WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



December 1973 cruise took only two immature 

 specimens at night in 10 oblique tows less than 

 650-m maximum depth. Six oblique tows from 400 

 to 1,200 m took a total of 62 shrimp, although high 

 seas resulted in some catch spillage in two cases. 

 Sergia gardineri clearly does not migrate near full 

 moon. 



Population Size, Growth, and 

 Reproduction (Figure 22) 



Sergia gardineri was by far the most numerous 

 sergestid in the Teuthis collections, the average 

 population density of 8.65 per 100 m- estimated 

 from all horizontal tows being more than twice as 

 high as the next most abundant species. Horizon- 

 tal tows taking more than 100 shrimp occurred in 

 February 1971 (night), June 1971 (day and night), 

 November 1972 (day), and May 1973 (night). In 

 addition, the open tows of the December 1970 

 cruise took large numbers, including 129 in a night 

 tow. Sergia gardineri appeared to have been much 

 less abundant during the first half of 1972, al- 

 though most of these cruises occurred near full 

 moon, when the normal vertical distribution pat- 

 terns seem to be disrupted. The estimate from 

 night tows affected by moonlight, 2.66 per 100 m-, 

 was much lower than the daytime or moonless 

 night estimates. The oblique series of September 



Figure 22.-QuarterIy size-frequency distribution of Sergia 



gardineri. 



1972 and May 1973 gave figures of 10.00 and 1.90 

 per 100 m'-', respectively. 



Recruitment was highest during the third 

 quarter (July-September), although small shrimp 

 began to enter the population in June. The median 

 carapace length increased from 4.9 mm to 6.4 mm 

 between the September 1972 and November 1972 

 cruises, giving a growth rate of about 1.2 mm CL 

 per month. From November to May the growth 

 rate was much lower, about 0.25 mm CL per month. 

 The average size of females was largest in May, 

 although a few very large females were still 

 present in June. Sergia gardineri has a total life 

 span of about 1 yr. 



Diet (Table 5) 



Thirteen of the nineteen specimens of S. gar- 

 dineri taken during DSB III had empty stomachs. 

 The others contained calanoid copepods, an 

 ostracod, a larval decapod, bivalve larvae, fora- 

 minifera, and greenish fibrous matter. 



Sergia bigemmea (Burkenroad 1940) 



Vertical Distribution (Figure 23) 



Most of the few daytime captures of S. bigem- 

 mea during the Teuthis series were of immature 

 shrimp less than 8 mm CL. A tow between 610 and 

 690 m took 15 in July 1971; 5 were caught in 

 November 1972 in a tow probably around 750 m. 

 The peak around 1,100 m resulted from two tows 

 that fished as shallow as 820 m. Two of the three 

 daytime captures of adults during the Teuthis 

 series were between 1,000 and 1,100 m; the other 

 was around 750-850 m. The December 1970 cruise 

 took 20 adults in open tows between 800 and 1,200 

 m. The nighttime distribution varied with size; 

 shrimp smaller than 10 mm CL generally occurred 

 between 50 and 225 m, while the adults ranged 

 between 125 and 250 m. The February 1973 cruise 

 (DSB III) took several large hauls of S. bigemmea, 

 including 49 specimens in a 1-h tow at 150-175 m. 

 Only a few were caught under moonlit conditions; 

 most of these were between 250 and 350 m. The 

 December 1970 cruise took 5 S. bigemmea at 250 m 

 and 11 at 750 m, indicating that much of the 

 population was not migrating. 



The vertical distribution patterns of S. bigem- 

 mea appeared to be affected by avoidance. While 

 the females of most sergestid species grow con- 

 siderably larger than the males, in S. bigemmea 



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