LIFE HISTORY AND VERTICAL MIGRATION OF THE PELAGIC SHRIMP 

 SERGESTES SIMILIS OFF THE SOUTHERN CALIFORNIA COAST 



Makoto Omori' and David Gluck^ 



ABSTRACT 



Sergestes similis in the southern California eddy was observed with respect to reproduction, daily and 

 ontogenetic vertical migrations, growth, and longevity. The period of highest spawning activity occurs 

 between late December and early April, but small pulses of spawning are occasionally observed in late 

 spring and summer. The release of eggs takes place close to shore above the continental slope, and then 

 the eggs sink to 200 m or deeper. Nauplius larvae ascend and protozoeal and zoeal laivae stay mostly 

 above 100 m. The daily vertical migration becomes evident after the second protozoeal stage. Adults 

 are abundant between 50 and 200 m at night and 2.50 and 600 m in the daytime. 



The spawning activity of .S. similis becomeshighest during the period when the verticaUhicknessof 

 the optimum temperature zone (10^-15^Cl is the greatest. The authors speculate that the local 

 population off the southern California coast may be joined by the subarctic population. It is possible 

 that multiple spawnings occur from females of the southern California population. 



The lifespan ofS.sirntlis is 2.0-2.5 years for females and about 1.5 years for males. Sexual maturity is 

 reached at about 1 year in both sexes. Females reproduce in two successive spawning seasons, and 

 males seem to accomplish multiple fertilizations. Growth trends are similar to those reported for S. 

 similis off Oregon. Growth rates are described using growth curves fitted by the von Bertalanffy and 

 logistic equations. 



Sergestes similis Hansen is the most abt lani. 

 oceanic, pelagic shrimp in the Nonh Pacific Drift, 

 lat. 40°-50°N. This subarctic a- i transitional 

 species occurs mainly in watei. rthfre t mpera- 

 ture ranges between 3° and 13 J. Its di.-; ration 

 extends from Japan to the coast of North America 

 as far south as lat. 27°N (Pearcy and Forss 1969: 

 Omori at al. 1972). 



In the cooler part <if thj California Current, S. 

 similis composes a substantial ., action of all mi- 

 cronekton. The adults perform extensive vertical 

 migrations, living between 250 and 600 m in the 

 daytime and ascending to 50-200 m depths at 

 night. According to Barham ( 1963 ) and Clarke,^ S. 

 similis is consistently associated with the lower 

 component of a sonic scattering layer oif southern 

 California. 



Sergestes similis sheds eggs in the sea. From 



'Institute of Marine Resources. Scripps Institution of 

 Oceanography, University of California, San Diego, La JoUa, 

 Calif; Ocean Research Institute, University of Tokyo, Nakano, 

 Tokyo, Japan; present address: Division of Marine Sciences. 

 UNESCO, Place de Fontenoy, 75700 Paris, France. 



-Institute of Marine Resources. Scripps Institution of 

 Oceanography. University of California, San Diego. La Jolla. 

 Calif.; present address: Department of Biological Sciences, Uni- 

 versity of California, Santa Barbara, CA 93106. 



^Clarke, W. D. 1966. Bathyphotometric studies of the light 

 regime of organisms of the deep scattering layers. U.S. AEC 

 Res. Dev. Rep. UC4S, Biol. Med.. TI D4500, 47 p. 



Manuscript accepted August 1978. 

 FISHERY BULLETIN. VOL. 77. NO. 1. 1979. 



eggs hatch the first of four naupliar stages (Nl- 

 N4), which go on to develop three protozoeal stages 

 (PZ1-PZ3), and .wo zoeal stages (Zl, Z2) before 

 entering postlarval stages (PL) (Omori 1979). 



Sergestes simtlis plays an important role in the 

 dynamics of northern Pacific oceanic ecosystems. 

 As an adult, it feeds mainly on copepods and 

 euphausiids and is, in turn, preyed upon by squids, 

 mesopelagic fishes, rockfi- !:es, albacore, basking 

 shark, and baleen wha' Pereyra et al. 1969; 

 Judkins and Fleminger l;'72; Omori et al. 1972; 

 Mutoh and Omori 1 978 ). In certain areas there is a 

 strong possibility that the enormous standing 

 stock can be exploited by commercial fisheries 

 (Omori 1974). 



In spite of the great importance of this species, 

 little is known about its life history, especially its 

 reproduction, development, and growth. Although 

 the distribution and daily vertical migration of 

 adult S. similis off the coasts of California and 

 Oregon have been studied (Barham 1963; Clarke, 

 see footnote 3; Pearcy and Forss 1966; Da vies and 

 Barham 1969; Pearcy et al. 1977), no work has 

 been done on the biology of larval and early post- 

 larval stages. Details of the spawning season and 

 lifespan of the species have not yet been confirmed. 

 Barham ( 1957) stated that S. similis in Monterey 

 Bay, Calif., reached maturity at age 1 yr and dis- 



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