Research Leads to New Estimates of Body Size at Sexual Maturity for Hawaiian Ehu

Researchers in the PIFSC Life History Program (LHP) recently derived preliminary re-estimates of median body lengths at sexual maturity for female ehu (Etelis marshi) collected from the main Hawaiian Islands (MHI) and compared these estimates with those previously calculated for female ehu from the Northwestern Hawaiian Islands (NWHI). Other biological characteristics were also studied. Plots of standardized Gonadosomatic Indices (GSI) versus body size (fork length, FL, in cm) suggest greater energy allocation to ovaries at smaller lengths in the MHI versus NWHI (Fig. 1). Fits of percentage maturity to body length using a logistic curve indicate that median length-at-maturity (L50) of females is several cm smaller in the MHI than in the NWHI (Fig. 2); estimates of L50 were 24.5±0.3 cm and 27.7±1.0 cm FL) in the MHI and NWHI, respectively. To determine the relative extents to which these apparent geographic differences are influenced by latitude (e.g., water temperature), productivity, or different histories of extraction by Hawaiian bottom fish fisheries in the MHI and NWHI, will require more data than presently available.

Figure 1.  Scatterplot of Gonadosomatic Index (GSI = 100*[Gonad Wt./Gonad Free Body Wt.]) vs Fork Length (FL, cm) for female ehu 
        (Etelis marshi). Data for fish from (a) the MHI are indicated by solid circles and those for fish from (b) the NWHI by 
        hollow circles.
Figure 1. Scatterplot of Gonadosomatic Index (GSI = 100*[Gonad Wt./Gonad Free Body Wt.]) vs Fork Length (FL, cm) for female ehu (Etelis marshi). Data for fish from (a) the MHI are indicated by solid circles and those for fish from (b) the NWHI by hollow circles.
Figure 2  Curves (fitted using maximum likelihood) representing logistic equations of proportion mature by 2-cm FL class for female 
        ehu (Etelis marshi) from (a) the MHI (solid circles and dashed line) and from (b) the NWHI (hollow circles and solid 
        line), based on specimens collected during all months of year from the respective regions within the archipelago. Vertical drop 
        lines (MHI: dashed line; NWHI: solid line) indicate estimated FL ± 1 SE at which a median (50 %) of females from the region are 
        mature. Sample sizes (numbers of fish) for each 2-cm FL class are indicated.
Figure 2 Curves (fitted using maximum likelihood) representing logistic equations of proportion mature by 2-cm FL class for female ehu (Etelis marshi) from (a) the MHI (solid circles and dashed line) and from (b) the NWHI (hollow circles and solid line), based on specimens collected during all months of year from the respective regions within the archipelago. Vertical drop lines (MHI: dashed line; NWHI: solid line) indicate estimated FL ± 1 SE at which a median (50 %) of females from the region are mature. Sample sizes (numbers of fish) for each 2-cm FL class are indicated.