Michigan Department of Conservation
Institute for Fisheries Research Report No.1731, 1966

Effects of Marks upon the Growth, Survival, and Exploitation of Hatchery Rainbow Trout Fingerlings Planted in Hunt Creek, Montmorency County, Michigan


David S. Shetter


      Abstract.-Approximately equal numbers (995 to 1,000) of jaw-tagged, fin-clipped, and unmarked rainbow trout fingerlings were planted in experimental sections of Hunt Creek in October/ 1952. Observations on these fish during 1952-1957 provided data on the effects of marking on growth, survival, and angler exploitation. Jaw-tagged fish grew more slowly than did either the fin-clipped or unmarked fish; differences in growth increments were between 0.15 and 0.45 inch over a 2-year period. There was little difference in growth between fin-clipped and normal fish. Relatively few rainbow trout attempted to migrate, and no difference in extent of attempted migration was detected between marked and unmarked fish.

There was no significant difference in angler exploitation rates among the three groups of fish in any 1 year, but the 5-year totals for the three groups showed highly significant differences. Tagged, fin-clipped, and normal rainbow trout were caught in increasing numbers, in that order.

Calculations of instantaneous mortality percentages - indicated that significantly more tagged fish than normal fish were lost to causes other than fishing, and that fin-clipped fish were intermediate in this regard. The superimposition of 3,000 rainbow trout fingerlings on the Hunt Creek brook trout population in 1.75 miles of stream did not noticeably affect either the brook trout population or the brook trout angling during the 5 years involved. Many investigators have used marked fish to obtain information on growth, survival, movements, exploitation rates, and other aspects of fishery biology. Typically, results are based on examination of fish recaptured at various intervals of time after their release. In many studies the possibility of adverse effects from the marking was not determined. In this study I found that the attachment of jaw tags to fingerling rainbow trout retarded their growth and had related effects, but fin-clipping had little effect on the fish.