The Icelandic Waters ecoregion contains over 25 commercially exploited stocks of fish and marine invertebrates. The main demersal species include cod, haddock, saithe, redfish, Greenland halibut and various other flatfish, wolffish, tusk, and ling. The main pelagic species are capelin, summer-spawning herring, Norwegian spring-spawning herring, and mackerel.
Most fish species spawn in the warm Atlantic water off the southern and southwestern coasts. Fish larvae and 0-groups drift west and then north from the spawning grounds to nursery areas on the northwestern, northern, and eastern Iceland shelf, where they grow in a mixture of Atlantic and Arctic water.
Several major changes in the abundance, distribution, and migration patterns of the pelagic fish stocks around Iceland have taken place in recent decades, resulting from fishery, oceanographic conditions, prey availability and/or stock density. In the late 1960s, the three herring stocks found in the Icelandic Waters ecoregion collapsed. While the Icelandic summer-spawning herring recovered within several years, the Icelandic spring-spawning stock has not recovered yet. The Norwegian spring-spawning herring disappeared from the whole Icelandic Waters ecoregion simultaneously, but after recovery it has since the early 2000s progressively reoccurred on its traditional feeding grounds east and north of Iceland. From the mid-2000s, Atlantic mackerel extended its feeding grounds, moving from the Norwegian Sea to Icelandic waters in large quantities. At the same time the summer feeding grounds of capelin moved westward, from the Icelandic Waters ecoregion to Greenlandic waters, while the main spawning grounds remained southwest of Iceland.
For the stocks with analytical assessments, reference points have been defined and the spawning-stock biomass is in all cases above Btrigger (figure 10). The trends in survey biomass for gadoids and other species (redfish, tusk, ling, and wolffish) show biomass indices that are two to three times higher than their lowest observed value. The average survey biomass for the flatfish species is currently around two times the lowest observed value (figure 11).
The pelagic fish stocks are also assessed with analytical methods. The SSB of Icelandic summer-spawning herring was at its historical maximum around 2008, but has since decreased caused by mortality as a result of Ichthyophonus sp. infection and poor recruitment (figure 10). The abundance trends for the highly migratory stocks, mackerel, blue whiting, and Norwegian spring-spawning herring, are presented in the Norwegian Sea ecosystem overview.
Figure 10: Relative spawning-stock biomass (SSB to Btrigger ratios) for cod, haddock, saithe, golden redfish, ling, tusk and herring. The dotted line denotes Btrigger.
Figure 11: Trends in survey biomass, relative to its lowest value observed for plaice, lemon sole, witch, dab, cod, haddock, saithe, golden redfish, Atlantic wolffish, ling, and tusk. Note that the average (dashed line) is also standardized relative to its lowest value.