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

Abstract

We present a weight–length relation and use rapid and low-cost histological methods to generate preliminary reproductive parameters for Monotaxis grandoculis (Forsskål, 1775), based on specimens collected in Guam and Pohnpei [W = 0.033(FL)2.91]. We estimated female L50 at 30.0 cm FL and male L50 at 35.4 cm FL. The species is gonochoric.  Overall and operational sex ratios were not significantly different from 1:1; however, among mature individuals, the proportion of females was an inverse function of length with no females > 33.5 cm FL but males to 44.5 cm FL. Batch fecundity was an exponential function of length but, because females were absent in the largest size classes, the highest per capita egg production was by individuals at 31.7 cm FL, only 71.2% of maximum observed specimen length. Boat-based creel surveys in Guam showed that the mean length of M. grandoculis in the catch decreased below both female and male L50 from 2010 to 2019, suggesting a significant decline in spawning stock biomass.

Keywords

• maturation
• sex ratio
• fecundity
• Pohnpei
• Guam