Spatial patterns in cohort-specific mortality of red throat emperor, Lethrinus miniatus, on the Great Barrier Reef

Rates of mortality were estimated for individual cohorts of red throat emperor, Lethrinus miniatus, over a 5-year period (1995-1999) by using fisheries independent catch rates as a measure of abundance. Estimates of mortality were considered to be close approximations of natural mortality (M) as all reefs sampled had been no-take areas for at least 10 years prior to sampling. Cohort-specific mortality rates were compared between individual reefs within the Townsville, Mackay and Storm Cay regions of the Great Barrier Reef (GBR) and between these regions. Mortality rates were found to be similar between cohorts and between individual reefs within each region but varied substantially between regions. Mortality rates were significantly and consistently higher in the Mackay region than in the Townsville and Storm Cay regions. These spatial patterns have important implications for fisheries sustainability as populations with lower rates of natural mortality may be more vulnerable to over-exploitation than populations with higher rates of natural mortality. Consequently, L. miniatus populations in the Townsville region may be more at risk of over-fishing than populations in the Mackay and Storm Cay regions. The observed regional differences in structure and dynamics of L. miniatus populations needs to be incorporated into fisheries stock assessments for this species if model outputs are to be reliable, and management is to be optimised.