Sympatric Trout Research Articles

Widespread Distribution of Ceratonova shasta (Cnidaria: Myxosporea) Genotypes Indicates Evolutionary Adaptation to its Salmonid Fish Hosts.

The distribution of the freshwater myxozoan parasite Ceratonova shasta in the Pacific Northwest of North America is limited to overlap in the ranges of its 2 hosts: the polychaete Manyunkia sp., and Pacific salmonids. Studies in the Klamath River (Oregon/California) and Deschutes River (Oregon), showed that the parasite population is comprised of multiple sympatric genotypes, some of which correlate with particular salmonid host species and with differences in clinical disease in those hosts. The 3 primary genotypes O, I, and II are defined by the number of a specific tri-nucleotide repeat in the internal transcribed spacer-1 region. To understand the spatial extent of host-parasite genotype patterns, we sequenced the parasite from 448 salmonid fishes from river basins in California, Oregon, Washington, Idaho, and British Columbia, Canada. We sampled intestinal tissues from 6 species of salmon and trout, both those that exist naturally with the parasite (sympatric) and those that do not naturally co-occur with the parasite and were exposed artificially in cages (allopatric). In most river basins we detected the same primary C. shasta genotypes that were described from the Klamath and Deschutes rivers, and we did not detect any novel primary genotypes. Host-parasite genotype patterns were consistent with previous data: genotype O was found in sympatric trout only; genotype I predominantly in Chinook salmon, and genotype II in all 6 fish species but dominant in coho salmon. Our findings of widespread, consistent host-parasite genotype patterns support the hypothesis that C. shasta has a long evolutionary history with salmonid fishes in the Pacific Northwest, and impels additional studies to determine if these parasite genotypes should be considered different species.

Brook trout use of thermal refugia and foraging habitat influenced by brown trout

The distribution of native brook trout (Salvelinus fontinalis) in eastern North America is often limited by temperature and introduced brown trout (Salmo trutta), the relative importance of which is poorly understood but critical for conservation and restoration planning. We evaluated effects of brown trout on brook trout behavior and habitat use in experimental streams across increasing temperatures (14–23 °C) with simulated groundwater upwelling zones providing thermal refugia (6–9 °C below ambient temperatures). Allopatric and sympatric trout populations increased their use of upwelling zones as ambient temperatures increased, demonstrating the importance of groundwater as thermal refugia in warming streams. Allopatric brook trout showed greater movement rates and more even spatial distributions within streams than sympatric brook trout, suggesting interference competition by brown trout for access to forage habitats located outside thermal refugia. Our results indicate that removal of introduced brown trout may facilitate native brook trout expansion and population viability in downstream reaches depending in part on the spatial configuration of groundwater upwelling zones.

Changes in the density and growth of brown trout (Salmo trutta) after intensive removal of sympatric Arctic charr (Salvelinus alpinus) in the sub‐Arctic lake Møkkelandsvatn, Norway

AbstractThis study tests the basic hypothesis that the removal of charr, Salvelinus alpinus (L.), would cause an increase in both the growth and density of a sympatric trout population, Salmo trutta L. The charr population was characterised by slow‐growing individuals, with a high proportion of mature fish, that is typical for so‐called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990–1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60–80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back‐calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr.

A Legacy of Divergent Fishery Management Regimes and the Resilience of Rainbow and Cutthroat Trout Populations in Lake Crescent, Olympic National Park, Washington

Abstract As a means to increase visitation, early fisheries management in the National Park Service (NPS) promoted sport harvest and hatchery supplementation. Today, NPS management objectives focus on the preservation of native fish. We summarized management regimes of Olympic National Park's Lake Crescent, which included decades of liberal sport harvest and hatchery releases of 14.3 million salmonids. Notably, nonnative species failed to persist in the lake. Complementary analyses of annual redd counts (1989–2012) and genetics data delineated three sympatric trout (one rainbow; two cutthroat) populations that exhibited distinct spatial and temporal spawning patterns, variable emergence timings, and genetic distinctiveness. Allacustrine rainbow trout spawned in the lake outlet from January to May. Cutthroat trout spawned in the major inlet tributary (Barnes Creek) from February to June and in the outlet river (Lyre) from September to March, an unusual timing for coastal cutthroat trout. Redd counts for ea...

