Diet Of Seals Research Articles

Changes in the cephalopod diet of southern elephant seal females at King George Island, during El Niño-La Niña events

Possible effects of ‘El Niño’ Southern Oscillation (ENSO) components ‘El Niño’ and ‘La Niña’ on populations of southern elephant seals, Mirounga leonina, were analysed. Changes in the cephalopod diet composition of moulting females at King George Island, Antarctic Peninsula were considered. The diet of female elephant seals sampled in 1991–1992 and 1992–1993 (El Niño years) were compared with those taken in 1995–1996 (La Niña year) at the same site and employing the same methodology. The squid Psychroteuthis glacialis constituted the main cephalopod prey of the seals. A reduction in the ‘Index of Biomass Ingested’ by female elephant seals (IBIF) of this prey species was observed in ‘El Niño’ years (1992, 1993) compared with the ‘La Niña’ year (1996). This reduction in biomass applied to all squid species in the seals' prey with the exception of Galiteuthis glacialis, which occurred in low numbers, but was more abundant during El Niño years than in the La Niña year.

Interactions between harbour seals, Phoca vitulina, and fisheries in complex coastal waters explored by combined Geographic Information System (GIS) and energetics modelling

A 1680 km 2 coastal archipelago area in Norway around Sandøy (62°N 6°E), with a resident population of approximately 750 harbour seals was modelled in a geographic information system (GIS). The proportions of different habitat types available to harbour seals for foraging were estimated. Empirical data on levels of activity and foraging of VHF radio-tracked harbour seals were used to parameterise an energetics simulation model based on activity, body size, and composition. The harbour-seal energy requirement was simulated for a period from 20 June to 31 August. The diet of seals in the area was established from otoliths in faecal samples. The daily food requirements of the 750 harbour seals averaged 3 t based on a diet of mainly Gadidae. A procedure to extrapolate from individual movements and foraging activities of radio-tracked seals to population-level habitat use of foraging seals was adopted. The habitat use of the population was then used to integrate the results of the energetics simulations into the GIS model. The distribution of fishing operations was included and the co-occurrence of fishing operations and seals was analysed. The largest potential for interaction between fisheries and harbour seals was a bottom-set gillnet fishery at 100–200-m depth just off the slope separating the archipelago and adjacent shelf waters. Seals were foraging on fish species targeted by this fishery and the entanglement of seals in this type of fishery was assumed to have an effect both on seal population growth rate and on gillnet fishing efficiency. An estimated total of 32.1 t of fish was removed by seal predation from the areas actually fished by bottom-set nets (117 km 2 ) during the 73 days simulation period. The corresponding figures for the areas fished by Danish seine (140 km 2 ) and shrimp trawl (153 km 2 ) were 20.4 and 40.6 t of fish, respectively. While seal predation of fish probably caused negative effects on gillnet and Danish seine catches the removal of benthic-feeding fishes may cause a positive effect on shrimp catches.

Foraging ecology of a generalist predator, the female New Zealand fur seal

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 227:11-24 (2002) - doi:10.3354/meps227011 Foraging ecology of a generalist predator, the female New Zealand fur seal Robert G. Harcourt1,2,*, Corey J. A. Bradshaw3, Kate Dickson1, Lloyd S. Davis1 1Department of Zoology, University of Otago, PO Box 56, Dunedin, New Zealand 2Marine Mammal Research Group, Graduate School of the Environment, Macquarie University, Sydney, New South Wales 2109, Australia 3Antarctic Wildlife Research Unit, School of Zoology, University of Tasmania, PO Box 252-05, Hobart, Tasmania 7001, Australia *E-mail: rharcour@ecosys.gse.mq.edu.au ABSTRACT: This study examined how diet, foraging location and diving behaviour of female New Zealand fur seals Arctocephalus forsteri at Otago Peninsula, New Zealand (45°52¹S, 170°44¹E), varied in relation to prey abundance among seasons in 1994 and 1995. Time-depth recorders measured the diving behaviour of 24 lactating female fur seals, during summer, autumn or winter of 1994 and summer and autumn of 1995. Foraging locations were obtained by deploying satellite transmitters in summer, autumn and winter of 1994 only. Estimated biomass of prey items was determined from 690 scats and 166 regurgitates collected over summer, autumn and winter of both years, and compared with abundance data from research trawls in the same area. Foraging trip duration increased during the cooler seasons. Female fur seals showed a clear bout structure in dive behaviour, with the relative proportion of 3 main bout types (Long, Shallow, Deep) varying with season. Time between bouts (IBI) and bout duration varied with season, suggesting that prey distribution and prey encounter rate also varied. Linear discriminant analysis of the dive and foraging trip characteristics of individual females demonstrated clear seasonal differences. Females foraged on or near the continental slope in summer and farther offshore in autumn. Satellite telemetry locations and diet suggest principally inshore foraging during winter. Fur seals ate predominantly arrow squid Nototodarus sloanii during summer and autumn of both years, although fish, particularly myctophids, were persistent in the diet. Arrow squid were less common in winter when diet was more varied, and an inshore, benthic fish, ahuru Auchenoceros punctatus was dominant. There was no relationship between the annual changes in abundance of major prey species as measured by research trawls and their occurrence in seal diet. Overall, changes in dive behaviour may reflect changes in prey selection as prey abundance and availability change among seasons. KEY WORDS: Fur seals · Diet · Dive behaviour · Dive bouts · Foraging trips · Satellite telemetry · Seasonal differences Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 227. Online publication date: February 13, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Antarctic fur seals foraging in the Polar Frontal Zone: inter-annual shifts in diet as shown from fecal and fatty acid analyses

