Sympatric Salmonids Research Articles

Differences in Energy Storage in Sympatric Salmonid Morphs with Contrasting Lifestyles

Differences in Energy Storage in Sympatric Salmonid Morphs with Contrasting Lifestyles

Spatial and temporal variability of movements among sympatric salmonids in an unfragmented inland watershed

AbstractObjectiveOur aim was to determine the movement patterns of three abundant salmonids—Brown Trout Salmo trutta, Mountain Whitefish Prosopium williamsoni, and Rainbow Trout Oncorhynchus mykiss—in the Smith River watershed of Montana.MethodsWe tagged 7172 fish with passive integrated transponder (PIT) tags, monitored their movements past 15 stationary PIT arrays over 4 years, and located tagged fish between arrays by conducting mobile surveys.ResultMovement patterns varied seasonally, among species, and among locations. Movement was greatest in the middle portion of the watershed, which included a pristine main‐stem canyon and lower reaches of major tributaries. Fish rarely left the canyon, but movement into the canyon from other regions was common. Mountain Whitefish were most likely to move, and Brown Trout were least likely to move. Most fish travelled less than 10 km, but some fish travelled over 100 km. Distinct movement patterns were not evident; rather, a continuous spectrum of movement behaviors was apparent. Movements by Mountain Whitefish and Rainbow Trout increased during their spawning periods. Movements peaked when mean daily water temperatures were between 11.3 and 17.1°C.ConclusionMovements were diverse and probably contributed to metapopulation dynamics, population resiliency, and species diversity. Fish movements along stream networks connect populations across diverse landscapes, and therefore, protecting and restoring stream connectivity along inland streams such as the Smith River is critical to maintaining productive fish assemblages.

Patterns and repeatability of multi‐ecotype assemblages of sympatric salmonids

AbstractAimHigh repeatability among assemblages of closely related but ecologically distinct ecotypes implies predictability in evolution and assembly of communities. The conditions under which ecotype assemblages form predictably, and the reasons, have been little investigated. Here, we test whether repeatability declines as the number of ecotypes builds.LocationPostglacial lakes with a circumboreal distribution.Time PeriodData were extracted from studies published between 1982 and 2019.Major Taxa StudiedEcotype assemblages from two Salmonid genera – Salvelinus and Coregonus. Fish in postglacial lakes commonly occur as pairs of ecotypes, typically with a pelagic and a littoral/benthic form, but in Salvelinus and Coregonus, assemblages commonly contain multiple sympatric ecotypes.MethodsWe used a meta‐analysis of Salvelinus and Coregonus to empirically assess how repeatability varies across assemblages of two to seven ecotypes. We examined repeatability of use of broad niche categories as well as underlying phenotypic traits.ResultsWithin Coregonus, repeatability across multi‐ecotype assemblages did not break down with the addition of a third or fourth ecotype. However, in Salvelinus, repeatability was largely absent and independent of the number of ecotypes. Repeatability of trait frequency distributions was absent in both genera, yet associations between trait means and niche categories were evident, especially in Coregonus.Main ConclusionsThese results show that repeatability can vary greatly between lineages; that repeatability need not break down as the number of ecotypes builds; and that high repeatability of broad niche categories may result despite marked differences in the underlying frequency distribution of trait means. These findings not only affirm the presence of repeatable ecotype assembly and early stages of divergence in postglacial fishes at a global scale, but also highlight variability among taxa and underlying phenotypic traits.

Environmental Impacts on Skin Microbiomes of Sympatric High Arctic Salmonids

In the region of King William Island, Nunavut, in the Canadian high Arctic, populations of salmonids including Arctic char (Salvelinus alpinus), cisco (Coregonus autumnalis and C. sardinella) as well as lake whitefish (C. clupeaformis) are diadromous, overwintering in freshwater and transitioning to saline waters following ice melt. Since these fish were sampled at the same time and from the same traditional fishing sites, comparison of their skin structures, as revealed by 16S rRNA gene sequencing, has allowed an assessment of influences on wild fish bacterial communities. Arctic char skin microbiota underwent turnover in different seasonal habitats, but these striking differences in dispersion and diversity metrics, as well as prominent taxa involving primarily Proteobacteria and Firmicutes, were less apparent in the sympatric salmonids. Not only do these results refute the hypothesis that skin communities, for the most part, reflect water microbiota, but they also indicate that differential recruitment of bacteria is influenced by the host genome and physiology. In comparison to the well-adapted Arctic char, lake whitefish at the northern edge of their range may be particularly vulnerable, and we suggest the use of skin microbiomes as a supplemental tool to monitor a sustainable Indigenous salmonid harvest during this period of change in the high Arctic.

