Comparison of different methods of census of juvenile salmonids (Salmonidae) in the small river Mikocheva (Western Kamchatka)

Seinings of the lowland bed of a typical small river of Western Kamchatka demonstrated that of several methods for the census of juveniles of salmonids (Salmonidae) the most accurate result in comparison with complete removal is obtained by three-fold seining with calculation of abundance by the Zippin method. In comparison with a seine, a drive-in trap and electrofishing possess a lower average catching efficiency and a higher selectivity. The average density of fish estimated by the results of seining at the investigated stretch was 0.55–0.57 specimens/m².     

Quality and status of fish stocks in lakes: gillnetting,seining, trawling and hydroacoustics as sampling methods

All sampling methods give selective or biased estimates of fish species abundance, distribution and size structure. This creates problems, e.g. in regard to the Water Framework Directive of the European Union, which demands evaluation of the quality and status of fish stocks in lakes. We compared fish sampling by means of Nordic multimesh gillnets, seining, trawling and hydroacoustics in two Finnish lakes in summer 2007 and 2008. Sampling methods were used ‘as such’, i.e. no special design was implemented for method comparison. In the shallow eutrophicated lake the species’ composition of gillnet sampling and seining were very different. The biomass-% of percids dropped from gillnet (61%) to seining (9%) and that of cyprinids grew from 39 to 90%, respectively. In the deep pelagic area of the oligotrophic lake, vendace and smelt predominated in trawl catches. The number of fish caught by gillnetting in that area was too small to make any conclusions about the species composition. In the eutrophicated lake, the combined length distribution for all fish species differed significantly between gillnetting and seining. In the oligotrophic lake, the gillnet catches were too small for any comparison of fish size. The difference in the length distribution of fish between trawl and echosounding was significant in most analysed depth layers. In upper depth layers acoustics sampled larger fish than trawling, and in deeper layers smaller fish. Using a combined acoustic-trawl method, the pelagic fish biomass was estimated to be approx. 17 kg ha⁻¹ in the deep and oligotrophic lake. We conclude that in large and deep-water areas, the use of active gear is enough in fish sampling to evaluate the quality and status of fish stocks. Gillnetting together with seining is an appropriate method to work out the quality and status of fish stocks in shallow and littoral areas of large lakes. Variation in the catch selectivity of fish sampling gear requires a discrete ecological classification for each type of gear.     

Fish habitat use response to anthropogenic induced changes of physical processes in the Elwha estuary, Washington, USA

The Elwha River estuary has been significantly influenced by anthropogenic changes to the river, including two large dams upriver and rock dikes installed in the estuary. Together these have disrupted hydrodynamic processes and subsequent sediment delivery throughout the watershed. This article defines the functional response of fish distribution within the estuary as a result of these changes. We assessed fish distribution of three main areas of the Elwha estuary using standard beach seining techniques from March to August 2007. Species composition, ecological indices, and relative proportion of all salmonids, and in particular Chinook salmon (Oncorhynchus tshawytscha), were consistently significantly different across the estuary. Differences corresponded to a rock dike installed 30 years ago, and a sediment lens that was observed to form at the entrance to the east estuary. Sediment lenses are documented to be a common occurrence in the Elwha nearshore, and symptomatic of documented, severely disrupted sediment processes of the Elwha River. Combining the fish distribution documented in this study with the rock dike and observed sediment lens and the sediment processes documented by other researchers we, therefore, conclude: (1) Fish use within the Elwha River estuary is complex, and even fragments of connected estuary are critically important for migrating salmon; (2) Anthropogenic effects, including in river damming and diking of the estuary, can be an important ecological driver in nearshore habitat function that should be appropriately considered in estuary habitat research, management, and restoration; and (3) Juvenile salmonids appear to be able to respond to dynamic sediment environments if there are habitat options available.     

