On fishing selectivity of hadrah (fixed stake trap) in the coastal waters of Kuwait

The hadrah is an inter-tidal fixed stake trap, and a traditional fishing gear in Kuwait. The fishing selectivity of hadrah was investigated by comparative experiments in three locations in Kuwait's coastal waters. At each location, one control hadrah with the standard mesh size and one comparative hadrah with a larger mesh size were built to collect fish samples. Length frequency data of the major fish species caught by the two hadrahs were used to fit to logistic fishing selectivity curve to obtain the 50% retention length (L50) and to be compared by two values of the Akaike's information criterion (AIC). The results showed that: among the 40 selected cases (pairs of length frequency data for different species and different locations), 31 cases showed no difference between the selectivity curves of the control and comparative hadrahs. Within the nine cases with different selectivity observations, six cases showed a positive difference in L50 (the comparative hadrah having the larger L50); these results were considered to be caused by the mesh-size differences between hadrahs. On the other hand, three cases showed negative difference (the comparative hadrah having smaller L50), and these were not considered to be caused by the mesh size differences. The comparative hadrahs had limited selectivity variation in their catch compositions. The AIC method described in this paper detected all the large positive L50 differences and should be a useful tool for comparing selectivity curves.