752 



Fishery Bulletin 97(4), 1999 



Ln 



U(mid- size, ^,y) 



U(Cuban,^,y) 



40 50 60 



Total Length (cm) 



80 



90 



Figure 3 



Trend in catchability-at-length differences, between Mexican midsize and Cuban fleets for the 

 period 197.5 to 1979, as expressed by Equation 11. Positive values indicate higher vulnerability for 

 immature fish for the midsize fleet than for the Cuban fleet. Vulnerability of adult fish to both 

 fleets is equal. 



Amount of fishing and density-dependent 

 catchability 



As in Equation 9. values of fHy) from Table 3 were 

 fitted against fishing effort at time t. Figure 4 shows 



the tendency for both the midsize and Cuban fleets. 

 For the midsize fleet, the model gives the following 

 values for the parameters: aiE) = 0.1252, (iiE) = 4.8 • 

 lO-*^; R~ = 0.74. Although the tendency for the Cuban 

 fleet was also negative, the observed variability was 



