Dee and Parrish: Reproductive and trophic ecology of Myripnstis amaena 



517 



ber of common soldierfish species. Johnston Atoll 

 provided a logistically good base for study, where M. 

 amaena was the dominant Myripristis species, with 

 populations not seriously depressed by fishing. The 

 species was plentiful and easily collected at many 

 locations throughout the year, and a good range of 

 sizes was readily available. The importance of M. 

 amaena in the fishery at JA facilitated collection of 

 specimens and fishery data. 



Materials and methods 



Specimen collection and handling 



Most specimens used in all analyses were taken at 

 Johnston Atoll, a remote, coral-rich, oceanic pinnacle 

 about 1250 km SW of Honolulu (Halstead and Bun- 

 ker, 1954; Amerson and Shelton, 1976; Randall et 

 al., 1985; Maragos and Jokiel, 1986). Smaller collec- 

 tions were made from a rich, fringing coral reef tract 

 at Puako in South Kohala on the leeward coast of 

 Hawaii Island (Hayes et al., 1982). Afew specimens 

 were collected from the almost uninhabited North- 

 western Hawaiian Islands (NWHI), primarily from 

 shallow, coralline areas at French Frigate Shoals and 

 Midway ( located about 750 and 2000 km, respectively, 

 northwest of Honolulu). 



Specimens from all three locations contributed to 

 size-frequency analysis, visual assessment of gonad 

 condition (maturity), and analysis of gut contents. 

 At JA and Puako, gonad weight was taken to deter- 

 mine reproductive season and size at first reproduc- 

 tion; at JA, gonad samples were preserved for histo- 

 logical examination and estimation of fecundity. 



Most specimens at all locations were collected from 

 shallow waters (<15 m). The major methods of col- 

 lection were spearing, bait casting with a line, and 

 some spot applications of ichthyocide. At JA, we col- 

 lected specimens from several sites inside the lagoon 

 and just outside the barrier reef. Collections and ex- 

 tensive underwater observations were made at fre- 

 quent intervals between February 1984 and Janu- 

 ary 1986. Sampling was less intensive in some 

 months because of constraints on travel to JA. At 

 Puako and in the NWHI, specimens were collected 

 rather widely within coralline habitats. At Puako, 

 about half the specimens were collected as quickly 

 as feasible (May-June 1981), once the species was 

 found to be in reproductive season. Other collections 

 there were distributed throughout the year. In the 

 NWHI, specimens were collected in March, April, 

 May, August, and November. 



Standard (SL), fork (FL), and total (TL) lengths of 

 all captured specimens were measured to the near- 

 est millimeter, and weights were taken to the near- 



est 0.1 g. (Appendix A provides functions, fitted by 

 regression, to convert between SL, FL, and TL.) 

 Whole guts and gonads were excised and preserved 

 in 10% buffered formalin for further analysis. Some 

 specimens were frozen whole and stored for some 

 weeks or months before processing. 



Source of size-frequency data 



At JA, Puako, and the NWHI, length and weight data 

 from all specimens collected for other purposes were 

 available for size-frequency estimation. In addition, 

 at JA, creel census data were obtained from fisher- 

 men's catches on many days over the period of study. 

 Fish landed by boat and shore fishermen were ex- 

 amined, and each specimen was measured and 

 weighed as above. These data provided a much larger 

 and possibly more representative sample than our 

 collections alone. 



Feeding 



The volume of each complete gut specimen was mea- 

 sured by displacement of water before and after the 

 gut was opened and all contents removed. The total 

 volume of contents was determined by difference. All 

 diet items were sorted into systematic categories and 

 identified to the lowest possible taxa. For each prey 

 category, the number of individuals, length, extent 

 of digestion, location in gut, and volume were re- 

 corded. Whole reference specimens were used as an 

 aid in identifying prey items and estimating the origi- 

 nal size of the prey by comparison of the dimensions 

 of recognizable parts. Volume of remains in each prey 

 category was estimated by displacement of water 

 (Wolfert and Miller, 1978).' 



A measure of overall importance of each prey cat- 

 egory was calculated by using the Index of Relative 

 Importance (IRI), as defined by Pinkas et al. (1971): 



IRI = frequency % x (numerical c k + volume %), 



where frequency % = 



numerical % = 



and volume % 



(the number of guts contain- 

 ing prey of one category di- 

 vided by the total number of 

 guts that contained any iden- 

 tifiable prey) x 100; 

 (the number of individuals of 

 one prey category divided by 

 the total number of prey in- 

 dividuals found in all the 

 gutslx 100; 



(the volume of one prey cat- 

 egory divided by the total 

 volume of all prey found in 

 the guts) x 100. 



