SIZE STRUCTURE AND GROWTH RATE OF Euphausia pacifica 

 OFF THE OREGON COAST' 



Michael C. Smiles, Jr.^ and William G. Pearcy' 



ABSTRACT 



Euphaiisia pacifica (Hansen) oflf Oregon has a maximum life expectancy of about 1 year. During this 

 time it grows rapidly to a length of 22-24 mm. Furcilia larvae were found throughout the year but 

 were most abundant during the autumn months. The population density and the proportion of juve- 

 niles was higher within 25 miles of the coast than in offshore oceanic waters. 



Growth rates off Oregon are about twice those previously reported for this species from other re- 

 gions. Spawning also appears to be later in the year. All these features may be explained by the 

 high primary production which is extended throughout the summer by coastal upwelling and by the 

 lack of wide seasonal fluctuations of water temperatures along the Oregon coast. 



Euphausia pacifica is one of the most abundant 

 euphausiids in the North Pacific Ocean. Dense 

 populations are found in Subarctic and Transi- 

 tional waters (Brinton, 1962a; Ponomareva, 

 1963) and off the Oregon coast (Hebard, 1966; 

 Osterberg, Pearcy, and Kujala, 1964 ; Pearcy 

 and Osterberg, 1967). 



Euphausiids are important food for many 

 marine carnivores (see Mauchline and Fisher, 

 1969, and Ponomareva, 1963, for reviews) , and 

 Euphausia pacifica is no exception. It is preyed 

 upon by salmon (Ito, 1964), baleen whales (Ne- 

 moto, 1957, 1959; Osterberg et al, 1964), her- 

 ring (Ponomareva, 1963), sardine and mack- 

 erel (Nakai et al, 1957, as cited by Ponomareva, 

 1963; Komaki,1967),rockfish ( Pereyra, Pearcy, 

 and Carvey, 1969), pasiphaeid and sergestid 

 shrimp (Renfro and Pearcy, 1966), pandalid 

 shrimp (Pearcy, 1970), and myctophid fishes 

 (Tyler, 1970). 



Studies on the growth of several species of 

 euphausiids are reviewed in the monograph by 

 Mauchline and Fisher (1969). Data on the 



' This research was supported by the National Science 

 Foundation (GB-5494) and the Atomic Energy Com- 

 mission (AT (45-1) -1750; RLO 1750-50). 



° Formerly, Department of Oceanography, Oregon 

 State University; present address: Biology Depart- 

 ment, State University of New York, Farmingdale, N.Y. 

 11735. 



' Department of Oceanography, Oregon State Uni- 

 versity, Corvallis, Oreg. 97331. 



growth and life history of E. pacifica are lim- 

 ited. Nemoto (1957) presented some growth 

 data for E. pacifica from the Japanese-Aleutian 

 area. Ponomareva (1963), in her study on the 

 distribution and ecology of euphausiids of the 

 North Pacific, estimated the growth of E. po/- 

 cifica from plankton samples collected during 

 the winter and spring. Lasker (1966) deter- 

 mined the growth of E. pacifica reared in the 

 laboratory. Preliminary growth rates of E. pa- 

 cifica based on some of our data were also pre- 

 sented by Small (1967). 



Because growth rates are needed to under- 

 stand the ecology and energetics of a species, 

 we undertook this study on the abundance, size 

 structure, and growth rate of E. pacifica off 

 Oregon. 



COLLECTION METHODS 



We made a total of 174 collections using 1-m 

 mouth diameter plankton nets between June 

 1963 and July 1967 at stations located 15, 25, 45, 

 and 65 miles off Newport, Oreg. In addition, 25 

 collections were obtained from stations 85-285 

 miles off Newport. These provided samples of 

 E. pacifica for all seasons of the year over a 

 4-year period. Nets had 0.57 1-mm mesh open- 

 ings and were used with a flowmeter placed in 



Manuscript received September 1970. 



FISHERY BULLETIN: VOL. 69, NO. I, 1971. 



79 



