Precision of Cleithrum and Sagittal Otoliths Used to Estimate Ages of Northern Pike

Precise age estimates can be difficult to obtain for northern pike. The cleithrum, a bone in the pectoral girdle, is the structure thought to produce the most precise age estimates for northern pike. However, otoliths have been found to provide the most precise age estimates for many other fish species; yet, otoliths have never been evaluated for northern pike. Our objective was to determine if sagittal otoliths or cleithrum provide more precise age estimates for two northern pike populations. Sagittal otoliths and cleithrum were collected from 82 northern pike (size range 323–1005 mm) from Devils Lake, North Dakota and 56 northern pike (size range 254–610 mm) from Cable Lake, Wisconsin. Cleithrum were viewed in whole submerged under water in a black dish and ages were estimated by three independent readers. Sagittal otoliths were mounted in epoxy and thin-sectioned, and ages were estimated by the same three independent readers. Precision of age estimates was quantified using percent reader agreement and mean coefficients of variation (CV), and bias between readers and structures was compared using age-bias plots. Cleithrum were more precise than sectioned otoliths for the Devils Lake northern pike. Cleithrum mean CV was 10.1%, complete reader agreement was 42.3%, and partial reader agreement was 91.5%. Sectioned otolith mean CV was 18.1%, complete reader agreement was 15.3%, and partial reader agreement was 90.3%. Age bias plots showed no biases among readers or structures. We expect similar results for the Cable Lake northern pike sample.