Recovery of Thermally Marked Otoliths from Lake Trout Stocked as Fry in Lake Superior

摘要

Lake trout Salvelinus namaycush fry with thermal marks in their otoliths were stocked annually at Sve's Reef in Lake Superior from 1994 to 1996 in an attempt to supplement lake trout populations that include both naturally reproduced fish and those stocked as fin-clipped yearlings. Lake trout from these year classes were sampled during annual gill net assessments from 2000 to 2002, and otoliths from unclipped lake trout captured near the stocking reef were processed and examined for the presence of a thermal mark. Thermal marks were identified in otoliths from 21 fish out of 836 examined. The accuracy of mark identification was confirmed by examining and correctly identifying otoliths from a random mixture of hatchery-reared marked fish and recaptured clipped lake trout (without thermal marks). While thermal marks are relatively simple and inexpensive to apply to large numbers of fry, mark retrieval is more labor-intensive and time-consuming. Many otoliths were examined from fish in non-target year-classes due to the wide overlap in size-at-age of this species. Most lake trout in the targeted year-classes were immature.