Actually Colin,we must remember that the amount of water in the river,the colour of the water,the temperature of the water,the speed on the current,whether or not the dams up river have been opened,or closed,sunlight,cloud cover,high tide,low tide,kingfishers depleting the shoals of catfish,leaves on the track etc,etc all have a bearing on the amount of fish not caught.God it's tough being a  'specimen hunter'.