We studied the dietary preferences of Antarctic fur seals Arctocephalus gazella from Cap Noir, Iles Kerguelen, foraging in the Antarctic Polar Frontal Zone (PFZ) in February of 1998, 1999 and 2000. Scats were collected and analyzed for remaining prey hard parts in each of the 3 years, and in 1999 and 2000, the fatty acid (FA) composition of fur seal milk samples was also examined for longer- term dietary preferences. Scat analyses revealed that seals foraged primarily on fish and some squid in all 3 years with 25 species of fish being taken during the study. Myctophid fish accounted for an aver- age of 94% by number of all fish consumed with 3 species, Gymnoscopelus nicholsi, G. piabilis and Electrona subaspera, forming the core diet. Inter-annual differences in dietary species composition were apparent, however, with the presence of the mackerel icefish Champsocephalus gunnari in 1998 and the myctophid Protomyctophum tenisoni in 1999 accounting primarily for the differences ob- served between years. While reconstituted prey biomass per scat was similar between years, scats from 1998 represented less energy per gram than those from 1999 and 2000. This study highlights the usefulness of using FA signature analysis to confirm longer-term shifts in dietary intake of fur seals us- ing milk samples. Polyunsaturated fatty acids (PUFAs) were significantly more prevalent in the 1999 milk samples, which were also lower in overall lipid content (43% vs 53%). G. nicholsi, a particularly oily fish, occurred in higher proportions in the diet in 2000, perhaps explaining the higher incidence of monounsaturated fatty acids (MUFAs) in this year and the generally higher lipid levels present in milk samples. The inter-annual variation in the diet of Antarctic fur seals confirmed by these 2 techniques lends support to the hypothesis that previously identified variations in oceanographic conditions surrounding Iles Kerguelen in 1998, 1999 and 2000 affect the availability of fur seal prey resources.

Sealworm (<i>Pseudoterranova decipiens</i>) dynamics in Sable Island grey seals (<i>Halichoerus grypus</i>): seasonal fluctuations and other changes in worm infections during the 1980s

The abundance of P. decipiens sampled from the stomachs of 553 grey seals (aged 0-48 years) collected during 14 field trips to Sable Island in 1983 and 1989 did not change significantly between years, even though the seal population has been increasing at over 12% annually and there has been a substantial decline in the fish biomass upon which they depend. The proportion of mature worms in the seals’ stomachs has decreased, however. Seal growth, expressed in terms of either age orlength, showed the strongest correlation with total worm abundance. These infections were not completely eliminated at any time during the year, but a seasonal pattern in worm abundance was apparent. Among the youngest seals an inverse relationship was demonstrated between the abundance of P. decipiens and another parasitic nematode, Contracaecum osculatum. Sexually mature P. decipiens were found in pups within 3 to 4 months of the commencement of independent feeding, and the abundance of P. decipiens progressively increased throughout the first year of life. Male pups contracted more worms than female pups of the same age. P. decipiens abundances in juvenile seals were primarily associated with seasonal pattern and age, with C. osculatum abundance still influencing the abundance of P. decipiens, but to a much lesser extent than seen with pups. Length of seals was the main predictor of total worm abundance in adult seals, with a seasonal pattern being next in order of importance. Age was also significant, possibly representing a component of growth not accounted for by length alone. No relationship between the abundances of P. decipiens and C. osculatum was apparent for adult seals. The seasonal pattern in total worm abundance of juvenile and adult seals was characterized by declines during the winter and mid-summer. We suggest these declines are due, respectively, to the breeding season fast and one or both of 1) a change in seal diet from primarily highly infected fish species to less infected ones, and 2) a partial fast during the annual moult. The proportion of mature worms increased during reductions in worm abundance throughout most of the year, but during the breeding fast both total abundance and the proportionmature declined.