Assessment of errors associated with harbour seal (Phoca vitulina) faecal sampling

Six harbour seals, ages 4–8 years, were held as pairs in a 10 times 20 times 2 m tank filled with sea water, and on 60 occasions were fed a meal of a specific species of fish or cephalopod of known size. The tank was drained periodically, and harbour seal faeces were collected on a 0.5 mm sieve. Number and size of otoliths and beaks found in faeces were determined. Fifty-eight percent of 670 fish and 37% of 36 cephalopods fed to harbour seals were represented by their otoliths or beaks in faeces. Estimated number of prey consumed was determined from the greatest number of left or right otoliths or upper or lower beaks collected in faeces. Estimated length ofprey was determined from measurements of otoliths and beaks recovered in the tank and relationships of otolith and beak measurements to prey length. Estimated number of fish eaten was not significantly different among pairs of harbour seals, but was different among species of fishes. Only 24–35% of fish species with small otoliths were represented in faeces, whereas more robust otoliths from other species were less apt to be completely dissolved. Estimated length of fishes was significantly less than lengths of fishes fed to harbour seals in 39 (76.5%) of 51 trials. Cephalopod beaks were not affected by passage through the harbour seal digestive tract. Amount of otolith dissolution was not related to species of fish; estimated fish length was underestimated by an average 27.5%. Although some (7.4%) of the otoliths were collected within 100 h after the fish were ingested, more than 90% were recovered within 24 h after the fish was eaten. Correction factors were developed which will allow researchers to estimate more reliably number and size of fish and cephalopod prey eaten by harbour seals.     

不同猎物及密度对巴氏新小绥螨和拉戈钝绥螨同类相残和集团内捕食作用的影响

明确不同猎物及密度下巴氏新小绥螨Neoseiulus barkeri与拉戈钝绥螨Amblyseius largoensis(Muma)的同类相残和集团内捕食作用,为其协同应用控制橡胶树害螨提供依据.在室温27±1℃、湿度75％±5％、光周期12 L∶12D 条件下,以六点始叶螨 Eotetranvchus sexmaculatus(Riley)、比哈小爪螨Oligonychus biharen(Hirst)和东方真叶螨Eutetranychus orientalis(klein)为集团外猎物,观察巴氏新小绥螨和拉戈钝绥螨对集团内和集团外猎物的捕食选择行为,以及不同集团外猎物密度下两种捕食螨对同种和异种捕食螨的捕食作用.巴氏新小绥螨和拉戈钝绥螨对异种个体及集团外不同猎物的捕食偏好性及捕食时间存在明显差异.巴氏新小绥螨偏好取食集团外猎物,异种捕食螨拉戈钝绥螨残存率达到80.00％以上;拉戈钝绥螨偏好取食集团外猎物六点始叶螨和比哈小爪螨,而当东方真叶螨存在时,其更偏好取食异种捕食螨巴氏新小绥螨(残存率为26.67％);发生集团内捕食时,拉戈钝绥螨为集团内捕食者,而巴氏新小绥螨为集团内猎物.集团外猎物密度可显著影响巴氏新小绥螨和拉戈钝绥螨相残作用,尤以猎物六点始叶螨对巴氏新小绥螨和东方真叶螨对拉戈钝绥螨影响最为明显,其充足时比无猎物时捕食量分别下降了 68.85％和62.90％.巴氏新小绥螨和拉戈钝绥螨的集团内捕食分别以比哈小爪螨和六点始叶螨的影响最大,猎物充足时比无猎物时捕食量下降了 80.00％和69.44％,但拉戈钝绥螨在以东方真叶螨为猎物时集团内捕食受猎物密度影响较小,猎物充足时取食量与猎物不足时接近,比无猎物时捕食量只下降20.83％.集团外猎物六点始叶螨、比哈小爪螨存在时,巴氏新小绥螨和拉戈钝绥螨表现为偏好选择集团外猎物,密度增加对两种植绥螨的同类相残和集团内捕食作用有明显抑制作用,但东方真叶螨充足与否,拉戈钝绥螨对巴氏新小绥螨的集团内捕食作用影响差异不显著.     

Large-scale use of fish traps for monitoring sea trout (Salmo trutta) smolts and sea lice (Lepeophtheirus salmonis) infestations: efficiency and reliability

Lice-infected sea trout populations were monitored using fish traps in the Romsdalsfjord (Norway). The reliability and efficiency of this capture technique, which allows estimation of lice infestation rates without killing the fish, was evaluated through a mark–recapture study. A total of 2447 sea trout smolts were captured, tagged and released over a three-year period. There was a considerable variation in capture rates (range: 0.4–17.7 fish per day) and sea lice numbers (number of lice per fish: 2.8–30.3; number of lice per gram body weight: 0.02–0.69) among localities, sampling times and years. Recapture rates of tagged fish with traps, which were low (2% or 0.11 fish per day), showed that the risk for pseudoreplication was minor, in terms of counting lice on the same fish several times. Most of the tagged sea trout (90%) were recaptured within the first two months after release, and no significant variations in lice numbers were found between tagging and recapture. The lack of differences in lice levels between tagging and recapture during the first week after tagging indicated that the method most likely would not significantly underestimate the lice infestations due to loss of lice during handling. Therefore, our results confirm that the use of fish traps is a suitable method for estimation of lice numbers on wild salmonids.     

