. 2: 153–163. J. US, 16: 151–152. Wilson, V.J. 1975. A second survey of seals in the Testa, J.W. 1994. Over-winter movements and King Haakon VII Sea, Antarctica. S. Afr. J. Ant- diving behaviour of female Weddell seals arct. Res., 5: 31–36.

65 Southwell et al. 1 2 3 4 5 5 6 6 5 5 6 5 5 4 6 5 8 9 10 11 12 6, 7 6, 7 38400 45600 49400 17200 69200 64900 32 000 331000 799000 302000 800000 800000 ------Gilbert and Erickson (1977); 7 (77000–576 000) (144000–759 000)* providedpublication. in 8000 7 300 300 7 t because sighting surveys were too late to late too were surveys sighting because t 61400 48600 55200 28700 68000 23200 40 000 15000 13200 296500 152500 200000–500 000 Laws (1984); 6 ------Bester (2000) Odendaal and (3 500–65000) (3 700–14500) (3 700–23100) 12 not stated or estimate not estimate or stated not 5100 23700 37500 18900 17500 64000 22600 55900 51 400 10 000 220000 220000–440 000 131400 ------those estimates fromthose estimates Ericksonsurveys identified in EricksonHanson and (11700–43 700)* Erickson and Hanson (1990); (27700–187 500) 5 632700 806400 745 900 900 745 938900 203700 472400 946400 798000 772000 3564 000** - 1 1931400 7 000000 1 2931000 3187 000 1736 000 1686 000 1000 000 Southwell al. et (2008a,2008b, 2008c); 15000 000 ≥ 11 ≥

er and leopard seal estimates derived from this survey effor survey this from derived estimates seal leopard and er Erickson(1971); et al. 4 (726400–1 396700) 2000 000–5 000 000 20 000–50000 100000–300 000 1 754 000–4 748 000) 4962 000–8 081 000 (1000–2219 472000) eal) or didn’t cover all fast-ice (Weddell seal) (Weddell fast-ice all cover didn’t or eal) Estimates are rounded to the nearest 100. - Information rounded Estimatesare the- 100.nearest to ear(s) ear(s) Crabeater Ross Leopard Weddell Reference the population the size of seals. Only ice-breeding - - Forcada and Trathan (2008); and Forcada Trathan 10 er estimates to be positively biased. positively be to estimates er Eklundand Atwood (1962); 3 Bengtson (2011);al. et 9 Scheffer (1958); (1958); Scheffer 2 FalklandIs. Dep. 60°W–20°W 1968/69 and 1969/70 8246 800 and10 597 500 2500 and10 200 38 300 and 82400 211800 and46 900 170°E–160°W 1976/77–1979/80 Circumpolar Circumpolar Circumpolar 60°W–20°W 1956/57 20°W–20°E 20°W–10°E 1968/69 and 1969/70 20°E–70°E 1982/83 2241 300 and2 780 900 20°E–90°E 1968/69–1972/73 90°E–160°E 1968/69–1972/73 80°E–140°E 1982/83 145°E–170°E 1972/73–1973/74 160°E–130°W 1968/69–1972/73 1972/73 135°W–80°W 1971/72–1972/73 130°W–60°W 1971/72 Circumpolar 1971/72 Circumpolar 1968/69–1972/73 Circumpolar 1968/69–1982/83 1968/69–1969/70 50000–75000 000 000 90°W–30°W 64°E–150°E 1998/99 26°W–7°W 1999/00 1997/98 (1990) as the most reliable are included. are reliable most the as (1990) Laws (1953); (1985); Ainley Survey Survey Region y Survey construct reliable correction for haul-out (Ross s (Ross haul-out for correction reliable construct 8 ** Preliminaryauthorsanalysis: consid * crabeat for than range geographic smaller a cover estimates These 1 Table 1: 1: Table of estimates circumpolar and Regional surveys/ Early estimates Erickson surveys Sea Ross surveys APIS surveys 150°E–100°W 1999/00

