Rapid reproductive analysis and weight-length relation of the humpnose big-eye bream, Monotaxis grandoculis (Actinopterygii: Perciformes: Lethrinidae), from Micronesia with implications for fisheries

Many immature individuals and largest size classes lacked females for three coral reef fishes (Actinopterygii) in Fiji market surveys: Implications for fishery management

“…For instance, in the presently reported study, we misclassified sex and/or maturity status in 20.0%-60.2% of specimens (L. gibbus and P. indicus, respectively). Similar differences between histological and macroscopic results have been reported elsewhere (Vitale et al 2006;Grandcourt et al 2011;Longenecker et al 2013aLongenecker et al , 2013bLongenecker et al , 2020. Although the accuracy of macroscopic staging improves as personnel gain experience, the misclassification rate exceeds 40% for many gonad stages, even when workers are experienced (Mackie and Lewis 2001).…”

“…3B,5B,7C). This pattern has been reported elsewhere; however, its impact on the size classes overwhelmingly responsible for population-level egg production is under-recognized (but see Longenecker et al 2014Longenecker et al , 2017Longenecker et al , 2020. The common pattern of large females producing exponentially more eggs than small females has led to a longstanding assumption that large fish are disproportionately responsible for population-level egg production (Roberts and Polunin 1993;Allison et al 1998;Halpern 2003;Froese 2004;Sale et al 2005;Birkeland and Dayton 2005).…”

“…No live animals were used. The methods we used for reproductive analysis followed established, statistical methods (Longenecker et al 2020), summarized below, to describe weight-length relations (WLR), size at maturity, sexual pattern, and sex ratios.…”

“…For example, empirical relations (Froese and Binohlan 2000) that underly the Fish-Base life history tool (Froese and Pauly 2019) increasingly overestimate female size at maturity as the maximum size of a species increases Longenecker et al 2017). Also, macroscopic evaluation of gonads results in misclassification of sex and/ or reproductive status of up to half of the inspected specimens (Longenecker et al 2013a(Longenecker et al , 2013b(Longenecker et al , 2020, with the misclassifications tending to overestimate the number of mature females (Longenecker et al 2013a(Longenecker et al , 2013b, underestimate female size at maturity (Grandcourt et al 2006(Grandcourt et al , 2011, and overestimate female spawning biomass (Vitale et al 2006). Finally, histological analysis is required to diagnose sex change (Sadovy and Shapiro 1987).…”

“…In this case study from Fiji, we used rapid, low-cost, onsite, histology-based reproductive analysis (Longenecker et al 2020), to assess the reproductive parameters including size at maturity and per capita egg production of three coral reef fishes. Each is vital to Fiji's subsistence and/or artisanal fisheries, has been identified by Fiji's Ministry of Fisheries as vulnerable to overexploitation, and is common across Pacific Island countries and territories: the humpback red snapper, Lutjanus gibbus (Forsskål, 1775), the Indian goatfish, Parupeneus indicus (Shaw, 1803), and the steephead parrotfish, Chlorurus microrhinos (Bleeker, 1854).…”