.i^L-^:^=^ 



./h(}^. 



^!C>^1^^ 



./i. 



Z^^:x:^ 



5I.P 



5I.L 



tt^ 



U.L 



UP 



Figure 3. — Comparison of the size composition 

 of the northward- and southward- 

 moving albacore. The curves 

 represent the length groups. 

 Those marked "L" are the 

 longline-caught (southward- 

 moving) fish; those marked "P" 

 are the northward-moving fish 

 taken on pole and line. 



are indicated. Figure 3 shows the size of the 

 albacore taken at 140 E. to 160 E. , divided 

 according to the periods of northward and 

 southward movement. According to this 

 figure , 



(1) The length range of the southward- 

 moving albacore is 50 cm. - 120 cm., while 

 that of the northward-moving fish is 50 cm. - 

 100 cm., or about 20 cm. narrower (see Suda 

 1954a). Consequently, Group VI does not ap- 

 pear at all in the northward-moving albacore, 

 and even Group V barely appears in some 

 years. The group of large fish of 100 cm. - 

 120 cm. (Group V and Group VI) which is seen 

 in the southward-moving albacore is almost 

 absent from the northward-moving fish.^/ 



(2) Even when Groups V and VI are 

 omitted and only the fish under 100 cm. in 

 length are considered, we see rather funda- 

 mental differences between the two. Whereas 

 in the southward-moving albacore there are 

 four length groups appearing repeatedly year 



after year, with a strong tendency for Group in 

 and Group IV to increase and decrease alternate- 

 ly every other year, in the northward-moving 

 albacore the nunnber of length groups appearing 

 varies randomly (2-4 groups )J./. The difference 

 between the two can be expressed as "stability of 

 the southward-moving albacore as contrasted with 

 instability of the northward-moving albacore, " 



(3) The concentration of sizes is much more 

 marked in the northward-moving fish. For the 

 period of 1951-1954, with the exception of 1953, 

 almost all of the catch was concentrated within 

 a range of about 30 cm. In the southward-moving 

 fish we see no single length group which makes 

 up a majority of the whole, but in the northward- 

 moving fish, in most years, we see groups which 

 overwhelmingly predominate over the others. 



When we consider the relationship between 

 these two groups of albacore, it is thought that 

 some of these points of difference may be of im- 

 portant significance in marking a separation be- 

 tween them. However, even though some points 

 of separation may exist in the size composition 

 of the two groups, the fact that in both the 

 southward- and northward-moving albacore the 



— Uda cmd Tokunaga (1937), dealing with 

 the size of the albacore taken in the winter long- 

 line fishery, have reported that those caught in 

 areas closer to Japan are smaller and those 

 taken farther off shore are larger. It is con- 

 ceivable that the fact that the pole -and-line fish- 

 ing grounds are limited to waters comparatively 

 close to Japan may be the reason for the size 

 difference between the fish taken while moving 

 northward and those taken while they are moving 

 southward. However, figure 3 shows a compar- 

 ison of the sizes of these two groups offish 

 taken between 140 E. and 160 E. longitude, and 

 the difference between them is still clear even 

 when the area is limited in this way. 



— If we do not limit the area considered to 

 140°E. -160°E. , but broaden it to cover 140°E. - 

 180 , the regularity which we see in the compo- 

 sition of the southward-moving albacore is even 

 further heightened. That is. Group III and Group 

 IV each increase on a 2-year cycle. Group HI 

 in even-numbered years and Group IV in odd- 

 numbered years, with the result that the two 

 groups alternate in predominance every other 

 year. The fact that this rule breaks down and 

 becomes less clear as the consideration is 

 limited to areas closer to the Japanese coasts 

 was reported at the Tokyo meeting of the Japa- 

 nese Soceity of Scientific Fisheries in April 1954. 



19 



