Changes in the pattern of feeding of kokanee <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> from Lake Tolmachevskoe during the formation of its population

Analysis of the feeding of kokanee Oncorhynchus nerka from Lake Tolmachevskoe, which was relocated here from Lake Kronotskoe more than 20 years ago, was studied. Lake Kronotskoe is inhabited by two forms of kokanee that differ in the pattern of feeding (plankton-eaters and benthos-eaters) and some morphological characters. According to the number of rakers at the first gill arch, kokanee from Tolmachevskoe Lake corresponds to plankton-eaters from Kronotskoe Lake; however, in the target water body, only single fish and only in the autumn period feed on plankton. The bulk of feeding is comprised of larger organisms: in summer of insect imagines and in autumn of benthos. Feeding of large and small fish in different areas of the lake from July to September is characterized. The change in the lake ecosystem related to the construction of Tolmachevskaya Hydraulic Power Plant and the formation of the reservoir apparently affected the pattern of fish feeding from 2003 to 2007, the number of prey in stomachs and the stomach fullness index considerably decreased, and the proportion in the food bolus of nonfood items, mainly plant remains, drastically increased.     

Formation of scale structure in lacustrine sock-eyed salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> from water bodies of Kamchatka and determination of its age

The formation of the first annual zone in three populations of resident sock-eyed salmon—kokanee Oncorhynchus nerka of Kamchatka—has been studied. The length of fingerlings in mid-August did not reach 30 mm; in most analyzed juveniles, the remains of the yolk sac were present. In early September in lakes Tolmachevskoe and Kronotskoe, the length of the fingerlings was about 40 mm. The scales in fish from different populations begin to form in early September. Towards November, no more than nine sclerites are formed; a similar amount has been recorded at the beginning of summer also in fingerlings. When scales of adult fish are studied, there are 4 to 19 sclerites in the first annual zone. Apparently, the first annual ring does not form in a considerable portion of fingerlings.     

Results of the introduction of the resident form of nerka <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> in Tolmachevskoe Lake (Kamchatka)

Data on the present-day (2003–2007) state of the population of kokanee Oncorhynchus nerka introduced in Tolmachevskoe Lake more than 20 years ago are provided. Since the moment of introduction, the population of kokanee has underwent considerable changes: a decrease occurred in the specific rate of growth, average length and weight of fish in catches, and fecundity. The pattern of feeding changed from planktonic to benthic. Kokanee began to feed during spawning. Spawning shifted to later dates (from the beginning of September to the end of September and beginning of October).     

Ecology of Slaty-Backed Gull (<Emphasis Type="Italic">Larus schistisagus</Emphasis>) Breeding on Kronotskoe Lake,Kamchatka Peninsula

The slaty-backed gull population of Kronotskoe Lake has not been subjected to anthropogenic impact for many decades. The number and distribution of the breeding colonies of the slaty-backed gulls on the islands of this largest freshwater reservoir of the Kamchatka Peninsula are presented. Data on the breeding phenology, the seasonal dynamics of the food composition of breeding gulls, the foraging distance, and breeding success are considered. These data are compared to the results obtained earlier for Kuril’skoe Lake. Both gull populations are unique in that they are the only freshwater colonies within the distribution range of this marine species. The breeding success of the slaty-backed gulls on Kronotskoe Lake suffers from predation, both intra- and interspecific, in the latter case from brown bears and sea eagles. The hatching period and the fledging time of chicks in this population are both shifted to the end of summer, when gulls have the most abundant food available within the lake area, which increases successful survival of the fledglings. Despite considerable differences between the ecosystems of Kronotskoe Lake and Kuril’skoe Lake, there are several common features in the diets of the gull populations living on the lakes: (1) Despite the fact that gulls perform foraging flights to the sea coast, they only take fish and almost never collect marine invertebrates there. (2) Nearly half of all food items are taken within a 40-km distance from the colony. (3) During the growth period of chicks, gulls from both lakes rely on salmonids (anadromous in Kuril’skoe Lake, resident in Kronotskoe Lake) that they hunt in the lakes near their colonies.     

