44 



Fishery Bulletin 89( 



1991 



go through a transitional phase, usually maturing as 

 a female the following year at age 2%. Age-1 shrimp 

 that mature directly into females, bypassing the male 

 phase, are called primary females. We examined the 

 data for trends in the percentage of primary females 

 and the overall percentage of male shrimp. 



Results 



We found significantly improved growth of pink shrimp 

 for the 1979-88 period as compared with the 1966-78 

 period. Mean carapace lengths for all four age-1 index 

 area-months were significantly greater in 1979-88 

 (Table 1, Fig. 3) based on two-tailed F -tests. Mean 

 carapace lengths were also greater for the four age-2 



index area-months (Table 1, Fig. 4). Since age-2 shrimp 

 are fully recruited to the trawl gear, this result rules 

 out any apparent increase in mean length due to fishery 

 or gear selectivity or accelerated sex change of age-1 

 shrimp. The time-series of catch per unit effort (Fig. 

 2) indicates that the population biomass has been 

 reduced since 1978. 



The increase in growth demonstrated for the 

 1979-88 catch years represents a substantial increase 

 in average weight. Using the age-1 composite growth 

 index, the mean carapace length of age-1 shrimp has 

 increased from 16.1 to 17.4mm. From the length- 

 weight relationship developed by Zirges et al. (1982); 



In W = -7.94746 + 3.20971n L, 



