Date of Award

Spring 5-10-2019

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Yong Chen

Second Committee Member

Walt Golet

Third Committee Member

Michael Palmer

Abstract

Over the past several decades, the Atlantic cod (Gadus morhua) stock in the Gulf of Maine (GOM) has experienced a steep decline in abundance and exhibited changes in spatial distribution. Although the cod fishery in the Eastern Gulf of Maine (EGOM) remains open to fishing, low stock density and complex bathymetry have resulted in little fishing effort and sparse data collection. In an effort to fill gaps in the available data, the Eastern Gulf of Maine Sentinel Survey is a longline/jig survey that targets groundfish species, such as Atlantic cod, Atlantic halibut (Hippoglossus hippoglossus), white hake (Urophycis tenuis), and cusk (Brosme brosme), to collect fine-scale fisheries-independent and dependent data to improve the existing stock assessments for commercially important groundfish species. This research aims to evaluate the methodology for the jigging portion of the EGOM Sentinel Survey for sources of bias which may skew estimates of relative abundance in addition to developing a robust modeling framework that will produce accurate estimates of abundance for groundfish species in the EGOM. Statistical models will be used to make inferences about groundfish abundance and assess potential sources of bias from survey methodology. Furthermore, the established Gulf of Maine cod stock assessment/management strategy assumes unit stock structure in which life history parameters are consistent among individuals across the GOM such that any differences would not impede the stock-rebuilding plan. Given the variation in habitat, ecosystem structure, and food availability across the GOM, such simplifying assumptions may inhibit efforts to rebuild the overall cod stock and reduce overfishing across the GOM. This research aims to improve the analysis and interpretation of the fine-scale hook-and-line surveys, provide suggestions to improve fishery survey designs, and provide more information to better inform regional science and management efforts in the Gulf of Maine. In addition to evaluating survey methods and modeled estimates of abundance, age-specific absolute growth (e.g. change in length, weight, and condition factor) will be evaluated for cod in spatially explicit regions of the Gulf of Maine using a non-parametric bootstrap approach to evaluate inter-regional growth rates of Atlantic cod between the EGOM, western GOM, and George’s Bank.

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