Pectoral fin ray aging: an evaluation of a non-lethal method for aging gars and its application to a population of the threatened Spotted Gar

摘要

Spotted Gar (Lepisosteus oculatus), a species listed as Threatened under the Canadian Species at Risk Act (SARA) was collected during May and June, 2007 from several sites in Rondeau Bay, a shallow coastal wetland of Lake Erie. The first pectoral fin ray was removed from 78 individuals to age the fish and to determine individual growth characteristics. To assess the validity of using pectoral rays to age Spotted Gar, we compared techniques (otoliths, branchiostegal rays and pectoral rays) for ten individuals captured in southwestern Michigan. Agreement between readers and amongst the three structures was high; thus aging of Spotted Gar using sectioned pectoral rays is an effective method. Rondeau Bay specimens varied in age from 3 to 10 years and from 515 to 761 mm total length. Regression analysis of length vs. age data was calculated to be y = 19.217x + 491.19( R2 = 0.22 ) {hbox{y}} = {19}.{hbox{217x}} + {491}.{19}left( {{{hbox{R}}^{{2}}} = 0.{22}} right) . The low R 2 value is attributed to having males and females, which differ in growth rates, combined. Growth rates of Rondeau Bay specimens were compared to a Louisiana population using ANCOVA. No significant difference was found in the rate of growth between these populations; however, condition was low as compared to a standard weight equation. This may lead to lower fecundity, contributing to the species’ rarity in Canada.