THE GEOGRAPHIC DISTRIBUTION AND ENVIRONMENTAL 
LIMITATIONS OF THE PACIFIC SALMON 
(GENUS ONCORHYNCHUS ) 1 
By Frederick A. Davidson, Ph. D., Aquatic Biologist, and Samuel J. Hutchinson, B. S., Junior 
Aquatic Biologist, United States Bureau of Fisheries 
J* 
CONTENTS 
Page 
Introduction 667 
Geographic distribution 668 
Native 668 
Foreign 669 
Environmental limitations to occurrence 673 
North Pacific region 673 
South Pacific region 680 
North Atlantic region ' 685 
South Atlantic region 687 
Summary 687 
Literature cited 688 
INTRODUCTION 
There are five principal species of Pacific salmon, all of which are classified in 
the genus Oncorhynchus. They are cliinook, or quinnat ( 0 . tschawytscha ) ; sockeye, 
or red ( 0 . nerka)-, coho, or silver ( 0 . kisutch ); pink, or humpback ( 0 . gorbuscha) ; and 
chum, or dog (0. keta). These fish are anadromous; they spend part of their lives in 
the sea and part in the streams. The eggs are deposited in gravel beds in the streams 
and lakes during the summer and fall and hatch out during the following spring 
months. The fry remain in fresh water for varying lengths of time, depending upon 
the species, but all eventually migrate to the sea where they make over 95 percent of 
their growth. Upon attaining maturity in the sea the adults return to the streams 
where they spawn and die. The studies of Gilbert (1913), Snyder (1921-24), Rich 
and Holmes (1928), Pritchard (1933), Davidson (1934), and Foerster (1936), on the 
life histories of the Pacific salmon show that they have a pronounced homing instinct 
and in general return to their parent streams to spawn. 
The locations and depths at which the salmon feed while in the sea have not 
been definitely determined. Catches of cliinook and coho salmon are made by the 
troll fishery as far as 100 miles offshore and at depths as great as 90 fathoms. Com- 
mercial and Government vessels operating in Alaskan waters have reported the 
presence of the salmon even farther out to sea. The continental shelf along the 
Pacific coast of North America averages less than 40 miles in width, thus it is evident 
1 Bulletin No. 26. Approved for publication January 14, 1938. 
667 