EFFECT OF AGE ON THE FISHING ABILITY OF SANDWICH TERNS STERNA SANDVICENSIS

The fishing ability of first-winter and older Sandwich Terns was compared at foraging sites used by both age-groups on the coast of Sierra Leone between January and March 1970 when first-winter birds were about 7–9 months old. The methods used for measuring various parameters of fishing ability are described. It was found that a significantly larger proportion of plunge dives by the older age-group yielded prey although the difference between the two age-groups was only slight.
There were no major differences between the age-groups in diving rates or in size of fish captured. Older birds tended to dive from higher than first-winter birds.
By driving shoals of small fish to the surface, predatory fish enhanced the fishing success of both age-groups on certain days. Where man's beach seining operations yielded a superabundance of small fish near the tideline, these were captured equally well by both age-groups.
First-winter birds were not seen being fed by older birds, and although food-begging behaviour was observed once in late January it is clear that the first-winter birds were self-sufficient for food by the time this study was made.
Some implications of the observed differences in fishing success are discussed. It is suggested that, after fledging, Sandwich Terns gradually gain the judgment and skill necessary to dive profitably from increasing heights and so learn to exploit prey in a greater range of water depth as they get older.     

The diet of Antarctic fur seals,Arctocephalus gazella,during the summer-autumn period at Mossman Peninsula,Laurie Island (South Orkneys)

Summary From mid January to April 1988 a total of 105 faecal samples of non breeding male fur seals, Arctocephalus gazella, was collected at Mossman Peninsula, Laurie Island. Examination of scats containing prey remains showed that fur seals fed mainly on krill, occurring in 100% of samples but fish were also a common food item (78.8%). Myctophids constituted more than 90% of fish taken by fur seals. Squid beaks occurred in 34.3% of scats, being more common in the autumn period.     

Fish prey of southern elephant seals, <Emphasis Type="Italic">Mirounga leonina</Emphasis>, at King George Island

Between November and February in the years 1993/1994 to 1999/2000, 153 southern elephant seals, Mirounga leonina, were stomach lavaged at King George Island. Fish occurred in 16 of 108 stomachs containing food items. Myctophids were the dominant fish prey, contributing 76.6% of the 145 sagittal otoliths found. The most important prey species was Gymnoscopelus nicholsi, which constituted 69% of the otoliths and occurred in 75% of stomach samples. Next in importance was the nototheniid Pleuragramma antarcticum, which occurred in 31.3% of samples and represented 11.7% in numbers. We suggest that while myctophids may be the dominant fish prey of elephant seals in areas close to King George Island, they are probably replaced by P. antarcticum as seals migrate towards higher latitudes where this fish is extremely abundant.     

The effect of submergence on heart rate and oxygen consumption of swimming seals and sea lions

Respiratory, metabolic, and cardiovascular responses to swimming were examined in two species of pinniped, the harbor seal (Phoca vitulina) and the California sea lion (Zalophus californianus). 1. Harbor seals remained submerged for 82-92% of the time at swimming speeds below 1.2 m.s-1. At higher speeds, including simulated speeds above 1.4 m.s-1, the percentage of time spent submerged decreased, and was inversely related to body weight. In contrast, the percentage of time spent submerged did not change with speed for sea lions swimming from 0.5 m.s-1 to 4.0 m.s-1. 2. During swimming, harbor seals showed a distinct breathhold bradycardia and ventilatory tachycardia that were independent of swimming speed. Average heart rate was 137 beats.min-1 when swimming on the water surface and 50 beats.min-1 when submerged. A bimodal pattern of heart rate also occurred in sea lions, but was not as pronounced as in the seals. 3. The weighted average heart rate (WAHR), calculated from measured heart rate and the percentage time spent on the water surface or submerged, increased linearly with swimming speed for both species. The graded increase in heart rate with exercise load is similar to the response observed for terrestrial mammals. 4. The rate of oxygen consumption increased exponentially with swimming speed in both seals and sea lions. The minimum cost of transport calculated from these rates ranged from 2.3 to 3.6 J.m-1.kg-1, and was 2.5-4.0 times the level predicted for similarly-sized salmonids. Despite different modes of propulsion and physiological responses to swimming, these pinnipeds demonstrate similar transport costs.     

