Schiel and Breen: Population, ageing, and fishing mortality of Hahotis ins 



689 



Figure 6 



Yield-per-recruit as a function of the natural mortality rate 

 (M), fishing mortality rate (F), and the minimum legal size. 

 In A, M = 0.05; B, M = 0.1; C, M = 0.15. 



Figure 7 



Egg production as a function of the natural mortality rate 

 (M), fishing mortality rate (F), and the minimum legal size. 

 In A, M = 0.05; B, M = 0.1; C, M = 0.15. 



sampling through time, and appropriate experimenta- 

 tion, can distinguish among these alternatives. 



Ageing and growth 



Despite the fact that growth rings in H. iris are quite 

 distinct, as has been reported for other species (Prince 

 et al. 1988), they are evidently not annual in at least 

 some populations. Predicted growth increments from 

 ring count data were much less than observed incre- 



ments from mark-recapture. This suggests that more 

 than one ring is laid down annually, but it is not clear 

 whether the deposition of growth rings follows a 

 regular annual pattern. We examined the hypothesis 

 that the growth rings are semi-annual, but predicted 

 and observed growth increments still did not agree. 

 Consequently, the ring counts overestimate age in two 

 study regions. This appears to be borne out by length- 

 frequency analysis of mortality in which the estimates 

 are higher than those from catch curves. 



