WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



represents a tenfold increase over the previous 

 one. 



The oblique tows of September 1972 (Teuthis 

 XVIII) and May 1973 (Teuthis XXII) provided 

 data that yield two estimates of the population 

 densities of the various species, using the method 

 of Maynard et al. (1975). Summing over the entire 

 water column the depth-specific population densi- 

 ties obtained from the horizontal tows provides a 

 third estimate of population densities. The results 

 of these estimates are reported as numbers per 100 

 m- of ocean surface in Table 3. Sample sizes and 

 standard deviations are given for the mean values 

 of the oblique series. Because of the nature of the 

 calculations for the horizontal tows, no standard 

 deviations can be figured, but the variation is 

 probably of the same order as those of the oblique 

 series, since horizontal tows sampled each depth 

 interval about the same number of times and for 

 roughly the same total amount of time as the 

 oblique tows. 



The Teuthis data are poorly suited for inves- 

 tigating growth and reproduction of sergestids. 

 The sampling program was designed primarily to 

 investigate the vertical distribution of mid-water 

 animals. Depth coverage varied widely from cruise 

 to cruise, and the cruises were spaced irregularly 

 throughout the year. In order to smooth the 

 irregularities as much as possible, the data are 

 lumped into 3-mo periods. The cruises invoved are: 



Jan. -Mar. T4, T5, Til, T12, T13 



Apr. - June T6, T7, T8, T15, T16, T21, T23 



July - Sept. T9, TIO, T17, T18 



Oct. - Dec. T19, 70-12. 



Histograms show the size-frequency distribution 

 of males and females for each species. For Ser- 

 gestespectinatus only, data from the oblique series 

 of May 1973 (Teuthis XXII) are added into the 

 second quarter histogram. 



Because of the problem of feeding in the trawl 

 (discussed above), only the stomach content data 

 from DSB III (February 1973) are presented. 

 Table 4 shows the average condition of the 

 stomach contents for each tow. The two indices 

 reported represent the quantity of food present 

 and its state of digestion. Both are based on an 

 arbitrary scale of 1 to 5: 



2. More than half 



full. 



3. 25-50% full. 



4. Less than 25% 



full. 



5. Empty. 



Body still mostly intact, ap- 

 pendages separated, some 

 digestion of soft parts. 



All soft parts digested, cuti- 

 cle remaining, usually dis- 

 articulated. 



Cuticle broken into small 

 fragments. 



Empty. 



Contents 



1. Packed full, 

 distended. 



Digestion 



Whole animal, with little 

 evidence of digestion. 



Stomach contents with a digestion state of 1 were 

 seldom found in the DSB III samples but were 

 rather common in the Teuthis material, probably 

 because of feeding in the trawl. 



Table 5 shows the kind and number of food items 

 found in the stomachs of each species. Often the 

 stomach contents were too well digested for 

 identification. Food items were not identified 

 beyond the general categories presented except 

 for the calanoid copepod genus Pleuromamma, 

 which has a prominent shiny knob on the side of 

 the metasome that is highly resistant to digestion. 



RESULTS 



Sergestid species occurring in Hawaiian waters 

 are listed in Table 6, along with the total number 

 caught. Serge^fes and Sergia until recently were 

 considered to be subgenera of genus Sergesfes s.l.; 

 however, Omori (1974) has rightly elevated the 

 subgenera to full genera. This paper follows his 

 usage but gives feminine endings to species of 

 Sergia. A paper presenting systematic descrip- 

 tions of Hawaiian species is in preparation. 



Sergestes atlanticus Milne Edwards 1830 



Vertical Distribution (Figure 1) 



The normal daytime range of S. atlanticus was 

 550 to 725 m. Small individuals had a more re- 

 stricted range than the larger ones; shrimp less 

 than 5.5 mm CL stayed between 550 and 650 m. 

 Sergestes atlanticus was occasionally taken at 800 

 m or below. The small concentrations between 800 

 and 1,050 m in Figure 1 all resulted from the June 

 1973 cruise. In addition, the December 1970 cruise 

 took seven shrimp in an 800-m tow. At night S. 

 atlanticus occurred over a wide range from the 

 surface to about 300 m. The large concentration in 

 the upper 25 m resulted from a single large capture 

 in May 1973. This depth interval was extensively 

 sampled by only three tows, so it is unclear 



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