Interactions between fish and angler behaviour affect species-specific catchability of sympatric native charr and two introduced trout

Catchability is a key determinant of fishing pressure, and plays an important role in the management of recreational fisheries. We investigated the catchability of three sympatric salmonid species in a recreational fishery in Lake Shikaribetsu, Japan—the endemic Miyabe charr (Salvelinus malma miyabei), introduced masu salmon (Oncorhynchus masou), and introduced rainbow trout (O. mykiss)—using a combination of stock assessment and angler survey data. Catchability differed among species, angling gear, and the interaction between these two, even when a similar fishing gear was used. Because of its migratory behaviour and fishing gear restrictions, the catchability of Miyabe charr was the lowest of these species, which became lower as fish density was lower. Conversely, the density-dependent changes of the catchability were not detected in masu salmon which few anglers targeted specifically. Rainbow trout catchability by fly anglers was the highest, possibly because the fishing tactics of fly anglers targeting this species were tailored to its foraging behaviour. We regarded differences in catchability among these three salmonids to be related to differences in fish and angler behaviours. These results indicate that behavioural characteristics of both fish species and anglers can cause different fishing pressure in a single recreational fishery targeting multispecies fish via interspecific catchability, and they should be taken into account for their management.

High summer macrophyte cover increases abundance, growth, and feeding of juvenile Atlantic salmon.

Aquatic habitats are severely threatened by human activities. For anadromous species, managing freshwater habitats to maximize production of more, larger juveniles could improve resilience to threats in marine habitats and enhance population viability. In some juvenile salmonid habitats, complexity created by large substrates provides resources and reduces competitive interactions, thereby promoting juvenile production. In lowland rivers, which lack large substrates, aquatic plants might provide similar complexity and enhance fish productivity. To test the influence of aquatic plants on juvenile Atlantic salmon and sympatric brown trout in a lowland river, we directly manipulated the cover of the dominant macrophyte, Ranunculus, in nine sites during summer and autumn for two years. We quantified the abundance, site retention and growth of salmon and trout under high, medium or low Ranunculus cover. To investigate the effects of Ranunculus cover on feeding opportunities and interspecific competition, we quantified available prey biomass and body size, fish diet composition and compared dietary niche overlap. Experimentally increased Ranunculus cover supported higher salmon abundance in summer and autumn, and higher site retention and growth of salmon in summer. Trout abundance and growth were not influenced by Ranunculus cover, but trout site retention doubled in high, relative to low, cover sites. Despite the weak effects of Ranunculus cover on prey availability, salmon and trout inhabiting high cover sites consumed larger prey and a higher biomass of prey. Furthermore, dietary niche overlap was lower in high, relative to low, cover sites, suggesting that abundant Ranunculus reduced interspecific competition. This field experiment shows that high Ranunculus cover can support more and better growing juvenile salmon, and facilitate foraging and co-existence of sympatric salmonid species. Maintaining or enhancing natural macrophyte cover can be achieved through sympathetic in-river and riparian vegetation management and mitigating pressures on them, such as sediment inputs and low flows, or through planting. Further research should test whether macrophyte cover benefits propagate to subsequent life stages, particularly juvenile overwintering associated with high mortality. This knowledge, in combination with our findings, would further clarify whether beneficial juvenile habitat can improve the viability of at-risk salmonid populations. Overall, our findings suggest that the aims of river restoration might be achieved through promotion of in-stream aquatic vegetation.

Ambient temperature as a factor contributing to the developmental divergence in sympatric salmonids.

Factors and mechanisms promoting resource-based radiation in animals still represent a main challenge to evolutionary biology. The modifications of phenotype tied with adaptive diversification may result from an environmentally related shift having occurred at the early stage of development. Here, we study the role of temperature dynamics on the reproductive sites in the early-life divergence and adaptive radiation of the salmonid fish Salvelinus malma dwelling in the Lake Kronotskoe basin (North-East Asia). Local sympatric charr ecomorphs demonstrate strict homing behaviour guiding the preordained distribution along tributaries and, hence, further development under different temperatures. We thoroughly assessed the annual temperature dynamics at the spawning grounds of each morph as compared to an ancestral anadromous morph. Then we carried out an experimental rearing of both under naturally diverging and uniformed temperatures. To compare the morphs’ development under the dynamically changing temperatures, we have designed a method based on calculating the accumulated heat by the Arrhenius equation. The proposed equation shows a strong predictive power and, at the same time, is not bias-susceptible when the developmental temperature approximates 0°C. The temperature was found to significantly affect the charrs’ early ontogeny, which underlies the divergence of developmental and growth rates between the morphs, as well as morph-specific ontogenetic adaptations to the spawning site’s temperatures. As opposed to the endemic morphs from Lake Kronotskoe, the anadromous S. malma, being unexposed to selection оn highly specific reproduction conditions, showed a wide temperature tolerance, Our findings demonstrate that the hatch, onset timing of external feeding, and size dissimilarities between the sympatric morphs reveal themselves during the development under contrast temperatures. As a result of the observed developmental disparities, the morphs occupy specific definitive foraging niches in the lake.

