416 U. S. BUREAU OF FISHERIES 



large number of herring passing tlirougli the shore stations. The 

 device is dependent on the bridge-circuit principle, in which the 

 presence of the metal passing through the coils creates an unbalance 

 which may be converted into a power impulse to eject the individual 

 bearing the tag. The instrument proved feasible, and 66 tags were 

 recovered during the season. The advantages of the device lie in 

 the facts that it is possible to determine with greater accuracy the 

 origin of the tags; to better evaluate the mortality imposed by the 

 fishery; and by examination of the individuals bearing the tags, to 

 determine the effect of the tags on the host. 



There has always been a question as to how large a percentage of 

 the population is taken by the fishery. The popular belief has been 

 that only an immeasurable part is caught, and that the decline in 

 abundance observed in certain intensively fished areas has been due 

 entirely to the emigration of herring from that region. 



Assuming that the tagged fish are distributed with the remainder 

 of the population in a random manner, which appears to be the 

 case from the fact that tags are returned from the various separate 

 markings (throughout a greater part of the season), then the per- 

 centage recovery of tags gives a measure of the percentage of the 

 total population taken. The figures herein given are admittedly in 

 error, and represent the absolute minima of imposed mortality. 

 There are tliree knovrn sources of error which, at present, cannot be 

 evaluated. First, there is probably a mortality caused by the tag- 

 ging; second, there may be a loss of tags by their working out of the 

 fish in life; third, there is a failure to obtain all the tags recovered 

 by the fishermen due to inefficiency of the magnets, the loss of tags 

 to souvenir hunters, etc. 



Without considering these sources of error, however, it it evident 

 that the fishery takes a considerable toll from the populations in the 

 more intensively fished areas. That this is the case in the Cape 

 Ommaney fishery is evidenced by the recovery of 101 or 4 percent 

 of the Sitka tags in 1933; 482, or 4.4 percent in 1934; and 1,628 

 or 7.2 percent in 1935. Tlie second main stock from which the 

 fishery is drawing is that which spawns at Craig. For this fishery 

 a 2.0 percent return (149 tags) in 1934, and a 2.3 percent return 

 (233 tags) in 1935, indicates that this stock is not as intensively 

 fished as is the Sitka population. These figures represent the recov- 

 eries of only one type of tag — others have been experimented with 

 in an attempt to find the most suitable type possible. 



For the past few years, 70 to 85 percent of the entire catch for 

 southeastern Alaska has come from the Cape Ommaney region. 

 There was a marked decline during 1935 in the catch per unit of 

 effort in this area. This decline is accounted for by the failure of 

 the normal increment of 4-year-olds to enter the catch. The catch 

 for 1934 was dominated by the 4-year-olds from the brood year 

 1931; during that year they represented approximately 66 percent 

 of the catch. The next year, however, owing to the failure of the 

 new class of 4-year-olds to appear, this same 1931 brood furnished 

 89 percent of the catch; while the 1932 brood year, entering 

 the catch for the first time, constituted only 3 ])ercent of the catch. 

 Thus the 5-year-olds, a class which had already been subjected to 

 intensive fishing during one season, and suffered the inroads of 