The diet of Antarctic fur sealsArctocephalus gazella during the breeding season at South Georgia

 The diet of lactating female Antarctic fur seals Arctocephalus gazella at South Georgia was investigated during the pup-rearing period (January/March) of 1991–1994. Antarctic krill Euphausia superba was the main prey item, occurring in 88% of all scats (n=497), whereas fish occurred in 47% and squid in 5% of all scats. There was considerable intra- and inter-annual variation in the characteristics of krill taken by fur seals. The distribution of krill sizes taken suggests that fur seals are not actively selecting particular sizes of krill and, therefore, that the krill in the diet reflects the krill available around South Georgia. The absence of group 3 krill (44–48 mm in length) in the South Georgia area, as indicated by their absence in the diet of seals, is suggested as a possible reason for low availability of krill and the subsequent reproductive failure among krill predators. The frequency of occurrence of fish was much higher than in previous studies; the pattern of fish consumption showed a consistent seasonal pattern in 3 of the 4 years studied. Of the total number of the myctophid Protomyctophum choriodon, the most numerous fish taxon, 98% were taken between early February and the middle of March. Champsocephalus gunnari and Lepidonotothen larseni agg., which both feed on krill, dominated the fish component of the diet outside this period and together constituted 94% of the total estimated biomass of fish consumed. The intra- and inter-annual variability in the diet of Antarctic fur seals emphasise the need for diet studies to be conducted during the entire pup-rearing periods of several years. Received: 15 March 1995/Accepted: 13 May 1995     

Effect of mink, Mustela vison Schreber, predation on cohorts of juvenile Atlantic salmon, Salmo salar L., and brown trout, S. trutta L., in three small streams

Two cohorts of Atlantic salmon parr and one of brown trout were studied in periods with and without the presence of mink, Mustela vison . In all localities a marked increase in mortality rate was observed during periods when mink were present. Mink were observed catching salmon parr, and approximately 10% of the parr had bite marks, especially on the tail fins. In the smallest stream with brown trout, the mortality rate was 0.80 during a few days with mink present; remnants of trout were found along the stream. The present study suggests that mink predation may be a major cause of mortality of salmonids in small streams. The results indicate that predation efficiency may vary with characteristics of the habitat, especially stream width and discharge, and fish density.     

The effectiveness of two common sampling methods for assessing imperilled freshwater fishes

This study tested the hypothesis that the most common gear type used to sample fishes in wadeable systems, electrofishing, was more effective than another commonly used gear type, seining, for sampling fish species at risk. Five predictions were tested. At sites where species at risk were detected, (1) the probability of detecting the species at risk, (2) the probability of only one gear type detecting the species at risk and (3) the estimated catch per unit effort of the species at risk, was as high as, or higher, when using electrofishing than when using a seine. (4) The number of sample sites required to detect a species at risk within a watershed and (5) the number of subsections required to detect a species at risk within a site, were as low as, or lower, using electrofishing than the number required using a seine. Based on analyses of these measurements, electrofishing was a more effective gear type than seining for sampling fish species at risk, irrespective of the unit (presence or absence or catch per unit effort) or scale of measurement (watershed or site level). Dissolved oxygen, turbidity, specific conductivity and nitrate concentrations were measured at each site and did not account for the between gear differences. Selection of sampling gear can be a fundamental consideration for the assessment of fish species at risk, where, unlike common species, they may be particularly influenced by small population sizes, restricted geographic ranges and narrow habitat preferences. Resource managers must weigh differences in the risks of injury of fish species at risk against differences in the effectiveness of each gear type when deciding between gear types and the utility of the assessments they represent.     

