Temporal and spatial variation in recreational catches of anadromous brown trout, Salmo trutta, in Norwegian rivers

Abstract

Overall, it has been shown that production of diadromous fishes is declining within the North Atlantic basin reaching the lowest levels in recent years compared to their historic baselines. However, these decreases in abundance, ascribed to numerous factors, are species specific and might differ across each species’ distributional range. Here we used recreational angling catch data for anadromous brown trout Salmo trutta in multiple Norwegian rivers having relatively high annual reported catches to elucidate its spatio-temporal patterns since the late 1960s. Rivers lacking or having very low annual catch reports for various reasons were not included. The catches have increased at a rate of ~15% per decade though trends varied geographically with larger increases at northern latitudes and decreases at more southern latitudes. Larger catches were obtained at elevated levels of runoff during summer and early autumn, and at positive NAO phase during the year preceding the catch. Additionally, higher average catch and more pronounced increasing temporal trends in catches were obtained in larger rivers with shallower slopes, respectively. Furthermore, stronger relationships with runoff occurred in steeper rivers. Other factors such as Gyrodactylosis or fish farming seemed not to have detectable signals in the overall pattern of brown trout catches.