Growth estimates from tagged white sturgeon suggest that ages from fin rays underestimate true age in the Kootenai River, USA and Canada

We used tagging data for 760 recaptured Kootenai River white sturgeon Acipenser transmontanus that had been at large for as long as 23 years to examine the validity of ages assigned from pectoral fin rays. Growth estimates from tagged white sturgeon in the Kootenai River indicated that age estimates from fin rays were underestimates of the true ages. Bias was estimated from growth differences between length-at-age relationships derived from fin ray ages and recaptures of tagged fish. Growth of tagged fish was substantially less than predicted from fin ray length-at age curves. Age-specific lengths estimated front fin rays cannot be achieved at the growth increments observed for tagged fish. Ages estimated from fin rays were 30-60% less than the apparent ages from tagging data. Thus, actual ages may be 1.5-2.0 times the ages estimated from fin rays. Apparent aging bias will result in substantial changes in population parameters estimated from strength, which will have significant age, including growth, mortality, longevity, and year-class implications for efforts to preserve this endangered species and enable it to recover.