Date of Award

Spring 5-12-2018

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Marine Biology


Yong Chen

Second Committee Member

Robert Steneck

Third Committee Member

Joseph Zydlewski

Additional Committee Members

Kate Beard

Burton Shank


Of the most iconic fish species in the world, the Atlantic cod (Gadus morhua, hereafter, cod) has been a mainstay in the North Atlantic for centuries. While many global fish stocks have received increased pressure with the advent of new, more efficient fishing technology in the mid-20th century, exceptional pressure has been placed on this prized gadoid. Bycatch, or the unintended catch of organisms, is one of the biggest global fisheries issues. Directly resulting from the failed recovery of cod in the GoM, attention has been placed as to possible sources of unaccounted catch. Among the most prominent is that of the GoM American lobster (Homarus americanus) trap fishery. My dissertation research contributes to solving these problems by making progress in five areas: Evaluating cod discard survivability, characterizing lobster effort, estimating cod bycatch, incorporating various bycatch scenarios into the current stock assessment framework, and providing an in-depth policy analysis for management to move forward. This dissertation proceeds as follows: Chapter 1 will briefly introduce regional fishing history, and the study species. Chapter 2 a will provide a preliminary habitat analysis and field project with the object of understanding when and where cod are caught as bycatch, and their subsequent survivability post-release. Chapter 3 develops a quasi-stationary bootstrapped Generalized Additive Model method to estimate Maine’s effective lobster effort spanning 2006-2013. Chapter 4 builds on the same methodologies to estimate Atlantic cod bycatch rates on the congruent spatiotemporal scale, then incorporates uncertainties from both lobster effort and bycatch rates to estimate spatiotemporal cod bycatch. Chapter 5 uses estimates from the previous chapter alongside available federal cod data to estimate historic age-structure and magnitude of cod bycatch from 1982-2016. Then, multiple scenarios are evaluated in the current assessment framework and I report on updated assessment model diagnostics and a novel approach to retrospective analysis. Chapter 6 will conclude with a detailed policy analysis of the state of fisheries in the GoM, and how cod bycatch from the lobster fishery may be equitably incorporated as to ensure productive fisheries across groundfish and lobster sectors while minimizing conflicts.

2017M0.2_DONTCHANGE.DAT (86 kB)
Base M=0.2 model, no discards

Base 2017 MRAMP model, no discards

BASE_2017_M0.2_DISCARDS.DAT (107 kB)
100% discards median M0.2 model

100% discards median MRAMP model

50% mort median MRAMP scenario

BASE_2017_M0.2_DISCARDS_MOD.DAT (106 kB)
Legault modified discards

Legault modeified discard model median catch

2017M0.2_DONTCHANGE.DAT (86 kB)
10 x discards, try to break, model not converged