Estimating Atlantic Cod (Gadus morhua) by-caught and discarded in the Gulf of Maine Lobster Fishery

Atlantic cod (Gadus morhua) in the Gulf of Maine (GOM) are currently at or near historically

low population levels. Reliable estimates of discards from Maine’s lobster fishery, which are

unavailable and not included in the current stock assessment, are potentially critical for

rebuilding the stock. Cod bycatch data collected in the Marine Department of Marine Resources

sea sampling program cannot be used directly in estimating cod bycatch because of non-random

spatial and temporal sampling efforts.  A standardized framework is developed in this study for

estimating the cod bycatch in Maine’s inshore lobster fishery. We employ environmental

variables into random forest and generalized additive model approaches to standardize cod

bycatch per unit effort (BCPUE) and lobster catch per unit effort (CPUE) for the years 2006-

2013. Lobster CPUE is integrated with high spatio-temporal resolution landings data to estimate

effective lobster effort, which we combine with standardized cod BCPUE to estimate discards

for the inshore GOM lobster fishery. Modeling results remain consistent throughout the study

years, suggesting robustness in our approach. The developed framework yields reliable estimates

of cod bycatch in the lobster fishery, potentially leading to improved estimates of the total GOM

cod mortality and subsequent refinements of the stock assessment.