Scale measurements as a conservation tool in endangered Zingel asper (Linnaeus, 1758)

Abstract

1. Zingel asper (a percid) is a highly endangered endemic fish of the Rhone catchment (France). Scale reading was used to estimate age and growth rates in one of the two last remaining populations that are still present in relatively high densities (River Beaume). 2. Scale reading was validated for the first time in Z. asper by comparing back-calculated lengths from scale annual increment to actual lengths obtained by individual mark-recapture monitoring. The impacts of age or sampling site on individual growth rates were explored using generalized linear models. 3. No major discrepancy was observed between actual and back-calculated lengths. Longevity of Z. asper was inferred from the age data and did not exceed 3 years. Results showed variation in growth rates among ages (20 times higher for 1+ fish than for 2+ or 3+ fish) and also among sampling sites. 4. The present work provided the first estimates of annual growth rates in the Beaume population. This study also showed that scale reading allowed a valuable trade-off between accuracy and conservation imperatives that often imply avoiding invasive techniques such as the implantation of passive integrative transponders. 5. Scale reading will be a valuable tool for future ecological studies in Z. asper and will help in developing conservation strategies for this species as longevity and growth patterns are two life-history traits of major importance for the management of endangered populations. Copyright © 2007 John Wiley & Sons, Ltd.