THE HOMING INSTINCT AND AGE AT MATURITY OF THE 
PINK SALMON ( ONCORHYNCHUS GORBUSCHA ) 1 
By Frederick A. Davidson, Pli.D., Associate Aquatic Biologist, United States Bureau of Fisheries 
CONTENTS 
Introduction 
Marking pink salmon fry 
Interpretation of results from marking experiments 
Homing instinct 
Age of pink salmon at maturity 
Pink salmon marking experiment in British Columbia 
Summary 
Literature cited 
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INTRODUCTION 
The pink salmon, Oncorhynchus gorbuscha (Walbaum), like the other species of 
Pacific salmon spend part of their life cycle in the sea and part in the rivers and 
creeks where they spawn and die. In southeastern Alaska, the pink salmon begin 
their spawning migration from the sea in the latter part of June and continue until 
late in September. Although the salmon migrate into the streams during the early 
summer months spawning does not begin until the second or third week in August. 
In March and April of the following year, the fry which have developed in size to 
a little over an inch in length (see fig. 1) and weigh less than 0.008 of a pound, emerge 
from their nests in the gravel and migrate directly to the sea. During their sojourn 
in the sea the fry develop into adult salmon weighing from 3 to 8 pounds and upon 
reaching maturity return to the streams to spawn. 
The population of mature pink salmon that returns to spawn in any stream 
varies in size from year to year. This is due not only to the influence of changes in 
the natural elements of the habitats (stream and ocean) in which the population 
develops but likewise, and to a far greater extent, to the changes in the intensity of 
the commercial fishery that is imposed upon it during its migration from the sea. 
In view of this fact the Bureau of Fisheries is endeavoring to regulate the intensity 
of the commercial salmon fishery in Alaska so as to provide for an adequate run of 
pink salmon in every stream each season. 2 In order to secure an accurate count of 
the number of mature pink salmon migrating each season into each of several impor- 
tant salmon streams in southeastern Alaska, the Bureau has constructed weirs (see 
fig. 7) through which the salmon are counted on their way to the spawning grounds. 
1 Bulletin No. 15. Approved for publication, Feb. 21. 1934. 
2 On June 6, 1924, Congress approved an act which provided that not less than 50 percent of all the adult salmon returning to 
any stream should be permitted to ascend the stream to spawn. 
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