WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



tal closing tows; these were all daytime tows 

 between 450 and 550 m. Several were captured in 0- 

 to 400-m oblique night tows, indicating that S. 

 cornutus is a vertical migrator. Donaldson (1975) 

 found S. conmtus mostly in the upper 50 m at 

 night. 



Population structure and diet were not studied 

 because of the small sample size. 



tures in the 350- to 475-m range; immatures were 

 found between 175 and 250 m. The peak in the 

 upper 25 m is a sampling artifact. There was no 

 positive evidence of full moon nonmigration in the 

 horizontal samples, but the December 1970 cruise 

 took a dozen shrimp in the 575- to 700-m range, 

 suggesting that about 20-30% of the population 

 was not migrating. 



Sergestes erectus Burkenrozd 1940 

 Vertical Distribution (Figure 3) 



Sergestes erectus was abundant in our collection, 

 but nearly half of the shrimp came from daytime 

 tows of the November 1972 cruise. The daytime 

 vertical range was about 550 to 800 m, with 

 maximum catches between 625 and 750 m. Imma- 

 ture shrimp did not occur below 750 m. The night- 

 time range varied with size. Small immature 

 shrimp less than 12 mm CL occurred between the 

 surface and 200 m, mostly below 125 m. Inter- 

 mediate-sized shrimp between 12 and 16 mm CL, 

 including immature and newly mature shrimp, 

 ranged between 150 and 250 m. Adult shrimp 

 larger than 16 mm CL were found between 250 and 

 325 m. Moonlight depressed the vertical range of 

 adults very little, although there were some cap- 



200 

 1400 

 600 

 800 

 1000 

 1200 



200 

 UOO 

 600 

 800 

 1000 

 1200 



200 

 100 

 600 

 800 

 1000 

 1200 



8 12 16 20 2M 28 

 CflflRPRCE LENGTH IMMl 



20 HO 

 NO. PER 10^ m3 



Figure 3.— Vertical distribution of Sergestes erectus. 



Population Size, Growth, and 

 Reproduction (Figure 4) 



Sergestes erectus was the second most abundant 

 species in the horizontal series, the average 

 population density estimated from all horizontal 

 tows amounting to 3.81 per 100 m-. Like S. atlan- 

 ticus, it was taken in larger numbers during the 

 daytime than at night, the population density 

 estimated from daytime horizontal tows amount- 

 ing to 5.55 per 100 m-. These numbers reflect its 

 extreme abundance during the November 1972 

 cruise, when as many as 157 were taken in a single 

 3-h tow. The oblique series of September 1972 and 



SERGESTES ERECTUS 



.oA 



p '' < I — ^ 



6 10 14 18 



APR -JUN 



9 



JAN - MAR 



^V^^T>. 



o-" [—' — I 1 r 



6 10 14 18 22 26 



r-^ :i^->y% 



"T 1 r 



6 10 14 18 



6 10 14 18 22 26 



>"  'i ^ — I 1 P" — ' "' i 1 1 1 T 1 



6 10 14 18 



6 10 14 18 22 26 



CARAPACE LENGTH (mm) 



Figure 4.-Quarterly size-frequency distribution of Sergestes 



erectus. 



809 