Genetic diversity of sockeye salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> Walbaum of Kamchatka and the Commander Islands based on analysis of the variability of microsatellite DNA

The genetic diversity of the resident and migratory forms of sockeye salmon is investigated in 14 populations from various water bodies of Kamchatka and the Commander Islands by ten loci of microsatellite DNA. There are considerable differences in the frequencies of alleles among the populations of kokanee from Lake Kronotskoe, the residual form of sockeye salmon from Lake Kopylie, and other populations analyzed. Clustering of samples corresponds to their geographic position. No differences in the frequencies of alleles of the investigated loci are found between two forms of resident sockeye salmon from Kronotskoe Lake. In the sockeye salmon from the Commander Islands, a relatively low genetic diversity is found, as well as the greatest remoteness from the other Kamchatka group.     

The state of gonads of resident sockeye salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> from the Tolmachev Reservoir

Morphology of gonads and structure of sex cells in females and males of the resident sockeye salmon Oncorhynchus nerka—kokanee—from Tolmachevskoe Reservoir are investigated. Anomalies in structure of sex cells and structure of oocytes are found. Partial or mass resorpbion of cells in the ovaries of males and testes of males is found, leading to sterility of gonads. The relationship between anomalies found in structure of the sex system of kokanee, changes in biological parameters of fish and the increase of the population abundance is discussed.     

Variability of kokanee and rainbow trout food habits,distribution, and population dynamics,in an ultraoligotrophic lake with no manipulative management

Crater Lake is a unique environment to evaluate the ecology of introduced kokanee and rainbow trout because of its otherwise pristine state, low productivity, absence of manipulative management, and lack of lotic systems for fish spawning. Between 1986 and 2004, kokanee displayed a great deal of variation in population demographics with a pattern that reoccurred in about 10 years. We believe that the reoccurring pattern resulted from density dependent growth, and associated changes in reproduction and abundance, driven by prey resource limitation that resulted from low lake productivity exacerbated by prey consumption when kokanee were abundant. Kokanee fed primarily on small-bodied prey from the mid-water column; whereas rainbow trout fed on large-bodied prey from the benthos and lake surface. Cladoceran zooplankton abundance may be regulated by kokanee. And kokanee growth and reproductive success may be influenced by the availability of Daphnia pulicaria, which was absent in zooplankton samples collected annually from 1990 to 1995, and after 1999. Distribution and diel migration of kokanee varied over the duration of the study and appeared to be most closely associated with prey availability, maximization of bioenergetic efficiency, and fish density. Rainbow trout were less abundant than were kokanee and exhibited less variation in population demographics, distribution, and food habits. There is some evidence that the population dynamics of rainbow trout were in-part related to the availability of kokanee as prey.     

Microsatellite DNA Data Indicate Distinct Native Populations of Kokanee, Oncorhynchus nerka, Persist in the Lake Sammamish Basin, Washington

Large-scale introductions of resident and anadromous salmonids from exogenous sources and urbanization have led to major changes in, and concern for the fate of, indigenous fish populations of the Lake Sammamish/Lake Washington Basin. Specifically, introductions of kokanee (the resident form of Oncorhynchus nerka) from the Lake Whatcom Hatchery and sockeye (the anadromous form of O. nerka) from Baker Lake have caused uncertainty about the ancestry of the kokanee that currently spawn in the basin. We used nine microsatellite loci to investigate the inter-relationships of kokanee populations that spawn in streams in the Sammamish sub-basin, sockeye salmon populations that share spawning areas with the kokanee, Lake Whatcom Hatchery kokanee and Baker Lake sockeye, and an outgroup, Meadow Creek kokanee, from Lake Kootenay which drains into the upper Columbia River. We observed high levels of genetic variation (5–49 alleles per locus). Explicit tests of population sub-division revealed that collections from most spawning aggregations differed from each other. Observed allele frequency distributions strongly suggest that natural spawning kokanee in the basin are not descended from recent Lake Whatcom stock introductions. We found no compelling evidence to suggest that the kokanee sampled from spawning areas within the Lake Sammamish sub-basin have resulted from, or been altered substantially by, past introductions of non-native kokanee or sockeye.     

