Interactions between 0-group Saithe (Pollachius virens) and 0-group Cod (Gadhus morhua) in shallow nursery areas

Abstract

In this study diet width and overlap between 0-group saithe (Pollachius virens) and 0-group cod (Gadhus morhua) was studied. Along with studying if habitat characteristics, length of the fish (cod and saithe), fjord distance, predator specie (cod or saithe) had an impact on the diet composition of the sampled fishes. A diet comparison between my diet findings and findings in earlier studies. The samples were obtained from Porsangerfjord (70-71 ˚N and 25-26 ˚E) in August 2023. The 0-groups were sampled using a beach seine in the intertidal. A total of 93 0-group saithe and 63 0-group cod were analysed in the laboratory. Diet width of the 0-group cod and saithe were similar, and there was a clear overlap in the diets of the two species, with important common prey groups ssuch as Harpacticoida, bivalves and shrimp. This overlap was found to be the largest in the outer and middle parts of the fjord. Station and species (0-group cod and saithe) was found to have the most impact on the diet composition, with fjord distance and predator length not having as much of an impact. Comparison of my diet data with earlier studies revealed a similar diet composition in my samples as in previous ones. Key differences between my diet data and previous diet data were the heavily reduced number of pelagic copepods in my data, but an increase in benthic copepods.