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Using Maxillae to Estimate Ages of Lake Trout

Wellenkamp, William, He, Ji X., Vercnocke, Darren
North American Journal of Fisheries Management 2015 v.35 no.2 pp. 296-301
Salvelinus namaycush, fins, fish, otoliths, sport fishing, Lake Huron
Previous evaluations of calcified structures used to estimate fish ages have not included maxillae. While otoliths are considered the superior structure for assessing the age of Lake Trout Salvelinus namaycush , it can be difficult to collect and analyze sufficient samples for annual stock assessment, particularly from recreational fisheries. We used maxilla sections to estimate ages of 1,145 Lake Trout collected from Lake Huron in 2013, including 83 fish of known age with coded wire tags (CWT). Maxilla removal was 287% faster than extraction of otoliths. Maxilla sections were cut using inexpensive tools commonly used for processing spines and fin rays. Multiple sections could be made easily from each maxilla, allowing for the use of a superior section that exhibited easily identifiable annuli; in contrast, a single cracked otolith yields only two opportunities to assign age since the cut must be made through the otolith focus. From blind estimates by two independent estimators, made without prior knowledge of the true CWT-derived ages and before the decision rules were fully developed, exact match of maxilla-based ages to the CWT-derived ages was 59–67%; agreements with a bias less than or equal to 1 year were 88–89%, and agreements with a bias less than or equal to 2 years were 94–95%. These measures were higher than those obtained using otoliths sampled from Lake Trout of the same CWT-derived ages. After analyzing the sources of errors and finalizing detailed decision rules, we found that all maxilla sections exhibited a full complement of annuli comparable with the true CWT-derived age, except for two samples affected by errors occurring during sample collection rather than during maxilla processing and interpretation. Received December 16, 2013; accepted December 12, 2014