Age-based demography of humpback grouper Cromileptes altivelis: Implications for fisheries management and conservation

Abstract

The humpback grouper Cromileptes altivelis is listed as Vulnerable on the IUCN Red List because of concerns about unsustainable levels of harvest. Quantitative estimates of life history parameters are scarce, limiting formal assessment of long-term harvest rates and conservation risk and the design of robust management measures. We provide the first estimates of age-based population parameters for C. altivelis, using samples from the Great Barrier Reef (GBR) and Torres Strait, Australia. Population parameters did not differ significantly between regions. The maximum observed age was 19 yr, the von Bertalanffy growth parameters were K = 0.30 yr–1, L∞ = 597 mm, and total mortality rate, estimated from an age-based catch curve, was 0.26 yr–1. Preliminary estimates of natural mortality for the GBR, based on samples from reefs closed to fishing, were 0.23 yr–1 (Hoenig regression) and 0.26 yr–1 (catch curve), suggesting recent fishing mortality was low. C. altivelis was found to be a protogynous hermaphrodite with 50% of individuals being male at length 547 mm and age 9.6 yr. Peak spawning was between October and January. These results contrast with previous perceptions of life history traits of this species and suggest that C. altivelis may not be as vulnerable to managed fishing pressure as previously thought. Notwithstanding this, there remains considerable uncertainty in unfished abundance and average recruitment levels for C. altivelis populations. We consider a combination of management strategies including size limits, effort controls and no-take areas that are likely to be most effective in minimising the conservation risk for C. altivelis populations and provide sustainable yields across the species’ range.