Efficiency and Selectivity of Flag Gill Nets Fished In Lake Bistineau, Louisiana

n order to determine the efficiency and selectivity of flag gill nets in catching game fish, experimental flag gill nets were fished in Lake Bistineau during the period March through August, 1956. Flag gill nets contain no lead line and are hung on a top line which contains no floats. The experimental nets used consisted of the following mesh sizes: 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.5 inch square mesh. For summary purposes the various species of fish were grouped into 3 types: (1) commercial fish (2) game fish and (3) other fish. The more valuable commercial fishes were caught at higher rates in the larger mesh sizes. Game fish were caught at higher rates in the smaller mesh sizes. Data are presented on the frequency distributions of the catches per net day which should give a somewhat better idea of the potential of the various mesh sizes of flag gill nets when fished under commercial conditions than the mean catches. The size of fish available to be caught had in many instances a definite effect on the mean length of the fish caught by the various mesh sizes of flag gill nets. The catch of fish by the flag gill nets for the period March through May was compared with the catch for the period June through August and the catch for shallow sets was compared with the catch for deep sets. In order to determine the selectivity of flag gill nets, the relative composition of the flag gill net catches was compared to estimates of the relative composition of the fish population made by rotenone poisoning. Commercial fish and other fish were much more relatively abundant in the flag gill net samples while game fish were considerably more relatively abundant in the samples taken by rotenone poisoning. Attempts have been made to close Lake Bistineau to all commercial fishing. I doubt that either restricting or allowing commercial fishing on Lake Bistineau will have much effect on the fish population. Nevertheless commercial fishing should be allowed since it utilizes a resource that would otherwise be wasted. I would recommend a minimum legal size of 3.0 inch square mesh for gill nets fished in Lake Bistineau based on 2 considerations: (1) the catch of game fish in the various mesh sizes and (2) characteristics of the commercial fishery.

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