Incorporating Spatial Structure in Stock Assessment: Movement Modeling in Marine Fish Population Dynamics

Abstract

Investigations into population structure have been at the forefront of fisheries research for decades, yet it is generally ignored in stock assessment models. As the complex nature of marine population structure has been uncovered, models have attempted to accurately portray it through the development of spatially explicit assessments that allow for movement between sub-populations. Although current tag-integrated movement models are highly complex, many arose from the relatively simple models of Beverton and Holt (1957). This article traces the historical development of these models and compares their features. Originally estimation of movement utilized only tag-recapture models, but now tag-integrated assessment models incorporate several sources of fishery, survey, and tag-recapture information to inform movement estimates. As spatial management measures become more widely used, it is increasingly important that assessment models include the spatial complexities of population structure and patterns of fishery removals, in order for more reliable monitoring of population rebuilding to take place. A generalized metapopulation model is proposed for use in fisheries stock assessment, which allows for adult movement among spatially discrete sub-populations. The input requirements for the model include region-specific catch-at-age, a tag-recapture dataset, and auxiliary information, such as a fishery-independent abundance index.

Keywords:

• movement
• population dynamics
• spatial modeling
• stock assessment
• mark-recapture

ACKNOWLEDGMENTS

This collaboration was formed during an American Fisheries Society Symposium on “Tagging and Its Use in Stock Assessments” (2008, Ottawa, Canada); the authors thank Doug Vaughn, Paul Conn, and John Hoenig for organizing the symposium. This review developed through interactions associated with a “Workshop on Spatial Structure and Dynamics of Walleye Pollock in the Bering Sea” (2009, Seattle, Washington, USA), funded by the Pollock Conservation Cooperative Research Center, and benefited from input from colleagues Jim Ianelli, Jon Loehrke, Sara Miller, Peter Hulson, and others. This work was helped by the many visionary fishery scientists whose work was reviewed. Thanks also to Chris Legault, Brian Rothschild, and Geoff Cowles who provided input and insight as part of DRG's graduate committee. Finally, this review was completed during TJQ's sabbatical at the University of Massachusetts-Dartmouth (supported by the University of Alaska, Fairbanks, and the Massachusetts Marine Fisheries Institute) and was improved by feedback from students and co-instructor Tony Wood during a graduate course on “Analysis of Tagging Data.”