Size,relative abundance,and catch‐per‐unit‐effort of round goby,Neogobius melanostomus,in anthropogenically modified and natural habitats in the western basin of Lake Erie

To determine if anthropogenically modified habitats possess greater numbers of round goby and serve as dispersal vectors, we used angling to compare catch‐per‐unit of effort for 64 natural and modified habitat areas. In addition, a gravel natural habitat was seined to compare length frequency distribution with anthropogenically modified habitats. Natural habitats included gravel beaches and natural rubble and cliff wall, while modified habitats included artificial riprap, concrete sea wall, and metal sheet piling. No significant difference in relative abundance was observed in round goby preference among modified habitats (P = 0.52), but natural gravel habitats were significantly different from modified habitats that included artificial riprap (P = 0.002), concrete sea wall (P < 0.001), and metal sheet piling (P = 0.003). When habitat subcategories were compared using anova , the natural gravel beach habitat was significantly different from the three artificial substrates and from natural rubble and cliff wall substrates (P < 0.004). No round goby were caught from gravel beach habitats; thus, this habitat was removed from further analysis. A Student t‐test indicated no significant difference between habitats was found between the natural rubble and cliff wall habitat and the three other artificial habitats (concrete sea wall, P = 0.33; riprap, P = 0.53; metal sheet piling, P = 0.11). We further evaluated gravel beach habitats to determine the reason for the lack of goby capture. We seined gravel beach habitat and collected 328 individuals, with which we evaluated the length‐frequency distribution and calculated length–weight relationships by sex. Our results indicated that only 5.2% of the goby population was available for capture by angling on the gravel beach habitat. A t‐test comparing the demographic attributes between seining and angling indicated a significant difference between goby length (P < 0.001) and weight (P < 0.001). The regression slope indicated an ontogenetic habitat shift occurred near 62 mm standard length. Smaller round goby individuals were found in less structurally complex gravel beach habitat, while larger individuals were associated with complex habitat.     

Fish prey of Antarctic fur seals,Arctocephalus gazella,during the summer-autumn period at Laurie Island,South Orkney Islands

The fish component in the diet of Antarctic fur seals, Arctocephalus gazella, was investigated at Laurie Island, South Orkney Islands from mid January to April 1988. Fish otoliths occurred in 78.8% of faecal droppings. Most of the otoliths extracted from scats belonged to Myctophid fish (93.4%), mainly Electrona antarctica and Gymnoscopelus nicholsi. These two fish species thus constituted the bulk of the diet. A greater percentage of the otoliths from G. nicholsi (31.1%) in this study were considered suitable for measurement in comparison with 10.3% from scats at Heard Island in 1990 and 11.4% at Macquarie Island in 1988/89. This lesser degree of erosion would suggest that foraging areas of fur seals during this study were closer to land than during previous studies. During the period studied, the commercial fishery around the South Orkneys was not based on Myctophid fish so there was no direct competition for fish between the fur seals and fisheries.     

The diet of Antarctic fur seals, Arctocephalus gazella, at King George Island, during the summer–autumn period

The diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, was investigated at Stranger Point, King George Island, by scat analysis from February to April 1996. Overall, krill and fish were the most frequent prey, occurring in an average of 97% and 69% of samples (n=128), followed by cephalopods (12%). Myctophids constituted almost 90% of the fish predated, with Electrona antarctica and Gymnoscopelus nicholsi being the most abundant and frequent species consumed. All fish taxa identified were krill-feeding species suggesting that seals foraged primarily on krill and opportunistically on fish species associated with krill swarms. A seasonal change observed in the relative proportions of the different fish prey taxa indicates that fur seals spent more time foraging over the shelf in summer and off the shelf in autumn. During the study period, commercial fishing in the area was not based upon any of the fish identified in this study.     

Release method and anatomical hook location: effects on short-term mortality of angler-caught Acanthopagrus australis and Argyrosomus japonicus

One field and 3 aquaria experiments were done to quantify the short-term mortality of yellowfin bream Acanthopagrus australis and mulloway Argyrosomus japonicus after being angled and subjected to 3 general handling treatments. Anglers were supplied with identical J-type hooks and asked to handle hooked fish by either (1) physically removing the hook or (2) cutting the line (5 cm from the mouth of the fish) and leaving the hook in. Some hooked A. japonicus were subjected to a third handling treatment where the line was cut underwater without exposing the fish to air. Technical and biological data were collected before all fish were released into sea cages and monitored for 5 d. Control fish were seined and similarly caged and monitored. Concentrations of plasma glucose and cortisol were collected from a sample of fish on the first and last day of the experiments. Significant predictors of mortality for both species involved the presence of blood at the mouth and an interaction between anatomical hook location and hook removal. A. australis and A. japonicus that had their ingested hooks removed experienced the greatest mortalities (87.5 and 72.7%, respectively). Typically, these fish suffered damage to their oesophagus, stomach wall and vital organs. Mortality rates of A. australis and A. japonicus were significantly decreased to 1.7 and 16%, respectively, when they were released with their lines cut, with some of these fish free of hooks after 5 d. In contrast, few mortalities occurred in either species when the hooks were removed or the lines cut on mouth-hooked fish or in A. japonicus when it was released with no air exposure. For A. australis, the field- and aquaria-based experiments provided comparable results in terms of identifying treatment-specific effects, but there were potential biases in rates of hook ingestion. Irrespective of the treatment of fish, all experiments caused physiological changes measured as elevations in either plasma cortisol or glucose. We concluded that anglers should cut the line from hook-ingested A. australis and A. japonicus, but remove the hook from mouth-hooked individuals to prevent subsequent ingestion. Further research is required to examine the longer-term consequences of these handling practices on fish health.     

