Relations between seasonal migrations and fat content in Norwegian spring spawning herring (Clupea harengus L.)

The relationship between seasonal migrations and fat content in Norwegian spring spawning\nherring (whole herring and fillets) was examined using data for the period 1994-1996. During\nthe feeding period (April-August) in the Norwegian Sea the herring stored a considerable\namount of fat as energy reserves. When the stock entered the wintering area in Vestfjorden in\nautumn (August-September), the fat content was approximately 21-22%. From the time of\narrival in Vestfjorden to the end of spawning (March-April) the herring did not feed. During\nthis period the fat store was used for metabolism and gonad development. The decrease in fat\ncontent during the wintering period (September-December) was only around 2%. However,\nthe energy expenditure during spawning migration was quite extensive. The fat content was\nreduced by approximately 10% during the spawning migration and spawning period (January/April).\nThe fat content was higher in the body fillets (muscles and skin) than in the whole\nherring during the wintering period and spawning migration, and lower after spawning and\nduring feeding season. The fat content was approximately 3% lower in fillets without skin\ncompared to fillets containing skin.\nA positive correlation was found between the fish weight and fat content in herring\nfrom the spawning area off Møre, while no correlation was found in the wintering area. This\nindicates that the energy expenditure during spawning migration is higher in small herring\ncompared to larger individuals. There was no consistent difference in fat content between\nmale and female herring.