A Note on the Seasonal Change in Fat Content of the Autumn-Spawning Herring in the Northern Irish Sea

Abstract

Brander & Dickson (1984) observed that fish production in the Irish Sea is low compared with fish production in the North Sea. They identified the lower number of recruiting fish as being the main reason for this difference. They presented circumstantial evidence suggesting that the low recruitment of fish is in turn linked to the shorter and later production cycle in the Irish Sea but the nature of this link is not understood. An example of the way that fish populations are affected by timing of events in the plankton production cycle is provided by the annual fat cycle of herring. Many workers have shown conclusively that the fat content of the herring is intimately connected with feeding and the time of spawning (e.g. Milroy, 1907; Johnstone, 1915; Bruce, 1924; Hansen, 1955).