This method has proved fairly successful at trout fisheries where, following the stocking of relatively large trout, the cormorants have subsequently switched their diet to the resident coarse fish populations or have moved to other sites. Both Rutland Water and Grafham Water, two of the best-known trout stillwater reservoirs in England, have followed such a successful stock management programme in recent years. Although the minimum size of the fish stocked has been increased from about 1lb to 1.4lb (with a high proportion above 2lb), the increased rearing costs are reported to have been covered by the better catch return rates and greatly reduced levels of ‘scarring’ damage. It is also apparent that the size of the cormorant winter roost and breeding population near Grafham has fallen since these measures were introduced.

However, such an approach has limited use for coarse fisheries, especially in rivers. Natural, sustainable fisheries cannot be established if stock regimes are constantly being manipulated. Fish of a size that are too big for cormorants to eat do not occur naturally in many species and are not available commercially in others. The possible exception is stocking with carp of 2lbs and larger but this is not applicable to river fisheries and is regarded by many people as inappropriate for many of our stillwater fisheries, on environmental grounds.