Results from Plantings of Marked Trout of Legal Size in Streams and Lakes of Michigan

Abstract

Intensive creel censuses served as the chief basis for estimates of the effectiveness of plantings of marked legal-sized brook trout, brown trout and rainbow trout at various seasons over a period of from 1 to 3 years in sections of five public streams and in two private streams. Similar data are presented for plantings of rainbow trout in five lakes. Returns from fall planting in streams never exceeded 5.3 per cent; spring and open-season plantings resulted in the recovery by anglers of from 4.9 to 61.9 per cent of the fish released. Fall plantings of rainbow trout in lakes yielded returns up to 66 per cent. Plantings of from 100 to 160 trout per mile of stream averaging 50 feet in width yielded higher percentage returns than did plantings of larger numbers of fish, benefited relatively more anglers, and did not stimulate the catch of native fish. The increase in the catch per hour and the percentage of hatchery fish in the total catch appeared to be inversely proportional to the density of the native population of the species stocked and directly proportional to the number of fish planted. The percentage of the total catch contributed by plantings of moderate numbers of trout in the spring or during the season varied from 1.8 to 30.4. It is concluded that in northern Michigan streams, major dependence for good fishing must be placed on the native or “wild” stock. Rainbow trout and brown trout were caught for at least 8 weeks following planting, although the majority was removed by the end of 4 weeks; few if any brook trout were taken after 4 weeks. Very few planted trout survived one or more winters even in private streams not subject to intensive angling. Most of the trout were taken within 5 miles of the point of release and usually downstream; of the three species, rainbow trout migrated most extensively. From 5.7 to 20.6 per cent of the fisherman-day records showed the capture of marked trout. Apparently as many anglers benefited frown “spot” plantings as from wider distribution by boat. Control experiments proved that jaw-tagging and fin-clipping provided effective methods of tracing fish during the period of investigation and that mortality and the effect on growth of either method were negligible.