Diver and Underwater Television Observations of Fish Behavior in a Great Lakes Commercial Trap Net

Abstract

Behavior of lake whitefish ( Coregonus clupeaformis) and lake trout ( Salvelinus namaycush) in commercial trap-net pots was observed by scuba divers and by a low-light sensitive, underwater television (UTV) system. During the day, lake whitefish schooled and swam in circular patterns within the pot, keeping at least 1 m off the lake bottom. Occasionally, lake whitefish that were outside the net were observed swimming in concert with fish inside the pot. Whitefish schools disbanded at dawn and dusk, presumably because of reduced visual acuity during periods of low light. Lake trout were most often in groups of two or three individuals which were generally segregated from whitefish schools. Aggressive, escapement, and feeding behavior were not observed for either species. As nets were lifted, fish became very excited and darted about wildly. Net leads may have elicited schooling responses from fish, causing them to enter the pot. Fish stayed 3 to 5 m away from divers, making observations of behavior difficult. However, divers were able to make some observations which were not possible with UTV. Physical presence of UTV equipment did not alter fish behavior as did diver presence. Compared with divers, UTV could be deployed longer and at lower light levels. UTV also provided a permanent record (video cassette) that could subsequently be reviewed. An integration of UTV and diver observations gave the best understanding offish behavior in trap-net pots.