78 



THE MIGRATION AND CONSERVATION OF SALMON 



lowing statement by Davidson and Christ- 

 ley (1938) that "These salmon no doubt 

 migrated across Clarence Strait to the west 

 shores of Gravina and Annette Islands and 

 then turned back to the localities on the 

 east shore of Prince of Wales Island in 

 area 2. Whether or not the salmon make 

 this journey may depend to some extent 

 upon the prevailing winds. If a southeast 

 wind is blowing the opposite course is more 

 apt to be taken. No definite conclusions 

 may be drawn because of the lack of suffi- 

 cient information, at the present time, con- 

 cerning the influence of wind direction on 

 migration." There is no doubt that wind 

 can divert the flow of the less mixed fresh- 

 salt waters at the surface. This being the 

 case the direction of the gradient to which 

 salmon responds would be changed ; thus, 

 the change in the path of the movement of 

 the salmon. 



From tagging experiments and otherwise 

 the king salmon is known to make the long- 

 est and most extensive migratory move- 

 ments when at sea. It also moves deepest 

 below the surface. The fresh-salt water 

 mixture at depths at which the king salmon 

 migrates would be more stable and less 

 modified by the tide. 



A more crucial test of the theory that 

 the salmon find their spawning grounds by 

 reacting to environmental factors is to 

 compare the behaviors of the red and king 

 salmon as they ascend the rivers to their 

 spawning grounds. In fresh water the 

 king salmon still moves at greater depth 

 than the red salmon. The red salmon 

 moves at and near the surface of the water. 

 When a choice must be made between two 

 forks of a river the red salmon is said to 

 choose the fork having a lake above. The 

 king salmon is said to be indifferent in the 

 choice. Powers (1928) and Powers and 

 Hickman (1928) found that in the Eraser 

 and Columbia River systems the fork of the 

 river with a lake above always had a carbon 

 dioxide tension nearest the carbon dioxide 

 partial pressure of the atmosphere. This 

 is not only true according to observation 

 but it is most reasonable. Surfaces of lakes 

 are well aerated. Most spring and seep 



water as a general rule contain carbon 

 dioxide at a higher tension than the carbon 

 dioxide partial pressure of the atmosphere. 

 This, with the Karluk Lake observation 

 (Gilbert and Rich, 1927b) where the red 

 salmon spawned in the streams with best 

 aerated water, leaves one to conclude that 

 the red salmon responds positively to a car- 

 bon dioxide tension nearest the carbon 

 dioxide partial pressure of the atmosphere. 

 This is also reasonable since the red salmon 

 moves nearest the surface and at times near 

 shore in rivers where the carbon dioxide 

 tension would be most nearly in equilib- 

 rium with the carbon dioxide partial pres- 

 sure of the atmosphere. Even though 

 chemical receptors located in the regions of 

 the gills were not sensitive to changes in 

 carbon dioxide tension the alkali reserve of 

 the blood would have to be modified in 

 order to be adjusted to the new carbon 

 dioxide tension. The adjustment would be 

 least if the red salmon chose the water hav- 

 ing a carbon dioxide tension most nearly 

 the same carbon dioxide tension of the 

 water in which it had been moving. There 

 are abundant data that show that a fish's 

 blood is continuously adjusting its alkali 

 reserve to the carbon dioxide tension of the 

 water. The king salmon may or may not 

 respond to a carbon dioxide tension gradi- 

 ent. The alkali reserve in its blood can be 

 adjusted up or down. The advantage 

 would be in the water requiring the least 

 adjustment. This would depend upon the 

 relative volumes of the two waters making 

 up the mixture. This would in turn de- 

 pend upon the volume of the two streams 

 and the position of the king salmon in the 

 mixed waters below the forks. Thus, the 

 king salmon could be said to be indifferent 

 to the change in the carbon dioxide tension, 

 though its choice between the two forks 

 would depend upon its position in the 

 stream below the two forks. 



A very important observation made by 

 Ward (1921) was that red salmon in the 

 Copper River system enter streams that do 

 not have any lake above. The salmon 

 always chose a stream having a lower tem- 

 perature. The Copper River is supplied 