Distribution and abundance of sealworm (<i>Pseudoterranova decipiens</i>) and other anisakid nematodes in fish and seals in the Gulf of St. Lawrence: potential importance of climatic conditions

Prevalence and abundance of sealworm (Pseudoterranova decipiens) and other anisakid nematodes were determined in a variety of fishes from the Gulf of St. Lawrence in 1990 and 1992. Sealworm abundance and prevalence were also determined in three species of seals in the Gulf between 1988 and 1992. Atlantic cod (Gadus morhua) and shorthorn (Myoxocephalus scorpius) and longhorn sculpin (M. octodecemspinosus) were the fishes most heavily infected with sealworm. Grey seals(Halichoerus grypus) proved to be the most important definitive hosts for sealworm in the Gulf. Abundance of sealworm increased, whereas that of Anisakis simplex and contracaecine nematodes decreased, from north to south in the Gulf. Abundance of sealworm increased compared to earlier surveys in most areas of the Gulf, but decreased in both cod and grey seals during the course of this study. In contrast, abundance of Contracaecum osculatum and Phocascaris spp. in grey seals and cod continued to increase during the study period. Observed increases of nematodes are attributed to growing populations of grey seals (for sealworm) and harp seals (for Contracaecinea). Levels of A. simplex remained relatively constant between 1988 and 1992 in both grey seals and cod. There is no evidence suggesting that observed patterns in nematode abundance were due to changes in grey seal diet. Nor was there any evidence of competition between P. decipiens and C. osculatum in grey seals affecting either sealworm abundance or fecundity. The trends detected herein are attributed to climatic events in the Gulf of St. Lawrence, where water temperatures in the cold intermediate layer consistently decreased between 1986 and 1994. It is suggested that low temperatures inhibited development and hatching of sealworm eggs, but not those of C. osculatum.

DIET OF RINGED SEALS (PHOCA HISPIDA) ON THE EAST AND WEST SIDES OF THE NORTH WATER POLYNYA, NORTHERN BAFFIN BAY

AbstractIn conjunction with the International North Water Polynya Study (NOW) in northern Baffin Bay, we examined the diets of ringed seals (Phoca hispida)1 on the west (Grise Fiord, Nunavut) and east (Qaanaaq, Greenland) sides of the polynya, using conventional stomach content analysis, as well as inferences from stable isotope ratios in seal muscle. Between May and July 1998, stomach and muscle tissue samples were collected from 99 ringed seals taken near Grise Fiord and 100 taken near Qaanaaq. The amphipod Themisto libellula was the dominant prey type in the diet of immature ringed seals from Grise Fiord, whereas arctic cod (Boreogadus saida) and polar cod (Arctogadus glacialis) predominated in the diet of adults. Both immature and adult seals collected near Qaanaaq fed predominantly on arctic cod. Overall, seals collected near Grise Fiord had significantly higher δ13C values than those collected near Qaanaaq (P < 0.001), but there was no statistical separation in δ15N values between the two samples (P= 0.06). Differences in diets of ringed seals from the east and west sides of the North Water Polynya may be due to differences in prey distribution and/or differences in biological productivity and fish biomass within the polynya.

Stomach contents of two Mediterranean monk seals (Monachus monachus) from the Aegean Sea, Turkey

This study provides a description of the Mediterranean monk seal (Monachus monachus) diet from the Aegean Sea coast of Turkey. A total of 23 prey items belonging to five species were identified from the two stomachs examined. Cephalopods constitute the dominant prey group by weight (94·01%). Sarcotragus sp. (Porifera) and Posidonia oceanica (Magnoliophyta) are assumed to be incidental prey. Of the cephalopods identified, Eledone moschata and Bathypolypus sponsalis were encountered for the first time in a monk seal stomach.

