Pelagic Biogeography of the Armorhead, Pseudopentaceros Wheeleri, and Recruitment to Isolated Seamounts in the North Pacific Ocean
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PELAGIC BIOGEOGRAPHY OF THE ARMORHEAD, PSEUDOPENTACEROS WHEELERI, AND RECRUITMENT TO ISOLATED SEAMOUNTS IN THE NORTH PACIFIC OCEAN GEORGEW. BOEHLERT~AND TAKASHISASAKI~ ABSTRACT The pelagic armorhead, Pseudqmtaceros uheeleri, occurs widely in the North Pacific Ocean. Benthic specimens have been taken from Japan, the Hawaiian Archipelago,and the west coast of North America, but the main reproductive populations are located on southern Emperor-northern Hawaiian Ridge sea- mounts between lat. 29” and 35’N. The period between spawning and recruitment to the seamounts is apparently between 1.5 and 2.5 years, suggesting an extended pelagic existence. We describe the distributional patterns in the North Paciiic based upon over 30 years of published and unpublished records. The majority of pelagic specimens are captured in the subarctic water mass in the northeast Pacific. Based upon the distributional patterns and the oceanography of the North Pacific, we propose migratory paths for both the main population and for the individuals that occur rarely in other locations. The long pelagic period and variability in ocean conditions may play an important role in recruitment to seamounts and the variability in year-class strength for this species. The pelagic armorhead, Pseudopentaceroswhleri, separated the Pentaceros richardsoni complex is a member of the boarfish family Pentacerotidae. from other members of the genus by referring it to Until recently, considerable confusion existed about Pseudopentaceros Bleeker, based on morphological its taxonomy and distribution. Originally described considerations. Second, he separated the complex as Pentaceros richurdsoni Smith 1844, it was into three species: P. richurdsoni confined to the thought to be distributed virtually worldwide, with Southern Hemisphere, and P. wheeleri and P. centers of abundance in the North Pacific and in the pectoralis in the North Pacific. The features used South Atlantic near South Africa (Fujii 1986). Oc- to distinguish P. wheeleri and P. pectoralis were currences were typically sporadic; most records largely morphological. PsaLdopentaeeros pectoralis were from pelagic captures, hence the name pelagic is more robust and deeper bodied and its dis- armorhead. Several authors, including Welander et tribution is typically pelagic; P. wheeleri was al. (1957), Clemens and Wilby (1961), and Wagner known only from benthic specimens on sea- and Bond (1961), used the name Pseudopentaceros mounts. Hardy (1983), however, lacked transitional richardsoni, but more recent studies used the specimens; subsequent work based on morpho- original binomial following Follett and Dempster logical and electrophoretic grounds revealed that (1963). P. wheeleri was a morphological derivative of The 1967 discovery of large concentrations of P. pectoralis, with changes occurring after settle- armorhead in the mid-Pacific, over southern ment. The deeper bodied pelagic form ceases growth Emperor-northern Hawaiian Ridge (SE-NHR) in length after recruiting to the seamounts and seamounts (from lat. 29” to 35”N) (Sasaki 1974; instead transforms body shape to a leaner form. Uchida and Tagami 1984) stimulated increased “Fat” and “lean” specimens of the same length thus interest in this species. Over the next 10 years, differ significantly in appearance (Humphreys et al. nearly 1million metic tons (t) were taken by Soviet in press). and Japanese trawlers (Borets 1975; Takahashi and Pseudopataceros wheeleri has an unusual life Sasald 1977). The increased availability of specimens history. Spawning occurs at the benthic population allowed Hardy (1983) to revise the family. He first centers at the SE-NHR seamounts between Novem- ber and March (Sasaki 1974; Borets 1976; Bilim et ’Southwest Fisheries Center Honolulu Laboratory, National al. 1978). Larvae and juveniles are pelagic (Honma Marine Fisheries Service, NOAA, 2570 Dole Street, Honolulu, HI and Mizusawa 1969; Fedosova and Komrokov 1975; 96822-2396. *Far Seas Fisheries Research Laboratory, 5-7-1Orido, Shimizu, Borets and Sokolovsky 1978) and widely distributed Shizuoka 424, Japan. in the North Pacific. Recruitment to the seamounts Manuscript accepted April 1988. 453 Fishery Bulletin: Vol. 86, No. 3, 1988. FISHERY BULLETIN: VOL. 86, NO. 3 occurs between ages 1.5 and 2.5 years, but in the both published and unpublished accounts, consider major spawning population centers, over 95% of the this distributional pattern in light of general ocean- fish are <2 years (Uchiyama and Sampagas). This ographic conditions in the North Pacific, propose lack of older specimens and presence of fish in poor hypotheses about the migration and recruitment of physiological condition has led to suggestions that armorhead to the seamounts of the central North this species is semelparous, with death after a single Pacific, and assess interannual variation in abun- spawning (Humphreys and Tagami 1986; Hum- dance and how it may relate to oceanographic phreys et al. in press). The long