Selective segregation in intraspecific competition between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

Interactive segregation has been suggested as the ruling competition mechanism determining niche and niche segregation between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Results from allopatry–sympatry observations of habitat use in both nature and in experiments were contrary to predictions derived from the interactive segregation hypothesis. Habitat use parameters under natural conditions such as distance to shore for Atlantic salmon parr were nearly identical in allopatric (mean ± SD; 3.2 ± 1.4 m) and sympatric (3.3 ± 1.4 m) situations. Occupied water depths largely reflected available water, but water depths <15 cm were avoided by salmon parr. Under experimental conditions, habitat use of allopatric salmon was density independent and salmon size had only minor effects, with smaller fish being more likely to occur in the shallow. Habitat use of salmon in sympatry with trout did not differ from allopatric salmon habitat use, and only salmon size had minor effects on depth choice – occurrence of trout or fish density had no effect. Allopatric trout was in general more frequent in the shallow habitat than salmon. Habitat use of sympatric trout was affected by the occurrence of salmon and trout size, resulting in a higher use of the shallow habitats for small trout. To conclude, selective segregation has a dominant role in salmon habitat use (not affected by trout occurrence), whereas a mixed situation occurs in trout habitat use with elements of interactive segregation when competing with Atlantic salmon (affected by salmon occurrence).

Genetic differentiation and hybridization in two naturally occurring sympatric trout Salmo spp. forms from a small karstic lake

In this study, multiple molecular markers [genotyping of 12 nuclear microsatellite loci and the protein-coding gene ldh-c1* plus sequencing of the mitochondrial DNA (mtDNA) control region] were employed to investigate the genetic structure of the two trout forms, Salmo cettii and Salmo fibreni, inhabiting Lake Posta Fibreno, central Italy. The two forms were found to share a unique mtDNA haplotype, belonging to a widespread Mediterranean haplogroup (AD). Bayesian clustering analyses showed that these two forms correspond to well-defined autochthonous gene pools. Genetic introgression between the two gene pools, however, was observed, whose frequency appears to correlate with the environmental features of the spawning sites. The interplay of selection for the spawning sites, philopatry and natural selection can be argued to maintain genetic differentiation despite the lack of complete reproductive isolation.

Environmental factors associated with reproductive barrier breakdown in sympatric trout populations on Vancouver Island.

The incidence of hybridization between coastal cutthroat (Oncorhynchus clarki clarki) and rainbow trout (Oncorhynchus mykiss) varies widely among populations. The breakdown of reproductive isolation is of concern to managers, and raises the question: how have the two species retained their genetic and morphological divergence? Using a combination of mitochondrial DNA and nuclear DNA markers coupled with watershed attribute and disturbance data, we determined the distribution and frequency of trout hybridization on Vancouver Island, BC and the environmental factors associated with the hybridization. We found 284 hybrids (among 1004 fish) in 29 of 36 sampled populations. High variation in levels of hybridization was observed among populations, and no single environmental factor was found to dominate in determining hybridization levels. However, logging activity, urban infrastructure development, and stocking of hatchery rainbow trout played significant roles in determining hybridization levels, and populations in small watersheds are more at risk of reproductive barrier breakdown. This study illustrates that cutthroat–rainbow trout reproductive barrier breakdown is widespread on Vancouver Island and that anthropogenic disturbance plays a role in the process. As similar environmental disturbance is common in much of coastal trout habitat, large-scale hybridization may be occurring elsewhere and thus may represent a critical management issue for Pacific trout species.

Hybridization dynamics between sympatric species of trout: loss of reproductive isolation

Although reinforcement should enhance reproductive barriers in sympatric species, sympatric trout species do hybridize. Using mitochondrial and nuclear species markers, we investigated hybridization directionality, hybrid mating biases, and selection against hybrids in 13 sympatric cut-throat and rainbow trout populations on Vancouver Island, Canada. Approximately 50% of the genotyped fish were hybrid (F1 or higher-order) and populations ranged from very recent (all F1 hybrids) to extremely advanced higher-order hybridization. Overall, interbreeding was reciprocal, although some populations showed directional hybridization. Pronounced cytonuclear disequilibrium in post-F1 hybrids indicated a remarkable mating bias not previously reported, which is most likely because of behavioural reproductive preferences. Selection against hybrids was observed in only two populations, indicative of extrinsic selection. Two populations were 'hybrid swarms', with a complete loss of reproductive isolation. The complex hybridization dynamics in this system represent a valuable natural experiment of the genetic and evolutionary implications of recent and on-going interspecific hybridization.

Changes in use of lake habitat by experimentally segregated populations of cutthroat trout and Dolly Varden char

The role of competition in a lacustrine community of two salmonid species, cutthroat trout Oncorhynchus clarki and Dolly Varden char Salvelinus malma, was studied in three coastal British Columbia lakes Habitat use by the species alone (allopatric) and in coexistence with each other (sympatric) was investigated by gill netting at 0-40 m depth contours (surface to bottom) so that several habitats (littoral, epipelagic. pelagic, epibenthic) were sampled From June to October, trout used mainly littoral and epipelagic habitats in sympatry and allopatry Char used all habitats in allopatry. and deep habitats (pelagic, epibenthic) not frequented by trout in sympatry The two species were thus spatially segregated with depth in sympatry Diel (day, night) and seasonal changes (spring, summer, autumn) in habitat use were not pronounced The shift in habitat use by experimentally allopatric char but not trout suggests that the effects of competition between sympatric trout and char for habitat resources are greater on the char

