FISHERY BULLETIN: VOL. 74, NO. 4 



200 

 400 

 600 

 800 

 1000 

 1200 



200 

 400 

 600 

 800 

 1000 

 1200 



200 

 400 

 600 

 800 

 1000 

 1200 



6 8 10 12 14 

 CRRfiPfiCE LENGTH (MM) 



16 



5 10 

 NO. PER 10^ m3 



Figure 23. -Vertical distribution of Sergia bigemmea. 



the maximum size was the same in both sexes, 

 suggesting that the largest shrimp were escaping 

 capture. Daytime catches were much smaller than 

 nighttime catches, indicating that avoidance was 

 more effective during the day. However, the max- 

 imum size captured was the same during the 

 daytime as at night. It is curious that neither 

 Sergestes erectus nor Sergia fulgens showed any 

 signs of avoidance, though those caught are larger 

 than S. bigemmea; perhaps S. bigemmea is par- 

 ticularly fast for its size or better at sensing the 

 approach of the trawl. 



Population Size, Growth, and 

 Reproduction (Figure 24) 



Sergia bigemmea was one of the less common 

 sergestids in our collection; the average population 

 density estimated from all horizontal tows was 

 only 0.64 per 100 m-. Most catches occurred at 

 night, the figure for nighttime tows being 1.48 per 

 100 m'-. Very few S. bigemmea were captured 

 during the first half of 1972, when most sampling 

 was done near full moon. The oblique series of 

 September 1972 took moderate numbers, produc- 

 ing a population density figure of 2.35 per 100 m-, 

 higher than any other all-red sergestid except S. 

 gardineri. It was also moderately abundant dur- 



SERGIA BIGEMMEA 

 d 



JAN - MAR 



jj-q- 



-x-A 



oM 



m!^ 



nJ 



3 



h^ 



h 



- JUL - SEP 



r^' — I r 



£ 10 



JUL- SEP _ 



h 



n nlh^n 



10 14 



£lU 



M 



rX 



Ar^ 



CARAPACE LENGTH (mm) 



Figure 24.-Quarterly size- frequency distribution of Sergia 



bigemmea. 



ing the December 1970 cruise, which had the only 

 large daytime catch: 23 in an 800- to 900-m open 

 IKMT tow. The largest catches of S. bigemmea 

 occurred during the February 1973 cruise (DSB 

 III) when it was the most abundant species taken, 

 with 49 in a 1-h open tow. The May 1973 oblique 

 series took only a handful, giving a population 

 density estimate of 0.31 per 100 m-. 



None of the seasonal size-frequency histograms 

 are significantly different from the others 

 (Kolmogorov-Smirnov test: P>0.05). Females 

 larger than 12 mm CL were proportionately most 

 abundant in the third quarter (July-September). 



Diet (Table 5) 



The surprisingly large catch of S. bigemmea 

 during DSB III produced a more detailed picture 

 of its diet than for the other species. Only 11 of the 

 88 shrimp had empty stomachs. Sergia bigemmea 

 ate crustacean zooplankton, including calanoid 

 copepods, amphipods, and ostracods; ostracods 

 ■appeared to be a more important prey item than in 

 the other species. Smaller prey were also 



820 



