Movement, spillover and gene flow within a network of northern marine reserves

• Main Author: Huserbråten, Mats
• Format: Master Thesis
• Language: English
• Published: 2012
• Subjects: VDP::470; European lobster; Homarus gammarus
• Online Access: http://hdl.handle.net/10852/35139; http://urn.nb.no/URN:NBN:no-33677

The lack of empirical knowledge on how marine reserves should be effectively designed has impeded their extensive implementation as fisheries management tools. While current knowledge is largely based on computer models, few studies have verified them in the field. This study addresses several aspects of European lobster (Homarus gammarus) biology, directly related to future design of lobster reserves. First, spillover from reserves was measured by capture-mark-recapture studies. Second, probability of lobsters’ presence within a reserve over time, along with their seasonal depth use, was quantified by acoustic telemetry. Third, connectivity of lobsters in Skagerrak was extrapolated from gene flow by microsatellite markers. Out of 2067 lobsters tagged within three reserves (0.5 km2-1 km2), only 3.6% was caught beyond reserve boundaries, with a mean spillover distance of 3.7 km. In comparison, 36.4% of tagged lobsters were recaptured within reserves. Moreover, individual lobsters were 50% likely to stay within a 0.5 km2 reserve for a whole year. Males, and especially ovigerous females, used deeper habitats throughout the winter (≤58m), compared to mean depth use (≈24 m). Furthermore, analyses of microsatellite markers revealed a subtle, although significant genetic structure ( FST= 0.000, 95% CI:from 0.001 to-0.001, p =0.039). Despite their small area, the reserves appeared to be sufficiently large to both contain a significant number of lobsters, and supply moderate levels of spillover to surrounding (fished) areas. Extensive gene flow within the study area indicates high connectivity. An extrapolation into effective migrants, done based on overall FST 95% confidence limits and effective population sizes ranging from 50 to 1000 individuals, showed that: at least 35 to 183 individuals were exchanged among sampled sub-populations every generation, and at most there was full exchange of migrants. Thus genetic data suggests that reserves could (hypothetically) exchange a demographically relevant number of migrants, given high effective population sizes within large reserves. These results could be of great importance for future design of reserve-networks containing species with a similar life history as the European lobster.