Stocking impact, population structure and conservation of wild brown trout populations in inner Galicia (NW Spain), an unstable hydrologic region

Abstract

1. Brown trout (Salmo trutta) is an important conservation resource in the Iberian Peninsula. The Atlantic is considered the most hydrologically stable region for the species, although inner Galicia (NW Spain) shows Mediterranean (unstable) climatic conditions. The Galician region, threatened by past releases of brown trout individuals from central European origin, harbours two native lineages, one of them endemic to the Iberian Peninsula. These populations are thus highly valuable for conservation, as well as being important for recreational fisheries. 2. In total, 546 individuals from 16 sampling sites (15 natural locations from inner Galicia and one from a central European hatchery stock) were genotyped for 11 nuclear markers (10 microsatellite loci and the LDH‐C* locus) to analyse genetic variability, population structure and introgression impact from stocking in order to assess the conservation status of brown trout in the region. Moreover, correlation among hatchery introgression and environmental variables relevant for species population dynamics was also investigated. 3. Genetic variability was within the range of Iberian brown trout (He = 0.500–0.600). Stocking impact was higher than previously reported values for the Atlantic region and was related to environmental instability. Highly significant native population differentiation was observed in the whole region (FST = 0.283), at least four main genetic groups being detected across the geographic distribution studied. 4. Conservation strategies at local level (including the creation of genetic refuges and temporal monitoring of genetic composition) are suggested to agencies and administrations for the sustainable management of brown trout.

Salmonid stocking in five North Atlantic jurisdictions: Identifying drivers and barriers to policy change

“…Westley & Fleming, ). It is only quite recently that in its native range concern has been expressed about the stocking of non‐native populations of brown trout (Ryman, ; Vera, Martinez, & Bouza, ). All European countries have a long history of brown trout hatcheries based on a few preferred populations (often expressing large body size and fast growth) for transfer to other basins and across biogeographical zones.…”

“…Westley & Fleming, 2011). It is only quite recently that in its native range concern has been expressed about the stocking of non-native populations of brown trout (Ryman, 1981;Vera, Martinez, & Bouza, 2018 Sweden. An awareness and the use of local broodstock for hatchery production and stocking have increased in all European countries, except where local broodstock is unavailable or hatcheries still operate based on foreign stocks.…”

Influence of historical and human factors on genetic structure and diversity patterns in peripheral populations: implications for the conservation of Moroccan trout

“…Trout stocking for fishing is a common practice worldwide (Petereit et al, 2018;Vera et al, 2018). In Mediterranean countries, the impact of releasing trout from hatcheries as a means to reinforce natural populations is one of the main threats for the conservation of these populations, especially in rivers in which demand for sport fishing outweighs productivity (Škraba et al, 2017;Saint-Pé et al, 2018).…”

“…Thus, conservation measures different than those currently in effect in Morocco, and aimed at keeping local adapted populations or at creating genetic refuges, as has been proposed for the Iberian Peninsula (Araguas et al, 2017;Vera et al, 2018), should be planned, especially for those geographically isolated populations from High Atlas Mountains.…”

Genetic diversity and population structure of burbot Lota lota in Germany: Implications for conservation and management

“…In recent decades, burbot have also been increasingly stocked into some German rivers, that is the Main, Ems, Vechte (Bosveld et al, 2015), the River Odra in Poland (Witkowski et al, 2012), the River Morava, Czech Republic (Adámek et al, 2013) and the rivers Grote Nete and Bosbeek in Belgium (Dillen et al, 2008). However, overall genetic structure of German burbot seems to be less affected by stocking than other commercial freshwater fishes such as brown trout Salmo trutta L. (Berrebi, Poteaux, Fissier, & Cattaneo-Berrebi, 2000;Vera, Martinez, & Bouza, 2017). Intensive stocking of brown trout took place frequently without obtaining information of the genetic structure (Meraner, Cornetti, & Gandolfi, 2014) and knowledge of the genetic consequences for wild populations.…”