Do gadoids really prefer Calanus? The prey selection through metamorphosis in Irish Sea cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangus merlangus)

No abstracts are to be cited without prior reference to the author.

Calanus is thought of as a preferred prey of gadoids in many seas, however, the Irish Sea is an area of known low Calanus and highly variable abundance. Diets of cod, haddock and whiting were studied throughout development from the yolk-sac to juvenile stage. Prey items in the stomach contents were analysed and compared to their natural abundances in the environment via an index of prey preference. Cod, haddock and whiting all selected nauplii at the onset of feeding (late yolk-sac stage), as expected, with little difference between species. As the larvae developed the prey preferences changed as small sized copepods (especially Pseudo/Paracalanus) were selected. Cod and whiting showed a similar transition of prey species preference. In both cases there was a clear preference for Calanus post-metamorphosis, above all other species of copepod. The diet composition in haddock differed to cod and whiting in that nauplii remained in the diet later into development and there was little preference for individual copepod species. It was concluded that Irish Sea cod and whiting were dependent on Calanus abundance in the Irish Sea but haddock had a considerably different diet composition at a comparable developmental stage.