interval between variability. spawning and recruitment for this species suggests that oceanographic conditions in the North Pacific MATERIALS regulate its distribution (Boehlert 1986). Published records of the pelagic distribution of The data sources used include published and un- P. wheelai are too few and varied to understand its published collection records from throughout the biogeography. In different years, specimens have North Pacific Ocean. Published records on occur- been caught in the Gulf of Alaska, near the Aleu- rences in Japan (Abe 1957,1969; Zama et al. 1977; tian Islands, and off the coasts of Japan, Oregon, Okamura et al. 1982), the eastern North Pacific California, and British Columbia. In this paper, we (Welander et al. 1957; Larkins 1964; Honma and document the pelagic and benthic occurrences from Mizusawa 1969; Chikuni 1970; Ignell et al. 1986), and the west coast of North America (Wagner and 'Uchiyama, J. H., and J. Sampaga. In review. Age and growth Bond 1961; Follett and Dempster 1963; Smith 1965) of the pelagic armorhead, PsaLdopentaceros wheeleri, at Hanccck were typically of single or a few specimens. Larger Seamounts. Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA. 2570 Dole Street, numbers of unpublished collection records were in Honolulu, HI 96822-2396. data from large-scale surveys (Table 1).These data TABLE1 .-Data bases searched for pelagic annorhead. pseudopenracaros wheelen', captures excluding single collections and literature reports. Areas and seasons are averages over the years covered. Area Data source Years, season effective Lat. N Long. Salmon drift gill-net surveys' 1972-86, springfall 38'45' 140°E-166"W University of Washington (FRI) purse seining, longlinin 1956-82, springsummer 42"-60' 165'E-l25'W Canada salmon longlinin$ 1962-67, springsummer 42'-54O 120°-1450W Bureau of Commercial Fisheries salmon gill net23 1955-71, springsummer 4Oo-6O0 165'E-l25'W Oshom Maru salmon 1963-66, 1968, 1969, 1971, gill-net-longline surveys' 1974-86, springsummer 36'46' 163°E-1240W Hokusei Maru squid and salmon gill-net surveys' 1973-86, summer 18'-58' 141°E-156'W Japan Marine Fishery Resource Research Center pomfrel surveys5 1979-82. all months 22O49O 143°E-1240W Japanese commercial whaling reports' 1952-79, summer 40'-58' Pacific Biological Station 1983, 1985-86. gill-net surveys' spring-summer 47O-54O 138°-1300W Taiwan Fisheries Research Institute squid Surveys' 1986, July-August 38"-46O 153OE-175OW National Marine Fisheries Service Auke Bay cooperative squid gill-net surveyss 1985-86 43O-55O 145O-175OW Japan Fisheries Agency squid gill-net surveys 1986-87. JUly-AuguSt 36'47' 150°-1650W 'Wmon research data file. Nodh PaciW Ocean. 1972-85 Wmon Dim.Far Seas Fshenes Research Laboratory. Shimuu. Japan. 'Macy e1 a1 1978. 'Larkins 1964. .Data record of oceanographic observations and exploratory fishing. No. I (IE.+No. 28 (1%). Faculty of Fishenes. Hokkaldo University 'Japan Marine Fishery Resourse Research Center 1980. 1983a, 1983b. 1985. *Biologid data file 01 whak in the North Pacific Ocean. 1952-79. Whale Section. Far Seas Fisheries Research Laboratory. Shimiru, Japan See also Chikuni (1970). 'Sloan 1983: Robinson and Jamieson 1984 '2. Shyu. Taiwan Fisheries Research Institute. Kwlung 20220, Taiwan, pers. commun. May 1987. 'Ignell et al. 19%. 454 BOEHLERT and SASAKI: PELAGIC BIOGEOGRAPHY OF THE ARMORHEAD are seasonally limited to primarily spring, summer, region, bounded by lat. 29'-35"N and long. 171'E- and early fall months, but cover 1952-87 and pro- 179"Wflakahashi and Sasaki 1977; Humphreys and vide broad geographic coverage between lat. 18" Tagami 1986). These reproductive fish are typical- and 66"N. Greater detail and a summary of many ly between 23.0 and 28.5 standard length (SL) of these surveys are provided by Macy et al. (1978). (Sasaki 1986) and range in age from 1.5 to 2.5 years Since armorhead were an incidental catch, it is dif- (Uchiyama and Sampaga fn. 3). They are found at ficult to assess the relative value of the different depths between 200 and 500 m (Takahashi and surveys with respect to sampling effort. Sasaki 1977). Other benthic occurrences have been The most typical sampling gears used were long- recorded but are sporadic (Fig. 1). Several speci- lines, gill nets, and purse seines targeting salmon, mens were captured off Japan in 1957 (Abe 1957), squid, or pomfret; rarer collections were made with 1969, 1971-73, 1976 (Zama et al. 1977), and 1979 plankton nets, dip nets, or hook and line. Thus, (Okamura et al. 1982). These fish were typically the sampling was typically in surface waters, most likely same size as those captured on the seamounts, but in the upper 50 m; the true depth distribution of the no mention of reproductive status was made. Fish pelagic animals, however, is unknown. The only of similar length occur rarely on the west coast of other "gear" was the sei whale, Balaaoptma bore- North America, but only between lat. 37'00' and alis, from which stomach contents were studied for 44'25" (Wagner and Bond 1961; Follett and Demp- about 27 years; Chikuni (1970) reported armorhead ster 1963; Smith 1965). Again, reproductive status in the stomachs.