198 



Fishery Bulletin 89(2). 1991 



Figure 3 



Photomicrographs of California halibut otoliths. 



(A) Sagitta from halibut 6.94 mm SL, estimated 

 age 22 days. Distance of drawn radius, 70(jm. 



(B) Sagitta from halibut 48 mm SL, estimated 

 age 109 days. Distance of drawn radius, 890 ^m. 



two models were simple linear esti- 

 mates, using a linear regression of 

 In-transformed abundance-at-age 

 on age (constant mortality rate with 

 age) and on ln(age) (age-specific 

 mortality rates). The sum of squared 

 deviations of observed abundance- 

 at-age from the calculated or trans- 

 formed abundance-at-age predicted 

 by each model was used to deter- 

 mine the model that best fit the 

 data. 



Mortality estimates for halibut 

 from the open coast include loss of 

 juveniles from the open coast popu- 

 lation due to emigration into the 

 bays. These estimates are used to 

 calculate age-specific emigration 

 rates by comparing the apparent 

 mortality (= mortality + emigration) 

 on the open coast to the total mor- 

 tality calculated for the population 

 on the open coast and in the bays. 



Results 



Effects of season and 

 location on size-at-age 



Relationships between halibut length 

 and age did not vary significantly 

 between seasons or between habi- 

 tats. Analysis of covariance indicated no significant dif- 

 ference in length-at-age between fish that had birth- 

 dates in the spring and those with birthdates in the late 

 summer and fall, but the sample size was small for fall 

 fish (n 9) (Table 2). The common slope was 0.6206 (SE 

 0.0905). 



Figure 4 



Relationship between otolith radius 

 (/im) and standard length (mm) of 

 California halibut (n 120). 



