Distribution and abundance of Norwegian spring spawning herring during the spawning season in 1999

Abstract

During the period 15.02-21.03.99 the maturing and spawning herring (Clupea havengus L.) were distributed along the Norwegian coast from 57°N to 69°N. Between 61°N and 69°N the biomass and abundance estimates were 7.1 million tonnes and 27.6 billion individuals respectively, whereas between 57°N and 60°N the respective estimates were 90 thousand tonnes and 323 million individuals at the highest. The 1992 and 1991 year classes predominated the spawning stock with 42.7 % and 27.3 % respectively, but the proportion of 1991 year class tended to increase northwards from 62°N. The average overall body length, condition factor, somatic condition factor and gonad condition factor tended to increase southwards. This tendency was also recorded within year classes. The temperature and salinity increased with depth. In addition these parameters tended to decrease northwards and southwards from 62°N at all depths, and they tended to decrease at bank areas (depth < 200 m), i.e. spawning areas. North of 61°N the herring mainly spawned at depths between 100-200 m with ambient temperatures at 6-8°C and a salinity of 33.5-35 ‰. South of 61°N the majority of the herring spawned at depths below 75 m with temperatures at 3.5-6OC and a salinity at 32.5-34 ‰.