Natural Barriers and Internal Sources for the Reproductive Isolation in Sympatric Salmonids from the Lake–River System

Natural Barriers and Internal Sources for the Reproductive Isolation in Sympatric Salmonids from the Lake–River System

Distinct intestinal microbial communities of two sympatric anadromous Arctic salmonids and the effects of migration and feeding

Although intestinal microbial communities from anadromous Arctic char (Salvelinus alpinus (Linnaeus, 1758)) in Kitikmeot, Nunavut, Canada, differ depending on the timing and location of capture, determinants of gut microbiota in other wild Arctic salmonids are largely unknown. Using high-throughput 16S rRNA gene sequence data, we compared intestinal microbiota from Arctic char to those from a related and sympatric salmonid, lake whitefish (Coregonus clupeaformis (Mitchill, 1818)). Shifts in lake whitefish gut microbial community composition were observed between brackish water and freshwater, similar to impacts of salinity reported previously for Arctic char. Despite these similarities, gut community profiles for the two salmonids differed, with whitefish having higher diversities and increased proportions of taxa affiliated with potential pathogens. Geography seemed to have a greater impact on freshwater whitefish gut microbiota than on corresponding Arctic char. Additionally, microbiota diversity was significantly more affected by feeding behavior in whitefish compared with sympatric Arctic char. As sampled whitefish were at their northern range limits and grew slowly, we speculate that they, and their microbial consortia, could be more vulnerable to certain abiotic and biotic factors than Arctic char, which are well adapted to conditions found in these high latitude environments and have the most northern distribution of any freshwater fish.

Variability of isotopic partitioning between sympatric brown trout (Salmo trutta) and European grayling (Thymallus thymallus) in the Loue River (France)

AbstractTrophic partitioning, defining how individuals or populations differ in their resource use, is expected to promote coexistence of sympatric species by reducing resource overlap. We used stable isotope measurements (δ13C and δ15N) to address niche characteristics (δ13C and δ15N ranges, isotope convex hull and standard ellipse areas, mean nearest neighbour distances and trophic positions) and trophic partitioning of sympatric brown trout (Salmo trutta,n = 110) and European grayling (Thymallus thymallus,n = 63) in two sampling locations of a French river. Aquatic resources predominantly fuelled both species, yet both terrestrial resources (TER) and trophic positions (TP) were higher for trout (~36 ± 13% TER, 3.6 ± 0.7 TP) than grayling (~26 ± 9% TER, 2.7 ± 0.6 TP) supporting difference in their trophic niches. Isotope analyses showed that trout had a larger isotope niche than grayling suggesting more opportunistic trophic behaviour. Their isotopic overlapping was higher at the upstream site (isotopic nestedness = 0.8 ± 0.1) than that at the downstream site (isotopic nestedness = 0.4 ± 0.2). Euclidian distances of stable isotopes and TP for the two species increased with salmonid size, while aquatic resource use decreased with salmonid size. These results demonstrate an increase in isotopic niche partitioning and change in trophic attributes with ontogeny. Our study showed that despite relying on similar resources, these two sympatric salmonids exhibited clear trophic differences that were amplified with ontogeny. The consideration of fish ontogenetic dietary shift would hence be a determinant driver of the trophic niche partitioning for these sympatric salmonids.

Impacts of ontogenetic dietary shifts on the food-transmitted intestinal parasite communities of two lake salmonids.