Genetic structure and diversity of Japanese kokanee Oncorhynchus nerka stocks as revealed by microsatellite and mitochondrial DNA markers

Genetic structure and diversity of nine Japanese kokanee (landlocked) Oncorhynchus nerka stocks and anadromous O. nerka from the North Pacific and the Canadian Lake Cultus population were examined using microsatellite and mitochondrial DNA. Sequence analyses of the cytochrome b region of mtDNA for Japanese kokanee O. nerka stocks on Honshu and Hokkaido islands revealed that most Japanese stocks were monomorphic of one major haplotype, which was also dominant in the Lake Cultus population and anadromous O. nerka in the North Pacific. Assignment tests using microsatellite DNA revealed that there was no clear-cut population structure in Japanese kokanee O. nerka stocks.     

Basic description and some notes on the evolution of seven sympatric morphs of Dolly Varden Salvelinus malma from the Lake Kronotskoe Basin

The study examines the basic morphological and ecological features of Dolly Varden from Lake Kronotskoe (Russia, Kamchatka). Seven valid morphs different in head proportions, feeding, timing, and place of spawning have been determined in this ecosystem. The basic morphometric characteristics clearly separate Lake Kronotskoe morphs from each other, as well as from its potential ancestor (Dolly Varden). According to CVA analysis, the most notable morphological characteristics determining the mouth position are the length of a lower jaw and rostrum. Furthermore, five of seven morphs inhabit different depth zones of the lake and feed on different food resources. Our data suggest that reproductive isolation may be maintained by temporal/spatial isolation for two morphs with lacustrine spawning, and by spatial isolation only for the rest of the morphs with riverine spawning. The sympatric diversity of the Lake Kronotskoe charrs is exceptionally wide, and there are no other examples for seven sympatric morphs of genus Salvelinus to coexist within a single ecosystem. This study puts forward a three‐step hypothetical model of charr divergence in Lake Kronotskoe as a potential ground for future studies.     

Postglacial genetic differentiation of reproductive ecotypes of kokanee Oncorhynchus nerka in Okanagan Lake, British Columbia

Okanagan Lake, south-central interior of BC, contains two reproductive ecotypes of kokanee Oncorhynchus nerka ; individuals spawn in tributary streams ('stream-spawners') as well as on shoreline gravel areas ('beach-spawners'). We tested the hypothesis that these sympatric ecotypes comprise a single panmictic population by assaying variation in morphological traits and at allozyme, mitochondrial and minisatellite DNA loci in fish collected from three stream-spawning and two beach-spawning sites. No morphological traits consistently distinguished the reproductive ecotypes with the exception of the number of anal fin rays which was greater in stream-spawning kokanee. Four of 18 allozyme loci screened were polymorphic, but no significant allele frequency differences were detected among populations within ecotypes or between ecotypes. Similarly, allele frequencies at two minisatellite DNA loci were not significantly different among populations or between ecotypes. By contrast, significant differences in the frequencies of mitochondrial DNA restriction fragment length polymorphism (mtDNA RFLP) haplotypes were detected between stream- and beach-spawners, but not among populations within ecotypes. Further, two RFLPs that distinguished stream- and beach-spawning adults were found in juvenile kokanee sampled from the limnetic zone of Okanagan Lake. The two mtDNA RFLPs and a d-loop sequence variant appear to be unique to Okanagan Lake kokanee because we did not observe these haplotypes in sockeye salmon and kokanee sampled outside of Okanagan Lake. Our data suggest that: (i) there is restricted female-mediated gene flow between stream- and beach-spawning kokanee in Okanagan Lake, (ii) the forms have diverged within the lake basin since the retreat of the Wisconsinian glaciers (< ≊ 11 000 years ago), and (iii) distinct reproductive niches may promote divergence in north temperate freshwater fish faunas.     

