366 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



similar migrations. Some of the smelt, however, do not enter fresh- 

 water streams, but deposit their eggs in the fine gravel of the ocean 

 beach among the breaking waves. But the habits of fish spawning 

 in the ocean surf cannot be told here — that is another story. 



The salmon, in their great urge to reach the proper habitat for 

 deposition of their eggs, often wear themselves out in their attempt to 

 navigate waterfalls or fish ladders placed in dams (pi. 3). It is said 

 that Pacific salmon will jump vertically as much as, or more than, 

 five to sLx times their length in an attempt to go over waterfalls. 

 Sometimes tliis is fatal to the fish as it falls backward and strikes 

 sharp rocks. If he is not seriously injured, upon recoverj'^ he will 

 continue to leap until either successful in going over the obstruction 

 or until he is completely exhausted and falls prey to birds, bears, or 

 other predators, as he drifts downstream. The urge to go upstream 

 is so great in both salmon and trout that they expend a great amount 

 of their stored energy by the time they have spawned, leaving them 

 weakened and emaciated. 



Tills worn-out condition Ls not the chief cause of the death, after 

 spawning, of the five species of Pacific salmon. Instead, they have 

 reached the end of their life cycle, and even those fish in good condi- 

 tion die shortly after their reproductive period Ls completed (pi. 4). 

 Trout, steelhead, (pi. 1, fig. 2) and the Atlantic salmon may spawn 

 for several successive years before completing their life cycles. 



Finally, after traversmg great distances or but a few miles, all 

 species of salmon and trout attempt to locate a particular type of 

 stream bottom in which to lay their eggs. Their nests are built only 

 in the gravelly or stony sections of a stream which has nearly clear, 

 rapidly flowing water of a rather low temperature. If the fish are 

 unsuccessful in locating these conditions, they seldom lay their eggs 

 and may die instead. There is evidence, too, that the great majority 

 of Pacific salmon, as well as some species of trout, seek and usuallj^ 

 find the stream in which they grew up as babies, even though a few 

 intervening years were spent in the far-away sea and entirely outside 

 the influence of the "parent stream" (Davidson, Science, vol. 86, 

 pp. 55-5G, 1937). This is known as the "homing" instinct of 

 salmon and trout and is often referred to under the name "parent 

 stream theory." 



The time of the year when salmonids migrate and lay their eggs is 

 highly variable. Pacific salmon spawn any time from March to De- 

 cember, depending on the locahty and the species. Steelhead, or 

 rainbow trout, spawn in late autumn and winter, or in certain regions 

 m the early spring. Cuttliroat trout typically are spring spawners. 

 The Atlantic salmon, eastern brook trout, western dolly varden, lake 

 trout, and brown trout, all breed in the autunm. 