66 Review of abundance, habitat use and diet data of ice-breeding seals r no 1 10 11 12 2, 3 6, 7 3, 8 3, 9 3, 4, 5 Erickson 6 References References Bengtson et al. (2011); (2011); al. et Bengtson 11 reeding seals. Methods fo reeding b Methodfor estimating density density estimating Erickson et al. (1971), (1971), al. et Erickson 5 Ainley (1985); No ST/O No ST/O 10 observers observers Independent Independent from observational data; DL – from data logger; N – N data logger; – from DL observational data; from Erickson et al. (1969);Erickson al. et 4 (m) 300 rip transect; LT – line transect; transect;linerip LT MRLT – mark-recapture Strip half-width half-width Strip Erickson et al. (1983); (1983); al. et Erickson 9 (local hr) (local Time of day day of Time for haul-out probability; O – probability; for haul-out Erickson and HansonErickson(1990);and 3 Erickson et al. (1974); (1974); al. et Erickson 8 (month) (month) Dec–Jan 6–21 Unlimited No ST/N Jan–Mar 4–18 Unlimited No LT/DL Feb–Mar 00–24 200 Siniff et al. (1970); al. et Siniff 2 1968/69 1971/72 1973/74 Jan–Feb - Jan–Mar Daylight 1982/83 Jan–Feb - 201 232 3–23 Jan–Mar No ST/O - 1999/00 232 No No ST/O ST/O No Dec–Jan 8–18 ST/O Unlimited Yes MRLT/DL Gilbert and Erickson(1977); 7 estimating on-ice density: PE – personal experience; ST – st ST – experience; personal PE – density: on-ice estimating on-ice density of correcting transect/method correction. - Information not stated in publication. publication. in stated not - Information correction. Survey Survey year(s) Survey of year Time Southwell (2008a,al. et 2008b, 2008c) Eklund and Atwood (1962); (1962); Atwood and Eklund 12 et al. (1972); 1 Table 2: Table of shipboardsurveys estimationfor density inice- relatingthe details of to sampled Surveystrips Earlysurveys ‘Erickson’surveys 1967/68 1956/57 surveys RossSea APISsurveys 1976/77–1979/80 Dec–Jan 1999/00 0–23

67 Southwell et al. 1 1, 2 1 1, 3 4 5 6 7 8 9 10 11 12 Bengtson Bengtson 7 References References Plötz et al. (pers. (pers. al. et Plötz 12 re line transect/method transect/method line re Information not stated. not Information LT/DL / Methodfor Erickson (1984); 6 estimating density density estimating y type:– aerial photographic AP Blix (pers. comm.); 11 No AP/ST/- No SS/LT/DL No Yes SS observers observers Independent Independent Erickson et al. (1983); (1983); al. et Erickson 5 - (m) Unlimited Unlimited SS/MRLT/DL Yes Strip half-width half-width Strip Bester (2000); Odendaal and transect; LT – line transect; MRLT – mark-recaptu MRLT – – line transect; LT transect; 10 - (m) Erickson (1974); al. et 4 Altitude Speed Speed (knots) - - 350 600 - Erickson et al. (1973); 3 (local hr) Time of day day of Time Southwell (2008a,al. et 2008b,2008c); 9 hod for estimating on-ice density: ST – strip – ST density: on-ice hod for estimating (month) (month) Erickson et al. (1972); (1972); al. et Erickson 2 1971/72 Jan–Feb - 1971/72 Jan 1972/73 - 152 Jan 1973/74 Jan–Feb 463 - 11–14 - 152 - 1982/83 Jan–Feb 10–20 - - 350 463 1983/84 No - 76 SS/ST/O Nov 600 - 8–19 - 463 No 91 SS/ST/O 463 No 1998/99 Jan AP/ST/O - No 1999/00 Dec–Jan SS/ST/N No SS/ST/N 9–15 1997/98 Jan–Mar 11–15 90130 60 61 No 1996/97 1000 SS/ST/N 312 1996/01 - Dec–Jan 10–18240 152 Yes SS/MRLT/DL No - 35 SS/ST/N 10091 No AP/ST/DL Forcada and Trathan (2008); (2008); Trathan and Forcada 8 survey; SS – sighting survey/met – sighting survey; SS of correcting on-ice densityofon-icecorrecting for haul-out probability:observational– from O data from logger; –no– N correction. DL data; - Survey Survey year(s) Survey year of Time Gilbert and Erickson (1977); comm., 2011a to 2011e) 2011e) to 2011a comm., et al. (2011);al. et 1 Table 3: 3: Table Surve seals. of ice-breeding surveys aerial for strips sampled in density of estimation the to relating details Survey ‘Erickson’surveys 1970/71 Nov APISsurveys 1999/00 Jan–Mar 7–18 90 91 519

