FISHERY BULLETIN; VOL. 69, NO. Z 



Because many more shrimp were measured dur- 

 ing some cruises than during others in the same 

 season, we weighted the data in Figure 12 and 

 Appendix Table 4 to give each cruise equal 

 weight, irrespective of the number of shrimp 

 in the samples. Figure 12 demonstrates that 

 the peak of spawning is during the winter and 

 spring. Spawning probably is not extensive be- 

 fore December and is essentially completed 

 by June, although some spawning continues 

 throughout the year. Figure 12 also indicates 

 that few females less than 150 mm long have 

 ripe ovaries. 



The occurrence of small specimens reported 

 by Burkenroad (1936) in March corresponds 

 with our estimate of the peak spawning season. 



AGE CLASSES 



In compiling total length distributions for 

 males and females, we have again given equal 

 weights to data from each cruise irrespective 



10 20 30 <0 50 60 70 80 90 100 110 1J0 130 1*0 150 160 170 180 190 JOO 310 



IQ ^0 30 40 50 60 70 BO 90 100 110 IJQ 130 MO 150 160 170 IBO 190 JOO JIO 



5 15 25 33 45 55 65 75 85 M 105 115 125 135 145 155 145 175 185 l» 205 215 

 TOT*l LENGTH (MM) 



Figure 12. — Seasonal length distributions of female 

 H. robtistns by ovarian stage.s. (UN = undeveloped; 

 D = developing; P ^= pink; R == ripe.) 



o! 6 



I ' I ' I ' I ' I ' I ' I  I ' M I ' I  I ' I  I I I ' I I I ' I  I ' I ' 



/A ... 



./ "X. ' ' 



T I '"! 1' 'I ' ! ' I ' I ' 1 ' I 



JAN - FEB 



- 1,579 MALES 



- 2,051 fEMAlES 



/ 



A^. 



TT^ 



2 6B6 MAlES 

 3.872 FEMALES 



/ 



\ /•■'■""\ 





I I I I I I I I I'i'rT'r V ' I ' I 1 I I I ' I 1 I I I I r 



JUIT - SEPI A 



I I I ' I ' I ' I ' I ' I ' I ' I ' I ' I I I ' I ' I ' I 



■rn-- 



1,304 MALES 

 I.9SS FEMALES 



.,.J- 





y?. 



f-r 



TOTAL LENGTH (MM) 



Figure 13. — Length distributions of H. robustus by sex 

 and season. 



of the number of shrimp measured, and we pre- 

 sent the data for the same seasonal periods used 

 to show the spawning season (Figure 13 and 

 Appendix Table 5). The relative heights of the 

 modes can be misleading because the data are 

 scattered sparsely through 11 years and the 

 appearance of a dominant year class in one 

 sample (as occurred in November 1964) can 

 have a disproportionate effect when applied to 

 the material as a whole. 



The graphs for the females are more readily 

 interpreted than those for the males. In No- 



322 



