Management of pikeperch migrating over management areas in a Baltic archipelago area.

Pikeperch Sander lucioperca (L.) were tagged in an area where ten small independent management units regulate fisheries, in order to analyze the relevance of migrations for the management. A total of 465 fishes were tagged in connection with the spawning migration. The number of recaptures was 96. The distribution of recaptures between areas and that of total catches, estimated from questionnaire to housholds and, individuals in the survey area, were correlated. The comparison of tagging and recapture dates showed that the same pikeperch migrated to the spawning areas at the same time in two subsequent years, indicating the existence of individual spawning behavior. A modified yield/recruit-model demonstrated that in situations where the dispersal area of a pikeperch stock overlaps with several management areas, the risk of overfishing is very high. Management of this kind of fisheries needs cooperation between units as well as sound data on the movements of pikeperch to define the effects of fishing regulations.

Spatial genetic structure of northern pike (Esox lucius) in the Baltic Sea.

The genetic relationships among 337 northern pike (Esox lucius) collected from the coastal zone of the central Baltic region and the Finnish islands of Aland were analysed using five microsatellite loci. Spatial structure was delineated using both traditional F-statistics and individually based approaches including spatial autocorrelation analysis. Our results indicate that the observed genotypic distribution is incompatible with that of a single, panmictic population. Isolation by distance appears important for shaping the genetic structure of pike in this region resulting in a largely continuous genetic change over the study area. Spatial autocorrelation analysis (Moran's I) of individual pairwise genotypic data show significant positive genetic correlation among pike collected within geographical distances of less than c. 100-150 km (genetic patch size). We suggest that the genetic patch size may be used as a preliminary basis for identifying management units for pike in the Baltic Sea.