Kjell Tormod Nilssen

Feeding habits of harp seals (Phoca groenlandica) during early summer and autumn in the northern Barents Sea

The feeding habits of harp seals (Phoca groenlandica) in the Barents Sea were examined in studies conducted during June 1991, September 1990 and 1991, and October 1992. Analyses of stomach and intestinal contents were carried out and concurrent estimates of prey abundance were made using trawl gear. Harp seals appeared to feed at low intensity in the pack ice belt during the first half of June. There was little potential prey in the water column, but prawns (Pandalus borealis), capelin (Mallotus villosus) and polar cod (Boreogadus saida) were abundant close to the bottom. In September, the seals sampled in the northern pack ice areas of the Barents Sea fed on the pelagic amphipod Parathemisto libellula, krill (Thysanoessa spp.), prawns and, to a lesser extent, on fish species such as polar cod, sculpins (Cottidae) and snailfish (Liparidae). Trawling revealed that large quantities of Parathemisto libellala were present in the upper layers of the water column. Fish, mainly capelin and polar cod, were less abundant and occurred in deeper waters. In mid-October, the diet of seals in the northern Barents Sea consisted mainly of amphipods (Parathemisto sp.). Later in October, when increasing pack ice cover forced the harp seals to move south, the diet seemed to change from amphipods to fish prey, predominantly capelin and polar cod.

Diets of hooded seals (Cystophora cristata) in coastal waters and drift ice waters along the east coast of Greenland

Abstract To provide data on the diets of hooded seals (Cystophora cristata) in the Greenland Sea, seals were collected for scientific purposes on expeditions conducted in the pack ice belt east of Greenland in September/October 1999, 2002 and 2003 (autumn), July/August in 2000 (summer), and February/March in 2001 and 2002 (winter). The results from analyses of stomach and intestinal contents from captured seals revealed that their diet was comprised of relatively few prey taxa. The squid Gonatus fabricii and polar cod (Boreogadus saida) were particularly important, whereas capelin (Mallotus villosus) and sand eels (Ammodytes spp.) occasionally contributed more. These four prey items constituted 60–97% of the diet biomass. Gonatus fabricii was the most important food item in autumn and winter, whereas polar cod dominated the summer diet, with important contributions from G. fabricii and sand eels. The latter was only observed on the hooded seal menu during the summer period, whereas polar cod, which was an important component during the autumn survey, was almost absent from the winter samples. During the latter survey, capelin also contributed to the hooded seal diet. Samples obtained from hooded seals in more coastal waters indicated a more varied diet based on fish such as polar cod, redfish (Sebastes sp.) and Greenland halibut (Reinhardtius hippoglossoides).

Spatial and temporal variations in northeast Atlantic minke whale Balaenoptera acutorostrata feeding habits

Abstract Stomach content samples from northeast Atlantic minke whales Balaenoptera acutorostrata, caught in scientific whaling operations in selected subareas during summer in 1992 and during spring, summer and autumn in 1993 revealed a diet where fish played a very prominent role. Considerable heterogeneity in prey species composition occurred both between areas and sesons and from year-to-year. In the 1992 summer survey, capelin dominated the whale diets in the two northmost study areas (Spitsbergen and Bear Island), while the dietary contribution of krill was much more conspicuous in both summer and autumn in 1993. This is consistent with an increase in krill and severe decrease in capelin availability in these areas from 1992 to 1993. The southern coastal areas (Kola, Finnmark, Lofoten/Vesterlen) were different from the north in that herring was the dominant planktivorous fish. In 1992, this species, 0-group in particular, was documented to be very abundant both in the resource surveys and in the whale stomach analyses. Herring was also the most important food item for the whales in the southern coastal areas in both summer and autumn in 1993. To some extent, the herring was accompanied by gadoid species during summer in both years, and the gadoids fish species dominated the whale diet in spring in 1993.

The effect of invading harp seals (Phoca groenlandica) on local coastal fish stocks of North Norway

Abstract Annual invasions of harp seals (Phoca groenlandica) into coastal areas and fjords of northern Norway during the last decade have created problems for fisheries in the area. Bottom-trawl survey data collected during 1986–1990 in Ullsfjord were used to evaluate possible interactions between invading seals and local fish stocks. The presence in seal stomachs (sampled in Ullsfjord) of saithe (Pollachius virens) and small cod (Gadus morhua), which were not frequent in trawl catches, seems to indicate that seals may pursue prey in waters other than the trawl areas. Many of the species occurring in the seal stomachs were, however, also encountered quite frequently in the trawl catches. Harp seals may cause considerable damage to gill-net catches by eating parts (usually the ventral soft parts) of fish entangled in the nets.

Harbour Seal ( Phoca vitulina ) Diet in Vester»len, North Norway

Results from analyses of stomach contents and faeces collected from harbour seals ( Phoca vitulina ) in Vester f len, north Norway, in 1990-1995 revealed a diet comprised mainly of saithe ( Pollachius virens ). Little variation occurred in the diet throughout the year, probably due to a large and stable abundance of saithe in the area. Other prey items that seemed to be important were herring ( Clupea harengus ), cod ( Gadus morhua ), sandeel ( Ammodytes sp.) and various flatfishes. The harbour seals seemed to prefer small fish, and older seals appeared to have a more varied diet than the younger animals. In a captive study, the recovery of otoliths was only 14.8% when harbour seals were fed whole fish. Recovery rates varied between species: 4.6, 47.7 and 46.6% of herring, haddock ( Melanogrammus aeglefinus ) and cod, respectively. The results from the captive study were used to illustrate potential biases in observed diets based on faeces.

