A. Ferguson

Fitness reduction and potential extinction of wild populations of Atlantic salmon, Salmo salar, as a result of interactions with escaped farm salmon.

The high level of escapes from Atlantic salmon farms, up to two million fishes per year in the North Atlantic, has raised concern about the potential impact on wild populations. We report on a two-generation experiment examining the estimated lifetime successes, relative to wild natives, of farm, F1 and F2 hybrids and BC1 backcrosses to wild and farm salmon. Offspring of farm and ‘hybrids’ (i.e. all F1, F2 and BC1 groups) showed reduced survival compared with wild salmon but grew faster as juveniles and displaced wild parr, which as a group were significantly smaller. Where suitable habitat for these emigrant parr is absent, this competition would result in reduced wild smolt production. In the experimental conditions, where emigrants survived downstream, the relative estimated lifetime success ranged from 2% (farm) to 89% (BC1 wild) of that of wild salmon, indicating additive genetic variation for survival. Wild salmon primarily returned to fresh water after one sea winter (1SW) but farm and ‘hybrids’ produced proportionately more 2SW salmon. However, lower overall survival means that this would result in reduced recruitment despite increased 2SW fecundity. We thus demonstrate that interaction of farm with wild salmon results in lowered fitness, with repeated escapes causing cumulative fitness depression and potentially an extinction vortex in vulnerable populations.

A critical review of adaptive genetic variation in Atlantic salmon: implications for conservation

Here we critically review the scale and extent of adaptive genetic variation in Atlantic salmon (Salmo salar L.), an important model system in evolutionary and conservation biology that provides fundamental insights into population persistence, adaptive response and the effects of anthropogenic change. We consider the process of adaptation as the end product of natural selection, one that can best be viewed as the degree of matching between phenotype and environment. We recognise three potential sources of adaptive variation: heritable variation in phenotypic traits related to fitness, variation at the molecular level in genes influenced by selection, and variation in the way genes interact with the environment to produce phenotypes of varying plasticity. Of all phenotypic traits examined, variation in body size (or in correlated characters such as growth rates, age of seaward migration or age at sexual maturity) generally shows the highest heritability, as well as a strong effect on fitness. Thus, body size in Atlantic salmon tends to be positively correlated with freshwater and marine survival, as well as with fecundity, egg size, reproductive success, and offspring survival. By contrast, the fitness implications of variation in behavioural traits such as aggression, sheltering behaviour, or timing of migration are largely unkown. The adaptive significance of molecular variation in salmonids is also scant and largely circumstantial, despite extensive molecular screening on these species. Adaptive variation can result in local adaptations (LA) when, among other necessary conditions, populations live in patchy environments, exchange few or no migrants, and are subjected to differential selective pressures. Evidence for LA in Atlantic salmon is indirect and comes mostly from ecological correlates in fitness‐related traits, the failure of many translocations, the poor performance of domesticated stocks, results of a few common‐garden experiments (where different populations were raised in a common environment in an attempt to dissociate heritable from environmentally induced phenotypic variation), and the pattern of inherited resistance to some parasites and diseases. Genotype × environment interactions occurr for many fitness traits, suggesting that LA might be important. However, the scale and extent of adaptive variation remains poorly understood and probably varies, depending on habitat heterogeneity, environmental stability and the relative roles of selection and drift. As maladaptation often results from phenotype‐environment mismatch, we argue that acting as if populations are not locally adapted carries a much greater risk of mismanagement than acting under the assumption for local adaptations when there are none. As such, an evolutionary approach to salmon conservation is required, aimed at maintaining the conditions necessary for natural selection to operate most efficiently and unhindered. This may require minimising alterations to native genotypes and habitats to which populations have likely become adapted, but also allowing for population size to reach or extend beyond carrying capacity to encourage competition and other sources of natural mortality.

Genetic impact of escaped farmed Atlantic salmon (Salmo salar L.) on native populations: use of DNA profiling to assess freshwater performance of wild, farmed, and hybrid progeny in a natural river environment

McGinnity, P., Stone, C., Taggart, J. B., Cooke, D., Cotter, D., Hynes, R., McCamley, C., Cross, T., and Ferguson, A. 1997. Genetic impact of escaped farmed Atlantic salmon (Sulmo salar L.) on native populations: use of DNA profiling to assess freshwater performance of wild, farmed, and hybrid progeny in a natural river environment. - ICES Journal of Marine Science, 54: 998-1008. Since Atlantic salmon (Salmo salur L.) used for farming are usually genetically different from local wild populations, breeding of escaped farmed salmon potentially results in genetic changes in wild populations. To determine the likelihood and impact of such genetic change, an experiment was undertaken, in a natural spawning tributary of the Burrishoole system in western Ireland, to compare the performance of wild, farmed, and hybrid Atlantic salmon progeny. Juveniles were assigned to family and group parentage by DNA profiling based on composite genotypes at seven minisatellite loci. Survival of the progeny of farmed salmon to the smolt stage was significantly lower than that of wild salmon, with increased mortality being greatest in the period from the eyed egg to the first summer. However, progeny of farmed salmon grew fastest and competitively displaced the smaller native fish downstream. The offspring of farmed salmon showed a reduced incidence of male parr maturity compared with native fish. The latter also showed a greater tendency to migrate as autumn pre-smolts. Growth and performance of hybrids were generally either intermediate or not significantly different from the wild fish. The demonstration that farmed and hybrid progeny can survive in the wild to the smolt stage, taken together with unpublished data that show that these smolts can survive at sea and home to their river of origin, indicates that escaped farmed salmon can produce long-term genetic changes in natural populations. These changes affect both single-locus and high-heritability quantitative traits, e.g. growth, sea age of maturity. While some of these changes may be advantageous from an angling management perspective, they are likely, in specific circumstances, to reduce population fitness and productivity. Full assessment of these changes will require details of marine survival, homing and reproductive performance of the adults together with information on the F, generation. 0 1997 International Council for the Exploration of the Sea

