Activity and Distribution of Cod in the Ipswich Bay Spawning Area

The overall goal of the project is to study the activity and fine scale distribution of cod in the Ipswich Bay spawning area. To accomplish this goal, 200 adult, pre-spawning cod will be equipped with data storage tags (DSTs), and 30 of these will also be equipped with an acoustic tag. Cod equipped with acoustic tags will be located approximately every other day by the fishing vessels engaged in the project. The position of each acoustic tag (fish) will be found using a towed, or handheld directional hydrophone. Location, depth, substrate type, and notable bathymetric features will be recorded at each fish’s position each time it is located. Tracking will occur for 8 weeks, during May and June. To gather information about the daily activities of adult cod, we will locate multiple individuals every 30 minutes over the course of 24h. Each time an individual is located we will record time, depth, location, substrate type, and any notable bathymetric features. This fine scale daily sampling will occur 8 times, beginning in May and extending through June, at approximately weekly intervals, allowing us to sample over two lunar, and associated tidal cycles. The DSTs detect and archive data on pressure (depth), water temperature, and time, at a user-programmed time interval. The DST archived data from all recaptured fish will be down loaded to a computer. Information from the DSTs will be used to supplement the information recorded each time the fish is located. In particular, DST data will provide detailed information about the temperatures and depths occupied by each fish over time.

For thirty of the fish, the combination of a DST and an acoustic tag will allow us to construct a positional history of the fish (acoustic tag), and relate this positional history to habitat features (depth, proximity to bathymetric features, substrate type, and temperature) recorded synoptically during acoustic tracking, and archived on its DST. The associations will allow us to determine how horizontal movements, activity (vertical movements), and fine-scale distribution relate to important spawning habitat attributes such as depth, bathymetry, substrate type, and temperature. Integration of the data from all fish will allow us to broadly characterize the spawning habitat of cod in Ipswich Bay, and to determine how the spatial distribution of spawning fish relates to attributes of the spawning habitat. Time series analyses of depth variation over time will be used to determine if there are diel cycles in vertical movements. Swimming speed will be estimated as the distances between successive positional fixes divided by the elapsed time between fixes. Similar analyses will be used to determine if activity rhythms and swimming speeds are associated with lunar or tidal cycles.

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