Invasions of harp seals Phoca groenlandica Erxleben to coastal waters of nor way in 1995: Ecological and demographic implications

Abstract Since 1978, and in particular in 1986-1988, large numbers of harp seals Phoca groenlandica ERXLEBEN have invaded coastal waters of North Norway during winter and spring. After 1988 the harp seal invasions have been restricted to the northeastemmost parts of the coast of Norway. In 1995, however, a significant increase occurred in both the magnitude and the spatial extent of the harp seal invasions. Diet composition, age structure and body condition parameters were examined on seals taken incidentally in Norwegian gill net fisheries during winter and spring in 1995. In early winter immature animals were taken, while mature females dominated in the spring. Analyses of stomach contents soggested that the diet mainly contained fish, in particular saithe Pollachius virens (L.), haddock Melanogrammus aeglefinus (L.) and cod Gadus morhua (L.). Body condition parameters revealed that the one year old seals taken in February 1995 were in significantly poorer condition than harp seals of the ~arne age take...

Summer Diet of Grey Seals ( Halichoerus grypus ) in Faroese Waters

The ecological role of grey seals ( Halichoerus grypus ) as predators in Faroese waters was evaluated, based on reconstruction of the diet composition from stomach contents obtained from animals taken for scientific purposes in three main sampling areas during the summer in 1993-1995. Gadoids, sandeels ( Ammodytes sp.) and catfish ( Anarhichas lupus ) dominated the seal diet. Some regional variations were found in the grey seal diet, where gadoids and sandeels were most important in the Svínoy area, catfish and gadoids were most important in the Sandoy area, and sandeels and gadoids were most important in the Northwest area. Regional variations in diet may reflect variations in the abundance and availability of potential prey. Grey seals of different ages were found to have somewhat different feeding habits. Juveniles fed most frequently on sandeels, pre-adults fed on sandeels and saithe ( Pollachius virens ) and adults fed on cod ( Gadus morhua ) and catfish. Adults also fed on larger prey than the younger seals. The grey seals in Faroese waters were only observed to feed on fish, generally smaller than 30 cm in length, but the size range differed among prey species.

Estimation of hooded seal (Cystophora cristata) pup production in the Greenland Sea pack ice during the 2005 whelping season

In March 2005 aerial surveys were carried out to estimate pup production of Greenland Sea hooded seals, Cystophora cristata in three whelping patches using photographic strip transects. The majority of whelping occurred 17–23 March and surveys were carried out on 24 March. The temporal distribution of births and estimated proportion of solitary bluebacks present within the survey area were used to correct the abundance estimates. The total estimated pup production (15,250 pups, s.e. = 3,470; CV = 22.8%) was lower than an estimate from a comparable study in 1997. The current estimate is considered to be negatively biased, as it is uncorrected for pups born outside the whelping concentrations. Population modeling suggests a substantial decline with subsequent stabilization at a lower level for Greenland Sea hooded seals in recent decades. It is suggested that future research on the population explore possible factors (e.g. reduced fertility, predation, food shortage, disease, reductions in ice cover) that may have contributed to the apparent prevailing low abundance.

The status of grey seals Halichoerus grypus in North Norway and on the Murman Coast, Russia

Abstract The distribution and abundance of grey seals Halichoerus grypus were studied by aerial and ground surveys in North Norway and on the Murman coast, Russia, during the moulting (March–April) and breeding (October–December) seasons in 1986–1992. Numbers of grey seals may have increased throughout the area of investigation during the past 25–30 years. Based on observations of pup production, crude estimates of 900 and 3400 grey seals are suggested to inhabit colonies in Nordland county, North Norway and at the Murman coast, Russia, respectively. In Troms and Finnmark counties, North Norway, no reliable pup production estimates are available, but nearly 700 grey seals were observed at haul-out sites during the moulting period. Recorded moulting and breeding haul-out sites are noted for most of the study area.

Status of grey seals ( Halichoerus grypus ) in Norway

During the period September-December in 2001-2003, ship based surveys of grey seal ( Halichoerus grypus ) pups, including tagging, counting and staging of pups, were conducted along the Norwegian coast. All known and other potential breeding areas were surveyed from Rogaland county in the south to Finnmark county in the north. Most of the breeding sites were surveyed only once, but some sites were surveyed 2-4 times. The investigations resulted in a total minimum estimate of 1,159 grey seal pups born in Norwegian waters. Nordland county was the most important breeding area where about 50% of the pups were born. Total population estimates were derived from the recorded number of pups born using a range of multipliers (4.0-4.7), based on observed annual growth rates of approximately 7-12% in other grey seal populations. This gave a total estimate of about 5,800-6,600 grey seals including pups in Norwegian waters. However, the total pup production was probably underestimated due to only one pup count in most of the breeding sites. Observed mean pup mortality was 1.1% during the breeding season along the Norwegian coast.