Salmonid predator–prey dynamics in Lake Pend Oreille,Idaho, USA

Our objective was to evaluate the long-term sustainability of lake trout Salvelinus namaycush and rainbow trout Oncorhynchus mykiss populations subjected to a range of fishing mortality (F) in Lake Pend Oreille, Idaho, USA, while providing for bull trout Salvelinus confluentus and kokanee Oncorhynchus nerka recovery. In order to achieve our objective, we developed a density-dependent stochastic predator–prey simulation model for the three major predators (lake trout, rainbow trout, and bull trout) on kokanee in Lake Pend Oreille. As F increased from 0.0 to 1.0, lake trout numbers in 2015 declined 90% for gillnetting, 76% for angling, and 48% for trap netting. At fishing mortality rates observed in Lake Pend Oreille during 2006, all methods combined and angling alone suppressed the lake trout population, but not gillnetting or trap netting alone. As F increased from 0.0 to 0.3, rainbow trout numbers in 2015 declined by 38%. Abundance of adult bull trout increased by 5.8% per year during 1996–2006, after implementation of no-kill regulations, which met the Federal Recovery Plan criterion of a stable or increasing trend in abundance. By 2010, total consumption of kokanee by lake trout, rainbow trout, and bull trout would increase by 20% if fishing mortality on lake trout and rainbow trout declined by 30% from 1996 levels, and would decrease by 14% if fishing mortality on lake trout and rainbow trout increased by 30% from 1996 levels. At rates of fishing mortality exerted on lake trout and rainbow trout in 2006, the likelihood of kokanee collapse was 65% within the next decade. Therefore, fishing mortality would need to be at least 6% higher on both lake trout and rainbow trout to reduce the likelihood of kokanee collapse to 50%. We conclude that kokanee biomass is presently out of balance with predation in Lake Pend Oreille, because kokanee production cannot compensate for all predation loss. Our findings suggest that a combination of unusually high kokanee production and unusually low predation are likely needed for kokanee to survive the next decade in Lake Pend Oreille.     

Ecological differentiation of resident Dolly Varden <Emphasis Type="Italic">Salvelinus malma</Emphasis> (Salmonidae) from Lake Dal’nee,Kamchatka

Resident Dolly Varden Salvelinus malma of Lake Dal’nee (Paratunka River basin) is represented by two stable trophic groups: one group feeds on mainly amphipods while another on gastropods. The former group is dominantly infected by Cyathocephalus truncatus and Crepidostomum metoecus, whereas the latter group is infected with Crepidostomum farionis, Ichthyocotylurus erraticus, and Diplostomum spp. The fishes of the former group grow faster and defined by higher fat content of muscular tissue. In addition, they accumulate monoenic fatty acids in the muscles. The fishes of the latter group differ in a high content of omega-3 and omega-6 fatty acids in the muscles. The amphipod foragers are characterized by a larger head with elongated upper jaw and comparatively short fins. A similar ecological differentiation is observed in the littoral benthivorous charrs from Lake Kronotskoe. The group feeding on amphipods was found in both lakes. In Lake Kronotskoe, the second group consumes the most abundant sedentary benthos, mollusks and chironomids.     

Comparative biological characteristics of zander <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.) in Lakes Onega and Vygozero

The work on the introduction of the zander Sander lucioperca (L.) from Lake Onega to Lake Vygozero is reviewed. A comparative analysis is performed for the biological parameters of zander from these lakes. The zander population from Lake Vygozero differs from that of Lake Onega in its lower growth rate, later maturation, and lower fat content of internal organs; these differences are determined by the limnological parameters and food supplies of both waterbodies.     

