A review of techniques for the observation of fish behaviour in the sea

During the past 25 years there have been significant developments in the resolution and sensitivity of the instruments available for investigating fish behaviour in the sea. This paper reviews the principal techniques and instruments which have been devised. There are three main approaches: direct observation by humans, indirect observation using cameras, and the use of acoustics. Manned and unmanned vehicles are used to transport both divers and cameras close to the fish. Acoustics permits observation at greater range and is most useful for observing shoals of fish and tracking tagged individuals. The limits to performance of various methods are considered and development trends are discussed.