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Light traps and larvae: Preliminary results from KwaZulu-Natal coastal waters

Beckley, L.E. and Naidoo, A.D. (1998) Light traps and larvae: Preliminary results from KwaZulu-Natal coastal waters. In: International Conference for the Paradi Association and The Fisheries Society of Africa, 13 - 18 September, Grahamstown, South Africa.


Most reef fish have a bipartite life cycle with a pelagic larval phase and a substratum-associated adult phase. Transition between the two phases is known as settlement with the larvae acquiring colour, opacity and scales and settling into the reef environment. Larval fishes have traditionally been sampled using plankton nets but avoidance of nets by settlement stage larvae is problematic, particularly if assessments of recruitment and year-class strength are needed for fisheries management. In recent years, light traps have been used in some coral reef areas to assess settlement stage fishes and during 1996 and 1997 a prototype light trap was designed and tested in KwaZulu-Natal coastal waters. Overnight sampling sessions near the entrance to Durban harbour during different lunar phases yielded high numbers of larvae representing 23 fish families. Dominant families were Clupeidae, Gobiidae, Tripterygiidae, Ambassidae and Sparidae. In general, the larval assemblage was similar to that found in the harbour by an earlier net-based study but the mean size of the specimens caught in the light traps was larger. Replicate monthly samples taken further offshore in proximity to limestone Reef yielded 21 fish families. Although Clupeidae (particularly Sardinops sagax) dominated catches, larvae of several reef-associated families were also recorded. The pilot-study phase of this project has indicated the potential of light traps for assessment of settlement stage fishes in southern African coastal waters.

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