Abstract
To elucidate the historical biogeography of a species, the patterns of population divergence must be understood, and the evolutionary history of the species must be accurately known. For ...brown trout (Salmo trutta complex), estimating divergence times remains a challenge due to the lack of well-defined time calibration points and insufficient phylogeographic coverage in previous studies. The present work aims to improve molecular dating of mitochondrial control region sequences by using a multicalibration framework based on the latest paleogeological evidence for dating the origin of Lake Ohrid and two available Salmo fossils, including the overlooked Salmo immigratus. Our results clearly show that, contrary to common belief, the major divisions within the brown trout occurred in the Late Pliocene, not the Pleistocene. The Pliocene origin suggests that the brown trout lineages did not form because of geo(hydro)morphological changes during glaciation cycles but may be the result of orogeny and drainage evolution. In addition, increased sampling, particularly in Serbia, led to the identification of a new haplogroup (da-int) occupying an intermediate position with respect to da-es and da-bs haplogroups. While the control region can delineate brown trout lineages, its phylogenetic resolution is limited, so even extensive sampling could not further resolve the lineage level polytomies.
Recoveries of gray seal (Halichoerus grypus) populations across their eastern Atlantic distribution have led to a steady increase in seal‐fishery interactions. Fishers have estimated depredation of ...salmonids (Salmo spp.) and monkfish (Lophius spp.) as high as 40% and 59% respectively in Ireland. However, empirical evidence for the consumption of these species has been extremely limited due to diagnostic hard part remains not being found in scats or stomach samples. We applied species‐specific primers and tested for the presence of monkfish and salmonids in gray seal diet genetically using quantitative polymerase chain reaction (qPCR) on scats. Monkfish occurred in 29.7% of sampled scats, while salmonids occurred in 12.7%. Seasonal and regional variability in occurrence were noted for both species, likely related to the migratory behavior of the prey species and proximity of seal haul‐outs to aquaculture sites. Traditional hard part analysis of scats, including scats that tested positive for monkfish and salmonid DNA, failed to find any evidence of either species. This study provides important empirical evidence for the consumption of these species in Ireland that can inform management.
Alien fish introductions, conducted towards the ichthyofauna enhancement in local drainages, have been occasionally proved harmful for the indigenous freshwater fish populations. The present study ...was designed to assess the impact of stocking activities, carried out in the past decades with fingerlings originating from Acheloos river hatcheries, on the native trout (Salmo sp.) populations of Nestos River, Greece. Trout specimens collected from several tributaries of Nestos River and were analyzed by means of PCR-RFLP and sequencing targeting the mitochondrial ND5-ND6 genes and the entire control region, respectively. It should be mentioned that trouts from Acheloos mainly belong to the marmoratus mitochondrial DNA (mtDNA) lineage, while the autochthonous trouts from Nestos belong to the Adriatic lineage. Both methodologies demonstrated that most samples from the three tributaries located at the lower part of Nestos constitute offspring of the fingerlings transferred from Acheloos hatcheries. Therefore, these tributaries have been strongly affected by stocking activities with a potential complete loss of their autochthonous trout. On the other hand, it seems that trout populations from higher altitude tributaries have not been affected by stockings. Hence, efforts should be undertaken in order to prevent the prevalence of the non-indigenous translocated Salmo in higher altitude tributaries, in conjunction with a management plan designed for the total trout populations from the area, speaking of which it has been recently included to the National Park of Rodopi Mountains.
Ecological monitoring programmes should provide precise data to inform management, but the data quality is often limited by methodological challenges and the need for cost-effective sampling. ...Parasite infestations are particularly challenging to monitor due to complex interactions among hosts, parasites and the environment. In Norway, salmon lice infestations on wild salmonid fish have been monitored since 1992 to survey the potential transmission between farmed and wild salmonids. Here, we compared spatiotemporal variation in salmon lice levels with variations in local fjord conditions, including salinity, temperature and infestation pressure from salmon farms (measured as mean abundance of mature female lice × number of farmed fish). We tested 3 different measures of infestation with different statistical properties. Our results confirm that, even after correcting for temperature and salinity effects, infestation pressure from salmon farms significantly increases the probability of lice infestation in wild salmonids. The probability of infestation increases with fish body length, salmon farm infestation pressure and temperature, and decreases with increasing freshwater influence. Furthermore, we found a significant interaction between temperature and infestation pressure from salmon farms. When the infestation pressure from farms is low, temperature has a strong increasing effect on the probability of infestation, but as the infestation pressure from farms increases, temperature gradually becomes less important. The exact results vary somewhat depending on the measure of lice infestations used, but the same trend can be seen in all models. We discuss the statistical and biological complexities that make monitoring of salmon lice in wild populations challenging.
Behavioural endocrinologists have shown that stressors including competition for resources can affect an individual’s circulating level of cortisol, whereas agonistic interactions typically affect ...androgen levels. Conservation biologists have used such data to facilitate the restoration and management of biodiversity by monitoring social interactions and stress among individuals and species. Here, we examined whether competition and agonistic interactions with non-native salmonids is hindering restoration of native Atlantic salmon, Salmo salar, in Lake Ontario. Using semi-natural streams, we examined the effects of competition with non-native brown trout, Salmo trutta, and rainbow trout, Oncorhynchus mykiss, on plasma cortisol and 11-ketotestosterone (11-KT) concentrations in juveniles from three Atlantic salmon strains, as well as the relationship between these hormones and social dominance and growth. Basal hormone levels and the hormonal response to the presence of the trouts varied among the strains. Cortisol increased in the presence of the trouts for two strains and was associated with lowered aggression and food consumption. Conversely, the presence of the non-native species had little influence on overall concentrations of 11-KT in the Atlantic salmon, although unexpectedly, there was a negative relationship between 11-KT and initiated aggression when either one of the trouts was present. Interestingly, elevated 11-KT levels were associated with declines in both food consumption and growth. Overall, our results suggest that competition with non-native salmonids negatively impacts Atlantic salmon. We discuss how our results can improve poststocking success and restoration of Atlantic salmon in Lake Ontario.
► Non-native salmonids may be hindering the reintroduction of Atlantic salmon to Lake Ontario. ► We found that non-natives led to higher stress hormone concentrations in Atlantic salmon. ► Conversely, non-native salmonids did not affect androgen concentrations. ► We also found that some Atlantic salmon strains may be better able to cope with competition. ► Of three candidates, the currently stocked strain was the most chronically stressed.
There is intense debate over the potential impact of seal predation on declining salmon stocks in both the Pacific and Atlantic oceans. However, efforts to model such interactions have been ...constrained by a lack of data on the functional and numerical responses of these predators. Based upon theory, and data from small-scale terrestrial and freshwater systems, a type 3 functional response is expected to best describe predation by generalist pinnipeds. Similarly, theory also predicts that seal numbers should increase with salmon density in rivers following an aggregative response of predator to prey. We tested these predictions by studying the diet and local density of harbour seals in relation to seasonal variations in the abundance of salmonid in a Scottish river system. As predicted, the abundance of seals in the river was directly related to the abundance of returning salmon, and dietary data supported the type 3 functional response to changes in salmonid abundance. These studies provide empirical support for the use of type 3 response in modelling studies.
PDF
