IDENTIFYING SPATIAL SCALES OF FISHERIES STOCK STRUCTURE AND CONDITIONS THAT IMPROVE THEIR MANAGEMENT

Overfishing is widely recognized as a major impediment to the long term sustainability of seafood harvests. Overfishing is evident in the Gulf of Maine off the northeastern coast of North America where large predators experienced stock collapses in the late twentieth century. One hypothesis explaining the decline and subsequent lack of recovery of Gulf of Maine groundfish stocks is a mismatch of spatial scales between fisheries management and the boundaries of the fishes’ movement. Although such a mismatch may be unavoidable, it is important to identify when one occurs and implement policies or incentives to prevent overfishing.

This thesis highlights some techniques to describe the biological scale of a stock and tools to manage a stock sustainably despite a mismatch. The groundfish survey data showed evidence of small-scale variation in stock structure. While this small-scale variation suggests that the scale at which these stocks are currently managed should be adjusted to smaller scales, the model results emphasize that in the face of a mismatch, overfishing may be prevented with wise use of economic incentives and management policies. However, a sound understanding of biological parameters, such as recruitment levels, is critical to determine appropriate management strategies, and some control of the economic system surrounding fish harvests, such as prices, may be necessary to prevent overfishing. Although mismatches between fish stocks and management scales may be inevitable, an adequate understanding of the fisheries’ biology and economics can provide powerful tools for preventing overfishing.