A self-contained system for observing and quantifying the behavior of Atlantic cod, Gadus morhua, in an offshore aquaculture cage

A self-contained data collection system is described that was used to investigate the behavior of Atlantic cod (Gadus morhua) in an offshore net pen (Sea Station 3000) located 13 km off the coast of New Hampshire, USA. The entire system was housed inside a modified U.S. Coast Guard (USCG) navigational buoy that was retrofitted for this purpose. Power was provided by a combination of eight 12 V batteries, two solar panels and a wind generator. The behavior of the population of cod as a whole, during daylight hours, was monitored using four waterproof cameras connected to a four channel digital video recorder. The behavior of 4–12 individual fish implanted with ultrasonic transmitters was continuously recorded, during each of four study periods, using a HTI model 291 ultrasonic telemetry system. Laboratory studies showed no influence of transmitter implantation on swimming or feeding behavior. Transmitters were programmed to “ping” at intervals between 1.7 and 3.3 s and they typically lasted for about one month. The system successfully detected and plotted 84.9 ± 6.0% of transmissions, resulting in an average of 1283.4 ± 252.5 positional fixes for each animal, during each hour of the study. This preliminary evaluation of cod behavior in a net pen demonstrated that they are diurnally active and have a tendency to mill about, rather than school. Cod predominately used the lower half of the cage, except when rising to the feeding area during periods when feed was delivered. The system that was developed proved to be ideal for investigating the behavior of fish within a net pen, and it can be used by both inshore and offshore farms to gather behavioral data that can lead to improvements in the efficiency of aquaculture operations.