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.

Age-based demography of the glacier lanternfish (Benthosema glaciale) in the Flemish Cap

“…An unconstrained VBGF was initially fitted to the data, but the 2010 curve was found to be linear with unrealistic parameter estimates. This could be explained by the lack of smaller-sized fish, and thus younger age classes, since VBGF parameter estimates can be sensitive to the age range (Ferreira and Russ 1994;Williams et al 2009). Thereafter, a constrained VBGF was fitted for the overall length-at-age data.…”

Demographic Variation between Colour Patterns in a Temperate Protogynous Hermaphrodite, the Ballan Wrasse Labrus bergylta

“…Because the VBGF parameters estimate can be sensitive to the range of ages and sizes used and no fish of age 1 were collected, the intercept was constrained to 0 cm [30], [31]. Parameters L inf and K and their confidence intervals were obtained by bootstrapping with 1000 iterations [30].…”

“…The slope of this regression is an estimate of Z. Linear models were fitted from a minimum age of one year older than the maximum catch frequency (assumed full selectivity) up to the oldest age class that was preceded by no more than 2 consecutive zero frequencies [31], [43]. The annual mortality rate ( A ), i.e., the proportion of the population that suffers mortality in a given year, was calculated as: …”

Latitudinal and Cross-Shelf Patterns of Size, Growth and Mortality of a Tropical Damselfish Acanthochromis polyacanthus on the Great Barrier Reef

“…Bergmann's Rule and 'James Rule' refer to an increase in body size with latitude [9,10]. At some spatial scales regional differences in demographics are not been found to vary predictably over many degrees of latitude (e.g., 12 o , Cromileptes altivelis [11] ). For any correlative study it is often challenging to provide a strong case any of these patterns without sampling a wide latitudinal range and having multiple sampling sites.…”