The utility of otolith weight as a predictor of age in the emperor Lethrinus mahsena and other tropical fish species.
Abstract
This study examines the potential use of otolith weight as a proxy for age in the lethrinid Lethrinus mahsena from different sites in the tropical Indian Ocean: the banks of Seychelles, Mauritius and British Indian Ocean Territory (BIOT, Chagos Archipelago). The reliability of age鈥揻requency distributions and individual ages estimated using otolith weight鈥揳ge relationships was examined through comparison with those estimated through the standard method of ageing using otolith increments. Two other methods for estimating age鈥揻requencies using age-slicing via an estimated growth curve were also examined; these used growth curves estimated by a length-based method (ELEFAN), or by fitting directly to length-at-age data (an 鈥榓ge-based鈥� method). Age-slicing using length-based growth parameters failed to produce reliable age鈥揻requencies, due to inaccuracies in the growth parameter estimates. The use of age-based growth parameter estimates improved the results of age-slicing, however, age鈥揻requencies remained significantly different from those obtained from ageing using otolith increments in two locations. The use of otolith weight鈥揳ge relationships resulted in estimated age鈥揻requency distributions that in all locations were not significantly different from those assessed through otolith increment counts. In contrast, L. mahsena otolith weight鈥揳ge relationships could not be used to estimate individual ages accurately, due to the level of overlap in otolith weight between age classes. Where otolith increments are routinely used to age commercial fish species, the fact that otolith weight鈥揳ge relationships could not be used to age individuals accurately may limit its application. However, where routine ageing of individuals through otolith increments is considered impractical, for instance because of its cost, the use of otolith weight鈥揳ge relationships to derive catch age鈥揻requencies represents a viable alternative approach. With this in mind, this study has also demonstrated that there is the potential to use otolith weight鈥揳ge relationships for five other species caught around the Seychelles, following the validation of their otolith increments.
Citation
Pilling, G.M.; Grandcourt, E.M.; Kirkwood, G.P. The utility of otolith weight as a predictor of age in the emperor Lethrinus mahsena and other tropical fish species. Fisheries Research (2003) 60 (2-3) 493-506. [DOI: 10.1016/S0165-7836(02)00087-5]