Date of Award

Summer 8-19-2017

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Marine Biology


Yong Chen

Second Committee Member

Loretta O'Brien

Third Committee Member

Gayle Zydlewski

Additional Committee Members

Teresa Johnson

Linda Mercer


Cusk (Brosme brosme) are a National Oceanic and Atmospheric Administration species of concern, currently under internal status review for the Endangered Species Act, but are considered data limited. Current concerns for cusk include: decline in abundance, increase in fishing mortality relative to survey biomass, increased patchiness in habitat, and lack of management (72 FR 10710). Future management will require an improved understanding of cusk distribution, habitat use, spatial distribution of bycatch interactions, and the impact of bycatch on the population. This study set out to evaluate changes in cusk distribution and habitat, locations and levels of bycatch, and the feasibility of implementing conservation measures to reduce discard mortality of cusk bycatch.

Data limited approaches were developed to map cusk habitat and potential areas of bycatch. A spatio-temporal delta-Generalized Linear Mixed Model (GLMM) was used to combine observations from the Northeast Fisheries Science Center (NEFSC) spring and fall research bottom trawl survey with the NEFSC western Gulf of Maine (GOM) co-operative research longline survey. The resulting density estimates were then used to develop model-based habitat suitability index (HSI) maps for cusk with increased data resolution.

The American lobster (Homarus americanus) fishery is thought to be a significant source of mortality for cusk, as such bycatch of cusk within this fishery was evaluated. Bycatch ‘hotspots’ were predicted based on the overlap of cusk and American lobster high quality habitat. Field studies were conducted in collaboration with Maine lobster fishermen to evaluate the ability of cusk to survive incidental catches within the lobster fishery. These studies resulted in an estimated 75% survival rate in the medium-term (4 – 14 days) if recompressed. To evaluate the impact of implementing the recompression of cusk as a conservation measure throughout the Maine lobster fleet stock assessment simulations were conducted. Cusk bycatch was first estimated for the Maine lobster fishery to develop the simulation scenarios. These estimates indicate 2 – 9 cusk are caught per 10,000 trap hauls, depending on location. Life history parameters were also estimated for cusk for the simulations. The stock assessment simulations indicated that a decrease in fishing mortality would be beneficial to the population, but only decreasing mortality from the Maine lobster fishery would not be enough to significantly improve the population status.