The ecology of the gadoid larvae in the northern North Sea
A study was made on the ecology of the larval gadoid populations in the northern North Sea during May 1979, as a continuation of Minton's work on the same populations, conducted in April of the years 1974 and 1975 (R.C. Minton, 1977: "Species Interactions between Gadoid Larvae in the Northern North Sea." Unpublished PhD Thesis, University of Aberdeen).The study of the distribution, length composition and the feeding ecology of the larval gadoid populations, in relation to their biotic and abiotic environment, did not prove firm evidence of interactions between species. Larval mortality increased with increasing fish size and this was attributed to differential food availability for larvae of different sizes coexisting under plankton conditions of May.The characteristics of the production cycle, the timing of spawning of the fish species, as well as the morphological, anatomical and behavioural characters of the larval species, greatly determine the feeding efficiency of the larvae during the period of their planktonic existence, although most methods used to assess starvation of larvae at sea are shown to be untenable. Little evidence was found that direct inter or intraspecific competition for food happened under the larval and plankton concentration in May, although it was implied that indirect competition was possible in a subsequent season. The concept of the density dependent regulation of the size of a stock through intraspecific competition at the larval stage is critically discussed.