Interactions between Two Distantly Related Species, Brook Trout (Salvelinus fontinalis) and White Sucker (Catostomus commersoni)

We compared spatial distribution and food habits of an allopatric brook trout (Salvelinus fontinalis) population to one living sympatrically with white sucker (Catostomus commersoni) in two small oligotrophic lakes. Small brook trout (&lt; 20 cm) of both sympatric and allopatric populations were more abundant in the littoral than in the offshore zone whereas large [Formula: see text] were found equally in both habitats in May. From June to August, small and large trout from both populations shifted to the offshore zone; this shift was more pronounced for small sympatric trout. Allopatric trout fed mainly on zoobenthos whereas sympatric trout fed mainly on zooplankton except small ones which ate mostly zoobenthos during May and June. White sucker (&lt; 20 and [Formula: see text]) were generally found in the littoral zone, feeding mainly on zoobenthos. These results suggest that brook trout shifted their spatial distribution and/or their feeding habits in the presence of white sucker and that the nature of these interactions varied according to fish size. Diet overlap between trout and sucker was the lowest when the biomass of benthic prey in the littoral zone was lowest (July), indicating that the intensity of interaction among these species varies according to the abundance of food resources.

Retinal Structure of Sympatric and Allopatric Populations of Cutthroat Trout (Salmo clarki clarki) and Dolly Varden Char (Salvelinus malma) in Relation to their Spatial Distribution

Retinal structures of cutthroat trout (Salmo clarki clarki) and Dolly Varden char (Salvelinus malma) were compared to determine if these features were consistent with the different light regimes in which the species live, depending on their sympatry or allopatry in lakes. Cone cell density in sympatric trout was over twice that of sympatric char and rod cell density was slightly less. The cross-sectional size of cone cells in sympatric trout was approximately 30% less than in sympatric char. The ratios of photoreceptor cells to ganglion cells in sympatric trout and char retinas were approximately 40:1 and 80:1, respectively. There were no differences between sympatric and allopatric trout with respect to these structural features. Estimates of cone cell density, cone size, and number of photoreceptor cells per ganglion cell for allopatric char were significantly different and intermediate between those for sympatric trout and char. All four populations had similar cone cell mosaics with four paired cones surrounding each single cone. Results are considered in relation to differences in vertical distribution and feeding of sympatric and allopatric populations in three study lakes.

Comparison of allopatric cutthroat trout stocks with those sympatric with coho salmon and sculpins in small streams

Juvenile stocks of allopatric (upstream of barrier falls) cutthroat troutSalmo clarki and those sympatric (downstream of barrier falls) with coho salmonOncorhynchus kisutch and sculpinsCottus spp., were sampled during the late summer period of low flows in six small coastal streams in British Columbia. The objective was to obtain and compare information on pattern of habitat use and fish size distribution of these two trout types. In most instances, density (n m−2; g m−2) of cutthroat trout was considerably greater in pools and glides in the allopatric than in the sympatric stocks. The sympatric salmonids were dominated by juvenile coho salmon in pools and cutthroat trout in riffles. Sympatric cutthroat trout constituted from 7 to 45 % of the salmonids present in pools and from 50 to 90% in riffles. Glides were areas of intermediate densities for both salmonids, although coho salmon was the more abundant species in most instances. The density of sculpins was high in all three habitat types, and frequently it exceeded that of coho salmon and cutthroat trout combined. Sympatric cutthroat trout consisted primarily of underyearling fish, whereas allopatric cutthroat trout consisted primarily of two or more age classes with a large proportion of them living in pools. When tested in a laboratory stream both types of cutthroat trout had similar habitat preferences and agonistic behaviours, with the exception that allopatric trout made greater use of cover and defended pools more intensely than sympatric trout when the flow was increased. The results of this study provide insight of potential impact of coho salmon juvenile transplants into stream segments supporting allopatric cutthroat trout.

Resource partitioning between brook trout (Salvelinus fontinalis Mitchill) and creek chub (Semotilus atromaculatus Mitchill) in selected oligotrophic lakes of southern Quebec

The spatial distribution, food habits, and growth of an allopatric brook trout (Salvelinus fontinalis) population was compared with a trout population coexisting with creek chub (Semotilus atromaculatus). Sympatric trout differed in spatial distribution and food habits from allopatric trout suggesting a niche shift of the trout when they live with creek chub. Also, although there is a certain overlap in diet and spatial distribution, sympatric populations of the two species differed on these resource axes. However, growth of sympatric trout is not clearly related to the presence or absence of the creek chub, suggesting that factors other than interspecific competiton may affect growth in the seven study lakes.