Evaluation of Partial and Whole Maxillary Bone Excision as a Nonlethal Age Estimation Structure in Lake Trout

Partial excision, or clipping, of maxillary bones has been used for decades as a mark to assign year‐classes to hatchery fish stocked into the wild. Recent developments in the use of maxillary bones for age assignment purposes have raised the question of whether they could be used as age assignment structures that can be collected nonlethally. Such nonlethal tissue collections are of obvious importance to managers of low‐abundance and recovering populations or threatened and endangered species. We examined 120 Lake Trout Salvelinus namaycush from two cohorts in a hatchery setting for approximately 6 months to determine the feasibility of maxillary bone excision as a nonlethal sampling technique for age assignment purposes. Lake Trout were subjected to whole‐maxillary excision and partial‐maxillary excision and were evaluated for survival, efficiency of collection, and accuracy of age assignment. Survival in both the whole‐excision and partial‐excision groups was 97%, while untreated controls survived at a rate of 98% (not significantly different). There was no significant difference in sample collection time between groups. Age assignments from whole maxillary bones were more accurate than those from partial maxillary bones; assignments were more accurate when based on bones from younger fish than on bones from older fish. We conclude that for nonlethal collection purposes, excision of whole maxillary bones is advantageous over partial excision due to comparable efficiency, equal survival, and more accurate age estimation. While the value of maxillary bones as a reliable aging structure for Lake Trout has been noted, the use of maxillary bones for nonlethal tissue sampling in other studies, such as isotopic, trace element, and genetic analyses, may also be valuable.