To Lump, or to Split? maybe the wrong question for stock identification of fishery resoures

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Stock identification for fishery management typically involves delineation of allopatric groups that have relatively homogeneous vital rates, are essentially self-sustaining and reproductively isolated from other groups. However, geographic stock structure of marine populations is seldom so simple, and distinct population processes and fishery effects operate at different spatial scales. Some components of biological production are sensitive to large-scale oceanic and atmospheric factors, as illustrated by recruitment and growth patterns of cod (Gadus morhua) resources throughout the northwest Atlantic. Conversely, population structure is also influenced by small-scale processes that help maintain local spawning groups, as evidenced by fine-scale genetic structure of cod in the Gulf of Maine and elsewhere in the northwest Atlantic. The difficulties associated with monitoring and managing fishery resources as allopatric groups suggest that a more pluralistic and operational approach to stock identification may be more appropriate. For example, recognition of small-scale structure and groups with similar growth, maturity and mortality rates are most effective for short-term catch and spawning stock forecasts. At the other extreme, medium- or long-term rebuilding programs should consider large-scale factors that influence regional recruitment dynamics across many distinct spawning groups. The optimal spatial scale for catch monitoring and stock assessment modeling may be more determined by fleet dynamics (e.g., fishing grounds) and require stock composition analysis if fisheries harvest mixed stocks. Consideration of large-scale influences and sympatric population structure may improve the effectiveness of fishery management.