68 Review of abundance, habitat use and diet data of ice-breeding seals Davis et Davis 21 Kuhn et al. (2006); Nordøy et al. (1995); al. et Nordøy 10 5 Schreer and Testa (1995); and Testa Schreer 15 1, 2, 3, 4, 5 6 7, 8 9 10, 11 12 13 20,17, 18, 19, 15, 16, 14, 13, 23, 24, 25 21, 22, Fuiman et al. (2002); Fuiman 20 Fuiman et al. (2007). al. et Fuiman 25 Southwell (2005); Southwell 9 Burns et al. (2008); al. et Burns 4 Testa et al. (1989); al. et Testa 14 Hindell et al. (2002); Hindell ll seals in three sectors of Antarctica inof autumn, inAntarctica summer, three sectors seals ll 19 Mitani et al. (2004); al. et Mitani 24 Burns et al. (2004); al. et Burns 3 Blixand Nordøy (2007); 8 Sato et al. (2002); 13 Harcourt et al. (2000); Mitani et al. (2003); al. et Mitani 18 23 Hofmann et al. (2002); al. et Hofmann 2 Plötz et al. (2001); 12 BengtsonStewart and (1997); 7 Burns et al. (1999); 30°E–150°E 30°E–150°E 30°E–150°E 30°E–150°E 30°E–150°E 150°E–70°W 150°E–70°W 150°E–70°W 150°E–70°W 150°E–70°W 150°E–70°W 17 Watanabe et al. (2003); al. et Watanabe 22 spring and winter. The grey bars represent sectors and seasons where studies occurred; light grey represents diving diving represents grey light occurred; studies where seasons and sectors represent bars grey The winter. and spring depths of 0–100 m, dark grey > 100 m. m. 100 > grey dark m, 0–100 of depths Nordøy and Blix (2009); and Nordøy Testa (1994); Bengtson and Stewart (1992); Wall et al. (2007); Species Species Sector Autumn Summer Winter Spring References al. (2003);al. 6 11 16 1 Table 4: 4: Table Wedde and leopard Ross, crabeater, of studies Diving Crabeater 70°W–30°E Ross 70°W–30°E Leopard 70°W–30°E Weddell 70°W–30°E

69 Southwell et al.

Table 5: Proportion of fish, cephalopod, and (for the leopard seal) bird and seal prey found in the diet of ice-breeding seals in three sectors of Antarctica in summer, autumn, spring and winter obtained from analyses of scat (Sc), stomach contents (Sa), ratios of stable isotope in tissue (Is) and dive behaviour (D). Note × denotes the presence of a prey item where no proportion was given.

