354 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



which sampled an area between 140° W. and 

 180° longitude, from 30° to 50° N. latitude. 

 These fish, taken by longline, trolling, and gill 

 nets, were smaller, ranging in length between 

 50 and 112 cm. (6 to 65 lbs.) (fig. 1). 



Scales were collected from the region of the 

 body just below the second dorsal fin. The 

 selection of this region was largely based on re- 

 commendations of researchers in California who 

 were similarly engaged in the problem of aging 

 the albacore, and who found scales from that 

 region of the body "most promising" (personal 

 correspondence). The 15th and 16th caudal 

 vertebrae were selected for this study. While 

 past investigators have used the thoracic verte- 

 brae, our choice of the caudal vertebrae was 

 based chiefly on accessibility, or the ease with 

 which they could be acquired in the field or at 

 the auction markets. This difference in the choice 

 of vertebrae appears to be of little significance, 

 since a careful examination of each of the 38 

 vertebrae of a single albacore revealed no notable 

 differences in the appearance of the concentric 

 markings. 



METHODS 



The scales were soaked in water overnight, 

 after which the slime and adhering tissue were 

 easily removed. The scales were then either 

 dry-mounted between two glass slides or impressed 

 on 0.030-inch thick cellulose acetate (1" x 3") 



strips, which were first softened by immersing 

 in 95-percent ethyl alcohol for 5 minutes. 



Scale images were projected on a white paper 

 screen with a microprojector. Because of the 

 variable sizes of the scales, the distance between 

 the projected image and the microprojector was 

 varied so that approximately equal-sized images 

 could be produced. This tended to diminish 

 to some extent the influence of the scale size in 

 making ring counts. 



In processing the vertebrae for study, the tail 

 section, cut off at or near the 5th dorsal finlet, 

 was boiled in water until the flesh could easily 

 be removed from the bone. After washing, the 

 vertebrae were sun-dried for about 2 days. 



The method described by Partlo (1955) was 

 followed in preparing the vertebrae for study. 

 Where the 15th caudal vertebra was cut through 

 or damaged during collection, the 16th vertebra 

 was used. An electric jig saw was employed to 

 cut each vertebra along a sagittal plane 

 slightly to one side of the median line. The 

 larger of the resulting two parts was sanded down 

 until the center of the centrum was clearly exposed 

 (fig. 2). Additional cleaning and accentuating 

 of the concentric rings were done by immersing 

 the vertebra in a 1-percent solution of potassium 

 hydroxide for about 48 hours, followed by rinsing 

 in fresh water and preservation in 95 percent 

 ethyl alcohol. 



Figure 2. — Sectioned and prepared caudal vertebrae taken from albacore 113.9, 100.8, and 75.1 cm. long. 



