Theme D: Developing optimal release strategies
32. CARRYING CAPACITY IN JUVENILE STAGES OF EUROPEAN LOBSTER (HOMARUS GAMMARUS); ESSENTIAL KNOWLEDGE FOR RESTOCKING/SEA RANCHING
Ann-Lisbeth Agnalt, Eva Farestveit and Knut E. Jørstad
Institute of Marine Research, P.O. Box 1870 Nordnes, 5817 Bergen, Norway
ann-lisbeth.agnalt@imr.no
Carrying capacity in an ecological perspective can be defined as total number of individuals of a population a given environment can sustain. In aquaculture it refers to the potential maximum production that can be maintained within an area relative to available food and environmental resources. Carrying capacity can eventually reach a limit and thus reduce the production, either due to perturbations of the environment or to overexploitation of the food source. Lobster is highly valued seafood and has been commercially harvested along the coast of Norway for centuries. Declining wild populations have resulted in renewed interest in restocking as well as sea ranching. Wild juvenile European lobster (Homarus gammarus) smaller than 40 mm carapace length have rarely been captured, hence we have no knowledge of neither preferred substrate the juveniles live on/in nor carrying capacity. Previous experimental studies on early benthic phase indicated preference to settle in a complex substrate of sand/cobble. The sheltering behaviour in these early-life stages is considered an antipredator response. Knowledge of the early benthic stage of European lobster is considered crucial for restocking and sea ranching endeavours. A series of experiments were run aiming to estimate juvenile density under controlled conditions. Pelagic stage IV larvae were released at densities from 10 to 40 per m2 into tanks stocked with shell sand and shelter. After 8 months, the various experiments yielded from 8 to 20 juveniles per m2. Highest mortalities were found in the experiments with highest release density (82%). There were indications that the carrying capacity had not been reached in the experiments with lowest release density. This was also the experiments with lowest mortality (32%). Perspectives of possibilities to further increase the carrying capacity will be discussed.
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