CHINOOK SALMON MARKING, COLUMBIA RIVER 217 



It had previously been determined that the rayed fins regenerated if not removed 

 very close to the body of the fish, regeneration being most complete when only a 

 part of the distal portion of a fin was removed. When the fins were carefully re- 

 moved without leaving any stubs of the rays, there was shght regeneration of a 

 soft, fleshy tissue but no indication of regeneration of fin rays. The appearance of 

 the scars on the adult fish recovered gives further evidence of the slight amount 

 of regeneration. In these the point where the removed fins were inserted is typically 

 represented by a shght growth of flat or slightty projecting, soft scar tissue, the 

 surface of which is invariably smooth and bears no scales. In some cases, fin rays 

 have partly regenerated, but even in extreme cases the regenerated stub consists 

 of only three or four rays less than one third the length of those of a normal fin. 

 A typical scar resulting from the removal of one ventral fin is shown in Figure 2. 

 The appearance of the dorsal fin when the posterior half has been removed, as in 

 experiment No. 4, is shown in Figure 3. 



In order to test the immediate effects of the marking some of the marked fis*h 

 in each case and as a matter of routine were retained in the hatchery until they had 

 recovered fully. It was necessary to take this precaution in order that the per- 

 centage of return might not be affected by an unusually high mortality resulting 

 from the operation and the handling incidental to marking. In two instances 

 experiments were begun that had to be abandoned on account of the high mortality. 

 These two, however, presented unusual conditions, for in all other instances there 

 was no serious mortality; in fact, in most cases the fish showed no signs of injury 

 from the operation. 



The removal of fins from young salmon as a means of marking them for identi- 

 fication when they return to fresh water to spawn has been practiced for many years. 

 The earlier investigators who employed this method used marks that were duplicated 

 easily in nature or that did not persist throughout the life of the fish. As a result, 

 the reported returns from their experunents seem to have consisted, for the greater 

 part, of fish whose fins had been mutilated accidentally. The conclusions based 

 upon this erroneous evidence have since been shown to be incorrect, and the reliability 

 of this method of marking has been questioned. It therefore seems advisable to 

 point out the causes of error in the earlier experiments and to emphasize the precau- 

 tions taken in this series of experiments to assure positive identification of the marked 

 fish and thus to prevent similar confusion. 



The greatest cause of error in the earlier experiments was the failure of the 

 investigators to realize that salmon occasionally lose one or more of their fins in 

 other ways, and that as a result, if only one fin is removed experimentally, the mark 

 may be duplicated accidentally. For example, Hubbard removed the adipose fin 

 from chinook fingerhngs at the Clackamas hatchery in Oregon in 1895.' The re- 

 ported returns from this marking are so greatly opposed to the known facts of the hie 

 history and growth of chinook salmon that they are obviously in error, and there 

 can be no question that they included fish not marked by Hubbard. In 1903 

 Chamberlain marked sockej^e salmon at Naha Kiv^er, Alaska, by removing the two 

 ventral fins.^ Returns from this marking were reported as late as 1911, when the 



' For a description o! the experiment and returns, see Oregon Fisheries Department C1898 and 1900) and Gilbert (1913). 

 ' For a description of the experiment and returns, see Marsh and Cobb (1908, 1909, 1910, and 1911); and Chamberlain and 

 Bower (1913). 



