You have probably heard that salmon return to the stream in which they hatched. According to the story, after years of maturing in the ocean, the salmon arrive at the mouth of a river and swim upstream, choosing at each fork the stream that leads to the pool in which they hatched. Arthur D. Hasler's classic research investigated this homing instinct [reported in Hasler (1966) and Hasler and Scholz (1983)]. Here are two sets of data that he gathered.
a. These data help answer the question of whether salmon really do make consistent choices at the forks of a stream in their return upstream. Forty-six salmon were captured from the Issaquah Creek (just east of Seattle, Washington) and another 27 from its East Fork. All salmon were marked and released below the confluence of these two streams. All of the 46 captured in the Issaquah were recaptured there. Of the 27 originally captured in the East Fork, 19 were recaptured from the East Fork and 8 from the Issaquah. Use x2 to determine if salmon make consistent choices at the confluence of two streams. Calculate f and write an explanation of the results.
b. Hasler believed that the salmon were making the choice at each fork on the basis of olfactory (smell) cues. He thought that young salmon become imprinted on the particular mix of dissolved mineral and vegetable molecules in their home streams. As adults, they simply make choices at forks on the basis of where the smell of home is coming from. To test this, he captured 70 salmon from the two streams, plugged their nasal openings, and released the salmon below the confluence of the two streams. The fish were recaptured above the fork in one stream or the other. Analyze using chi square techniques and write a sentence about Hasler's hypothesis.
