INTRODUCTIONThe problems of observing the behaviour of mid-water animals are considerable. The depths involved are generally too great to allow free diving, and because the population density is low, useful observations from submersibles and remote cameras are rare. Animals brought to the surface are often in too poor a condition to behave at all normally. The hyperiid amphipods are one of the best groups to work with in trying to overcome these difficulties. They are relatively common and frequently observed from submersibles, where they congregate round the lights. They are tough, survive capture and behave well in aquaria at the surface (Land, 1992a). Compared with other groups, a reasonable amount is known about their habits, especially their associations with gelatinous animals on which they prey or have commensal relationships (Harbison et al., 1977; Madin & Harbison, 1977; Diebel, 1988). It is also known that they sometimes form swarms (Lobel & Randall, 1986).