Portable fish traps are extensively used in the Caribbean and other tropical seas. Daily observations made by divers have shown that the daily numerical ingress of reef fishes into unbaked traps set in the Port Royal reefs, on the south coast of Jamaica, tends towards a constant value, but that with increased duration of immersion (soak) an increasing proportion of the cumulative ingress escapes from the traps and the cumulative catch tends towards an asymptote. It is shown that a nearly constant fraction of the number of fishes contained in a trap escape each day, and that the catch stabilises when mean daily escapement equals mean daily ingress. The rate of escapement from Antillean fish traps of standard size (183 × 122 × 61 cm) varies within narrow limits and averages 11·6% per day. The relationships between ingress, escapement, soak and catch can be described by various equations and an index of “availability” can be calculated and used for comparing the catches of traps hauled after varying soaks, or as an index of stock density. Baiting a trap temporarily increases the rate of ingress, but when the bait is exhausted the rate of ingress decreases and the catch declines and stabilises at a point where daily escapement equals the daily ingress. When wooden-framed Antillean traps are baited, the shape of the trap is of relatively little importance and the catch is proportional to the size of the trap. It is believed that this is because the rate of escapement is inversely proportional to the area or volume within which the fishes are contained, the size of the entrance funnels being constant. Steel-framed stackable traps captured 22% less (by weight) than wooden-framed traps of almost identical dimensions. It is believed that the more complex visual outline of the wooden-framed traps may attract fishes in some manner and thus enhance rates of ingress into such traps.
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J.L. Munro (1974) studied this question.