Ontogenetic dietary shifts are common in fish and often impact trophically transmitted parasite communities. How parasite species composition and relative abundances change among size classes, and at what rate these changes occur, is rarely examined. Hosts with a broad trophic niche are potentially exposed to a large variety of parasite species. The degree of ontogenetic changes in parasite species composition versus changes in parasite abundance should suggestively differ between thropically generalist and specialist host species. In the present study, we explore ontogenetic dietary shifts and their impact on species composition and relative abundance of intestinal parasites in two sympatric salmonid fish species, Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) caught in the littoral habitat of a subarctic lake. Our results highlight a close interplay between ontogenetic dietary niche shifts and alterations in the acquisition of trophically transmitted parasites, leading to host-specific differences in the component community of parasites. Ontogenetic changes in the intestinal parasite community related to dietary niche shifts were distinct but less pronounced in Arctic charr than in brown trout due to a broader and more consistent dietary niche of the former and an ontogenetic shift toward piscivory in the latter. At the component community level, changes in parasite assemblages of both host species were driven by a faster increase in the heterogeneity of parasite relative abundance than in the compositional heterogeneity, a pattern that partly may be related to a rather species-poor parasite community of this subarctic study system. Separating compositional heterogeneity from heterogeneity in relative parasite abundance is important to understand how size-dependent variability shapes parasite communities of host populations.

An environmental DNA assay for detecting Arctic grayling in the upper Missouri River basin, North America

The upper Missouri River basin in the northwestern US contains disjunct Arctic grayling (Thymallus arcticus) populations of conservation concern. To assist efforts aimed at understanding Artic grayling distribution, we developed a quantitative PCR assay to detect the presence of Arctic grayling DNA in environmental samples. The assay amplified low concentrations of Arctic grayling DNA consistently, and did not amplify non-target species, including sympatric salmonid fishes.

Long-term species balance in sympatric populations: implications for Atlantic salmon and brown trout

The factors determining regional adaptation in salmonids are still unclear, but it is known that changes in their habitat imply changes in their population structure. In this preliminary study we integrate habitat data, molecular analyses (from both nuclear microsatellite and mitochondrial loci) and life-history traits (measured on archaeological vertebrae and modern scales) of two sympatric salmonid species: Atlantic salmon and brown trout. We propose that water temperature and geological characteristics changed the biogeographic patterns of these species through asymmetric migration and different (but complementary) population growth rates. As a consequence, differences in a life-history trait (mean number of years at sea) and population sizes were detected between regions, suggesting a process of substitution of Atlantic salmon by brown trout.

Long-term species balance in sympatric populations: implications for Atlantic salmon and brown trout

The factors determining regional adaptation in salmonids are still unclear, but it is known that changes in their habitat imply changes in their population structure. In this preliminary study we integrate habitat data, molecular analyses (from both nuclear microsatellite and mitochondrial loci) and life-history traits (measured on archaeological vertebrae and modern scales) of two sympatric salmonid species: Atlantic salmon and brown trout. We propose that water temperature and geological characteristics changed the biogeographic patterns of these species through asymmetric migration and different (but complementary) population growth rates. As a consequence, differences in a life-history trait (mean number of years at sea) and population sizes were detected between regions, suggesting a process of substitution of Atlantic salmon by brown trout.

Tiger muskellunge predation on stocked salmonids intended for recreational fisheries

Hatchery-reared fish are stocked widely to enhance recreational fisheries but are often consumed by predators. Stable isotope analyses were used to evaluate tiger muskellunge (northern pike [Esox lucius] × muskellunge [E. masquinongy]) predation on stocked salmonids (Oncorhynchus) relative to naturally reproducing white suckers (Catostomus commersonii), in 5 Colorado reservoirs. Stable isotope analyses coupled with a mixing model using a Bayesian framework indicated that tiger muskellunge primarily consumed stocked salmonids (53–84% by mass). These results suggest that stocking salmonids into systems that contain tiger muskellunge (and potentially other predators) may result in losses of valuable stocked fish. Further, the use of tiger muskellunge or other piscivores as biological control of less desirable species to benefit sympatric salmonid populations may be counterproductive to management goals. Finally, this study demonstrates the potential for managers to use this framework as a tool to identify and evaluate unintended losses of fishes to piscivores in other systems.

Population Genetics of Arctic Grayling Distributed Across Large, Unobstructed River Systems

AbstractWe investigated the population genetics of Arctic Grayling Thymallus arcticus distributed throughout several connected river systems in Alberta, Canada. Broad‐ and fine‐scale population structure was examined by genotyping nine microsatellite loci in 1,116 Arctic Grayling captured from 40 sites in the Hay, Peace, and Athabasca River basins. Genetic diversity tended to decline from north to south (allelic richness versus latitude: Spearman's rank correlation rs = 0.793, P < 0.05); the lowest level of diversity was detected in a stocked population. We found significant genetic divergence between and within major river basins (overall genetic differentiation index FST [θST] = 0.13) and strong isolation‐by‐distance patterns in the Peace River basin (Mantel's r = 0.97, P < 0.001) and Athabasca River basin (Mantel's r = 0.95, P < 0.001). Evidence for gene flow among sites in neighboring rivers (i.e., 25–100km apart) was common; significant genetic differentiation tended to occur at the subbasin level. The spatial scale of differentiation for Arctic Grayling is intermediate to those reported for other sympatric salmonid species that differ in population size and degree of spawning site fidelity.

