Answer:
Observational study
Explanation:
In a sample survey, participants answer a survey or questionnaire.
In an observational study, a sample is only observed without any manipulation.
In an experiment, random samples are selected. One sample is then given an experimental treatment, and the effects (if any) are measured.
In this case, the scientist is not randomly selecting his samples, controlling the variables, or directly manipulating the dolphins' environment. He is only observing the behavior of two different groups. So this is an observational study.