WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



density of 2.26 per 100 m-, an estimate of doubtful 

 meaning. The two oblique series produced very 

 different estimates. The September 1972 cruise 

 gave a figure of only 0.43 per 100 m'-, making S. 

 fulgens the least abundant of the 16 regularly 

 occurring species. On the other hand, the May 1973 

 cruise gave a figure of 15.95 per 100 m-, more than 

 3 times greater than any other species, and 37 

 times the September figure. 



The seasonal size-frequency histograms reflect 

 the fact that nearly all S. fulgens were caught in 

 the second and third quarters. The second quarter 

 (April-June) histogram is trimodal. The peaks at 

 5.5 and 8 mm CL represent the same cohort as 

 sampled in May and June (the Teuthis XXII 

 oblique series of late May took 6.5-mm shrimp), 

 giving a growth rate of 2.1-2.2 mm CL per month 

 for immature shrimp in this size range. The 

 assumption that the peak at 13-15 mm in May is 

 the same cohort as the peak at 7.5 mm from the 

 preceding November yields a growth rate of 

 1.0-1.2 mm CL per month, reflecting a slowing of 

 the growth rate as the shrimp approach maturity. 

 The presence of large numbers of immature 

 shrimp in the second and fourth quarters implies 

 that S. fulgens either has a very broad spawning 

 period or has two widely separated spawning 

 peaks. 



Diet (Table 5) 



DSB III took nine S. fulgens. Seven of these had 

 food in their stomachs, including a calanoid 

 copepod, an amphipod, and an ostracod, plus 

 smaller prey including larval bivalve and 

 foraminifera. 



Sergia scintillans (Burkenroad 1940) 



Vertical Distribution (Figure 19) 



The vertical distribution of 5. scintillans 

 showed a slight tendency for smaller shrimp to live 

 deeper than larger ones, both day and night. 

 Daytime ranges were about 575 to 700 m for 

 individuals less than 7 mm CL and 525 to 650 m for 

 those larger than 7 mm CL, with maximum catches 

 between 575 and 625 m. The small peak at 325-350 

 m resulted from two shrimp taken in a tow that 

 dipped as deep as 480 m; they were probably 

 captured at the deep end of the tow. At night the 

 adults were mostly between 25 and 125 m, but 

 immature shrimp less than 6 mm CL ranged 



200 



voo 



600 



800 



1000 



1200 



200 

 MOO 



600 



800 



1000 



1200 



200 

 UOG 

 600 

 800 



1000 

 1200 



8 10 12 m 16 



' » T I I T T T — < 



no 



80 



DRY 



:^ 



NIGHT 



MOON 



200 

 MOO 

 600 

 800 

 1000 

 1200 



200 

 UOO 

 600 

 800 

 1000 

 1200 



200 

 WO 

 600 

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H 6 8 10 12 lU 16 MO 80 

 CflRfiPflCE LENGTH (MMl NO. PER 10^ m3 



Figure 19.- Vertical distribution of Sergia scintillans. 



between 50 and 225 m. Although the population 

 was centered at 100-125 m for both sexes, few 

 males occurred shallower than 50 m. Three shallow 

 tows from the May 1973 cruise that caught 40 

 females and 12 males are primarily responsible for 

 this difl!"erence. Moonlight depressed the depth of 

 most of the population to 100-275 m, peaking 

 around 200 m. The peak in the upper 25 m is a 

 sampling artifact. There was no evidence of full 

 moon nonmigration. 



Population Size, Growth, and 

 Reproduction (Figure 20) 



Sergia scintillans was one of the most abundant 

 sergestids in Hawaiian waters. The average 

 population density estimated by all horizontal 

 tows was 3.31 per 100 m'-', the daytime and night- 

 time figures being similar. It was particularly 

 abundant in the shallow night tows of the May 

 1973 cruise (Teuthis XXI), one 3-h tow taking 179 

 shrimp. The oblique series of September 1972 and 

 May 1973 (Teuthis XXII) produced figures of 9.90 

 and 3.70 per 100 m-, respectively. 



Small shrimp were proportionally most abun- 

 dant in the third quarter (July-September). First 

 and second quarter populations were similar in 

 size-frequency, although the larger females oc- 

 curred in the second quarter (April-June). 



817 



