Date of Award

5-2014

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

James Wilson

Second Committee Member

Yong Chen

Third Committee Member

James Acheson

Abstract

Fisheries management bases its science on assumptions of broad-scale homogeneity of the behavior and dynamics of fishes and fishermen. However, the study and theory of complex systems such as fisheries calls into question these assumptions. Based on complexity theory, I hypothesized that trophic interactions in fisheries ecosystems exhibit scale-dependent, heterogenous organization, as do the decision-making processes and information networks of fishermen. I examined spatiotemporal factors that might influence spiny dogfish diet (Squalus acanthias, L.) in the Gulf of Maine using stable isotopes and stomach contents analysis. Through ethnographic research, including oral histories, semistructured interviews, and participant observation with Maine groundfish fishermen and Alaskan salmon purse seiners, I examined questions of scale and organization in fishermen’s decision-making processes and social structures.

Chapter one introduces some of the basic tenets of complexity theory, and from these draws the hypothesis that both the fish and the human components of fisheries so- cio-ecological systems exhibit heterogenous organization at multiple scales. The chapter then offers a primer on complexity theory, including the characteristics of complex systems, how they function, and why this might be important for examination of fisheries.

The second chapter focuses on scale-dependent spatiotemporal variation in spiny dogfish diet in the Gulf of Maine. This is of particular interest currently due to increasing spiny dogfish populations, historically low abundances of commercially important groundfish species that may have trophic interactions with spiny dogfish, and because ecosystems-based fisheries management is on the agenda nationally. My analysis of diet includes generalized linear models to determine the most important factors related to the importance of top prey taxa and groups in stomach contents, as well as models for stable carbon and nitrogen isotopes to test for what factors are related to benthic versus pelagic food habits and trophic level. Results from both stomach contents and isotope analysis show that season, decade, area within the Gulf of Maine, distance from shore, and total length of the predator are important factors. In particular, trophic interactions are different in the inshore, shallow East region of the Gulf of Maine.

Fishermen self-organize their decisions into scale-dependent hierarchies that greatly enhance the efficiency of adapting their decisions to scale-dependent patterns in the observed behavior of the fishes they target. Chapter three examines these decisions hierarchies, as well as the decreasing size of information networks at finer-scales of information sharing. Results from this research show scale-dependent heterogenous structure in the patterns fishermen observe in the natural environment, in information networks, and in the organization of decisions while fishing.

The final chapter discusses the results from the spiny dogfish diet study and the examination of the organization of fishermen’s decisions and information networks. The multiscale, heterogenous organization of both fish and fishermen found in this study contrasts with assumptions of broad-scale homogeneity in fisheries science and management. Meaningful, effective management will need to account for this organization especially as the United States moves towards ecosystems-based fisheries management.

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