Poster Abstract
2. CONDITIONING IMPROVES SURVIVAL OF HATCHERY-REARED JUVENILE EUROPEAN LOBSTER (HOMARUS GAMMARUS)
Ann-Lisbeth Agnalt1, Eva Farestveit1, Ellen Sofie Grefsrud1, Asbjørn Drengstig2 and Knut Eirik Jørstad1
1 Institute of Marine Research, P.O.Box 1870 Nordnes, 5817 Bergen, Norway
2 Norwegian Lobster Farm AS, P.O. Box 391, 4067 Stavanger, Norway
ann-lisbeth.agnalt@imr.no
Predation immediately after release has been regarded a major limitation with releases of European lobster (Homarus gammarus), whether for sea-ranching or restocking purposes. Lobster is traditionally reared individually, in single compartments deprived stimuli of substrate, shelter and interaction with con species, i.e. naïve (Fig 1a). A series of experiments were conducted to test if an enriched environment, i.e. conditioning, can improve performance and survival (Fig 1b). In the first set of experiments, 20 naïve and 20 conditioned juveniles of the same sizes were introduced into tanks (4 m2) with shell sand as substrate, and offered 20 shelters. The conditioning period had lasted from the settling stage IV until about 4 months of age. All the 40 individuals had to compete for the 20 shelters. The treatment groups were tagged with different colours of elastomer tags (Northwest Marine Technology), for later identification. After 12 days, all shelters were occupied by juveniles. Of those that had not found shelter, about 80% were from the single-compartment group. At the end of the experiment (3 months), about 88% of those that had found shelter had previously been conditioned.
In the second experiment, naïve juveniles were purchased from a commercial hatchery (Norwegian Lobster Farm AS). One group was conditioned for shell sand and shelter for 6 ½ week. The other group continued in single compartments for the same period. The treatment groups were tagged with different colours of elastomer tags, for later identification. The juveniles were released in equal numbers into two enclosures (10 m2), placed on the bottom of a lobster holding park facility. The bottom of the enclosures consisted of shell sand and shelter (empty shells of scallop and oyster). After 9 months, from 66 to 75% of the surviving lobsters were those that had been conditioned prior to release. These data are the first to demonstrate that hatchery-reared lobster juveniles can be conditioned and we suggest that this may serve as a strategy to train hatchery-reared lobster prior to releases into the wild.
Figure 1. a) single-compartment and b) conditioned environment with shell sand and shelter (in this picture: empty scallops).
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