MEPS prepress abstract  -  DOI:

Seabirds as guides for fisheries management: European shag Phalacrocorax aristotelis diet as indicator of saithe Pollachius virens recruitment

Svein-HÃ¥kon Lorentsen*, Tycho Anker-Nilssen, Kjell Einar Erikstad


ABSTRACT: In fisheries management assessing year-class strength and recruitment to commercial stocks is essential, yet might be difficult to obtain for fish species where the young stages are inaccessible for ship-based surveys. This is true for the Northeast Arctic saithe Pollachius virens, where the juveniles spend their first years in coastal kelp forests and therefore cannot be assessed before they enter the pelagic stock at 3 years of age. However, as top predators in marine ecosystems, coastal seabirds might prey on the same cohort 2-3 years earlier. Long-term studies of European shag Phalacrocorax aristotelis at a colony in Central Norway have revealed strong links between the birds’ breeding performance and the availability of 0- and 1-year old saithe in their diet. Following this, we wanted to explore if shag diet can be used as an early indicator of saithe recruitment by comparing it with abundance indices obtained by fisheries research. Our results indicate that the occurrence of 0-year old saithe in the shag diet is a poor predictor of saithe recruitment 3 years later. However, both the pre- and post-hatch biomass, the number and the frequency of occurrence of 1-year old saithe show a strong positive relationship with indices obtained from scientific surveys 2 years later, indicating that shag diet can be used as an early and reasonably reliable predictor of saithe recruitment. We suggest implementing the occurrence of 1-year old saithe in the shag diet as a supplementary tool for an adaptive management of the fisheries on young saithe.