Age Estimation and Composition 

 of Peiagic Armorliead 

 Pseudopentaceros wheeleri 

 from the Hancoci< Seamounts 



James H. Uchiyama 

 Jeffrey D. Sampaga 



Honolulu Laboratory, Southwest Fisheries Center 



National Marine Fisheries Service, NOAA 



2570 Dole Street, Honolulu. Hawaii 96822-2396 



The pelagic armorhead Pseudopen- 

 taceros wheeleri is widely distrib- 

 uted in the North Pacific, but rare- 

 ly collected until fishermen from the 

 Soviet Union discovered large con- 

 centrations on the central North 

 Pacific seamounts in the late 1960s 

 (Sakiura 1972). The Soviet Union 

 started a trawl fishery at the south- 

 ern Emperor-northern Hawaiian 

 Ridge (SE-NHR) seamounts (29°N, 

 179°E to 35°N, 171°E) in 1967, and 

 the Japanese entered the fishery in 

 1969 (Sasaki 1986). Since then,' in- 

 tensive fishing occurred at the 

 Northwest and Southeast Hancock 

 Seamounts, the southeast limit of 

 the pelagic armorhead seamounts. 

 During the 1970s, the pelagic ar- 

 morhead catch rate by Japanese 

 fishing vessels at the Hancock Sea- 

 mounts declined dramatically (Uchi- 

 da and Tagami 1984). Commercial 

 fishing at the Hancock Seamounts 

 ceased in 1984, and finally, a 6-year 

 fishing moratorium went into effect 

 in August 1986 (NMFS 1986). 



Pelagic armorhead have an un- 

 usual life history. At SE-NHR sea- 

 mounts, adults spawn during De- 

 cember-March, as indicated by ova- 

 rian studies (Sasaki 1974, BiJim et 

 al. 1978) and the occurrence of lar- 

 vae and young juveniles in Febru- 

 ary and March (Borets 1980). As 

 juveniles, they apparently are pela- 

 gic and occur to the north and 

 northeast of the seamounts as far 

 as the Alaskan gyre before return- 



ing to the seamounts (Fujii 1986, 

 Boehlert and Sasaki 1988). At the 

 SE-NHR seamounts, most of the 

 pelagic armorhead caught in the 

 fishery are 26-33 cm fork length 

 (PL), although 15-40 cm PL speci- 

 mens occur (Humphreys and Taga- 

 mi 1986). Larger specimens (>40 

 cm PL), but none 26-33 cm PL, 

 have been caught on the northern 

 Hawaiian Ridge, from Kure Atoll to 

 French Frigate Shoals (Tagami and 

 Humphreys, in prep.). 



Pelagic armorhead at the sea- 

 mounts exhibit three morphological 

 types: fat, intermediate, and lean 

 (Humphreys et al. 1984, 1989; Hum- 

 phreys and Tagami 1986). During 

 their pelagic phase and when they 

 recruit to seamounts, they are "fat" 

 and their gonads are in an early 

 stage of development. When gonads 

 begin developing and spawning oc- 

 curs, they transform from an "inter- 

 mediate" to a "lean" stage. It has 

 not been determined whether the 

 lean fish recover to spawn again. 



In this study, we determined 

 which hard part is the most suitable 

 for estimating armorhead age and 

 determined the temporal meaning 

 of perceived daily growth incre- 

 ments and apparent annual check 

 marks on the sagitta, the preferred 

 hard part. Chikuni (1970) and 

 Vasil'kov and Borets (1975) used 

 annuli on scales to estimate age, but 

 their estimates did not agree. Fur- 

 thermore, neither study used vali- 



dation procedures, nor did they 

 document the area of collection. The 

 criteria we developed were used to 

 estimate the age composition of 

 pelagic armorhead captured on 

 Southeast Hancock Seamount. 



Methods and materials 



Specimen collection 



Pelagic armorhead were obtained at 

 the Hancock Seamounts in 1976-85 

 from the Japanese trawler Kifa- 

 kami Maru, and by bottom trawl 

 and handline from the NOAA ship 

 Townsend Cromwell. Random sam- 

 ples were obtained by pooling speci- 

 mens from bucket scoops (range 

 2-100 kg/haul) on the Kitakami 

 Maru, during 1 August-15 October 

 1981, and from a single haul on the 

 Townsend Cromwell on 24 July 

 1984. Fish were measured for PL 

 to the nearest millimeter and sexed 

 by gonadal examination. Fish were 

 classified, on the basis of color and 

 body depth, to one of three body 

 types: fat, intermediate, or lean 

 (Humphreys et al. 1984). We also in- 

 cluded a few very large specimens 

 caught by handline on the northern 

 Hawaiian Ridge seamounts between 

 Kure Atoll and French Frigate 

 Shoals and postlarvae caught in a 

 surface tow with a Tucker trawl at 

 Southeast Hancock Seamount, 23- 

 24 February 1985. All postlarva! 

 specimens were preserved and 

 stored in 70% ethanol. 



Hard-part selection and 

 check-mark counts 



To determine which hard part was 

 most suitable for estimating age, 13 

 structures (Table 1) were dissected 

 from 5 specimens collected at the 

 Hancock Seamounts. The stractui'es 

 were prepared for examination fol- 

 lowing modified procedures of Six 

 and Horton (1977). The hy]oural 



Manuscript accepted 25 Julv 1989. 

 Fishery Bulletin, U.S. 88:217-222. 



217 