Squid in the diet of northern fur seals, Callorhinus ursinus, caught in the western and central North Pacific Ocean

The stomach contents of 89 northern fur seals ( Callorhinus ursinus) caught in the western and central North Pacific from December to August during the period 1981–1994 were examined. In total 2567 items including 2401 beaks and 166 digested bodies of squid were obtained. Fifteen species from eight families and four species from three families, respectively, were identified from squid beaks and bodies in the stomachs of seals from the western North Pacific and the central North Pacific. Watasenia scintillans was numerically the dominant prey for northern fur seals in the western North Pacific, while Onychoteuthis borealijaponica and Ommastrephes bartramii tended to be important prey in the central North Pacific. Most of the squid prey were estimated to be smaller than 150 mm dorsal mantle length (DML) except two individuals of Moroteuthis loennbergi and 10 individuals of O. bartramii. Mean size of W. scintillans was almost constant from January to April at 42–44 mm DML. This suggests that northern fur seals feed actively on mature females of W. scintillans when they migrate to shallow waters for spawning during winter and early spring in the western North Pacific, off Honshu, Japan.

Comparing the diet of cod (Gadus morhua) and grey seals (Halichoerus grypus): an investigation of secondary ingestion

Otoliths from the stomachs of 138 by-caught grey seals (Halichoerus grypus) from the west coast of Ireland were compared with otoliths from the stomachs of 364 commercially caught cod(Gadus morhua) to determine if there were any overlaps in type, number and size of prey that might be attributable to secondary ingestion. A total of 19 species/groups were common to both cod and seal stomachs accounting for 99·6% and 95·8% of the otoliths from cod and seal stomachs respectively. There were significant differences between the otolith/fish lengths of all six species/groups compared but there were overlaps in the size distributions. Analysis of the diet composition of the cod stomachs suggested that larger cod consumed mainly fish and smaller cod consumed mainly crustaceans. Cod and seals were utilizing the same fish prey but the seals were generally consuming larger fish. Overlaps between the size distributions of prey species/groups suggest that secondary ingestion was possible and should be considered in future seal diet studies.

Growth of Antarctic krill Euphausia superba at South Georgia

Antarctic krill Euphausia superba has a central role in the ecosystem of the Southern Ocean and knowledge of its growth rate is central to determining the factors influencing population dynamics. The length of Antarctic krill in the diet of Antarctic fur seals Arctocephalus gazella at South Georgia revealed a consistent increase in size between ca. 42 and ca. 54 mm over the period October–March, indicating growth rates much higher than predicted by existing models. Geographical variation in growth rate may result in 2-year-old krill at South Georgia attaining the same size as 3-year-old krill in the Antarctic Peninsula region. The effect of geographical variation in growth rate on the population structure of krill has important implications for comparing the fate of individual cohorts over large scales and in the interpretation of krill life-cycles.

Diet and estimated food consumption of Antarctic fur seals at Bouvetøya during summer

Collection and analysis of natural regurgitations and fresh scats, deposited by Antarctic fur seals at the Nyroysa colony, Bouvetoya, during December 1998 to February 1999, afforded a comprehensive description of the dietary composition of this expanding population during the summer months. Mature, adult Euphausia superba was the staple diet of fur seals at Nyroysa, while squid and myctophid fish appeared to be taken opportunistically. In metric tons, the total Bouvetoya fur seal population is estimated to have consumed a minimum of 14,365 t krill (representing 1.2713 × 1010 individuals of 1.13 g mass), 186 t fish, 184 t squid and 14,735 t over 3 months, but there are many possible sources of error in these estimates. It is presumed that over-indulgence in krill may cause animals to regurgitate ashore.

Feeding habits of harp and hooded seals in Greenland waters

Results of stomach contents analyses of harp and hooded seals collected in West Greenland waters in the period 1986-1993 are reviewed, and compared with published data and circumstantial information from local hunters. The diet of harp seals in this region is variable but consists mainly of pelagic crustaceans (Thysanoessa spp. and Parathemisto libellula) and small fish species like capelin (Mallotus villosus), sandeel (Ammodytes spp.), polar cod (Boreogadus saida) and Arctic cod (Arctogadus glacialis). Species of importance for commercial fisheries in Greenland, such as Northern prawn (Pandalus borealis), Atlantic cod (Gadus morhua), and Greenland halibut (Reinhardtius hippoglossoides) play a minor role in the diet of harp seals in this area.Variation in the diet of hooded seals is less well documented, but in addition to the species also taken by harp seals, larger demersal fishes like Greenland halibut, redfish (Sebastes spp.), cod, and wolffish (Anarhichas minor) are apparently important prey items.

