Survival, Growth, and Production of Domestic and Assinica Strain Brook Trout in Four Michigan Lakes
Howard Gowing
Abstract.-In fall 1973, matched plantings of domestic and Assinica strain brook trout fingerlings of the 1973 year class were stocked in three small oligotrophic lakes and one shallow flowage. Stocking rate was 125 fish per hectare for each strain or 250 fish per hectare for each lake. Populations of trout were monitored annually in fall for 4 years after stocking.
Nearly 98% of the Assinica trout were lost in the flowage during their first year after stocking from unknown causes. In a meromictic tic lake all trout died in the third winter as the result of a winterkill. For the remaining two lakes, domestic trout survived through age IV in both and a few are expected to survive an additional year whereas Assinica trout survived through age IV in one lake.
Growth rate of Assinica trout was superior to that of domestic trout in all lakes. From composite growth curves, Assinica trout attained 19% greater length than domestic trout in each of the 4 years after stocking. Growth in length was most rapid during the first year after stocking at age I, particularly in two lakes containing no minnows, and peaked in the third year at age III. Growth rate was sustained best in the lake containing minnows; maximum size fish was achieved in this lake, 437 mm for domestic trout and 472 mm for Assinica trout, both age III.
More than one-half of the domestic trout were sexually mature at age I; most had reached maturity at age II to age IV. For Assinica trout, only a few precocious males were mature at age II and about 62% of the females were mature at age III.
In the two lakes where trout survived best, 4-year production of Assinica trout in one lake (46. 89 kg/ha) exceeded that for domestic trout (39. 03 kg/ha) while domestic trout production (48. 28 kg/ha) was greater than Assinica trout production (45. 52 kg/ha) in the other lake.
The superior growth of Assinica trout over domestic trout provides an opportunity for improving the stocks of brook trout in the Michigan hatchery system and ultimately the catch of more desirable size trout by anglers.