Question

Commercial fishers often use nets to capture fish. The mesh size of the net determines which fish are captured. Those that are thinner than the mesh size can pass through the net and escape.

Imagine a very large lake in which fish have been captured for the past 150 years using the same net size. Fishermen & women have seen the number of fish captured steadily decreasing and the few fish they do catch seem to be longer and thinner than fish were “in the old days.”

Even though humans are the agent of selection in this case, explain to these anglers why the number of fish they are catching is decreasing and why the few fish being caught appear to be longer and thinner.

Answer 1

Fishes undego variety of adaptations to protect them from predators. A wolf-eel’s ribbonlike body shape helps it hide in crevices. Many are camouflaged to help them blend in with their surroundings. In my view he above mentioned scenario is due to adaptation of fish to escape fishing net as the same net has been used for long period of about 150 years which is considerable tme for evolution. This is the reason as fishermen are always trying to adapt nets to the circumstances they fish in. Nets are made to take advantage of the escape behaviour of fish and should focus on mesh size according to the requirement.The sleek bodies enables fishes for fast-swimming than less streamlined fishes which in term help in escape also.