Author

Bai LiFollow

Date of Award

Spring 5-12-2018

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Yong Chen

Second Committee Member

Richard A. Wahle

Third Committee Member

Andrew C. Thomas

Additional Committee Members

Kate Beard-Tisdale

Jui-Han Chang

Abstract

In spite of the high fishing pressure and landings, the Gulf of Maine (GOM) American lobster (Homarus americanus) population abundance has increased dramatically since the early 1990s. Various hypotheses have been developed to explain such an increase, ranging from improved habitat to conservation measures that protect female spawners. However, no systematic study has been done to evaluate these hypotheses. This study aims to examine roles of environmental drivers and conservation measures in regulating the dynamics of lobster population, and evaluate the performance of monitoring programs. A geographical weighted regression model was developed to examine the non-stationary environmental effects on the lobster distribution. An individual-based lobster simulator was used to assess the impact of minimum and maximum legal sizes on the lobster population dynamics from 1982 to 2013. Various quantitative measures were used to evaluate the effectiveness of existing sampling design for the lobster monitoring programs and the accuracy of modeled bottom water temperatures in the GOM. This study shows that bottom water temperature had a more significant positive impact on the increase of lobsters in the eastern GOM than in the western GOM. Minimum and maximum legal sizes also made a great contribution to the dramatic increase of the GOM lobster fishery. An increase of 2 mm carapace length in minimum legal size with no changes in maximum legal size would result in a 279.92% increase in landings compared with the reference landings in 2013. The current lobster and temperature monitoring programs could capture the temporal trend of lobster catches and bottom water temperature. A systematic subsampling of only 50% of the reference samples could produce similar information on lobster catches and size composition for the Lobster Sea Sampling Program. The estimation of locally varying relationships can further improve regionally informed management plans. The estimated impacts of conservation measures address some concerns from stakeholders regarding the necessity of these measures in the fishery. This study also provides spatial-temporal specific sampling advice for the monitoring programs and optimization which can be applied to other monitoring programs to facilitate the development of cost-effective surveys.

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