Connectivity between spawning and nursery areas for Pacific cod (Gadus macrocephalus) in the Gulf of Alaska

Abstract

In this paper, we present the results of a study of the connectivity between Pacific cod spawning and nursery areas, and settlement of Pacific cod in the Gulf of Alaska. This work was done to address the hypothesis that variability in recruitment (defined in this paper as the number of Pacific cod at the end of their 0-age year as estimated by the stock assessment model) is related to variability in connectivity between spawning and nursery areas. To accomplish this work, we developed a Lagrangian, biophysical, individual-based model of Pacific cod early life history and dispersal using the DisMELS framework. This model is driven by currents and scalars such as temperature from a version of the ROMS regional oceanographic model developed for the Gulf of Alaska. Results of our study show connectivity patterns predicted by the model which agree with hypotheses about Pacific cod early life in the Gulf, for example that retention (settlement of cod in their regions of spawning) is important. This work indicates that the Shumagin Islands region may be important as a nursery area, and for Pacific cod recruitment in the Gulf of Alaska. We also find correlations between individual-based model outputs and several large-scale climate indicators which appear to show that settlement in the important nursery areas, and recruitment overall are positively affected by slower gyre circulation in the Gulf of Alaska. We hypothesize that this is due to enhancement of retention, of settlement in the Shumagin Island region, and reduction of transport of young cod out of the Gulf to the southwest.