Genetic variation in Irish populations of brown trout (Salmo trutta L.): electrophoretic analysis of allozymes

Abstract 1. 1. Starch gel electrophoresis and isoelectric focusing of skeletal muscle, eye, brain, liver and heart extracts of Irish brown trout populations revealed extensive genetic heterogeneity. 2. 2. Twenty-three enzyme systems, comprising a putative 63 loci, were examined. Polymorphism was observed at 13 loci of which four, PGI-2, 5AAT-4, 2IDH-1 and 2IDH-2, have not previously been reported as polymorphic in brown trout. 3. 3. The value of the relatively high level of polymorphism, (22%) is discussed with respect to salmonid genetic research and management programmes.

Management of salmonid fisheries in the British Isles: towards a practical approach based on population genetics

The evidence for structuring of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) into distinct reproductive populations and for genetic differentiation and local adaptation is compelling. The effect of genetic variation among populations is demonstrably a factor determining the economic value of salmonid fisheries in the British Isles. Genetic considerations are, therefore, a matter of self-interest for fisheries managers and a shared interest with those advocating more general approaches to the conservation of diversity and variation. The local population is the basic unit of production and, therefore, the preferred unit of management. However, salmonid populations are numerous and many are small. These factors limit practical possibilities for management at the population level. We suggest that this difficulty can be addressed by combining populations in fisheries-biased management units that comprise interchangeable, nested groupings of populations that are both genetically and biologically meaningful. This population-based approach addresses the necessity of managing the fisheries in ways that are consistent with the conservation of adaptive potential in relation to the dynamic aspects of populations, their capacity to respond to changing environmental conditions, and the likelihood that salmonids will remain a worthwhile resource for the future.

Aspects of the population genetics of herring, Clupea harengus, around the British Isles and in the Baltic Sea

Abstract Electrophoretic variation within and among Clupea harengus L. samples taken from 10 locations in the northwest region of the British Isles and from a spawning site in the Baltic Sea and Thames Estuary were studied. Sixteen enzyme systems, coded by a putative 30 loci, were examined. Twelve loci were found to be polymorphic and were considered usable for population surveys. The proportion of polymorphic loci varied between 0.115 and 0.230 (0.95 criterion) and between 0.308 and 0.461 (0.99 criterion); average heterozygosity was 0.045 ± 0.02. Differentiation among samples was found to be low, even between samples from the west of Ireland and the Baltic Sea. The average Neis genetic distance was 0.0004 and FST value was 0.002. The magnitude of genetic differentiation between stocks, as indicated from genetic distance values, is within a much narrower range than found between geographically isolated populations of other fish species. Temporal stability over three different development stages and eight overlapping year classes of North Irish Sea herring was demonstrated.

Kinetic studies on the lactate dehydrogenase (LDH-5) isozymes of brown trout, Salmo trutta L.

The LDH-5 isozymes of brown trout, Salmo trutta L., were purified and subjected to enzyme kinetic analysis. A hierarchy of magnitude existed for both Km(pyr) and Km(lac) such that LDH-5(105/105) greater than (100/105) greater than (100/100). The results suggest that the 105 allele has been replaced by 100 at Ldh-5 under the action of natural selection.

An electrophoretically-detectable genetic tag for hatchery-reared brown trout (Salmo trutta L.)

Abstract The feasibility of incorporating a unique genetic marker into a hatchery strain of brown trout is investigated. The allele Pgi-3(110) is shown to have a very limited distribution among native trout populations in Great Britain and Ireland yet is present, at low frequency, in all three hatchery stocks examined. The potential therefore exists to breed a strain of hatchery brown trout homozygous for the Pgi-3(110) allele. Individuals of such a strain could be unambiguously distinguished from virtually all native stocks. The usefulness of the genetic tag is enhanced by the strong expression of Pgi-3 in adipose fin, permitting simple biopsying. Data from population surveys and the monitoring of experimental progeny suggest selective equivalence among Pgi-3 genotypes.

Lactate dehydrogenase isozymes and allozymes of the nine-spined stickleback Pungitius pungitius (L.) (Osteichthyes: Gasterosteidae)

Zymograms indicate the existence of three loci coding for lactate dehydrogenase in the nine-spined stickleback Pungitius pungitius. The skeletal muscle locus is polymorphic for two codominant alleles: Ldh-A(100). and Ldh-A(140). Differences in allele frequencies among nine samples, obtained from eight geographically isolated populations, proved not significant in 28/36 pairwise comparisons. The frequency of Ldh-A(100) varied from 0.426 to 0.715. Significant differences in apparent Km (pyruvate) values were found among the LDH-A allozymes suggesting a functional basis for the selective maintenance of this polymorphism.

Kinetic studies on the lactate dehydrogenase isozymes of the brown trout, Salmo trutta L.

Informative crosses have verified the genetic basis of a polymorphism at the Ldh-1 locus in brown trout and enzyme activity measurements indicate that the previously described polymorphism at this locus is best explained by a null allele. The LDH-1, LDH-2, LDH-3 and LDH-4 homotetrameric isozymes were purified and subjected to enzyme kinetic analysis. While LDH-1 and LDH-2 displayed catalytic equivalence, important kinetic differences were found between the LDH-3 and LDH-4 isozymes.