Extreme male-skewed sex ratios on spawning grounds for Atlantic cod Gadus morhua with typical coastal cod signatures of the Pan I (pantophysin) locus

Abstract

Large offshore and small inshore populations of Atlantic cod Gadus morhua L. display differences in migratory patterns and settling regimes, but little is known about possible differences in spawning behaviour. Cod presumably of the Norwegian coastal cod type were therefore sampled during 7 spawning seasons (2002-2013) in Malangen, northern Norway. Length, weight, sex and maturity stage were recorded for each individual fish. To verify their population assignment, frequencies of the 2 different Pan I (pantophysin) alleles were measured in 6 sampling years in Malangen and 3 in Balsfjord. The frequency of the Pan I[supA] allele of the Malangen cod was highly stable among years at close to 90%, showing that this spawning ground is exclusively used by coastal cod. This fiord is suggested to be more penetrable for the migratory NE Arctic cod with their high frequencies of the Pan I[supB] allele, making it a less exclusively coastal cod residence. In both fjords, length of mature males but not females varied among the Pan I genotypes.