NEW INFORMATION ON THE NATURAL HISTORY,DISTRIBUTION, AND SKULL SIZE OF THE EXTINCT (?) WEST INDIAN MONK SEAL,MONACHUS TROPICALIS

Our knowledge of the extinct West Indian monk seal, Monachus tropicalis , is scant due to heavy exploitation following European colonization of the New World. We present previously unknown accounts of the species, including unpublished field notes of biologist E. W. Nelson, who observed a small number of wild seals in June of 1900. Records indicate that M. tropicalis may have had a long pupping season, occurred in large groups (up to 100) when abundant, probably ate fish and crustaceans, were preyed upon by sharks, and that young and adult seals may have assorted themselves into different age groups when hauled out. Additional records extend the known range of M. tropicalis to include the north coast of South America as far east as Guyana. We also present previously unavailable measurements from a large series of adult skulls and mandibles ( n = 48). Two cases of histocytosis X, carcinoma, or other disease of the hard palate are documented from among these specimens.     

PUPPING PHENOLOGY AND DEMOGRAPHY OF HARBOR SEALS (PHOCA VITULINA RICHARDSI)ON TUGIDAK ISLAND, ALASKA

The number of seals on shore at Tugidak Island (Gulf of Alaska) declined 72%–85% between 1976 and 1988 and increased during the 1990s. We compared pupping phenology and the ratio of pupping-period counts to molting-period counts between declining (1976–1979) and increasing (1994–1998) years, and examined the sex/age structure of seals ashore during the 1990s. In the 1970s the onset and peak of pupping occurred 6–18 d later than in the 1990s. Rate of pup abandonment was higher in 1978 than in the 1990s. Between 1994 and 1995, the maximum and mean number of seals ashore increased >50%, largely due to an increase in non-pups. From 1995 to 1998, the sex/age structure of seals ashore was similar among years. We observed three to four times as many seals during the molting period than during the pupping period in the 1970s, whereas similar numbers were ashore during these periods in the 1990s, perhaps reflecting changes in demography and/or haul-out behavior. Changes in pupping phenology and demography may reflect environmental changes, such as food availability, and when monitored in conjunction with population counts, may help us better interpret changes in the number of seals ashore.     

Harp seal foraging behaviour during summer around Svalbard in the northern Barents Sea: diet composition and the selection of prey

The harp seal Pagophilus groenlandicus is a major high trophic level predator in the Barents Sea, and to better understand their function in the Barents Sea ecosystem, we need to understand their foraging behaviour during their most intensive feeding period. We analysed the diet composition and prey preference of 184 harp seals and 94 faeces samples, sampled in the northern Barents Sea (around Svalbard) during the period May–August in 1996, 1997, and 2004–2006. Concurrent with the sampling of seals, prey availability was assessed in one area in 1996 and 1997 and in two areas in 2006 using standard acoustic methods. Our study showed that harp seal diet composition varied significantly both in time (year) and space, and that their diets appeared to be size dependent. Both subadult (<150 cm) and adult seals were associated with pelagic crustaceans (particularly krill), whereas primarily adult seals were associated with fish (capelin, gadoids and flatfish). Krill was the most important prey group (63 %) followed by polar cod (16 %) and other fish species (10 %). The prey preference of harp seals varied in time and space; polar cod was often preferred by the seals whereas krill was commonly consumed in lower proportion than observed in the survey area. Gadoids and capelin had either been exploited in the same or less proportion as observed in the survey sea. This study emphasises the ecological significance of krill as prime food for harp seals during their intensive feeding period in summer.