Mr. hughes was walking 30 yards from the ocean shoreline when he heard a swimmer cry for . he continued walking, however, because he figured that one of the many swimmers in the vicinity would provide if it was needed. his reaction best illustrates:

the bystander effect.

Explanation:

According to the bystander effect one is less likely to help a person when there number of people in the vicinity is high.

The reasons why this happens is due to three factors, diffusion of responsibility, ambiguity and behaving according to social norms.

When there are a lot of people around one might think that someone else will take the responsibility of taking action. This may happen as one might think that someone else might be better suited to handle the situation

If the situation is not clearly understood by the bystander then they will be less likely to help.

One might think if they would help it would be going against the social norms and hence hesitate to do so.

Here, Mr. Hughes has decided not to help because of the diffusion of responsibility.

Hence, his reaction illustrates the bystander effect.