Fisheries Oceanographic Processes

The Fisheries Oceanographic Processes investigation within the Office of Marine Ecosystem Studies addresses a range of research problems that provides overarching integrative analyses of ecosystem management issues. These data are expected to satisfy the increasingly complex requirements of parameterizing models being developed cooperatively by the Northeast Fisheries Science Center and to address process response to climate change and variability. Model construction has the concomitant requirement of model validation, which in addition to providing evidence for model acceptance also shows how they can be improved and be made more realistic. Many of our studies provide the organism-based data that can be applied to model validation.

Ocean climate and the reproductive output of fishery resources

American shad is a diadromous species that ranges along the east coast of the United States. During their marine phase, they make up part of the pelagic food web on the continental shelf. Population sizes of shad have changed dramatically over time spurring interest in the reproductive success of individual river stocks. A five year study was undertaken to measure fecundity and egg size of shad entering the Connecticut River. Along with data on reproductive output, stable isotope composition of their scales were collected as indicators of feeding and condition. The condition and feeding history of individual fish appears to exert a direct control over fecundity. These results have spurred interest in the environment factors controlling feeding and growth.

Recent evidence suggests that gadoid species can suffer recruitment failure when reproductive output is compromised. The most obvious indicators of this problem are depressed fecundity and egg size. In other ecosystems comparable to those on the Northeast Shelf, recruitment failure, attributed to climate change, manifests itself in biological indicators such as growth, condition, and reproductive output. With refinements of image processing based techniques, systematic measurements of fecundity and egg size are underway with haddock and related species

Factors affecting the
availability of
Atlantic herring,
Clupea harengus

Retrospective growth
analyses of Atlantic salmon,
Salmo salar

The comparison of retrospective growth histories of a suite of Atlantic salmon stocks has revealed patterns of stock synchrony, provided estimates of migration mixing rates, helped locate juvenile nurseries areas, and elucidated recruitment mechanisms. Recently collected data from the Greenland fishery suggests that post-smolt growth of North American and European stocks is beginning to converge suggesting different recruitment mechanisms for the two stock complexes.

Many salmon stocks at the southern end of the species range in North America are threatened with extirpation. A number of hypotheses have been advanced to explain this decline, but clearly a major factor has been poor survival at sea. Ongoing investigations have detected a climate link at both the local and basin scales. Locally, salmon stocks appear to be impacted by a mismatch between juvenile seaward migration and the ocean conditions found by the juvenile fish. Basin wide, tele-connections between North American and European stocks suggest climate forcing, as expressed in the North Atlantic Oscillation and the position of the Gulf Stream, appears to affect both stock complexes.

The collapse of the filter feeding component of estuarine and coastal food webs is thought to be a major factor in the continued poor water quality conditions of a number of marine and estuarine systems. Critical to making informed management decisions about water quality and fisheries will be the advice derived from ecosystem models. Currently, menhaden filtration efficiency is incorrectly parameterized in these models, thus creating the need for better ontogenetic data on the filtering ability of relevant size ranges of the fish. This need is being addressed by analyzing the function morphology of the menhaden branchial basket.