Current status of the brown trout (Salmo trutta) populations within eastern Pyrenees genetic refuges

Abstract

Since the end of the 20th century, some headwaters of rivers in the eastern Pyrenees have been designated as genetic refuges to protect remaining native brown trout (Salmo trutta) diversity. The declaration was based on limited or no evidence of genetic impact from released non-native Atlantic hatchery fish. Hatchery releases were completely banned into the genetic refuges, but pre-existing fishing activities were maintained. Specific locations in each refuge have been monitored every 2-3 trout generations to update genetic information to accurately assess the contribution of these reservoirs to the preservation of native brown trout gene pools. This work updates genetic information to year 2014 in three of these locations (in Ter, Freser and Flamisell rivers). Previous studies identified hatchery introgressed populations within refuges and suggested discrepancies between the underlying intention of the genetic refuges and the gene pools detected. Therefore, we also examined genetic divergences among locations inside refuge river segments. Combined information at five microsatellite and the lactate dehydrogenase C (LDH-C*) loci showed reduced but significant temporal native allele frequency fluctuations in some of the above specific locations that did not modify overall levels of local diversity and river divergences. Bayesian clustering analyses confirmed the presence of differentiated native units within each genetic refuge. Some locations of the Freser River within the genetic refuge area showed high hatchery impact of nonnative fish (over 20%). We discuss additional local actions (releases of native fish, selective removals and fishery reinforcement with sterile individuals) to improve the conservation objective of genetic refuges.

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

“…Maintenance of genetic diversity is crucial to allow adaptation of natural populations to environmental changes (Frankham et al, ). Levels of genetic diversity observed here were similar to those previously described for brown trout in Galician (He ~ 0.500–0.600; Vilas et al, ) and other Iberian (Araguas et al, ; Vera et al, ) populations. Low genetic diversity is related to genetic drift caused by, for example, population isolation and low Ne.…”

“…Most locations analysed here showed no or very low stocking impact, suggesting the resilience of native genetic pools in this region. However, some locations displayed an impact similar to that detected in the Mediterranean region (Araguas et al, ; Vera et al, ), the Limia drainage and NAV (inside the Sil drainage) being the locations most affected by these practices (Table ; Figure a).…”

“…However, some locations displayed an impact similar to that detected in the Mediterranean region (Araguas et al, 2017;Vera et al, 2013), the Limia drainage and NAV (inside the Sil drainage) being the locations most affected by these practices (Table 2; Figure 2a).…”

Genetic changes caused by restocking and hydroelectric dams in demographically bottlenecked brown trout in a transnational subarctic riverine system

“…Conservation and management actions commonly aim to increase connectivity and demographic robustness by, for example, establishing dispersal corridors or releasing individuals into the wild to support local populations (Quiñones et al, 2014). However, potential genetic effects of such mitigating actions are often not considered or monitored, which increases the risk of losing natural genetic diversity in disturbed and altered populations (Araguas et al, 2009(Araguas et al, , 2017. Therefore, assessments of genetic diversity, connectivity, and structure are essential for ensuring long-term benefits of management actions (Quiñones et al, 2014).…”

“…It is ecologically and morphologically variable including, resident and migratory life-history forms like anadromous (i.e., natal rivers-sea-natal rivers' migrations), as well as potamodromous (i.e., natal rivers-lakes-natal rivers' migrations) that can coexist in the same habitat. Although not endangered as such, natural brown trout populations with high genetic integrity are becoming increasingly rare across the distribution range (Araguas et al, 2009(Araguas et al, , 2017Baric et al, 2010) due to anthropogenic habitat destruction and the long-term practice of translocations and stocking. Hydropower developments are widespread in many countries and affect a wide range of formerly continuous brown trout populations (Heggenes & to ensure long-term preservation of natural genetic diversity and integrity in brown trout and other species in regulated river systems.…”