Foreign brown trout in protected landscapes as a consequence of connectivity J. L. HORREO & E. GARCIA-VAZQUEZ Department of Functional Biology, University of Oviedo, Oviedo, Spain Abstract To preserve the local genetic patrimony of wild aquatic species, population enhancement should be limited to supportive breeding of native lineages and controlled releases in target areas with depleted population size. This is the case of brown trout, Salmo trutta L., in northern Iberia, a species of high economic and cultural value in the region. Employing a combination of conserved and hypervariable genetic markers, illegal stocking of domestic brown trout in protected areas (National Park, Natural Reserve) within the Cantabric chain was detected. The most likely origin of the domestic individuals was determined by assignment tests to hatchery stocks as a result of past releases conducted downstream and out of the protected areas. Where connectivity exists along a water course, the entire drainage should be considered as a single management unit to preserve the native genetic diversity of upstream protected areas. KEYWORDS: assignment test, conservation, illegal stocking, management unit, migration, Salmo trutta. Introduction Conservation of autochthonous lineages as reservoirs of genetic diversity is a priority in wildlife management, especially in protected areas such as National Parks. In northern Spain, for example, current legislation spe- cifically forbids releases of foreign stocks into fresh- water ecosystems (Article 52.2, Law 42/2007 of Natural Patrimony and Biodiversity). The National Park of Picos de Europa and the Integral Natural Reserve of Muniellos (Fig. 1) are the two main protected areas in northern Spain that act as reserves for some endan- gered fauna, such as the Eurasian brown bear, Ursus arctos arctos L., and the capercaillie, Tetrao urogallus L. Wild populations of brown trout, Salmo trutta L., in rivers in this area are disconnected by impassable obstacles (weirs, hydroelectric dams) that impede upstream movement of other native migratory fishes, such as European eel, Anguilla anguilla L. and Atlantic salmon, Salmo salar L. In the last half of the twentieth century, intense stocking of salmonids was carried out in northern Spain. Both Atlantic salmon and brown trout popu- lations were enhanced with domestic stocks imported from other European countries, and as a consequence, foreign genomes have introgressed native genetic pools at different levels depending on species and rivers (e.g. Moran et al. 2005; Ayllon et al. 2006; Izquierdo et al. 2006; Saura et al. 2008). Between 1995 and 2007, 7.7, 0.6 and 0.5 million brown trout juveniles of either foreign or native origin were stocked in the rivers Narcea, Sella and Cares, respectively. In Natural Reserves and National Parks, however, fish stocking is strictly restricted to releases of native fish for supplementing populations endangered by environ- mental catastrophes (droughts, accidents), always supervised by the Regional Government. Genetics is being increasingly applied to commercial and recreational fisheries enforcement (Kyle & Wilson 2007); for example, frauds in fishing trophies have been discovered (Primmer et al. 2000). Illegal releases and escapes of non-natives are harmful to native popula- tions because they may augment feral populations or establish new colonies (Manchester & Bullock 2000), causing detrimental ecological impacts. Genetics can help to identify foreign individuals and trace their origin, such as escapees of Atlantic salmon escapes from fish farms in Norway (Glover 2008). In this study, brown trout sampled within and around the natural Northern Spanish protected areas mentioned earlier were analysed genetically. The locus LDH-C1* was employed as a marker of genetic lineage because previous studies indicated fixed allelic differences for the LDH-5* locus between pure Correspondence: Jose Luis Horreo, Department of Functional Biology, University of Oviedo, C/Julian Claveria s/n. 33006-Oviedo, Spain (e-mail: horreojose@uniovi.es) Fisheries Management and Ecology, 2011, 18, 431–436 Ó 2011 Blackwell Publishing Ltd. doi: 10.1111/j.1365-2400.2011.00803.x 431 Fisheries Management and Ecology