Prey trait analysis shows differences in summer feeding habitat use between wild YOY Atlantic salmon and brown trout

We evaluated the vertical use of the water column for feeding by young of the year (YOY) of brown trout (Salmo trutta) and Atlantic salmon (S. salar) in a natural river during the summer. Prey trait analysis and diet composition demonstrated that brown trout showed a higher ability to feed on prey in the surface of the water column than Atlantic salmon. Hence, the differences in the ability to feed at different depths of the water column (surface vs. bottom) are important adaptive features that may reduce interspecific competition between the two sympatric fish species. Finally, results derived from the prey trait analysis provide useful information on resource partitioning between sympatric salmonid species.

Timing of smolt migration in sympatric populations of Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and Arctic char (Salvelinus alpinus)

A study over a 22-year period of first-time migrants (smolts) of three sympatric salmonids (Atlantic salmon ( Salmo salar ), brown trout ( Salmo trutta ), and Arctic char ( Salvelinus alpinus )) in a watercourse in northern Norway demonstrated that although there was considerable overlap in smolt migration timing among the species, Atlantic salmon migrated first, followed by Arctic char, and finally brown trout. The migration period of Arctic char had a smaller range and less annual variation than those of the two other species, possibly partly related to their more lake-dwelling habitat preference. For all species, water flow was important in explaining day-to-day variations in smolt runs. Water flow was most important for brown trout, change in flow for Atlantic salmon, whereas photoperiod was most important for Arctic char. These results suggest that both age and size of smolts and the timing of the smolt migration have been shaped by the different habitat preferences of these species both in fresh water and sea through local selection.

Resolving taxonomic uncertainties using molecular systematics: Salmo dentex and the Balkan trout community

The genetic structure of Salmo dentex and its phylogenetic relations to sympatric salmonids in the Neretva and Skadar River basins were evaluated using mitochondrial DNA (mtDNA) control region, eight microsatellites, and somatolactin (SL) gene. In the Neretva River basin of Bosnia–Herzegovina, the results based on mtDNA analysis showed extensive haplotype sharing between S. marmoratus, S. dentex, and S. trutta, and were therefore not conclusive; however, F-statistics and assignment testing based on nuclear DNA markers indicated that S. dentex of the Neretva basin were grouped in a genetically unified cluster with S. marmoratus in the Neretva basin. Using the same analytical approach, S. dentex from the Skadar basin in Montenegro appeared to be genetically distinct from S. marmoratus in the same basin and indistinct from local S. trutta. Molecular data also indicated that S. dentex of the Neretva basin in Bosnia–Herzegovina are not closely related to S. dentex of the Skadar basin in Montenegro. Based on these results, we hypothesize S. dentex to be a particular life history form of S. marmoratus in the Neretva basin and of S. trutta in the Skadar basin. These results clearly demonstrate that S. dentex does not represent a monophyletic lineage and should not be considered a distinct species.

Amplification and transport of an endemic fish disease by an introduced species

The introduction of American shad from the Atlantic to the Pacific coast of North America in the late 1800’s and the subsequent population expansion in the 1980’s resulted in the amplification of Ichthyophonus sp., a Mesomycetozoean parasite of wild marine fishes. Sequence analysis of the ribosomal DNA gene complex (small subunit and internal transcribed spacer regions) and Ichthyophonus epidemiological characteristics indicate a low probability that Ichthyophonus was co-introduced with American shad from the Atlantic; rather, Ichthyophonus was likely endemic to marine areas of the Pacific region and amplified by the expanding population of a highly susceptible host species. The migratory life history of shad resulted in the transport of amplified Ichthyophonus from its endemic region in the NE Pacific to the Columbia River watershed. An Ichthyophonus epizootic occurred among American shad in the Columbia River during 2007, when infection prevalence was 72%, and 57% of the infections were scored as moderate or heavy intensities. The epizootic occurred near the record peak of shad biomass in the Columbia River, and corresponded to an influx of 1,595 mt of infected shad tissues into the Columbia River. A high potential for parasite spillback and the establishment of a freshwater Ichthyophonus life cycle in the Columbia River results from currently elevated infection pressures, broad host range, plasticity in Ichthyophonus life history stages, and precedents for establishment of the parasite in other freshwater systems. The results raise questions regarding the risk for sympatric salmonids and the role of Ichthyophonus as a population-limiting factor affecting American shad in the Columbia River.