European lobster subpopulations from limited adult movements and larval retention

Øresland, V., and Ulmestrand, M. 2013. European lobster subpopulations from limited adult movements and larval retention. – ICES Journal of Marine Science, 70: 532–539. Adults and larvae of the European lobster, Homarus gammarus, were studied within and around the Swedish Kåvra lobster reserve (2.2 km2). Tagging of 4016 lobsters within the reserve showed that the lobsters have limited movement out of the reserve. Only 58 lobsters (1.4% of all tagged lobsters) were recaptured ≥1 km from the reserve and 5658 recaptures were obtained inside the reserve. Light trap catches showed that stage 1 larvae had a peak occurrence during <2 weeks, in early August, 2007–2009. The mean depth distribution of stage 1 larvae was 16 m and very few larvae were found in the low saline surface layer. No later stages were found in horizontal net tows. The lobsters inside the reserve provided stage 1 larvae to the nearby area. A persistent retention of water masses was found at 16-m depth (below the sharp halocline) in the area (16 km2) around the reserve using IMR GPS Current Drifters. In sharp contrast, surface drifters showed strong offshore and inshore movements. The Swedish archipelago might harbour many lobster and other decapod subpopulations, if the larval stages occur in a large proportion below the sharp halocline and if adult movements are limited.