Implicit in biotelemetry studies is the assumption that transmitter attachment does not affect fish behavior or performance. We conducted experiments to determine effects of external, surgical, and stomach tag attachments on the swimming performance and behavior of rainbow trout (Salmo gairdneri) and white perch (Morone americana). Only one rainbow trout changed dominance rank after dummy tag attachment. Subordinate fish had significantly lower weights than subdominant and dominant fish, but there were no significant differences in exhaustion times. Externally tagged trout had significantly lower exhaustion times than other tagged groups and controls. There was no significant difference in exhaustion times among tagged white perch and controls. Externally and surgically tagged perch contracted serious fungal infections during a 45-d survival study; however, few disease and no survival problems among tagged and untagged rainbow trout were noted up to 21 d. With all factors taken into account, it appears that stomach tagging is the best method of transmitter attachment, except when regurgitation and/or stomach atrophy are likely to be encountered.

No abstract

During the summers of 1981 and 1982, we studied resource partitioning by stocked lake trout Salvelinus namaycush, brown trout Salmo trutta, and Chinook salmon Oncorhynchus tshawytscha by fishing vertical gill nets at six distances from shore in south-central Lake Ontario. The nets were set at depths of approximately 15-45 m (nearshore stations, <4 km offshore) and more than 55 m (offshore stations, 4-24 km offshore). Salmonids were concentrated near shore, where they partitioned available habitat and, thus, food resources. Horizontal habitat was partitioned with respect to distance from shore; vertical habitat was partitioned in relation to temperature and the thermocline. Salmonids foraged for the most available prey items within their habitat. Overlaps in both food use and horizontal habitat use were inversely related to overlap in use of vertical habitat. There was increased habitat separation between sexes for those species caught farther from shore. At the salmonid stocking and prey density levels existing during our study, lake trout, brown trout, and chinook salmon appeared to partition resources and minimize deleterious trophic interactions during thermal stratification.