FEEDING OF LARVAL BLUE WHITING AND ATLANTIC MACKEREL - A COMPARISON OF FORAGING STRATEGIES

Fish larvae employ different feeding strategies depending on area and season of spawning and hatching of larvae. Feeding and growth of larva e of blue whiting Micromesistius poutassou and mackerel Scomber scombr us from Porcupine Bank and the Celtic Shelf Break, west of Ireland, we re compared based on prey concentrations in the environment and larval feeding behaviour. Both species were adapted to different environment al conditions. The mesopelagic blue whiting spawned in oceanic water t hat was well mixed. It was characterized by low production and low pre y densities with minimum prey densities <1.0 organism l(-1). Larvae of the Atlantic mackerel hatched later in the season in more productive water that was well stratified. Prey densities in the mackerel environ ment reached up to 100 l(-1). Blue whiting larvae displayed a rather r andom distribution in the water column. Mackerel larvae <7 mm standard length (L-s) were concentrated above the thermocline, while larvae >7 mm traversed the thermocline into deeper layers. Mackerel larvae >5 m m L-s displayed marked cannibalism, exceeding 70%. Daily ration calcul ated on the basis of gut contents was rather low in both species: betw een 2.6 and 5.0% in blue whiting, but only 0.6 to 5.4% in mackerel. Th e results are discussed in relation to the respective environment both species encounter during their early larval life. (C) 1997 The Fisher ies Society of the British Isles.