Historic changes in cod stocks and cod fisheries: Northeast Arctic cod

Observations made in Norwegian waters in this century have been used to interpret the fragmentary fishery and climate data from the period 1500 to 1900. During the Little Ice Age, lasting from about 1550 to 1850, the Northeast Arctic cod stock went through large fluctuations in stock size, as reflected in catch per unit of effort and in overall catch. Behind these fluctuations may have been faltering recruitment in periods with very cold climate and lack of herring or capelin in the Barents Sea, two main prey organisms, as both these species also experienced stock fluctuations. The potential detrimental influence of young herring on the capelin stock in the Barents Sea is also considered. The quantity of drift ice around Iceland is considered as an indicator of both the general climate influencing cod recruitment and of the productivity in the main summer-feeding area for Norwegian spring-spawning herring, northeast of Iceland. The deterioration of this area's productivity has coincided repeatedly with sudden collapses in the herring stock. In all cases, except after the fast decline in the 1960s, a recovery of the Bohuslän herring fishery followed these collapses. The fished quantities of cod and herring has increased almost 10-fold for every century during the Little Ice Age, from 50001 of herring in the 1640s to 1.2 million tonnes in the 1950s; and from 10000 t of cod in 1590 to 1.2 million tonnes in 1960s. These catch values may indicate an underexploitation of the cod and herring stock at least until the turn of the twentieth century.