The fish are not always caught near the shore, for the school frequently keep out at sea, where the fishermen go in search of them.  For this purpose two descriptions of boats are employed; the largest measures about thirty tons, the other is much smaller.  The fishermen use a number of nets--about twenty in all--called a set, which are then joined together; each is about forty feet deep, and one hundred and seventy feet long.  When united they form a wall three quarters of a mile in length, though sometimes they are much longer.  The fish are not caught by being encircled, but by running their heads through the meshes, where they are held by the gills, which open in the water like the barbs of an arrow, and consequently cannot be withdrawn; their bodies being larger than the meshes, they thus remain hanging, unable to extricate themselves.