Table 37. --Errors in assigning ages of male fur seals from 

 from whole canine teeth 



1/ Average of two readings. 



Table 38. --Errors in assigning ages of male fur seals 

 from sectioned canine teeth 



1/ Average of two readings. 



teeth for any age and Reader D had no signifi- 

 cant bias for sectioned teeth (P>.05). Among 

 observed errors, there was a tendency for 

 readers to call 3-year-old seals 1 year older 

 and 4-year-old seals 1 year younger than they 

 actually were. Ages 2 and 5 were the limits 

 and therefore cannot be used to show bias. 



An analysis of variance test of the percent 

 errors transformed by square root showed 

 that the readers, ages of seals, whether the 

 tooth was whole or sectioned, and all of the 

 interactions of these factors were highly 

 significant (P<.01). Duplicate readings were 

 not significant (P>.05). Interpretation of the 

 results for readers, ages, and methods 

 (whether the tooth was whole or sectioned) is 

 questionable because of the highly significant 

 interaction terms. The reader and method 

 with the lowest error, however, should give 

 the best results. 



We conclude that Reader A should determine 

 the ages of male seals 2 to 5 years old from 

 a single reading of whole teeth. Reader A had 

 lower errors for sectioned teeth from males 

 4 and 5 years old, but the improvement in 

 accuracy is not great enough to justify the 



extra effort required to section the canine 

 teeth of all 4- and 5-year-old males. These 

 results can be applied to the kill of seals on 

 the Pribilof Islands by calculating the possible 

 error in age classification of males taken. 

 Solving for "n" in the equation nP = A, will 

 give the corrected kill, where: 



n = the 1 by 4 matrix of the unknown cor- 

 rected number for each age 



P = the 4 by 4 matrix of the percentage 

 error by age for Reader A from 

 whole teeth 



A= the 4 by I matrix of the number as- 

 signed to each age in the kill on the 

 Pribilof Islands by Reader A. 



The assigned and corrected number of male 

 seals of each age taken on the Pribilof Islands 

 in 1966 is given in table 39, together with 

 the percentage errors in assigned ages. 



Females 



A sample of 527 whole teeth collected from 

 seals in ages 3 to 7 were used in the tests. 

 Whole teeth have been used for assigning ages 

 to females < 7 years on the Pribilof Islands 

 since 1963; ages of females older than 7 years 

 were not determined. Ages were determined 

 from whole teeth for females < 10 years old 

 from 1956 to 1962. Few females <^ 2 years 

 old are taken on the Pribilof Islands. A range 

 of 4.2 percent to 11.7 percent for 3-year-olds 

 to a range of 11.9 to 31.7 percent for 7-year- 

 olds was observed for two readings (table 

 A-23). Ninety-six percent of the assignedages 

 were within plus or minus 1 year of the cor- 

 rect age. Reader A had the lowest error 

 (table 40). 



A sample of 283 sectioned teeth collected 

 from female seals in ages 3 to 1 1 was tested. 

 A conference reading of readers A, B, and C 

 has been used since 1966 for data collected 

 since 1964. The procedure followed is: 

 (1) Each reader assigns an age for each seal 



Table 39. --Assigned and corrected number of male seals of 

 each age killed and the percentage errors in assigned ages, 

 Pribilof Islands, Alaska, 1966 



J./ Does not include thirty-three 6-year-olds killed on 

 St. George Island. 



39 



