BOEHLERT and SASAKI: PELAGIC BIOGEOGRAPHY OF THE ARMORHEAD 



are seasonally limited to primarily spring, summer, 

 and early fall months, but cover 1952-87 and pro- 

 vide broad geographic coverage between lat. 18° 

 and 66 °N. Greater detail and a summary of many 

 of these surveys are provided by Macy et al. (1978). 

 Since armorhead were an incidental catch, it is dif- 

 ficult to assess the relative value of the different 

 surveys with respect to sampling effort. 



The most typical sampling gears used were long- 

 lines, gill nets, and purse seines targeting salmon, 

 squid, or pomfret; rarer collections were made with 

 plankton nets, dip nets, or hook and line. Thus, 

 sampling was typically in surface waters, most likely 

 in the upper 50 m; the true depth distribution of the 

 pelagic animals, however, is unknown. The only 

 other "gear" was the sei whale, Balaenoptera bore- 

 alis, from which stomach contents were studied for 

 about 27 years; Chikuni (1970) reported armorhead 

 in the stomachs. 



RESULTS AND DISCUSSION 



Distributional Patterns 



The known center of distribution and spawning 

 for benthic P. wheeleri is in the SE-NHR seamount 



region, bounded by lat. 29°-35°N and long. 171°E- 

 179°W (Takahashi and Sasaki 1977; Humphreys and 

 Tagami 1986). These reproductive fish are typical- 

 ly between 23.0 and 28.5 standard length (SL) 

 (Sasaki 1986) and range in age from 1.5 to 2.5 years 

 (Uchiyama and Sampaga fn. 3). They are found at 

 depths between 200 and 500 m (Takahashi and 

 Sasaki 1977). Other benthic occurrences have been 

 recorded but are sporadic (Fig. 1). Several speci- 

 mens were captured off Japan in 1957 (Abe 1957), 

 1969, 1971-73, 1976 (Zama et al. 1977), and 1979 

 (Okamura et al. 1982). These fish were typically the 

 same size as those captured on the seamounts, but 

 no mention of reproductive status was made. Fish 

 of similar length occur rarely on the west coast of 

 North America, but only between lat. 37°00' and 

 44°25'N (Wagner and Bond 1961; Follett and Demp- 

 ster 1963; Smith 1965). Again, reproductive status 

 is unknown for these specimens. No benthic occur- 

 rences off British Columbia or Alaska have been 

 reported, despite extensive trawling surveys which 

 included seamounts (Hughes 1981; Alton 1986). 

 Large specimens have been taken rarely in the 

 Hawaiian Archipelago (Fig. 1; Randall 1980; 

 Humphreys et al. in press) and are typically 4-5 

 years old and appear to be in reproductive condi- 



120' 



150 



Figure 1.— Known distribution of benthic occurrences of pelagic armorhead, Pseudopentaceros wheeleri. Squares represent the main 

 population centers at central North Pacific seamounts. All others are rare or sporadic occurrences. 



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