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The consumption of various prey species, required by the Barents Sea harp seal (Phoca groenlandica) stock in order to cover their energy demands, has been estimated by combining data on the energy density of prey species and on seasonal variations in the energy expenditure and body condition of the seals. Data on diet composition and body condition were collected in the period 1990-1996 by sampling harp seals during different seasons, in various areas of the Barents Sea. All diet composition data were based on reconstructed prey biomass, and adjustments were made for differences in digestibility of crustaceans and fish. The number of seals representing different age and sex groups were calculated for the entire population, and the monthly food requirements were estimated. In 1998, the total Barents Sea harp seal stock was estimated to comprise 2.22 million seals based on a mean production of 301,000 pups. After adjustments for a pup mortality of 30% its total annual food consumption was estimated to be in the range of 3.35-5.05 million tonnes (depending on choice of input parameters). Assuming that there are seasonal changes in basal metabolic rate associated withchanges in body mass, and that the field metabolic rate of the seals corresponded to two times their predicted basal metabolic rate, the annual food consumption of the Barents Sea harp seal stock was estimated. If capelin (Mallolus villosus) was assumed to be abundant, the annual total consumption was estimated to be 3.35 million tonnes, of which 1,223,800 tonnes were crustaceans, 807,800 tonneswere capelin, 605,300 tonnes were polar cod (Boreogadus saida), 212,400 tonnes were herring (Clupea harengus), 100,500 tonnes were cod (Gadus morhua) and 404,200 tonnes were "other fish". A very low capelin stock in the Barents Sea (as it was in the period 1993-1996) led to switches in seal diet composition, with increased consumption of polar cod (from ca. 16%-18 % to ca. 23%-25 % oftotal consumption), other gadoids (dominated by cod, but also including haddock (Melanogrammus aeglefinus) and saithe (Pollachius virens)), herring, and "other fish". Using the same set of assumptions as in the previous estimate, the total consumption would have been 3.47 million tonnes, divided between various prey species as follows (in tonnes): polar cod 876,000, codfish (cod, saithe and haddock) 359,700, "other fish" 618,800, herring 392,500, and crustaceans 1,204,200. Overall, the largest quantities of food were estimated to be consumed in the period June-September.In 1999, the total Barents Sea harp seal stock size was estimated to be 2.18 (95% CI, 1.79 to 2.58) million animals, which would give an annual food consumption in the range of 2,69 - 3.96 million tonnes (based on upper and lower 95% confidence limits and adjusted for a pup mortality rate of 0.3) if capelin is assumed to be abundant.
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... Stomach, intestinal and faecal samples were collected in the period 1999-2010. The prey consumption estimates were based on a bio-energetic model (Nilssen et al. 2000). ...
... The bio-energetic framework used for harp seals, described by Nilssen et al. (2000), was used to estimate the annual prey consumption by grey seals in each area: ...
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... To date, studies of marine mammal consumption in the Nordic and the Barents Seas have focused predominantly on only a few commercially harvested species, primarily common minke whales and harp seals (e.g. Sigurjónsson and Víkingsson, 1997;Stefánsson et al., 1997;Bogstad et al., 2000;Folkow et al., 2000;Nilssen et al., 2000;Lindstrøm et al., 2009), and considered consumption of only a few key fish species such as Northeast Atlantic (NEA) cod, herring, and capelin. However, the broad array of marine mammal species inhabiting these systems, together with the volume and range of fishery removals, warrants a more comprehensive assessment of marine mammal-fisheries interactions. ...
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... Similar evaluations of populations' overall energy requirements and prey consumption have continued over the years (Banas et al., 2021;Bejarano et al., 2017;Benoit-Bird, 2004;Costa et al., 1989;Fortune et al., 2013;Gallagher et al., 2018;Guilpin et al., 2019;Kriete, 1995;Lockyer, 2007;Malavear, 2002;McHuron et al., 2017b;Noren, 2011;Noren et al., 2012Noren et al., , 2014Rechsteiner et al., 2013;Reisinger et al., 2011;Williams et al., 2004;Winship et al., 2002). Often, accounting models have been developed with the applied management goal of quantifying the levels of predation on prey stocks and potential competition with local fisheries (Acevedo and Urbán, 2021;Boyd, 2002;Cornick et al., 2006;Faure et al., 2021;Forcada et al., 2009;Markussen et al., 1992;McHuron et al., 2020;Mohn and Bowen, 1996;Nilssen et al., 2014;Olesiuk, 1993;Queiros et al., 2018;Trzcinski et al., 2006;Weise and Harvey, 2008). ...
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... Fish, mainly capelin (Mallotus villosus) and herring (Clupea harengus), dominate the diet in the southern Barents Sea during winter and early spring whereas various crustacean species (mainly krill Thysanoessa sp. and amphipods Themisto libellula) and polar cod (Boreogadus saida) dominate the diet along the drift ice in the northern Barents Sea during summer and autumn. From observed seasonal variation in the harp seal body condition, it is evident that the June-September period is when harp seals have the greatest increase in blubber mass, presumably due to increased food intake combined with increased energy content of prey (Nilssen et al., 1997(Nilssen et al., , 2000. The availability of high-energetic food, such as krill and amphipods in the northern areas in summer and autumn presumably provide the energetic advantage necessary to account for the long migrations of harp seals from their more sub-Arctic winter and spring distributions . ...
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Full-text available
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