if) 



_l 

 _l 



bJ 

 X 

 CO 

 Ll_ 



o 



UJ 

 CD 



FISHERY BULLETIN: VOL. 87. NO. 2. 1989 

 1980 



N = 564 



95 125 155 185 215 245 



SIZE(mm) 



Figure 5.— Size-frequency distributions of red abalone shells re- 

 covered in the tagging area by year, 1980-82 and 1984. The dashed 

 lines indicate sport (178 mm) and commercial (197 mm) legal mini- 

 mum sizes. 



basis of shell damage. Inspection of the size-fre- 

 quency distributions of the shells for 1980-82 (Fig. 

 5) suggests that a minimum of about 10% of the total 

 mortalities during this period can be ascribed to bar 

 cut injuries. 



Mortality Rate 



Using the values shown in Table 1, total mortal- 

 ity rate Z estimates ranged from 0.165 to 0.222. Sen- 

 sitivity of the estimate to initial conditions and 

 parameters was tested over a broad range of values; 

 the results from some of these tests are shown in 

 Table 6. The estimate was fairly robust to changes 

 in the assumed number of age classes, increasing 



as the number of age classes increased. Tagging 

 results suggest that 15 years are required on aver- 

 age for red abalones at Johnsons Lee to reach 200 

 mm (P. Haaker fn. 3), so we favor estimates based 

 on 16 age classes. Forcing the method to give an 

 estimated L„ consistent with the tagging results 

 had little effect. The estimate was sensitive to con- 

 straints on the standard deviations of length, in- 

 creasing as larger standard deviations were per- 

 mitted. Removing the first two age classes from the 

 estimation led to decreased estimates, but remov- 

 ing further age classes indicated a robust estimate 

 near 0.180. We conclude that the best estimate of 

 total mortality, based on realistic constraints, is Z 

 = 0.180. 



326 



