Final answer:
A river dam can affect migrating Pacific salmon by costing them too much energy to bypass—an aspect that can hinder their spawning journey and overall population.
Step-by-step explanation:
The physiological effect a river dam could impose on migrating Pacific salmon is b. The salmon may get past the dam, but their efforts cost them too much energy. Dams obstruct the upstream migration of salmon, crucial for spawning. Utilizing "fish ladders" may partly alleviate this issue, yet for salmon, the additional energy expended to bypass the dam is significant. Downstream migration can also be hazardous due to potential injuries from turbines. Furthermore, reservoirs and dam operations can lead to changes in water temperatures, chemistry, and flow characteristics, affecting the river's physical and ecological aspects, which in turn may impact the salmon's ability to navigate and survive.
An example of a possible physiological effect a river dam could impose on migrating Pacific salmon is c. The salmon may get past the dam, but subsequent navigation may be impaired. When a dam is constructed on a river, it can disrupt the natural flow and characteristics of the river, impacting the migration of salmon. While salmon may be able to pass through the dam, their ability to navigate and find their way upstream may be hindered. This can result in a reduction in the number of salmon reaching their spawning grounds.