Demography of coastal Atlantic cod in relation to the establishment of a marine protected area
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Use a mark-recapture approach to study the demography of Atlantic cod (Gadus morhua) in a small (1 km2) marine protected area (MPA) on the Norwegian Skagerrak coast. A total of 9713 Atlantic cod where tagged during 2005-2010. Inside the MPA, only hook and line fishing is allowed. Data are partly live capture-recaptures from the research fishing activity, and partly dead recoveries from commercial and recreational fishers. A high-reward system was applied to quantify the tag reporting rate from fishers. We estimated the tag reporting rate to be 72.4 % for recreational fishers and 73.8 % for commercial fishers. Based on this, our data suggests that recreational fishing has a larger impact on cod mortality than commercial fishing in this area. Adjusted for recovery rate we estimate that the recreational fishers captured 2289 of the tagged cod, corresponding to 71 % of all recoveries, while commercial fishers captured 954 fish, corresponding to 29 % of all recoveries. Capture-mark-recapture (CMR) modelling tools were used to estimate annual survival rates. Survival varied both in time and among areas. In the live-recapture model estimates apparent survival ranged between 0.3>- 0.6. The joint model the true survival range was 0.3< - 0.9. One year after protection both live-recapture model and joint model the survival estimates were higher in MPA then in the reference locality. Subjecting that the MPA might had an effect.
Masteroppgave i marin økologi - Universitetet i Nordland, 2012