Age-based demographic assessment of fished stocks of Lethrinus nebulosus in the Gascoyne Bioregion of Western Australia

Abstract

Age-based demographic analyses were undertaken to assess the current status of fished stocks of spangled emperor, Lethrinus nebulosus (Forsskål) in the Gascoyne Bioregion of Western Australia. Differences in age and growth characteristics were detected for samples collected from different assessment zones, with North Gascoyne fish observed to grow faster and reach a shorter average maximum length and younger average age than South Gascoyne fish. A significant difference in North Gascoyne catch-at-age data from different time periods demonstrated historical effects of fishing on population age structure. Instantaneous rates of fishing mortality (F) from catch-curve analyses of age-frequency data sampled for the North Gascoyne stock from recreational fishing catches from April 2007 to March 2008 were beyond the limit reference point compared with estimated instantaneous rates of natural mortality (M) (i.e. F>1.5M), indicating that there is currently a risk to the sustainability of that stock. © 2010 Department of Fisheries, Government of Western Australia.