498 



Fishery Bulletin 89(3). 1991 



population density indicated by the high- 

 est catches on record for other parts of 

 the archipelago where fishing is signifi- 

 cant. Data from the highest catches 

 reported (Cobb 1905) were used directly 

 where species were identified in the catch 

 statistics. Where species were reported 

 pooled in the statistics, they were separ- 

 ated by making the assumption that both 

 species of interest occurred as the same 

 percentage of all shallow-water, demer- 

 sal, large jacks in 1900— the year in which 

 the data of Cobb (1905) were collected— 

 as in 1981-86 (when catch data were 

 available by species). The catches of the 

 two species in 1900, thus reconstructed, 

 were converted to densities using the 

 summed area (Agegian 1985) within 

 these species' habitat depth range around 

 the main, inhabited Hawaiian islands 

 where the 1900 statistics were obtained. 

 These densities provide a lower limit to 

 estimates of the FFS population densities. 



The products of jack population estimates with the 

 respective rations of the representative individual for 

 each species produced estimates for total population 

 consumption (or predation pressure), including all prey 

 consumed. The predation pressure on each prey cate- 

 gory was obtained by multiplying these total consump- 

 tions by the volume percent (as a decimal fraction) for 

 that prey category. 



Results 



Age and growth 



The relationship between whole wet body weight (W) 

 and standard length (SL) was described for both species 

 by performing a log-linear power function regression 

 on these two variables (Table 1). For both species, 

 weight is approximately a cubic function of standard 

 length, indicating nearly isometric growth. The simil- 

 arity in parameter estimates (Table 1) is consistent with 

 the morphological similarity of these two species. 

 Linear regressions were performed to permit conver- 

 sion between standard, fork, and total lengths (Table 1). 

 Otolith growth increments from 14 C. melampygus 

 and 10 C. ignobilis (Table 2) were counted with the aid 

 of SEM (Fig. 2) to estimate age (Appendix A). Assum- 

 ing that increments were deposited daily, the data were 

 fitted to the von Bertalanffy growth equation (Fig. 3) 

 for fish SL, l t (in millimeters), as a function of age, t 

 (in years), 



w& 





'3£m). 



Figure 2 



Scanning electron micrograph of a sagitta from Caranx 

 melampygus. 



It = L M (1 



,-K(t- 



to>). 



The estimates for the parameters are shown in Table 2. 

 The accretion rate of otolith growth increments was 

 measured in C. melarrvpygus using six tetracycline- 

 marked animals, held 55 days after injection. A discrete 

 fluorescent line was discernible in all six subjects (Fig. 

 4), although marginal increments (developed peripheral 

 to the line) were evident in only five. Three thin rep- 

 licate sections were made from the sagittae of each, 

 and marginal increments were enumerated, although 

 one of the five specimens produced only two satisfac- 

 tory preparations. 



