Over 200 species of fish have been recorded in trawl catches during surveys in the Barents Sea, of which about 100 occur regularly. Different water bodies together with the bottom type and depth are important factors that determine the distribution of fish species. The distribution and abundance of zooplankton are additionally important factors for pelagic species. The most important demersal fish species are as follows:
- Northeast Arctic cod,
- Northeast Arctic haddock,
- Red fish,
- Greenland halibut,
- Long coarse dab,
- Wolf fish,
- European kitty,
Important pelagic species are Barents Sea capelin, arctic cod and immature Norwegian spring-laying herring. In some warm years, an increasing number of young blue whiting migrated to the Barents Sea. There have been great variations in the abundance of most of these species. These variations result from a combination of fishing pressure and environmental variability. The collection of Barents Sea fish species has varied greatly from year to year. This variability in breeding causes large changes in the biomass of pelagic forage fish, which are all short-lived or spend only a short part of their life in the Barents Sea. The most important reasons for breeding variability are differences in spawning biomass and hydrographic conditions. Also, changes in the circulation pattern affect food availability, predator abundance and distribution.
Recent studies on larval drift have shown that even small changes in spawning locations can have a major impact on the drift pattern of fish larvae. The drift of cod and herring eggs and larvae occurring in different locations along the Norwegian coast has been studied. The results show that spawning more in the open sea and more south gives the larvae a much higher probability of terminating west of Svalbard. On the contrary, more northern spawning results in higher proportion of larvae entering the Barents Sea. Also, the retention of the larvae was affected by the spawning ground and therefore the development stage when the larvae reached the entrance of the Barents Sea. A report on the knowledge base in the Lofoten area showed that around 70% of the egg, larvae and juvenile stages of total commercial stocks in Norway and the Barents Sea pass through the Lofoten -– Vesterålen area. About 12% of total stocks occur in the Barents Sea.
Cod is the most important predator of the Barents Sea fish species. Larger zooplanktons feed on a wide variety of prey such as shrimp and most fish species available, including their own offspring. Cod prefers capelin as prey, and fluctuations in capelin stock can have a strong impact on cod cannibalism as well as cod growth, maturation and fertility, and therefore stock uptake. The role of euphausiids in the cod diet increases in years when capelin stock is low. Also, annual variations in euphausiid abundance are important for cod survival in the first year of life, according to Ponomarenko.
Capelin is a major consumer of zooplankton biomass produced near the ice rim. Further south, the capelin is the most important prey species in the Barents Sea as it carries biomass from north to south. Barents Sea capelin stock has seen significant changes in stock size over the past three decades. Three stock collapses occurred in 1985–1989, 1993–1997 and 2003–2006, indicating the collapse of the capelin, according to data obtained in 2015. The slump had both up and down effects on the food web. The release of predatory pressure from the capelin stock led to increased amounts of zooplankton in the first two subsidence periods. When the capelin biomass was greatly reduced, its predators were impacted in various ways, and cod increased during the initial capelin collapse, growth decreased and maturation delayed.
Seabird mortality rates increased and total employment failed, and breeding colonies were abandoned for several years. There have been increases in food shortages and mortality rates due to harp seals invading coastal areas, catching fishing gears, and recruitment failures. There is evidence of differences in how the collapse of the three capelles affected predators. The effects were greatest during the 1985-1989 crash, but were much less affected during the second and third crashes. This is probably related to the increased availability of alternative food sources in the last two decades. Herring is also a great predator in zooplankton. It emerges on the west coast of Norway and the larvae drift into the Barents Sea and fjords along the coast. The offspring of herring stock that lay eggs in the spring in Norway are distributed in the southern parts of the Barents Sea.
They stay in this area for about three years before migrating west and south along the Norwegian coast and mixing with the adult part of the stock. It is explained that the presence of young herring in this region has a profound effect on the survival of capelin larvae and thus on participation in capelin stock. All three crashes in the past thirty years are due to recruitment failures, and all three are associated with the rich herring year classes living in the Barents Sea. Haddock is also a common species and migrates partly out of the Barents Sea. Stock has large natural variations in stock size. The water temperature in the first years of the life cycle can be used as an indicator of year class strength. The nutritional composition of haddock consists mainly of benthic organisms.
Saithe is found mainly off the coast of Norway, but is also found in the Norwegian Sea and the South Barents Sea. 0-group saithe drifts from spawning grounds towards coastal waters. Small individuals feed on crustaceans, while larger saithe depend more on fish for prey. The main fishing catches are young herring, Norwegian poultry, haddock, blue haddock and capelin, while the dominant shellfish catch is krill. The arctic cod is a cold-water species found mainly in the east and north of the Barents Sea. It looks like an important bait fish for a few marine mammals. There is very little fishing in this stock and it is clear that stock abundance is decreasing. Deep sea redfish and golden red fish are important elements of the fish fauna of the Barents Sea. However, due to overfishing, these stocks declined strongly in the 1980s and have remained at a low level since then. Young redfish are plankton eaters, but larger individuals receive larger prey, including fish.
Greenland halibut is a large fish catcher whose most important area is the continental slope between the Barents Sea and the Norwegian Sea. It is also found in the deeper parts of the Barents Sea and on the continental shelf. Research from 1980-1990 shows that cephalopods are dominant in Greenland halibut stomachs and fish. The ontogenetic shift in prey preference is evident by the decrease in the proportion of small prey and the increasing proportion of larger fish with increased predator length. The largest Greenland halibut contains sizable amounts of cod and haddock in the diet. Stockpiles are overfishing that led to low stock abundance in the 1980s.
The main distribution area of blue whiting is located in the Norwegian Sea and the Northeast Atlantic, and its marginal northern distribution is at the entrance to the Barents Sea. Generally, the blue whiting population in the Barents Sea is small. Blue whiting can enter the Barents Sea in large numbers in some years and may be a dominant species in western regions. This occurred between 2001 and 2003-2007, and since then, the abundance has declined strongly, but has increased in 2012. These fluctuations are likely due to a combination of changes in stock size and environmental conditions. While zooplankton predominates in younger age groups in feeding blue whiting, fish become increasingly important as the blue whiting ages.
Author: Ozlem Guvenc Agaoglu