Pelagic Fish and the Ecological Impact of the Modern Fishing Industry in the Barents Sea
The Barents Sea/Norwegian Sea ecosystem is inhabited by two large pelagic fish stocks, the Norwegian spring spawning herring and the Barents Sea capelin. The herring stock feeds in the high-production polar front area in the western Norwegian Sea, and spawns at the Norwegian coast. The larvae are transported into the Barents Sea, where they spend the first two to four years of life. The capelin stock spends its whole life in the Barents Sea, spawning along the southern coasts and feeding in the nutrient-rich areas in the northern parts of the sea. The herring stock was brought almost to extinction during the 1960s by the combined effect of overfishing and environmental conditions. This stock is now recovering. Much fishing effort was shifted to capelin when the herring fishery was stopped, and the capelin supported large fisheries in the 1970s. In the mid 1980s, the capelin stock size suddenly declined to a very low level. The factors involved were recruitment failure, low individual growth rates, high natural mortality, and, in the last phase, high fishing mortality. The recruitment failure was most likely caused by predation by some abundant year classes of herring in 1983-85. The low growth rate was probably caused by the scarcity of prey organisms, while the high mortality rate of the adult capelin stock was an effect of predation from abundant year classes of cod during the same period. After having recovered in the period 1989-91, the capelin stock once more collapsed during 1992-93. The reasons were the same as for the collapse in the 1980s, except that fishing had no effect on the most recent collapse.
Key words: Barents Sea, ecology, fisheries, capelin, herring, polar cod