Assessment of a brown trout Salmo trutta population in the River Gallo (central Spain):: angling effects and management implications (Salmonidae)

The brown trout population of the River Gallo (central Spain) was monitored every two months during 1996 to determine the current impact of angling. To evaluate the influence of additional parameters, physical habitat and food availability were also studied. To assess fishing pressure, trout harvest and angling explanation, a partial creel census was conducted during the 1996 fishing season. Differences were found in densities and biomass between exploited (1182.4 Ch ha(-1), 68.3 kg ha(-1)) and unexploited areas, the latter being markedly higher (3135.1 fish ha(-1), 208.2 kg ha(-1)). Production was quite superior in the unexploited area and decreased (from 144.5 kg ha(-1) yr(-1) to 37.2 kg ha(-1) yr(-1)) as fishing pressure increased. However, no consistent differences were observed in growth, condition factor, age diversity, mortality, recruitment age and turnover ratio. Sport fishing seems to be the main negative factor influencing the balance within population of brown trout in thr River Gallo and therefore management should be focused on more restrictive angling measures.