Feeding habits of harp (<i>Phoca groenlandica</i>) and hooded seals (<i>Cystophora cristata</i>) during late winter, spring and early summer in the Greenland Sea

Diet data were collected in the Greenland Sea pack ice (the West Ice) from March to June from harp seals (Phoca groenlandica) in 1987, 1990-1992 and 1997, and from hooded seals (Cystophora cristata) in 1992 and 1994, during Soviet Russian commercial sealing and on Norwegian scientific expeditions. The majority of both harp and hooded seal stomachs were empty but intestinal contents were found in most of the seals. The harp seal diet was totally dominated by the amphipods Parathemisto sp. and Gammarus sp., but krlll (Thysanoessa sp.) and polar cod (Boreogadus saida) were also eaten quite frequently. Hooded seals had been feeding mainly on the squid Gonatus fabricii, which was found most frequently in the intestines, but which also dominated in the few stomachs with contents. Polar cod also occurred quite frequently in the hooded seal diet, while crustaceans, such as amphipods and krill, occurred only sporadically.

Cephalopod diet of the southern elephant seal, Mirounga leonina, at King George Island, South Shetland Islands

In the summer of 1995/96, 25 southern elephant seals, Mirounga leonina, were stomach lavaged at Stranger Point, King George Island, South Shetland Islands. Cephalopod remains were present in 72% of the individuals sampled (n = 18). Seven species of squid and three of octopus were identified. The squid Psychroteuthis glacialis was the most important prey in terms of numbers (77%), biomass (80.8%) and frequency of occurrence (94.4%). Next in importance in terms of mass was the squid Alluroteuthis antarcticus (7.8%) in the diet of females and the octopodid Pareledone ?charcoti in the diet of males (13.2%). Females preyed on a wider variety of squid taxa than males (7 vs 3) but octopodids occurred only in stomach contents from males. The predominance of P. glacialis in the prey of the South Shetland Islands elephant seals can be explained by the southerly location of the foraging areas of this population compared to South Georgia, Heard and Macquarie islands, where the diet of southern elephant seals has previously been analysed. Psychroteuthis glacialis is the predominant squid in waters close to the Antarctic continent.

The diet of the Saimaa ringed seal Phoca hispida saimensis

The diet of the Saimaa ringed seal Phoca hispida saimensis Nordquist, 1899 was studied by the analysis of stomach contents and by feeding trials with a captive seal. Nine prey species were found in the stomachs, the most important being small schooling fish species: perch Perca fluviatilis, roach Rutilus rutilus, vendace Coregonus albula, smelt Osmerus eperlanus and ruff Acerina cernua. The importance of crustaceans in the diet of the ringed seal in Lake Saimaa is insignificant. Length of the intestinal tract of the Saimaa ringed seal is relatively shorter than those of marine ringed seals. In cafeteria tests on one captive seal the preferred fish species were vendace and smelt. The captive seal displayed clear seasonal variation in feeding activity. The consumption of fish was lowest in springtime and highest in autumn and winter.

Spring and summer predation on fish by the Antarctic fur seal, Arctocephalus gazella, at King George Island, South Shetland Islands

The fish component of the diet of nonbreeding male Antarctic fur seals, Arctocephalus gazella, was analyzed from 70 scats collected at Stranger Point, King George Island, South Shetland Islands, during the austral spring (n = 36) and summer (n = 34) of 1993-1994. Fish occurred in approximately 70% of scats that contained food remains irrespective of season. In spring, the main fish prey were Electrona antarctica, Pleuragramma antarcticum, and Notolepis coatsi, which together gave two-thirds of the 110 otoliths recovered. In summer, 457 otoliths were retrieved; the most frequent and abundant species were Gymnoscopelus nicholsi, E. antarctica, and P. antarcticum, which represented over 80% of the otoliths recovered. A substantial increase in the amount of fish ingested by fur seals occurred from spring to summer concomitant with a change in the relative proportion of fish taxa. Most fish species identified are pelagic and feed on krill. During the study period, commercial fishing in the area was not based upon any of the fish species identified.

