Effect of recruitment, individual weights, fishing effort, and fluctuating longline catchability on the catch of Faroe Plateau cod (Gadus morhua L.) in the period 1989-1999

The catch of Faroe Plateau cod fluctuated more in the 1990s than during almost any time in the previous 90 years, and one main aim of this study was to investigate whether the behaviour of cod was anomalous (e.g. large-scale migrations) during these years. It was found that the behaviour of cod was normal in the 1990s (except possibly in 1996) and that variations in recruitment, individual fish weights, fishing effort, and catchability (catch per unit effort divided by stock abundance) were the most important factors that determined the catch of cod. The fluctuating catchability especially applied to longlines where a negative relationship between catchability and individual growth rate of cod was found, indicating that cod preferred longline baits when the abundance of natural food organisms, was scarce. The study also shows that cod production was highly correlated with primary production. This indicates that primary production was the driving force behind recruitment and individual growth and hence the collapse of the cod stock in 1991 as well as its rapid recovery in 1995.