of the posterior part of the net and were thus 

 counted as being indicative of their general oc- 

 currence. 



Juvenile and adult S. similis were collected by a 

 6-ft(1.8-m) Isaacs-Kidd Midwater Trawl (IKMT), 

 having mesh width of 2 mm, on the continental 

 slope of the San Diego Trough, Calif., at five occa- 

 sions in 1976 and 1977. Sampling was done at 

 night and daytime by releasing the cable at 50m/ 

 min until the net reached a desired depth and then 

 retrieving. Ship speed was 4 kn while the net was 

 sinking, and 2 kn during the retrieval. Usually the 

 biomass of shrimp was large when the net was 

 towed at the depths of 50-200 m at night and 250- 

 600 m in the daytime. To fill in gaps where sam- 

 pling was sparse and to provide more information 

 on reproduction and growth of S. similis , six 

 IKMT collections from the SIO fScripps Institu- 

 tion of Oceanography) Invertebrate Collection 

 were examined. These samples were all collected 

 by 10-ft IKMT with mesh width of 5 mm between 

 lat. 32°28'N and 33°15'N and long. 117°29'W and 

 118°38'W (Table 2). 



T-ABLE 2. — Summary of data from .sergestid .samplmg with 

 Isaacs-Kidd Midwater Trawl off southern California. Six-foot 

 IKMT with 2-mm mesh size; 10-ft trawl with 5-mm mesh size. 



FISHERY BULLETIN: VOL. 77, NO. I 



1000 



X d 



An aliquot of V4 to 'h.: 'each CalCOi^ sample 

 was examined, and th ,iumber of indiv' lals of 

 each developmental stage from the first prt, "zoeal 

 stage to the second zoeal stage was counted. Post- 

 larvae having a body length (BL) < 5.0 mm (stages 

 I- VI) were classified together as early postlarvae. 

 In order to increase accuracy, if the initial aliquot 

 contained only two or fewer individuals of any 

 particular stage, a second aliquot of equal size was 

 examined for specimens of that stage. All counts 

 were then standardized for 1,000 m^ of water 

 filtered by the net. An estimateof the total number 

 of individuals of each stage beneath 1 m- of sea 

 surface was made using the equation. 



where 71 is number of individuals per square me- 

 ter, A^ is the number of individuals/1,000 m-', and 

 d is the depth of the stratum sampled. Data on 

 physical and chemical environments were ob- 

 tained from "Oceanic observations of the Pacific" 

 1951-53 (Scripps Institution of Oceanography 

 1963, 1965a, b) and "CalCOFI cruise 6401 data 

 report" (Scripps Institution of Oceanography''). 



In January and March 1977, a small number of 

 healthy females carrying well-developed eggs in 

 their ovaries were removed from the IKMT collec- 

 tion to be used for spawning and rearing experi- 

 ments. They were transferred immediately after 

 sampling to chilled filtered seawater in large con- 

 tainers and were brought back to the laboratory. 

 The spawning of eggs was observed individually. 

 The sinking speed of the eggs over a 70-cm dis- 

 tance was measured at 10° and 14°C in a constant 

 temperature room using a graduated glass cylin- 

 der of 70-mm diameter. Seawater used for the ex- 

 periment was obtained at the station where 

 ovigerous females were collected. It was filtered 

 through Millipore'^ filters HA (0.45 fj-m). Salinity 

 was 33.72%o. 



The remaining specimens in the IKMT collec- 

 tions were preserved in 59c Formalin-seawater. 

 Most specimens of S. similis having carapace 

 lengths (CL) >5.0 mm were sorted, counted, and 

 sexed. The carapace length from the tip of the 

 rostrum to the posterior margin of the carapace at 

 the dorsal midline was measured to the nearest 0.5 

 mm. 



Change through time in the carapace length- 

 frequency histograms of S. similis was graphi- 

 cally analyzed using probability paper (Harding 

 1949; Cassie 1954). In order to compare the growth 

 trends of the S. similis population off southern 

 California with trends in other waters, previous 

 data on the size-frequency distribution of S. 

 similisreporie6 by Genthe (1969), Pearcy and 

 Forss (1969), Omori et al. (1972), and Mutoh and 

 Omori ( 1978) were reanalyzed to obtain average or 

 modal carapace lengths" for the populations at 



■"Scripps Institution of Oceanography. 1965. Physical and 

 chemical data CalCOFI cruise 6401. 10 January-4 March 

 1964. SIO Ref. 65-7, 76 p. 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOA-'V. 



*BL/CL regression of Sergestes similis < >.5.5 mm CL) are as 

 follows: 



186 



