The predatory behaviour of Caranx melampygus (Pisces) in the channel environment of Aldabra Atoll (Indian Ocean)

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Abstract

Aspects of the predatory behaviour of free ranging Curanx melampygus have been examined in the shallow channel environment of Aldabra Atoll, Indian Ocean. Differences in the frequency of occurrence and number of fish hunting at two adjacent observation areas are described. The numbers of Caranx moving through the area appears to be influenced by tidal factors and possibly the abundance of prey and other environmental factors. The percentage offish hunting increases progressively throughout the day and is most commonly performed by solitary fish or small groups. While approximately equal numbers of Caranx move up or down stream significantly more fish engage in hunting activity when moving down stream which suggests the mechanical advantage of moving with the flow of water has advantages to the hunting fish. Several types of interspecific feeding association are described in which the Caranx is able to scavenge from others or to exploit the hunting methods of other species. More small Caranx form associations than do large Caranx. There is a relationship between the length of a hunting Caranx and the size and/or type of prey that makes an avoidance reaction to it. This relationship between different group sizes and the prey avoidance response is less clearly defined and it is suggested that whether hunting in groups or singly the final interaction is between a single predator and single prey. Ways by which group advantages may occur on grouped prey are described and are considered the result of independent individual action rather than group co-operation. Coastal observations indicate that Caranx use topographic features to shield their approach to areas of high prey density.

Ancillary