The lack of adaptations to the habitat most likely caused the walleye to move to a different river.
Adaptation
It is a biological mechanism that increases the chance of its survival in a new environment or the changes in the existing environment. Adaptation occurs as a result of evolution and allows the organism to survive and reproduce efficiently in its environment.
Physical adaptations include accumulating changes in the physical characteristics of an organism that help them to survive and reproduce better. Example: evolution of long necks in giraffes.
Behavioral adaptations are changes in the behavior or habits of organisms that help them to sustain in a changing or new environment. Example: Hibernation.
Due to some reason, the walleye were not able to adapt to the environment of the east river which is why they must have moved to a new river despite the presence of a lot of prey.
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