Impacts of acidification on brown trout Salmo trutta populations and the contribution of stocking to population recovery and genetic diversity

Abstract

Anthropogenic acidification in SW‐Scotland, from the early 19th Century onwards, led to the extinction of several loch (lake) brown trout (Salmo trutta) populations and substantial reductions in numbers in many others. Higher altitude populations with no stocking influence, which are isolated above natural and artificial barriers and subjected to the greatest effect of acidification, exhibited the least intrapopulation genetic diversity (34% of the allelic richness of the populations accessible to anadromous S. trutta). These, however, were characterised by the greatest interpopulation divergence (highest pairwise D EST 0.61 and F ST 0.53 in contemporary samples) based on 16 microsatellite loci and are among the most differentiated S. trutta populations in NW‐Europe. Five lochs above impassable waterfalls, where S. trutta were thought to be extinct, are documented as having been stocked in the late 1980s or 1990s. All five lochs now support self‐sustaining S. trutta populations; three as a direct result of restoration stocking and two adjoining lochs largely arising from a small remnant wild population in one, but with some stocking input. The genetically unique Loch Grannoch S. trutta, which has been shown to have a heritable increased tolerance to acid conditions, was successfully used as a donor stock to restore populations in two acidic lochs. Loch Fleet S. trutta, which were re‐established from four separate donor sources in the late 1980s, showed differential contribution from these ancestors and a higher genetic diversity than all 17 natural loch populations examined in the area. Genetically distinct inlet and outlet spawning S. trutta populations were found in this loch. Three genetically distinct sympatric populations of S. trutta were identified in Loch Grannoch, most likely representing recruitment from the three main spawning rivers. A distinct genetic signature of Loch Leven S. trutta, the progenitor of many Scottish farm strains, facilitated detection of stocking with these strains. One artificially created loch was shown to have a population genetically very similar to Loch Leven S. trutta. In spite of recorded historical supplemental stocking with Loch Leven derived farm strains, much of the indigenous S. trutta genetic diversity in the area remains intact, aside from the effects of acidification induced bottlenecks. Overall genetic diversity and extant populations have been increased by allochthonous stocking.

Anadromy, potamodromy and residency in brown trout Salmo trutta: the role of genes and the environment

“…Spawning of lake‐resident S. trutta occurs on shoreline gravels where there is sufficient wave action or diffuse water flow from the surrounding land to provide oxygenation. This type of spawning is typical of many small upland lakes (Prodöhl et al ., ). Spawning has been shown to occur in gravel areas in large lowland Irish lakes such as Lough Melvin (54° 24′ N, 08° 07′ W; Ferguson & Taggart, ) and Lough Mask (53° 36′ N, 09° 22′ W; P. Gargan, Inland Fisheries Ireland, pers.…”

Development and characterization of 12 microsatellite markers for the roundtail paradisefish ( Macropodus ocellatus ) using RAD sequencing

“…The microsatellite markers are widely used in the assessment of genetic diversity, population structure and gene flow in endangered or commercial fishes (Gkagkavouzis et al, ; Prodöhl et al, ; Song et al, ). The 12 novel markers developed here will be valuable tools to investigate the genetic background of M. ocellatus and related species, which can contribute to formulating appropriate strategies and policies for the conservation, management, and sustainable use of Macropodus species.…”

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

“…translocations) to increase population size and genetic diversity in the stocked populations, which has been also implemented in other regions for the brown trout (e.g. Prodöhl, et al, 2019), may be misguided mainly as a consequence of two main reasons: the negative impact of fish stocking and the loss of local adaptations.…”