FISHERY BULLETIN: VOL. 75, NO. 4 



46 60 



36 40 



31-35 



26 30 



DEPTH IN FATHOMS 



FIGURE 11. — Distribution by fishing zone and depth of the mean catch rate of shrimp for U.S. vessels fishing in the Guianas-Brazil 

 fishery, July 1972 to December 1974. Catch rate is expressed as pounds (and kilograms) of shrimp (heads-off weight) per hour of fishing. 



1964, the decline in the average production per 

 vessel was consistent with the increase in the 

 number of vessels. The average annual production 

 per vessel declined from 79,000 lb of shrimp in 

 1965 to 50,000 lb in 1974; during this time the fleet 

 size increased from 203 vessels (1965) to 460 ves- 

 sels (1974). 



The decline in annual catch per vessel suggests 

 that the average abundance of shrimp available to 

 the fishery has decreased as a result of fishing. 

 Total yields, however, are not depressed at present 

 levels of fishing effort. Apparently the productiv- 

 ity of the resource allows the present level of com- 

 mercial harvest and also sufficient recruitment to 

 the next generation. 



Surplus yield models have been applied in 

 shrimp fishery analysis, though certain assump- 

 tions in their use are not completely valid, e.g., 

 instantaneous recruitment, equilibrium condi- 

 tions, and behavior of the species and populations 

 as a single unit. Also, there is no evidence that the 

 abundance of shrimp recruits is dependent on the 

 abundance of the parent stock in this fishery. 

 Therefore, the prediction of maximum equilib- 

 rium yield by a surplus yield model, should be 

 interpreted with caution, especially when the 

 maximum is predicted to occur at fishing effort 

 levels beyond those observed. 



The historical shrimp catches follow closely the 

 trends predicted by the surplus yield model (Fig- 



712 



