FISHERY BULLETIN: VOL. 84, NO. 4 



with 95% confidence limits and sample sizes are 

 provided. 



The data show that the 55-60 mm CL class en- 

 compassed the largest shrimp observed. Virtually 

 all (95%) females >50 mm CL that were sampled 

 during August-February bore eggs. Conversely, up 

 to 35 mm CL no more than 1% of the shrimp ex- 

 amined were ovigerous. The figure shows further 

 that at a CL of 40 mm the percentage of ovigerous 

 females is one-half its maximum value, with 48% of 

 all sampled females bearing eggs. We conclude that 

 females become sexually mature at this size 

 (Gunderson et al. 1980). We have no data on matura- 

 tion in males. 



The data presented in Figure 4 show the sex ratio 

 of shrimp as it depends on size (CL mm). Plotted 

 are the percentage females, with 95% confidence 

 intervals and sample sizes, against 5 mm CL size 

 classes. The data clearly show that H. laevigatus 

 maintains a relatively uniform sex ratio from 10 to 

 45 mm CL, but that females predominate in the 

 largest length categories (45-65 mm CL). 



Because some studies (Clarke 1972; Wilder 1977) 

 have indicated that Heterocarpus females may 

 experience mass mortality after egg bearing, we ex- 

 amined the relationship of sex ratio to season (Table 

 4). Presented for each 2-mo sampling period are the 

 number of females and total number of shrimp 

 sampled, the proportion which are female, and the 

 standard error of the proportion. The results show 



that an unusually high fraction (0.72) of the shrimp 

 sampled during the peak of the reproductive season 

 (December-January) are female. Note that the in- 

 cidence of females in trap samples declines signifi- 

 cantly to a value of 0.45 in April-May as the breeding 

 season wanes. At first inspection these data support 

 the contention that females experience increased 

 mortality after bearing eggs, i.e., that//, laevigatus 

 may be semelparous. 



Table 4.— Sex ratio of Heterocarpus laevigatus by month sampled. 

 The standard error of the proportion is given by S p . 



Spatial Distribution 



The relationship between the sex ratio of H. laevi- 

 gatus and sampling depth is provided in Table 5. 

 These results demonstrate that the relative abun- 

 dance of the two sexes is not independent of depth 

 (X 2 = 165.6, df = 16, P < 0.001). As depth in- 

 creases (440-760 m) there is a significant decline in 

 the percentage of females in our samples (P = 0.05). 



100 



Carapace Length - mm 



Figure 4.— Sex ratio as a function of carapace length. Vertical bars represent 95% 

 confidence intervals and sample sizes are presented above. 



920 



