Who eats whom in the Barents Sea?

Abstract

An overview of the estimates of consumption by predators on the main fish stocks in the Barents Sea is given. The main predators are cod (Gadus morhua), harp seal (Phoca groenlandica) and minke whale (Balaenoptera acutorostrata). The results indicate that cod is the most important predator, consuming about as much food annually as harp seals and minke whales combined. The consumption estimates, together with data on the amount of fish removed by commercial fisheries, are compared to estimates of the abundance and removal through natural mortality of the various species of fish prey. The consistency between these estimates is discussed. The natural mortality values for cod and haddock used in assessments are found to be reasonably consistent with the consumption estimates. The consumption of capelin is found to be higher than what is available for predation in years of low capelin abundance, while in years of high herring abundance the consumption of herring does not explain all the mortality. The way in which the consumption estimates are and can be utilised in the assessment and management of fish stocks in the Barents Sea using multispecies models and approaches is described.

A review of the battle for food in the Barents Sea: cod vs. marine mammals

“…Cod is also the most important commercial valuable fish stock in the area. Similar to cod, harp seals and minke whales exploit several trophic levels in Arctic systems, and because of their large body size, high metabolic demands and abundance, they are thought to have an important top-down effect on the structure and function of the food web (see Bowen, 1997;Bogstad et al, 2000;Folkow et al, 2000;Nilssen et al, 2000;Wassmann et al, 2006;Kovacs et al, 2009). They have also been target species for important hunting activities for a long period of time (Øien et al, 1987;Skaug et al, 2007;Haug et al, 2011).…”

“…The three most important are cod Gadus morhua, harp seals Pagophilus groenlandicus and common minke whales Balaenoptera acutorostrata (Bogstad et al, 2000;Wassmann et al, 2006;Dolgov et al, 2011). There are several other piscivorous fish and marine mammal species that reside in the Barents Sea (see e.g., Dolgov et al, 2011;Haug et al, 2011), but we have decided to not take them into consideration in this paper as their impact on fish stocks probably is much less conspicuous than that of cod, harp seal and minke whale due to their stock sizes and diet compositions.…”

Carbon transfer in a herbivore- and microbial loop-dominated pelagic food webs in the southern Barents Sea during spring and summer

“…Microbial and zooplankton compartments are a reflection of the species groups found during the Arktisk Lys og Varme (ALV) sampling campaign, as described in a special issue dedicated to Barents Sea C-flux (Wassmann 2002). Fish compartmentalisation was inferred from Bogstad et al (2000). Representative food web compartments for the area are DOC, detritus, bacteria, heterotrophic flagellates, heterotrophic ciliates, phytoplankton (pico-and nanoplankton, diatoms and Phaeocystis sp.…”

“…Differences in food web efficiency or in dependencies between both food web structures are discussed based on differences in estimated carbon budgets. The southern Barents Sea was chosen as a model ecosystem because (1) its distinct seasonality allows studying both food web types in one ecosystem, (2) its fish population sustains one of the world's largest fisheries (Bogstad et al 2000), and (3) it contains characteristics that are present in many polar systems such as the seasonal migration of species induced by spatial heterogeneity (Carmack & Wassmann 2006). The choice for the Barents Sea is also a practical one, as data on lower trophic levels (Wassmann 2002) and the most important fish stocks (ICES 2008) are abundant, which facilitates the quantitative reconstruction of food web flows.…”

“…Chaetognaths eat copepods (Tonnesson & Tiselius 2005). The food web topology within the fish community and their food was set as in Bogstad et al (2000): capelin and herring eat krill, chaetognaths and copepods, while young cod feed on krill, chaetognaths, copepods, capelin and herring. Adult cod is the top predator and can eat all zooplankton and fish, including young cod.…”