Development of a Standardized CPUE for Atlantic Cod and Cusk Using Bycatch Data in the Coastal Gulf of Maine Lobster Fishery

Limited information is available about the abundance of Atlantic cod (Gadus morhua) and cusk (Brosme brosme) in the coastal Gulf of Maine (GOM).  Using lobster fishery bycatch data, we applied generalized linear models to develop standardized catch-per-unit-effort (CPUE), from which we can derive abundance indices. The catch data are characterized by a high percentage of zero observations, and we approached this skew distribution in two ways: modeling with different error distributions and aggregating the data spatially. We evaluated models with eight types of error distributions that account for zeros and aggregated the data at 6 spatial scales.  In all models, temporal, spatial, habitat, biological and fishing effort variables were found to significantly influence catch rates of cod and cusk. The standardized CPUEs were generally consistent among the models and among the spatial aggregation scenarios, suggesting that the CPUE standardization is robust with respect to spatial aggregation and choices of statistical models.  The standardized CPUE for cod generally declined between 2006 and 2011; and for cusk declined from 2006 to 2010, but increased dramatically in 2011. This study suggests that an abundance index for cod and cusk in the coastal GOM can be developed using lobster fishery bycatch data.