"Mesh size control has been advocated from the earliest days of the otter trawl fishery in tbe United States. Researchers determined that larger meshes in the cod end of a trawl reduce discarding by allowing small fish to escape; a process known as size-selection. This selectivity is measured by the selection factor - the relationship between the 50% retention length and the stretched length of the mesh. Selection factors vary by species, net material, duration of tow, speed of tow, size of catch, and with variations in mesh size"--Page 1.

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