Early effects of the strategies of creating a genetic refuge and direct translocation for conserving and restoring populations of native brown trout

Abstract

Summary 1. The conservation of salmonid inter‐ and intra‐specific diversity is a well‐known challenge, and general management guidelines and conservation processes are available. However, research demonstrating the outcomes of practical conservation actions is largely lacking. 2. We monitored the spatiotemporal genetic and demographic evolution of a native Mediterranean brown trout population in a river in the French Alps to assess the efficacy and early effects of genetic refuge (i.e. cessation of stocking) and wild trout translocation strategies. We also studied the use of angling as a tool to limit the introgression of the wild standing population. 3. We found that the rate of non‐native alleles in wild populations was age dependent, underpinning the importance of using age profiles in the design of genetic conservation studies. 4. Genetic refuge and direct translocation of wild trout resulted in a rapid and significant decrease in the percentages of non‐native alleles. Moreover, the genetic refuge strategy resulted in a significant reduction in the number of pure non‐native individuals, without changing trout densities, whilst direct translocations resulted in the establishment of dense, self‐sustaining native trout populations. Direct translocations changed the distribution of genotype categories and increased densities up to 55‐fold in 3 years. Our results also showed that angling resulted in a selective pressure on non‐native trout introduced at fry stage, whereas non‐native trout issued from natural recruitment were not affected. 5. Our study provides insights for improving the efficacy of practical conservation policies and can be used in other native freshwater fish conservation plans. Proactive measures such as direct translocation need to be implemented together with passive approaches such as genetic refuge policies. Before implementing such actions, accurate genetic and demographic studies at small geographical scales are essential to ensure that no self‐sustaining population of non‐native fish is present. To obtain rapid colonisation, we recommend introducing fish along whole river sections rather than concentrating on a few river stretches. Angling pressure can be used as an additional tool to improve restoration.

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

“…In particular, the legislation prohibits the introduction of alien species, subspecies or geographical races and illegal transplantation of individuals when they are capable of competing with native wildlife, altering its genetic purity or the ecological balance. The establishment of genetic refuges in Mediterranean rivers has not resulted in a rapid and significant decrease of hatchery alleles at regional scale (Araguas et al 2008Caudron et al , 2012. In spite of some isolation degree was revealed by contrasting levels of introgression at NU and QA locations in the absence of physical barriers, several studies support the spreading of hatchery genes from highly introgressed salmonids populations to neighbouring locations (Garc ıa-Mar ın et al 1998;Hitt et al 2003;Araguas et al 2008).…”

“…In spite of some isolation degree was revealed by contrasting levels of introgression at NU and QA locations in the absence of physical barriers, several studies support the spreading of hatchery genes from highly introgressed salmonids populations to neighbouring locations (Garc ıa-Mar ın et al 1998;Hitt et al 2003;Araguas et al 2008). However, maintaining fishery within genetic refuges has not been effective enough for recovering native gene pools in introgressed populations (Araguas et al 2008Caudron et al 2012). For instance, the highly introgressed collection of PAR14 in Segadell River might contribute to the introgression of neighbouring populations, such as PLA and RF, due to the lack of hydrological barriers among them.…”

“…Then, the dispersal of individuals from hybridised populations cannot be ignored as a possible threat that might contribute to the increase of hatchery introgression in adjacent populations. Thus, while genetic refuges have the potential to prevent further introgression, additional measures should be implemented to recover native gene pools, particularly within protected areas (Araguas et al 2008Caudron et al 2012). Similarly, these trout could reach populations located upstream of small weirs in the main stream, such as QA and QB, because it is observed that some larger trout easily overpass these physical obstacles (Ordeix et al 2011).…”

“…The supplementation of native individuals could be achieved by stocking with local native breeding stocks and/or by translocations of wild native individuals. The translocations of native Mediterranean trout also resulted in a significant decrease in the percentages of non-native alleles in the Borne River (Caudron et al 2012). For instance, stocking with fry from a native stock has led to the restoration of a functional Mediterranean trout population in the Ugine River (Caudron et al 2006).…”

“…With the aim to address both conservation of remnant native gene pools and transition towards self-sustained recreational fisheries, several river segments were designated as 'genetic refuges' based on the genetically demonstrated native status of their brown trout populations. Genetic refuges have also been implemented in French Mediterranean brown trout populations since 2005 (Caudron et al , 2012. In addition, the stocking ban was accompanied with measures to promote a self-sustaining fishery, with restriction on the number of captures and on the length of removed fish (revised in Araguas et al 2008).…”