Coastal cod and north-east Arctic cod - do they mingle at the spawning grounds in Lofoten?

Abstract

Abstract Cod (Gadus morhua L.) off northern Norway are divided into two main groups. The north-east Arctic cod (NAC) migrate southwards from the Barents Sea to the main spawning area near the Lofoten Islands on the coast off northern Norway. Coastal cod (CC) are relatively stationary, live and spawn along the entire Norwegian coast, including near the Lofoten Islands. In order to test if the two groups physically intermingle at the spawning grounds, cod were sampled by trawl and Danish seine at the traditionally important spawning grounds near the Lofoten Islands during the spawning season in 1995-97. Cod from 24 samples were examined for haemoglobin alleles, length, sex and stage of sexual maturity. The results indicate that: (I) NAC and CC did not mingle randomly. (2) However, specimens from both groups may stay simultaneously at the same local spawning ground within an area of less than 0.012 km2- (3) Distribution of NAC and CC overlapped vertically, although NAC was more abundant than CC in samples from deep waters. (4) The sex ratio was skewed towards males in a majority of the samples. (5) A larger percentage of males compared to females was ready to spawn. (6) Cod shoals may be size-assorted. The results are discussed in relation to existing hypotheses about cod spawning behaviour.