First Evidence of Validity of the Fin-Ray Method of Age Determination for Marine Fishes

Abstract
In 1978, tagged lingcod (Ophiodon elongatus) were injected with oxytetracycline to produce a time mark in the fin rays. Four fish were recovered after being at liberty for approximately 2 or .3 years and all had an oxytetracycline mark. Three of the four fish had formed a number of annual growth zones equivalent to the number of years at liberty, confirming that the mark thought to be an annulus did form once a year. One fish probably formed the appropriate number of annual growth zones but, because growth was reduced, the annuli were difficnit to identify. There was no indication that the age of lingcod would be overestimated by the fin-ray method. The use of fin-ray sections for age determi- nation provides a useful alternative to the more traditional methods that use scales or otoliths (Boiko 1951; Cuerrier 1951; Beamish 1981). The method is best known for its application to es- timate the age of sturgeon (Acipenseridae) but it can be used to age other fishes (Beamish 1981). Even though fin-ray sections have been used to age fishes for more than 60 years, there are only a few studies that have validated the method. In particular, we can find no evidence of its vali- dation for any species of sturgeon. There is evi- dence of the validity of the method for some freshwater fishes (Beamish and Harvey 1969; Beamish 1973; Mills and Beamish 1980) but we could find no documentation of its validity for a marine species. The importance of validating a method of age determination for any species should never be underestimated. Early studies on age and growth of fishes stressed the need to validate age esti- mates (Van Oosten 1941). However, it appears that with time the determination of ages became routine, and little attention was paid to proving that age estimates were correct despite the key role that age determinations played in many analyses. Recently, several studies have indicat- ed that previous estimates of age for some com- mon species could seriously underestimate their true age (Beamish and Harvey 1969; Aass 1972; Power 1978; Beamish 1979; Beamish and Chil- ton 1982). If these new interpretations are cor- rect, then the consequences of not validating age estimates could have significant effects on stock

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