Behavior Patterns 237 



apart follow distinctly separate lines of evolntion. Salmon belonging to 

 the genus Chworliyiicus die after spawning, while those belonging to the 

 genus Sol mo may return to the home stream on several annual spawning 

 trips. ^^ Many salmon have been marked, either as young on their seaward 

 migrations or as adults at sea. A few have been marked in the home 

 stream, caught and remarked at sea, and then recaptured in the home 

 stream.^ ^' -^"^^ ^^' These tag returns show that some salmon may migrate 

 1200 to 1700 miles to return "home." 



A salmon approaching sexual maturity and stimulated by an urge to 

 spawn is confronted by two problems: (1) finding the mouth of the 

 river to which the salmon's home rivulet is tributary, and ( 2 ) finding the 

 actual location in the rivulet that will satisfy the homing urge. 



The theory of odor recognition may be adequate to explain an upstream 

 migration to specific spawning grounds, but it can hardly be very useful 

 for finding the mouth of a home river from a distance of hundreds of 

 miles. However, the fact, that on sunny days white bass were able to 

 return to their spawning area in Lake Mendota after having been caught 

 in fyke nets, tagged, and released at one of several release stations, in- 

 dicates that some kinds of fishes have a type of sun-orientation ability.^'- 

 On cloudy days the white bass swam randomly. Perhaps salmon are also 

 capable of finding their way by sun orientation (Type II, a method for 

 maintaining fixed direction). Yet some observations have been made that 

 suggest true navigation. Salmon are known to migrate at night in the sea 

 and gill net fishermen make night sets for them. Hasler '''^ reports an 

 observation of Clifford Barnes (University of Washington) who saw 

 salmon migrating at night at right angles to his oceanographic research 

 vessel. Because of a luminescent sea, this school of large salmon was 

 easily observed. The fish swam on a fairly straight course until out of sight. 



The migration of salmon and other migratory species over long dis- 

 tances of open ocean certainly demands an ability to navigate. How else 

 could fishes keep from becoming "lost" and how else could they pinpoint 

 the mouth of a specific river along a thousand miles of shoreline? 



No warm-water fish shows migration habits and abilities for homing 

 comparable to that of some marine fishes. The objective of summarizing 

 homing in the salmon is to illustrate the extent of development of the 

 sensory organs in fishes and to emphasize the complexity of their instintive 

 behavior patterns. 



Responses of Fish to Angling 



Angling is a mortality factor along with natural predation, diseases, 

 senile degeneration and other things that may cause the death of fishes 

 (Chapter 7). Angling might be called unnatural predation: A natural 

 predator (man) causes the death of a fish through the degradation of a 



