UBC Theses and Dissertations

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UBC Theses and Dissertations

The development of an agent-based depletion model of Dungeness crab for the evaluation of seasonal management options Greenberg, Aaron


Dungeness crab (Cancer magister) range from the Aleutian Islands to Central California and grow by moulting in the springtime, entering soft-shell condition after they moult. Unmarketable soft-shell crabs become marketable after a few weeks when their shells harden. Only male crabs larger than 165mm in hard shell can be harvested and sold. This dissertation focuses on the Dungeness crab fishery in the Hecate Strait, British Columbia, between Haida Gwaii and the mainland, and develops fishery models using vessel monitoring system data, within-season harvest control rules, multiple types of biological variation, and seasonal closures. The questions in this dissertation were driven by the central trade-off; having a long fishing season while avoiding setting traps on soft-shell crabs. Four overarching questions related to the central trade-off are as follows: Which factors could most accurately predict weekly crabbing effort when it is of interest to model crab fishery dynamics in the evaluation of in-season crab fishery policy options? What type of population modelling approach is suitable for evaluating in-season fishery policy options for crustaceans where moulting causes the product to be unmarketable for several weeks each year? Which factors drive within season changes in the vulnerability of crustaceans to capture in fisheries, e.g., abiotic factors like sea surface temperature, biological factors like moult condition, or temporal factors like season? Would a management approach which closed and reopened the fishery based on a soft-shell survey lead to better long-term yields and catch rates than fixed date seasonal closures or no seasonal closures? The four main chapters in this thesis examine the Hecate Strait Dungeness crab fishery as a case study. Chapter 2 analyzes fishing effort over the course of the fishing season. Chapters 3 and 4 develop an agent-based depletion model to attempt to estimate various biological quantities. Chapter 5 simulates three alternative management control rules for setting opening and closing dates. This dissertation contributes new methods for evaluating fine timescale commercial catch and trap haul data from vessel monitoring systems and found that setting fishery openings and closures based on a weekly soft shell survey outperformed alternative management control rules.

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