Recapture Experiments Show the Low Sampling Efficiency of Light Traps
Abstract:Recapture experiments were used to examine the sampling efficiency of light traps. In the first experiment, pelagic juvenile reef fishes were collected with light traps and stained externally by immersing them in weak tetracycline solution. Tagged fishes were then returned to the sea at varying distances from traps to estimate recapture rates after 30 min. In 37 independent trials, recaptures were consistently low and did not exceed 12% even when fishes had no distance to travel. In a second experiment, pelagic juvenile reef fishes, larval and adult clupeids, and invertebrates were captured with light traps and released into mesocosms. The same light traps were then re-deployed in these mesocosms and fished for an hour. Recaptures within mesocosms were low: averaging 12, 10 and 15% for reef fishes, adult and larval clupeids, respectively. Recapture rates of invertebrates were significantly greater than those of fishes and averaged 38%. In a third experiment, light traps containing fishes that had just been collected were re-deployed complete with their catches into mesocosms in order to estimate escape rates. After 1 h, 5% of reef fishes, 20% of adult clupeids, 27% of larval clupeids and 13% of invertebrates had left the lit traps. We suggest that the inefficiency of ingress into light traps may result from the probability of fish encountering their relatively small entrances, although the same factor may also impede escapement. While these characteristics may be enhanced by design, we suggest that it is fruitless to expect to be able to convert light trap catches into densities, but emphasize that this limitation does not preclude light traps from providing useful measures of relative larval supply.
Document Type: Research Article
Publication date: 2000-11-01
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