Fine-scale activity, distribution and habitat utilization of Atlantic cod (Gadus morhua) on the Ipswich Bay spawning ground

Data storage tags (DSTs) and acoustic telemetry were applied to examine cod spawning habitat utilization in Ipswich Bay and compare seasonal activity patterns. I tagged 200 spawning cod in Ipswich Bay during April--May 2006 with DSTs recording depth and temperature. Twenty-six cod were also implanted with acoustic transmitters and relocated manually and with stationary listening stations during May and June. Twenty-five DSTs were returned, showing that most cod departed the spawning ground during May and June and dispersed throughout the western Gulf of Maine. Cod shared a low vertical activity pattern in Ipswich Bay, but adopted various site-specific vertical behaviors alter leaving. Spawning activity was concentrated in a ∼35 km2 area where cod aggregated alongside particular bathymetric features. These fine-scale movement and spawning data have implications for area closures, defining Essential Fish Habitat, and identifying cod population structure in the Gulf of Maine.