The death of north sea fish during the winter of 1962/63, particularly with reference to the sole, Solea vulgaris

Abstract

1. During the cold winter of 1962/63 fish mortalities were frequently reported over much of the North Sea to the south of the Dogger Bank. The sole populations certainly suffered the highest mortalities, but dead cod, plaice, whiting, dabs, turbot, brill and conger eel were also reported. 2. Fish began to die towards the end of February, and the numbers increased to a maximum in mid-March, after which they gradually decreased until reports ceased by mid-April. The development of mortalities was compared with the sea temperatures at the time. 3. The mortalities were on a large scale but not as great as previously reported for the cold winter of 1946/47; they may have been as heavy as those in 1928/29. Their distribution was more widespread than in either 1929 or 1947. 4. Analysis of fish blood serum showed abnormally high sodium levels in many fish caught in the colder waters. In some individuals the salt content appeared to approach lethal levels, but it was not known whether salt imbalance was the primary cause of death. 5. Flatfish were also attacked by a skin infection which certainly contributed to the deaths of many of these fish during the cold period. © 1964 Biologischen Anstalt Helgoland.