FISHERY BULLETIN: VOL. 77, NO. 1 



appeared after spawning. He found that the two 

 size-groups, which spawned in December-January 

 and June-July, respectively, showed the same de- 

 velopmental history but 6 mo out of phase with 

 each other. On the other hand, S. simi/is off the 

 Oregon coast spawned during most of the year but 

 predominantly during the winter and spring, with 

 the individuals living for about 1 yr (Pearcy and 

 Forss 1969). Genthe (1969) determined that the 

 lifespan for the southern California population is 

 2 yr and that the maximum breeding activity 

 occurs in the early summer and fall. The dis- 

 agreement in these conclusions is mainly due to 

 two factors: first, the difficulty of sampling a non- 

 randomly distributed population which moves 

 both horizontally and vertically with time and 

 spatial location; and second, the lack of knowledge 

 about the developmental biology of the larval 

 stages of S. simtlis . Knowledge of the development 

 and growth of larvae and juveniles of S. similis 

 has been severely restricted by the difficulties of 

 maintaining this oceanic species under laboratory 

 conditions. Recently, however, Omori (1979) 

 has successfully reared this species from the egg to 

 the eighth postlarval stage. This success prompted 

 us to examine the life history of S. similis off 

 southern California and to provide further biolog- 

 ical information about its population dynamics. 



The present study deals with the reproduction, 

 growth, longevity, and both daily and ontogenetic 

 vertical migrations of S. similis . The study area is 

 the southern California eddy, which is bounded on 

 the north by Point Conception, lat. 34°N, and on 

 the south by about lat. 30°N. The east-west extent 

 of the eddy is about 250 km. This region is the 

 southernmost in which S. similis is abundant. The 

 sluggish, cyclonic circulation of this eddy, defining 

 a singular water mass, permits substantial au- 

 tonomy for the resident population. Complex to- 

 pogi-aphy, including a scattering of islands, ba- 

 sins, and canyons in the area, appears to provide 

 substantial swarming grounds for S. similis. Be- 

 cause the majority of the population resides in an 

 area such as the southern California eddy, which 

 Brinton ( 1976) has described as "hydrographically 

 restricted," data on the life history of S. similis 

 may be measured more easily than in other 

 oceanic areas. 



MATERIALS AND METHODS 



In the present study, data on occurrence of the 

 larvae and early postlarvae were determined from 



examination of California Cooperative Oceanic 

 Fisheries Investigations (CalCOFI) samples. 



Samples were obtained from selected stations in 

 CalCOFI cruise 6401 (January-February 1964). 

 Stratified plankton sampling was carried out 

 along three parallel transects: Line 60, Line 90, 

 and Line 100 (Figure 1). The samples were col- 

 lected by oblique tow to various depths of water 

 with a standard CalCOFI net of 1-m diameter and 

 0.55-mm mesh openings (Ahlstrom 1948). The 

 mesh size of the cod end and the 40-cm section in 

 front of it was 0.25 mm. Opening-closing net series 

 were obtained to depths of approximately 100 m at 

 three stations and 450 m at one other station on 

 Line 60, and to depths of 400-600 m at all stations 

 on Line 90. Sampling was carried out at whatever 

 time of day the ship arrived on station. Both day 

 and night series, to approximately 600 m depth, 

 were obtained at all station on Line 100. In the 

 present study the samples obtained from the usual 

 habitat of S. similis , i.e., above 400 m depth, were 

 examined (Table 1). At each station, usually two to 

 six nets were towed in each of two or three series of 

 tows. The opening and closing of the nets were 

 messenger-activated, using a Leavitt-type device, 

 and a flowmeter was mounted within the mouth of 

 each net. A net filtered an average volume of about 

 600 m^/tow. A trace of depth vs. time was made 

 during the course of a tow by a recorder attached 

 near the bottom net. For a detailed description of 

 the sampling procedure and the analysis of depth 

 recorder traces, see Brinton (1967). 



The spawning season of S. similis was deter- 

 mined by examining CalCOFI standard oblique 

 haul samples obtained at Stn. 90.37 from January 

 1951 to December 1954. Station 90.37, lat. 

 33°11'N, long. 118°37'W, was selected because it 

 was located near the center of S. similis larval 

 distribution in CalCOFI 6401. Sampling was not 

 conducted in October and December 1952, May, 

 September, and November 1953, and June and 

 September 1954, but sampling from a nearby sta- 

 tion, 90.35, was done in May 1953. Details of this 

 sampling method are described by Ahlstrom 

 (1948) and Fleminger (1964). The net was towed 

 obliquely between the surface and a depth of about 

 140 m while the ship proceeded at a speed of about 

 2 kn. As explained later, this sampling depth cov- 

 ered the entire vertical distribution of protozoeal 

 and zoeal stages of S. similis. Because free eggs 

 and nauplii of S. similis are <0.5 mm, they were 

 not retained by the CalCOFI net. Specimens of 

 protozoeal stages were retained by the fine meshes 



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