362 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



(2) The sample represents fish taken by long- 

 line, trolling, and gill nets during the. period Jan- 

 uary 1955 to July 1956. 



(3) None of the various structures examined re- 

 vealed any markings which could be interpreted 

 as age marks. 



(4) Scales from 100 fish were examined ; of these, 

 the scales of 43 fish were considered unreadable. 

 Samples from the remaining 57 fish varied greatly 

 in degree of readability. A plot of the ring counts 

 against fish size showed considerable overlapping 

 between successive groups. 



(5) Scales taken from the same fish were often 

 of variable size. It was noted that small scales 

 contained fewer rings than large scales, indicating 

 that the origin of the scales was not uniform. 



(6) Because of the undetermined nature of scale 

 formation, and the fact that only about one-half 

 of the scales were considered readable, further 

 work with scales was discontinued. 



(7) A change was observed in the shape of the 

 caudal vertebrae with growth of the fish. Among 

 the smaller vertebrae, from fish of about 50 to 60 

 cm. in length, the ratio of the length of the anterior 

 cone to that of the posterior cone was nearly 1:1. 

 The posterior cone was larger than the anterior 

 in the larger vertebrae. Although the two cones 

 of a caudal vertebra grow disproportionately, each 

 cone in itself exhibits a linear growth with growth 

 of the fish. 



(8) In comparing independent sets of readings 

 made by readers A and B, the highest agreement 

 between the two readers was 44.8 percent. The 

 best agreement between any two readings of the 

 same reader was 38.9 percent for reader A and 

 43.9 percent for reader B. The most difficult rings 

 to distinguish were those near the vertex and the 

 margin of the cone. 



(9) Although the vertebrae of small albacore 

 were somewhat more readable than those of large 

 albacore, it was still not possible to achieve suffi- 

 cient consistency in ring counts and measurements 

 to validate this method of age determination. 



(10) The results indicated that the rings on the 

 vertebral centra are laid down randomly with 

 respect to time, rather than periodically. It is 

 realized, however, that the validity of this method 



of analysis is questionable, since it is based on the 

 recognition of the last ring and since the ring 

 counts could not be duplicated with any consist- 

 ency. If our results are valid, it would appear 

 that the rings are simply growth marks rather 

 than age marks. 



(11) Considerable personal bias was inadvert- 

 ently introduced into the readings and measure- 

 ments. It was almost impossible to make a read- 

 ing without first forming an opinion as to the 

 number of rings that should be expected on a 

 vertebra of a certain size. 



(12) The growth increments reported by pre- 

 vious investigators did not appear to give either 

 a reasonable or a consistent pattern of growth. 



(13) The growth estimates of past investigators 

 do not appear to be consistent with growth as 

 evidenced by tag returns. Although the data 

 derived from tagged fish are meager, they indicate 

 that albacore have a moderately rapid growth, 

 somewhat greater than the various estimates 

 provided by the vertebral method of age deter- 

 mination. 



(14) Unlike many north temperate species 

 which occupy limited environments, the albacore 

 appears to spend its life under fairly uniform 

 conditions by migrating to areas of abundant 

 food and favorable water temperature. Thus, 

 these fish are probably not subject to the extreme 

 summer and winter conditions which would cause 

 "winter" marks to appear on scales and vertebrae. 



(15) Although rings on the vertebrae are 

 probably not age rings which are laid down 

 annually or at such intervals that they could be 

 used to tell the actual age of the fish, it was pointed 

 out that the rings could possibly be used to assess 

 the relative age, that is, older fish would have 

 more rings than younger fish. 



(16) Results of a series of ring counts were 

 examined for differences between sexes. There 

 was evidence that the unbalanced sex distribution 

 among larger albacore, with a great predominance 

 of males, was largely due to differential growth 

 which sets in with the onset of sexual maturity, 

 after which the males grow at a faster rate than 

 the females. 



