STEVENSON and CARRANZA: MAXIMUM YIELD ESTIMATES FOR OPISTHONEM A SPF 



86"*W 85° 



84° 



83' 



Figure L — Map of Costa Rica showing 

 four thread herring fishing zones and 

 two principal ports on the Pacific coast. 



ATLAN TIC 



OCEAN 



ZONE 4 



GOLFO DULCE 



ZONE 3 



— II°N 



- 10' 



- 9' 



-8' 



the Costa Rican Ministry of Agriculture, the 

 maximum equilibrium yield which this resource 

 will support and the amount of fishing effort re- 

 quired to achieve complete utilization. The 

 methodology and the simplifying assumptions 

 used in this study were necessary given the scar- 

 city of biological information, the absence of 

 species-specific catch data, and the nature of 



available effort statistics, and illustrate some of 

 the problems which impede stock assessments in 

 developing countries. 



DEFINITION OF THE UNIT STOCK 



Three species of Opisthonema are harvested on 

 the Pacific coast of Costa Rica. Species identifica- 



o 



O 3,0 



< 2.0 



Z 



Z 1.0 



^ 0.5 



1972 



YEAR 



1 r~ 



974 



1 1 [ 



1978 1979 



< Z 



Figure 2.— Annual 1968-79 catch and catch per unit effort for 

 three species of thread herring captured on the Pacific coast of 

 Costa Rica (all zones). Catch and effort data were compiled from 

 sales receipts. 



1972 1974 



YEAR 



FIGURE 3.— Annual 1968-79 catch and catch per unit effort data 

 for three species of thread herring captured in the Gulf of Nicoya, 

 Costa Rica (zone li. Catch and effort data were compiled from 

 captain's reports and verified from sales receipts. 



691 



