Comparing Atlantic Cod Temporal Spawning Dynamics across a Biogeographic Boundary: Insights from Passive Acoustic Monitoring

Atlantic Cod Gadus morhua, which are overfished in the United States, are potentially vulnerable to disturbance from offshore wind energy (OWE) construction and operation during their spawning period. While many aspects of Atlantic Cod biology are well studied, little is known of their habitat use and spawning behavior at the extreme southern extent of the species' range. As Atlantic Cod form dense spawning aggregations and produce sounds associated with courtship behaviors, we used a combination of fixed-station and glider-based passive acoustic monitoring methods to evaluate the spatiotemporal spawning dynamics of Atlantic Cod in the Georges Bank stock. Additionally, we assessed potential interactions with OWE in designated offshore wind lease areas within southern New England waters of the western North Atlantic Ocean. Generalized linear modeling was used to evaluate correlations between cod grunt activity and multiple environmental cycles. Results from the southern New England spawning grounds were compared to similar data describing the geographically separated Massachusetts Bay winter-spawning subpopulation within the western Gulf of Maine stock. Temporal patterns in Atlantic Cod grunts suggest that spawning in southern New England waters is concentrated in November and December and is greatest near the new and full moons. Although there were fine-scale differences in the temporal dynamics of grunt presence between the two regions, the overall seasonality of inferred spawning was similar. Results suggest that Atlantic Cod spawning in southern New England overlaps with planned OWE construction in time and space. An understanding of cod spawning phenology in the western North Atlantic can be used to minimize disturbance to spawning through limiting construction timelines and consideration of turbine or cable placement.