FIELD ACTIVITY OF LAKE TROUT DURING THE REPRODUCTIVE PERIOD MONITOREDBY ELECTROMYOGRAM RADIOTELEMETRY

Many lake trout Salvelinus namaycush spawn in shallow areas along wind swept shores. However, precise determination of time and location of s pawning is limited by its nocturnal occurrence, and possibly by some p ostulated, but unproven, spawning in deep water by certain populations . In White Pine Lake, Ontario, a well-studied experimental lake, lake trout spawn in two shallow locations where some direct observation is possible. Radiotelemetry apparatus was used in 1991 to obtain records of the electromyograms (EMGs) produced by muscle activity in one adult male and one adult female lake trout, captured from the lake before t heir reproductive period and returned to the lake at the beginning of the spawning period. Both fish survived, though only the male was dete cted as active over the main spawning site, where it showed evening EM G activity patterns indicating considerable activity. At other rimes o f day, when not located over the spawning site, but present elsewhere in the lake, the male's EMG (i.e. muscle) values were considerably red uced. At the cessation of the spawning period, the transmitter-equippe d male's EMG record showed no further pattern indicative of high activ ity during what had formerly been the daily spawning period. The femal e was tracked as she moved around the lake, but based on both her loca tion and level of EMG activity, is thought not to have spawned. In 199 2, a second male was captured, equipped with a transmitter and release d again. This fish failed to show spawning activity but, as with the 1 991 female, moved fairly considerable distances in the lake. In one in stance, in a swim of short duration (6 min), well away from the spawni ng: grounds, this fish displayed EMG activity levels resembling those of the high activity of spawning. The results obtained appear to demon strate that EMG telemetry could be used to assess the level of muscula r activity occurring in lake trout, especially in relation to reproduc tive behaviour, and when they cannot be directly observed. (C) 1996 Th e Fisheries Society of the British Isles