Storskarvens artpreferenser och påverkan på Krankesjöns fiskfauna - kan partiell migration för mörten minska risken att bli prederad?

Sammanfattning: This study was conducted in two lakes, Krankesjön and Vombsjön, located in Lund, Sweden. We went out for four weeks during April in order to scan for PIT-tags eaten by cormorants (Phalacrocorax carbo). These PIT-tags have been implanted in more than 12000 fishes and 12 species during the period between 2003 and 2012. The total numbers of PIT-tags found were 403 and they were distributed over eight different fish species. The results indicated that the cormorants diet varies in composition. The highest predated biomass was roach (Rutilus rutilus) (60 %) followed by rudd (Carassius carassius) (20 %). In addition bleak (Alburnus alburnus) had the highest quotient of predated individuals divided by total tagged individuals while pike (Esox lucius) had the smallest. The results showed that rudd had a greater risk of being predated by the cormorant as compared with roach. Moreover roach that expressed migratory behavior had a significantly lower risk of mortality by cormorant predation compared to roach that were resident in the lake. Furthermore the probability of being prayed by the cormorant was negatively converted to the time a roach spend out of the lake. Finally, cormorants did not show any preference for any special body length of the fish. My results are of importance for local wild-life management and add more data about how migratory behavior can decrease predation risk in the wild.