WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



Diet (Table 5) 



DSB III took over 40 S. armatus, but two-thirds 

 had empty stomachs. Food items included calanoid 

 copepods, amphipods, an euphausiid, and an 

 unidentified decapod larva. Prey in the 0.4- to 

 0.6-mm size range, such as foraminifera or bivalve 

 larvae, were not found. 



Sergestes vigilax Stimpson 1 860 



Vertical Distribution (Figure 7) 



The daytime vertical range of 5. vigilax was 

 about 550 to 725 m, with a concentration at about 

 675 m. Nighttime captures were all in the 0- to 

 200-m depth range, peaking at about 50-75 m. 

 Moonlight depressed the peak to 150-200 m, but 

 some individuals remained shallower. There was 

 no evidence of full moon nonmigration. 



Population Size, Growth, and Reproduction (Figure 8) 



Sergestes vigilax was not abundant in Hawaiian 

 waters. The average population density estimated 

 from all horizontal tows was only 0.35 per 100 m-. 

 Daytime catches were larger than night catches, 

 the population estimate from the day tows being 



200 

 400 

 500 

 800 

 1000 

 1200 



200 

 400 

 600 

 800 

 1000 

 1200 



200 

 400 

 600 

 800 

 1000 

 1200 



6 8 10 12 14 

 CBRflPHCE LENGTH (MM) 



16 2 4 

 NO. PER 10^ m3 



Figure 7.- Vertical distribution of Sergestes vigilax. 



0.52 per 100 m-. The oblique series of September 

 1972 and May 1973 took larger numbers, yielding 

 estimates of 3.57 and 0.61 per 100 m-, respectively. 

 These larger population sizes may indicate that 

 the finer mesh of the I KMT sampled S. vigilax, a 

 relatively small species, more efficiently than did 

 the MT used for the horizontal tows. 



The seasonal size-frequency histograms are not 

 significantly different from one another. Shrimp 

 less than 5 mm CL were most abundant in the 

 third quarter (July-September). 



Diet (Table 5) 



Only a single individual was examined; it had an 

 empty stomach. 



Sergestes orientalis Hansen 1919 



Vertical Distribution (Figure 9) 



The daytime vertical distribution of S. orien- 

 talis varied with size; small shrimp less than 6.5 

 mm CL were taken from 450 to 575 m, while larger 

 ones were found between 500 and 625 m, mostly 

 between 550 and 600 m. The nighttime range was 

 from the surface to 125 m, with largest numbers in 

 the 25- to 50-m and 75- to 100-m zones. Small 

 shrimp less than 6 mm CL stayed above 75 m. 

 Moonlight depressed most of the nighttime 



SERGESTES VIGILAX 



JAN - MAR 



9 



, JAN - MAR 



4- 

 



■-■ n "^ n 



e- 



4- 

 



o e- 



'6' OCT- DEC 



12- 



K 



^ 



C4RAPACE LENGTH (mml 



Figure 8.-Quarterly size-frequency distribution of Sergestes 



vigilax. 



811 



