Canadian journal of fisheries and aquatic sciences vol:57 issue:7 pages:1404-1409
A model describing fish abundance resulting from fish migration and mortality in an upper estuary is presented. This model can be used to estimate biomass transports by fish migrations between estuary and sea and to assess production assimilated in the estuary. It was applied to herring Clupea harengus L., a marine species with 0+ juveniles that migrate during winter to temperate European estuaries. It was shown that different mortality regimes greatly affected the number of fish that eventually emigrated and, hence, the biomass that was exported during the seaward migration. The difference between imported and exported biomass was assessed under different growth conditions and varied from positive to negative as mortality rates increased. The discrepancy between export of biomass and in situ produced biomass showed that fish production was not necessarily transported to the sea when emigrating. It was tentatively concluded that export of biomass out of the estuary only occurs if populations move seaward before winter.