Comparative age and growth of Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis> L.) in lakes Nabugabo and Wamala,Uganda

Age and growth of Nile tilapia (Oreochromis niloticus) from Lake Nabugabo and Lake Wamala, Uganda, were determined using cross-sectioned sagittal otoliths. Marginal-increment and edge analyses of Nile tilapia otoliths from Lake Nabugabo indicated formation of two annuli per 12-month period. Opaque zones associated with faster growth were observed between April and June and between September and December, coincident with the two rainy seasons of the year. Within both lakes, males were larger at age than females. Nile tilapia from Lake Nabugabo, however, had faster growth rates than Nile tilapia from Lake Wamala, and fish >3 years old from Lake Nabugabo were larger at age than those from Lake Wamala. Ages ranged from 0 to 8.0 years for Nile tilapia from Lake Nabugabo, and from 0.5 to 6.5 years for tilapia from Lake Wamala. Differences in the patterns of growth in Nile tilapia between lakes may reflect, at least in part, the relatively energy-rich omnivorous diet of Nile tilapia in Lake Nabugabo versus a phytoplanktivorous diet in Lake Wamala. Diet differences of Nile tilapia between the two lakes are ascribed to trophic changes in the lakes due to the introduction of Nile perch (Lates niloticus) into Lake Nabugabo but not Lake Wamala. Alternatively, the greater exploitation of Nile tilapia in Lake Nabugabo may have resulted in increased growth rates, whereas Nile tilapia in Lake Wamala may be subject to slower, density-dependent growth. Handling editor: J. Cambray     

Resurrecting an extinct salmon evolutionarily significant unit: archived scales, historical DNA and implications for restoration

Archival scales from 603 sockeye salmon (Oncorhynchus nerka), sampled from May to July 1924 in the lower Columbia River, were analysed for genetic variability at 12 microsatellite loci and compared to 17 present‐day O. nerka populations—exhibiting either anadromous (sockeye salmon) or nonanadromous (kokanee) life histories—from throughout the Columbia River Basin, including areas upstream of impassable dams built subsequent to 1924. Statistical analyses identified four major genetic assemblages of sockeye salmon in the 1924 samples. Two of these putative historical groupings were found to be genetically similar to extant evolutionarily significant units (ESUs) in the Okanogan and Wenatchee Rivers (pairwise F_ST = 0.004 and 0.002, respectively), and assignment tests were able to allocate 77% of the fish in these two historical groupings to the contemporary Okanogan River and Lake Wenatchee ESUs. A third historical genetic grouping was most closely aligned with contemporary sockeye salmon in Redfish Lake, Idaho, although the association was less robust (pairwise F_ST = 0.060). However, a fourth genetic grouping did not appear to be related to any contemporary sockeye salmon or kokanee population, assigned poorly to the O. nerka baseline, and had distinctive early return migration timing, suggesting that this group represents a historical ESU originating in headwater lakes in British Columbia that was probably extirpated sometime after 1924. The lack of a contemporary O. nerka population possessing the genetic legacy of this extinct ESU indicates that efforts to reestablish early‐migrating sockeye salmon to the headwater lakes region of the Columbia River will be difficult.     

Organochlorine Pesticides and Polychlorinated Biphenyls in Tissues of Landlocked Kokanee Salmon from Tolmachevskoye Reservoir,Kamchatka

Concentrations of organochloride pesticides (OCPs) and polychlorinated biphenyls (PCBs) that were obtained in landlocked kokanee salmon (Oncorhynchus nerka kennerlyi) from the Tolmachevskoye Reservoir, Kamchatka, correspond to the levels found in freshwater bodies of background areas around the world. The spatial distribution of PCBs and OCPs in kokanee at the spawning ground and in the deepwater part of the reservoir, as well as its distribution in the kokanee organs, indicate the atmospheric input of contaminants and the ongoing technogenic impact, which was generated during the establishment and operation of the Tolmachevskoye Reservoir. The contaminants that enter from these sources into the water column are incorporated into the food web of the water body. The permissible consumption of kokanee fillet from the Tolmachevskoye Reservoir and caviar from red salmon from the Kuril Lake by population is 10–26 kg and 1.2 kg per year respectively.     

