AGE (MONTHS) 



FIGURE 3.— Growth of Macrobrachium faustinum in Cane River. 



80 



CO 

 LU 



60 



LU 



^40-1 



QC 



DC 



LU 



00 



u. 20-1 

 O 



i i i i i i i i i i i i i i i — i i i i i 

 FMAMJJASONDJ FMAMJ J AS 



73 



74 



FIGURE 4. — Seasonal variation in the percentage of berried Macro- 

 brachium faustinum in Cane River. 



The asymptotic relationship between Y/R and 

 fishing mortality suggests that the shrimps are un- 

 likely to be overfished from the viewpoint of optimal 

 yield of biomass. At the present level of fishing mor- 

 tality (F = 0.15) there would be substantial gains in 

 yield from small increases in fishing effort (Fig. 6). 

 However, sharp reductions in catch per unit effort 

 and in the mean size of shrimp captured would be ex- 

 pected to accompany increased exploitation. Macro- 

 brachium faustinum is already small, and we expect 

 that, except in the event of extreme food short- 

 age, the reduction in mean size and catch per unit 



5 J 



O 



cr 



o 



< 

 o 



1- 



g .o 





FULL RECRUITS 



F=2-M»0.1 5 



R-0.94 



N = 16 



•  



PRERECRUITS 

 M=Z=0.13 

 R = 0.96 



N= 1 9 



YEAR CLASS 

 O 1971 

 • 1970 

 O 1969 

  1968 



• ° r 



sjS 



*■ 



I I I — I — I I ' I ' I ' I ' I ' I I ' I ' I 



10 15 20 25 



AGE (MONTHS) 



15 



10 



O 

 -n 



H 



o 



> 



5 "" 

 O 

 > 



-i 



o 



30 



FIGURE 5.— Mortality of Macrobrachium faustinum in Cane River as 

 indicated by decline in abundance of year classes (catch per month), 

 and the age composition of the fishermen's catch (percent of total 

 catch). 



even at relatively high values of fishing mortality 

 (F= 2.0) egg production is only 37% less than at F = 

 0.1 (Fig. 7). 



Discussion 



Macrobrachium faustinum and other small shrimps 

 support important subsistence fisheries in the hilly 

 regions of Jamaica and throughout the Caribbean. 

 Management of a resource so widely and diffusely 

 distributed throughout the countryside is difficult. 

 Consequently, to assess the need for management it 

 is important to have some understanding of the likely 

 effects of increased exploitation on these shrimps. 



FISHING MORTALITY 



FIGURE 6.— The relationship of yield per recruit (Y/R) , mean weight 

 of shrimp caught (w), and the index of catch per unit effort (CPUE) to 

 fishing mortality for Macrobrachium faustinum in Cane River. 



658 



