Commercial fisheries already have a heavy burden of catch reporting through log-books, and there are large programmes of data collection by national fishery laboratories to establish the size and age compositions of catches, and quantities discarded. These are key inputs to scientific assessments of most fish stocks. For important recreational stocks, estimates of recreational catches would improve the accuracy of assessments of the state of the stocks. This would help to achieve conservation goals and eventually improve the availability of fish to sea anglers.