present samples had subsimilar A 1 and A 2, while in 

 P. japonica A 2 is considerably longer than A 1. Also, 

 the relatively short lengths of the present specimens, 

 many of which bore eggs or young, rules out their 

 being japonica (Bowman, I960). 



The relative abundance of P. pacifica decreased 

 markedly at night (Fig. 3), but it was always the most 

 abundant species. The numbers per 1,000 m-' seemed 

 to show no diurnal variation (Fig. 2), suggesting a lack 

 of diurnal vertical migration. Bowman (1960) found no 

 evidence for a diurnal vertical migration off Oregon 

 and California. 



Many of the females examined had eggs or brood 

 young. Also, many samples contained loose eggs and 

 young that were likely separated from females while 

 being caught in the net or during subsequent handling 

 and examination. This factor introduces a possible 

 error into the numbers of animals. An attempt to over- 

 come this was made by counting separately loose eggs 

 and what appeared to be brood young. Whenever 

 young appeared small enough, or undeveloped 

 enough, they were considered to be "preimmatures." 

 An "immature"" is taken to be a free-swimming, non- 

 brooding young, less than 3 mm in length. The num- 

 bers of animals or eggs thus designated are indicated 

 as footnotes in Table 3, and are not included in the 

 numbers collected, nor do they figure in estimated 

 number per 1,000 m^. There was no diurnal variation 

 in size range or sex ratio. Overall, the females out- 

 numbered the males by a ratio of 1.2:1, although this 

 difference is insignificant at the 5% level (hetero- 

 geneity X" test). 



Bowman (1960) showed that P. pacifica is widely 

 distributed in the subarctic Pacific and that it is the 

 most abundant epipelagic amphipod off Oregon and 

 California. He further stated, "It is apparent that P. 

 pacifica. like Sagitta elegans and Eiikmhnia hamata, 

 is by virtue of its temperature requirements an inhabi- 

 tant of the subarctic water, and like these chaeto- 

 gnaths can serve as a biological indicator of this cold 

 water of low salinity. However . . . the euphausiid, 

 Eiiphausia pacifica . . . has a distribution more nearly 

 like that of P. pacifica than does 5. elegans." 



Although no P. japonica were taken in the present 

 hauls, this species has recently been taken in the same 

 general area (Fukuchi, 1970). Since its population 

 center lies far to the southwest, the southeastern Ber- 

 ing Sea should be considered to be in the fringes of its 

 range. Its occurrence there is probably dependent on 

 intrusion of water from the western Bering Sea, andF. 

 japonica should probably be considered to be an indi- 

 cator species for western subarctic water in the east- 

 ern Bering Sea. 



Parathemisto libellula (Lichtenstein) 



One specimen in one haul (International Pacific 

 Halibut Commission). Length: 21.3 mm. female. 

 This specimen was taken in a shallow tow over shelf 



waters. Bowman (1960) reported the species as wide- 

 spread throughout the Bering Sea. 



Phronima sedentaria (Forskal) 



One specimen in one haul, plus another in a 

 0.505-mm mesh sample. Length: 16.5 and 17.7 mm, 

 both males. 



Thorsteinson (1941) recorded the species from the 

 Gulf of Alaska but gave no details on actual locations. 

 Fukuchi (1970) recorded the species from lat. 4r55'N 

 off Hokkaido, Japan, and Vinogradov (1956) reported 

 the species from the western Bering Sea at lat. 55°N. 



Primno macropa Guerin 



Six hundred and sixty-one (661) specimens in 17 

 hauls. Length: up to 16.0 mm for females and 10.5 mm 

 for males. 



This species is common in the North Pacific Ocean 

 from southern California (Brusca, 1967) northward to 

 the Gulf of Alaska (Thorsteinson, 1941), off the Kurile 

 Islands (Bulycheva, 1955), and in the western Bering 

 Sea (Vinogradov, 1956). 



The increase during the night hauls in numbers per 

 1,000 m^ and relative abundance (as high as 27% at 

 haul 11) strongly suggest a diurnal vertical migration 

 of this species. 



ACKNOWLEDGMENTS 



Thomas E. Bowman, Division of Crustacea, Na- 

 tional Museum of Natural History, Washington, 

 D.C., kindly verified my identifications of the am- 

 phipods, and offered useful advice on amphipod tax- 

 onomy and ecology. Jerry Larrance and Donald Day 

 gave useful comments on the manuscript. Stephen R. 

 Threlkeld and Arthur Cvar, respectively, measured 

 and sexed the Parathemisto pacifica specimens and 

 helped analyze the resulting data. The patient, careful 

 work of the Northwest Fisheries Center's Sorting 

 Center staff was invaluable in this study; in particular 

 I thank Janet Condon, Larry Landrie, and Beverly 

 Vinter. 



LITERATURE CITED 



BIRSTEIN, YA.A., and M. E. VINOGRADOV. 



1955. Pelagicheskie gammaridy (Amphipoda-Gammaridea) 

 Kurilo-Kamchatskoi vpadiny [Pelagic gammarids (Amphi- 

 poda-Gammaridea) of the Kurile-Kamchatka Trench]. 

 Tr. Inst. Okeanol., Akad. Nauk SSSR 12:210-287. 

 1958. Pelagicheskie gammaridy (Amphipoda, Gammaridea) 

 severo-zapadnoi chasti Tikhogo okeana [Pelagic gammarids 

 (Amphipoda, Gammaridea) of the northwest Pacific Ocean]. 

 Tr. Inst. Okeanol.. Akad. Nauk SSSR 27:219-257. (Transl. 

 1959, Fish. Res. Board Can., Transl. Ser. 253.) 

 BOWMAN, T. E. 



1953. The systematics and distribution of pelagic amphipods of 

 the families Vibiliidae, Paraphronimidae, Hyperiidae, Dairel- 

 lidae. and Phrosinidae from the northeastern Pacific. Ph.D. 

 Thesis, Univ. Calif., Los Angeles. 430 p. 