Species Sector Prey item Summer Autumn Winter Spring References Crabeater 70°W–30°E Fish × 3 3 1, 2, 3, 4, 5, 6 Cephalopods 2 2 Crustaceans × × 94 94 30°E–150°E Fish × × 7 Cephalopods Crustaceans 150°E–70°W Fish 8 Cephalopods Crustaceans × Ross 70°W–30°E Fish × × 22 22 1, 9, 10, 11 Cephalopods × × 64 64 Crustaceans 9 9 30°E–150°E Fish Cephalopods Crustaceans 150°E–70°W Fish Cephalopods Crustaceans Leopard 70°W–30°E Fish 3 3 13 53 1, 3, 12, 13, 14, 15, Cephalopods 1 1 1–11 11 16, 17, 18 Crustaceans 83 83 37 1 Birds 13 13–46 35 35 Seals × 53 53 × 30°E–150°E Fish 34 34 × 7, 19, 20 Cephalopods Crustaceans 18 18 × Birds 90 90 Seals 13 13 150°E–70°W Fish 8, 21 Cephalopods Crustaceans × × Birds × × Seals Weddell 70°W–30°E Fish 33–94 94 53 53–96 22, 23, 24, 25, 26, 27, Cephalopods 6–66 6 11 4–11 28 Crustaceans 1 × 1 1 30°E–150°E Fish 16–77 16–77 16–77 16–77 29, 30 Cephalopods 3–82 3–82 3–82 3–82 Crustaceans 1–20 1–20 1–20 1–20 150°E–70°W Fish 62–97 62–99 62–97 62–97 29, 31, 32, 33, 34 Cephalopods 1–4 1–4 1–4 1–4 Crustaceans × × × ×

1 Øritsland (1977) (St, Sc); 2 Bengtson (1982) (St); 3 Lowry et al. (1988) (St); 4 Burns et al. (2004) (Sc, D); 5 Burns et al. (2008) (Sc, D); 6 Nordøy et al. (1995) (D); 7 Green and Williams (1986) (Sc); 8 Dzhamanov (1990) (St); 9 Bengtson and Stewart (1997) (D); 10 Skinner and Klages (1994) (St); 11 Blix and Nordøy (2007) (D); 12 Hunt (1973) (O); 13 Stone and Meier (1981) (St); 14 Siniff and Stone (1985) (St); 15 Walker et al. (1998) (Sc); 16 Kuhn et al. (2006) (D); 17 Casaux et al. (2009) (Sc); 18 Nordøy and Blix (2009) (D); 19 Bester and Roux (1986) (O); 20 Hall-Apsland and Rogers (2004) (Sc); 21 Kooyman et al. (1990) (O); 22 Weiner et al. (1981) (St); 23 Lipinski and Woyciechowski (1981) (St); 24 Clarke and McLeod (1982) (St); 25 Plötz (1986) (St); 26 Casaux et al. (1997) (Sc); 27 Casaux et al. (2006) (Sc); 28 Plötz et al. (1991a) (St); 29 Green and Burton (1987) (Sc); 30 Lake et al. (2003) (Sc); 31 Dearborn (1965) (St); 32 Davis et al. (1982) (St); 33 Testa (1994) (Sc); 34 Burns et al. (1998) (Sc, Is)

70 Review of abundance, habitat use and diet data of ice-breeding seals

Figure 1: Areas surveyed by Eklund and Atwood (1962). Some of the place names in the text are shown.

71 Southwell et al.

Figure 2: Transect locations (ship sighting transects: dash lines; aerial photographic transects: dash-dot lines; aerial sighting transects: bold lines) in relation to the ice edge at the time of surveys (not shown for Weddell Sea, light line elsewhere) for ‘Erickson’ surveys from 1967/68 to 1982/83. 1 Erickson et al. (1969), Siniff et al. (1970); 2 Gilbert and Erickson (1977); 3 Erickson et al. (1972), Gilbert and Erickson (1977); 4 Erickson et al. (1973), Gilbert and Erickson (1977); 5 Erickson et al. (1974); 6 Erickson et al. (1983).

72 Review of abundance, habitat use and diet data of ice-breeding seals

Figure 3: Transect locations in the Ross Sea for surveys by Ainley (1985).

73 Southwell et al.

Figure 4: Transect locations (ship sighting transects: dash lines; aerial photographic transects: dash-dot lines; aerial sighting transects: bold lines) for APIS surveys from 1996/97 to 2000/01. Ice edge at the time of survey from 60°E–150°E shown as a light line. 1 Bengtson et al. (2011); 2 Forcada and Trathan (2008); 3 Southwell et al. (2008a, 2008b, 2008c); 4 Bester and Odendaal (2000); 5 Blix (pers. comm.); Plötz (pers. comm.).

74