The distribution of cod larvae and prey organism in the Lofoten area related to critical prey concentration

Abstract

The distribution of cod larvae and their main prey organisms in the first feeding areas off the Lofoten islands have been studied in sheltered and exposed areas in relation to feeding conditions. These findings are discussed in relation to laboratory studies on larval feeding dynamics and food density required to meet matebolic demands. It was found that the cod larvae are sporadic feeders having intervals of digestion between feeding periods. The maximu, gut filling of first feeding cod larvae was close to 3 prey/larval gut when nauplii were the dominant food organism. The larval gut evacuation processes were dependent on the value and state of degestion of the gut content. The critical prey density for first feeding cod larvae varied between 21 nauplii/1 and 190 nauplii/1 depending on larval swimming speed and feeding success. The highest concentrations of both cod larvae and its main prey organism, copepod nauplii, were found in the Austnesfjord, Hølla, Henningsvær and the Vesterålsfjord area. Patches of nauplii in densities between 50-100 per liter were found in these areas. From larval cod gut content analyses good agreement was found between feeding conditions and food density distribution. The effect of increased wind forces created a homogenous vertical distribution of both cod larvae and prey organisms causing reduced accessibility of food to the cod larvae.