Movements and foraging areas of grey seals in the North Sea

Summary 1. Grey seals Halichoerus grypus Fab. are large, numerous marine top predators. Fears concerning competition with fisheries have prompted calls for control measures. However, little is known about the areas where grey seals forage or the distances they may travel. 2. The movements of 14 grey seals caught at the Farnes in north‐east England (12) and Abertay in eastern Scotland (2) between August 1991 and July 1993 were investigated using Argos Satellite Relay Data Loggers (SRDLs). A total of 1461 seal days of location and behavioural data (mean 104·3 days per seal) covered all months of the year except February and March. 3. The seal movements were on two geographical scales: long and distant travel (up to 2100 km away); and local, repeated trips from the Farnes, Abertay and other haul‐out sites to discrete offshore areas. 4. Long distance travel included visits to Orkney, Shetland, the Faroes, and far offshore into the Eastern Atlantic and the North Sea. During travel the seals moved at speeds of between 75 and 100 km day–1 (0·87 and 1·16 m s–1). Most of the time, long distance travel was directed to known haul‐out sites. The large distances travelled indicate that grey seals that haul out at the Farnes are not ecologically isolated from those at Orkney, Shetland and the Faroes. 5. In 88% of trips to sea, individual seals returned to the same haul‐out site from which they departed. The durations of these trips were short (mean 2·33 days) and their destinations at sea were often localized areas characterized by a gravel/sand seabed sediment. This is the preferred burrowing habitat of sandeels, an important part of grey seal diet. This, and the fact that dives in these areas were primarily to the seabed, leads us to conclude that these were foraging areas. The limited extents of return‐trips from a haul‐out site (mean 39·8 km) suggest that the direct impact of seal predation may be greater on fisheries within this coastal zone, especially those near seal haul‐out sites, rather than on fisheries further offshore. 6. An average of 43% of all the seals’ time was spent within 10 km of a haul‐out site, although localized foraging areas were identified considerably further offshore. Proximity to a haul‐out may provide safety from predation. Alternatively, these periods may be used for rest or social interaction, or we may be underestimating foraging activity near haul‐out sites. 7. We suggest that the movement patterns observed in this study may persist through time and across the grey seals which haul‐out at the Farnes. We also suggest that a study such as this could be combined with diet studies and haul‐out censuses to map foraging intensity. Such information is an essential component of seal–fishery interaction models, upon which management decisions should be based.

The diet of itinerant male Hooker's sea lions, Phocarctos hookeri, at sub-Antarctic Macquarie Island

Scats were collected from itinerant male Hooker's sea lions, Phocarctos hookeri, at Macquarie Island and the uneroded faunal remains used to assess the diet. Uneroded sagittal otoliths were used to identify teleost fish and to calculate fish size. Prey items included 14 taxa of teleost fish, cephalopods, gastropods, crustaceans and fur seals. Fish constituted the primary component of the diet. Prey species previously uncommon in the diet of seals and penguins around Macquarie Island were commonly eaten by Hooker's sea lions. The sub-Antarctic horse fish (Zanclorhynchus spinifer) and the Patagonian tooth fish (Dissostichus eleginoides) were the two most abundant species and occurred in 62.5% and 41.7% of all scats respectively. There were no age-specific and individual differences in the diet of sea lions. Seasonal variances in diet were absent. Small plastic fragments (diameter ∼1 mm) were found only in association with otoliths of Electrona subaspera. Some overlap was seen between the diet of itinerant male Hooker's sea lions and the commercial fisheries that currently operate around Macquarie Island.

Seasonal variation in the diet of New Zealand fur seals (Arctocephalus forsteri) at Otago Peninsula, New Zealand

We examined the diet of New Zealand fur seals (Arctocephalus forsteri) at a rookery on Otago Peninsula, New Zealand, by analysing diagnostic remains from 500 faecal samples and 84 regurgitates collected between July 1993 and September 1994. In total, 27 taxa (species or genera) were identified. Small fish were numerically dominant in faecal samples, with five fish species (three species of lanternfish (Myctophidae), ahuru (Auchenoceros punctatus) and juvenile red cod (Pseudophycis bachus)) accounting for over 90% of prey items. Regurgitates occurred only seasonally and contained predominantly cephalopod remains (99% of prey items). Numerical analyses may prove misleading as an indicator of the composition of seal diet because the contribution of large fish that dominate estimates of prey biomass are underrepresented. Estimates of prey biomass were made by combining estimates from both faecal and regurgitate samples. Possible biases created by using this method are considered. A seasonal variation in prey composition was apparent, with arrow squid (Nototodarus sloanii) dominant in summer and autumn, replaced by a combination of barracouta (Thrysites atun), mackerel (Trachurus sp.) and New Zealand octopus (Octopus maorum) in winter and spring.