Effectiveness of lake trout (Salvelinus namaycush) suppression in Lake Pend Oreille,Idaho: 2006–2016

The nonnative lake trout (Salvelinus namaycush Walbaum, 1792) population in Lake Pend Oreille, Idaho increased exponentially during 1999–2006. This led to an unsustainable level of predation mortality on kokanee (Oncorhynchus nerka Walbaum, 1792), increased the conservation threat to native bull trout (Salvelinus confluentus Suckley, 1859), and jeopardized the popular recreational fishery for kokanee and rainbow trout (Oncorhynchus mykiss Walbaum, 1792). In response, lake trout were suppressed since 2006 using incentivized angling, gill netting, and trap netting. From 2006 through 2016, 193,982 lake trout were removed (50% by gill netting; 44% by angling; 6% by trap netting). During this period, age-8 + (adult) lake trout abundance declined by 64%, age-3 (recruit) abundance declined by 56%, and mean total annual mortality (A) was 31.1%. Lake trout did not show evidence of a density-dependent response. Kokanee did not collapse and rebounded to abundances not observed since before lake trout expansion. Bull trout abundance declined during suppression, but the population was sustained. Lake trout suppression allowed a harvest fishery for kokanee and trophy fishery for rainbow trout to be restored. We conclude that suppression can be an effective management action for mitigating effects of nonnative lake trout in a large, deep lake.

     

Lack of parallel genetic patterns underlying the repeated ecological divergence of beach and stream‐spawning kokanee salmon

Recent progress in methods for detecting adaptive population divergence in situ shows promise for elucidating the conditions under which selection acts to generate intraspecific diversity. Rapid ecological diversification is common in fishes; however, the role of phenotypic plasticity and adaptation to local environments is poorly understood. It is now possible to investigate genetic patterns to make inferences regarding phenotypic traits under selection and possible mechanisms underlying ecotype divergence, particularly where similar novel phenotypes have arisen in multiple independent populations. Here, we employed a bottom‐up approach to test for signatures of directional selection associated with divergence of beach‐ and stream‐spawning kokanee, the obligate freshwater form of sockeye salmon (Oncorhynchus nerka). Beach‐ and stream‐spawners co‐exist in many post‐glacial lakes and exhibit distinct reproductive behaviours, life‐history traits and spawning habitat preferences. Replicate ecotype pairs across five lakes in British Columbia, Canada were genotyped at 57 expressed sequence tag‐linked and anonymous microsatellite loci identified in a previous genome scan. Fifteen loci exhibited signatures of directional selection (high F_ST outliers), four of which were identified in multiple lakes. However, the lack of parallel genetic patterns across all lakes may be a result of: 1) an inability to detect loci truly under selection; 2) alternative genetic pathways underlying ecotype divergence in this system; and/or 3) phenotypic plasticity playing a formative role in driving kokanee spawning habitat differences. Gene annotations for detected outliers suggest pathogen resistance and energy metabolism as potential mechanisms contributing to the divergence of beach‐ and stream‐spawning kokanee, but further study is required.     

Influences of Lake Trout (Salvelinus namaycush) and Mysis diluviana on kokanee (Oncorhynchus nerka) in Lake Pend Oreille,Idaho

Research on Lake Pend Oreille, Idaho, has focused on the influence of two potential limiting factors for kokanee Oncorhynchus nerka (Walbaum, 1792): competition for food with Mysis diluviana (Loven, 1862, hereafter Mysis) and predation by lake trout Salvelinus namaycush (Walbaum, 1792). Population fluctuations of Mysis and lake trout have resulted in substantial heterogeneity in food web conditions, apparently altering both bottom-up and top-down dynamics. Therefore, relative importance of predation and competition were evaluated as drivers of kokanee abundance, biomass, and production. A series of general linear models was used to evaluate relative influences of Mysis and lake trout on kokanee. Kokanee production was a density-dependent process and the collapse of Mysis corresponded to an increase in the modeled maximum annual production of kokanee from 224 tonnes to 408 tonnes. Lake trout also negatively influenced kokanee biomass. A Mysis-mediated, predator-induced kokanee biomass collapse occurred when lake trout and Mysis abundances were both high. Sustainable management of this fishery requires recognition that competition with Mysis will define the scope of kokanee production and therefore the scope of sustainable predation.