WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



Crustacea, including calanoid copepods and a 

 euphausiid. 



Sergestes pectinatus Snnd 1920 



Vertical Distribution (Figure 15) 



The daytime range of 5. pectinatus was broad, 

 extending from 425 to 725 m. The peak at 425-450 

 m came from a single tow in the June 1971 cruise, 

 and the peak at 650-675 m was also from a single 

 tow in the November 1972 cruise. Most large 

 catches centered around 575 to 625 m. There was a 

 poorly defined size-depth trend. Small shrimp less 

 than 4 mm CL seldom occurred below 600 m, while 

 the very large females seldom occurred above 550 

 m. At night the size-depth trend was pronounced. 

 Males less than 3.5 mm CL were found in the upper 

 100 m, mostly between 25 and 75 m. From 4 to 5 

 mm CL, maximum catches were in the 75- to 250-m 

 range, peaking around 150 m. The largest males 

 were taken in the 200- to 275-m range. Females 

 showed a similar trend; maximum catches of 

 shrimp less than 4.5 mm CL occurred around 50 m, 

 increasing to 150 m for shrimp between 4.5 and 6 

 mm CL, and 200 m for shrimp larger than 6 mm 

 CL. A few shrimp were taken below 300 m; these 

 may have been contaminants. The moon depressed 



most of the population to about 150-250 m. The 

 peak in the upper 25 m is a sampling artifact. 

 None of the Teuthis samples showed any indica- 

 tions of full moon nonmigration. The December 

 1970 cruise took 14 specimens in three open tows 

 between 400 and 600 m, probably representing less 

 than 10% of the population. 



Population Size, Growth and Reproduction (Figure 16) 



Sergestes pectinatus appeared to be signif- 

 icantly undersampled by the MT. The average 

 population density estimated by all horizontal 

 tows was 1.71 per 100 m-. The IKMT with its finer 

 mesh captured many more shrimp than the MT. 

 Sergestes pectinatus was the most abundant ser- 

 gestid in the September 1972 oblique series, which 

 yielded a population density estimate of 26.67 per 

 100 m^. The shrimp from this cruise composed 

 nearly 40% of the entire catch of 5. pectinatus. The 

 May 1973 series gave a figure of 4.70 per 100 m'^, 

 second only to S.fulgens. In both cases, the aver- 

 age size of an individual was considerably smaller 

 than in a typical MT tow. Interpretation of the 

 size-frequency histograms is complicated by the 

 undersampling problem. For 5. pectinatus only, 

 data from the May 1973 oblique series were added 

 to the second quarter horizontal data. This means 



200 



noo 



600 



800 



1000 



1200 



200 



noo 



600 



800 



1000 



1200 



200 

 400 

 600 

 800 

 1000 

 1200 



M 6 8 10 12 14 16 6 12 

 CRRRPRCE LENGTH (MM) NO. PER 10= M^ 



Figure 15.- Vertical distribution of Sergestes pectinatus. 



SERGESTES PECTINATUS 



cr 



JAN->UR 



^:x 



rO. 



/ 



6 8 2 



CARA«C£ LENGTH (mml 



Including TnMilt 1001 



Figure 16.-Quarterly size-frequency distribution of Sergestes 

 pectinatus. April-June quarter includes data from Teuthis XXII. 



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