disappear. Annuli show more clearly on a 

 polished than on an unpolished tooth. The tooth 

 is then marked with the specimen number. 



Age Determination 



Growth lines on the teeth are counted by the 

 aid of a strong lamp, spectacle- type magnify- 

 ing glasses, a dissecting microscope, and 

 dissecting probes. The annuli are counted by 

 holding the teeth over the light and turning them 

 to give the angle of light that best shows the 

 growth pattern. 



Five hundred teeth, including available 

 known-age specimens from previous collec- 

 tions, are read by the examiner as training 

 before he begins to examine a new collection. 



Certain factors which may make age estima- 

 tion difficult are described below: 



Degree of grinding . — If a tooth is not com- 

 pletely ground to the midpoint or if it is ground 

 past the midpoint, growth lines may not show 

 clearly, or may show more than once. In teeth 

 from young animals where rapid growth has 

 made wide annuli, the degree of grinding is not 

 as critical as in older teeth where the annual 

 growth is reduced and annuli are narrow. Poor 

 or careless grinding of older teeth may obscure 

 or destroy the annuli. 



Variation in tooth structure . — In teeth up to 

 about age 5, annual growth lines are widely 

 separated and care must be taken to avoid 

 counting faint incremental lines. Annual ex- 

 ternal ridges are of value as a check on the 

 internal layers in young teeth. The pulp 

 chamber is usually open in male teeth to about 

 age 20 and in female teeth to about age 12. The 

 cementum layer is not very evident in young 

 teeth but is usually plainly visible in older 

 teeth and can be confused with an annual line 

 in the dentin. Old teeth have growth lines that 

 are comparatively close together and some- 

 times difficult to differentiate. 



All teeth are examined by two biologists. 

 Repeated examinations and conferences settle 

 any differences of opinion. Most of the teeth 

 are checked with the aid of a dissecting 

 microscope and are read eight or more times 

 before a final age is recorded. 



Stomach Examinations 



Stomachs are opened by slicing them from 

 end to end, with care taken not to cut into 

 the contents and ruin a food organism of 

 special value or interest. After the contents 

 are washed into a sieve and excess fluid re- 

 moved by draining, the food is weighed in grams 

 and the volume in cubic centimenters is ob- 

 tained by displacement. Material weighing less 

 than 5 g. is recorded as a "trace, " unless a 

 whole specimen or fleshy parts are present. 

 For contents with a weight of 100 g. or less, 

 the volume is not measured but is assigned a 

 value as though the contents had the same 

 density as water. 



A direct count of complete specimens can 

 be made. For specimens in an advanced state 

 of digestion, the skeletal remains are counted. 

 Counts are taken from total skulls, skull parts, 

 otoliths, or numbers of vertebrae approxi- 

 mating a complete fish skeleton. 



Specimens are identified by (1) comparing 

 them with known skeletal remains or preserved 

 specimens on file in the laboratory and (2) using 

 keys by Berry (1912), Clemens and Wilby 

 (1961), Evermann and Goldsborough (1906), 

 Sasaki (1929), Schultz (1953), and Wilimovsky. ' 

 Unidentified specimens are saved for later 

 study, and most of these are finally identified. 



Data for each stomach, with the specimen 

 number, are recorded when the stomachs are 

 examined. When two or more species that can- 

 not be easily separated occur in the same 

 stomach, the examiner estimates their pro- 

 portionate volume to thenearest 5 percent. The 

 weight and volume of each individual species is 

 calculated by multiplying its estimated percent 

 times total weight and volume. 



Personnel 



The following took part in pelagic fur seal 

 investigations in 1962: 



Permanent employees: Biologists Clifford 

 H. Fiscus and Gary A. Baines. 



'n. J. Wilimovsky. 1958. Provisional keys to the 

 fishes of Alaska. Bureau of Commercial Fisheries 

 Biological Laboratory, U.S. Fish and Wildlife Service, 

 Juneau, Alaska, 113 p. [Processed.) 



