Geographic variation in the sex ratio, sex specific size, and age structure of Plectropomus leopardus (Serranidae) between reefs open and closed to fishing on the Great Barrier Reef

Abstract

Variation in reproductive parameters of Plectropomus leopardus populations between coral reefs open and closed to fishing was examined in two geographic regions (off Townsville (19°S) and in the Swains (22°S)) of the Great Barrier Reef, Australia. The reproductive parameters that were examined included the operational (reproductive) sex ratio and size and age structure of mature females, sex-changing individuals (transitionals), and mature males. There was a greater proportion of males above the minimum size and age of harvest on reefs closed to fishing for 8-10 years than on reefs open to fishing, although the effect varied with geographic region. Nevertheless, neither the sex ratio, mean age, nor mean size of males or transitionals varied significantly with reef closure status. Females, however, were significantly older and larger on closed than on open reefs in both regions. Marked regional variations in the sex ratio and average age of transitionals were found independent of reef closure status, suggesting regional variation in reproductive strategies. Controlled manipulations, inclusion of broad spatial scales, and detailed studies of intra- and inter-specific variation in serranid reproductive biology are necessary to resolve such complexities in the responses of protogynous serranids to fishing pressure and management strategies.

Demographic profile of an overexploited serranid, the orange-spotted grouper (Epinephelus coioides), from northern Oman

“…It has been shown that if sex change is controlled by behavior, the removal of the larger, older males through fishing results in rapid sex change by a large female in a group (Huntsman and Schaaf, 1994). Such a compensatory effect means that sex ratios are not necessarily affected by fishing; however, the size and age at which sex change occurs is reduced significantly (Adams et al, 2000). For socially mediated sex change to occur, female assessment of either the size (size-ratio assessment) or sex (sex-ratio assessment) of the group is made.…”

“…The recent increase in demographic analyses of economically important reef fish stocks from the Indo-Pacific region has made a major contribution to our understanding of key population parameters (Ferreira and Russ, 1992;Newman et al, 1996;Adams et al, 2000;Grandcourt, 2002Grandcourt, , 2005Williams et al, 2003;Pears et al, 2006). What has emerged is increasing evidence that many exploited reef fish species have life history strategies of extended life spans, slow growth, and, in the absence of fishing, an accumulation of older individuals-strategies usually associated with species in temperate (10-25°C) and deep (>30 m) waters (Choat and Robertson, 2002;Pears et al, 2006;Wakefield et al, 2013Wakefield et al, , 2015.…”

“…Beverton and Holt 1957). It has also been suggested that populations in which sex change is predominately female to male, under a scenario of increased fishing mortality (F), lose reproductive capacity in 2 ways: through selective removal of larger, mostly male individuals that in turn cause sperm limitation (Coleman et al, 1996) and a decrease in the size of females that in turn reduces total fecundity (Sadovy, 1996;Adams et al, 2000;Sadovy de Mitcheson and Liu, 2008).…”

Life history characteristics and stock status of the thumbprint emperor (Lethrinus harak) in Saipan Lagoon

“…However, differences in other life history parameters (e.g., A 50 ) among thumbprint emperor from Saipan, Guam, and the Ryukyu Islands support the need for standardized methods to study reproductive maturity, as well as age and growth for coral reef species. Demographic plasticity for age and growth and in reproductive parameters pertaining to maturity, sex change, or both (Adams et al, 2000;Gust, 2004;Munday et al, 2006;Mariani et al, 2013) has been documented in both gonochoristic (Choat and Robertson, 2002;Robertson et al, 2005) and hermaphroditic (Gust et al, 2002;Donovan et al, 2012) species of coral reef fish.…”

Surrogates for reef fish connectivity when designing marine protected area networks

“…Plectropomus leopardus are pursued vigorously by commercial and recreational fisheries, and so MPAs will likely improve the density of exploited populations. Surveys on the GBR observed coral trout populations in MPAs that were several-fold greater than populations in non-MPAs, although this difference was regionally variable (Adams et al 2000).…”