Lake Populations Research Articles

Contemporary Growth and Survival of Stocked and Wild Lake Trout in Lake Champlain Evaluated Using Maxillary Age Estimates

AbstractThe population of Lake Trout Salvelinus namaycush in Lake Champlain has been sustained by stocking since 1973, but natural recruitment of wild fish has been observed since 2012. By 2020, continued recruitment and maturation of wild year‐classes indicated that updated population parameters were needed to assess and adjust management practices. Age estimation from historical methods (fin clips and scales) was undependable due to crowding of annuli in older fish and the inability to verify uncertain age estimates using a 5‐year fin clip rotation for older fish. We used maxillary bones to obtain precise and accurate age estimates for adult wild and stocked fish. In combination with preadult ages derived from fin clips and length–frequency analysis, we estimated the contemporary survival and growth of juvenile (age 2–3), early‐adult (age 3–4), and adult (age 5+) Lake Trout in Lake Champlain. The precision and accuracy of our maxillary age estimates were greater than or comparable to the precision and accuracy of otolith and maxillary age estimates of Lake Trout populations in the Great Lakes. Estimates of Lake Trout growth suggested that stocked and wild fish grew at different rates, with stocked fish having an early size advantage but ultimately reaching a similar maximum size. There were no significant differences in length–weight relationships between stocked and wild fish. Estimates of adult survival were slightly greater than range‐wide averages and well above recent estimates for stocked populations in the Great Lakes. Juvenile and early‐adult survival estimates were similar to each other and both far lower than adult estimates. Stocked and wild fish had similar survival rates in all age‐classes. Ultimately, the use of maxillary bones allowed us to make better estimates of contemporary population parameters necessary for informing management decisions.

Genetic population structure of cisco, Coregonus artedi, in the Laurentian Great Lakes

Management of a widely distributed species can be a challenge when management priorities, resource status, and assessment methods vary across jurisdictions. For example, restoration and preservation of coregonine species diversity is a goal of management agencies across the Laurentian Great Lakes. However, management goals and the amount of information available varies across management units, making the focus for management efforts challenging to determine. Genetic data provide a spatially consistent means to assess diversity. Therefore, we examined the genetic stock structure of cisco (Coregonus artedi) in the Great Lakes where the species is still extant. Using genotype data from 17 microsatellite DNA loci, we observed low levels of population structure among collections with most contributions to overall diversity occurring among lakes. Cisco from lakes Superior, Michigan, Ontario, and the St. Marys River could be considered single genetic populations while distinct genetic populations were observed among samples from northern Lake Huron. Significant within-lake diversity in Lake Huron is supported by populations found in embayments in northern Lake Huron. The Grand Traverse Bay population in Lake Michigan represents a distinct population with reduced levels of genetic variation when compared to other lakes. The different levels of within lake population structure we observed will be important to consider as future lake-specific management plans are developed.

Sensitivity analysis of a lake sturgeon population with early life stage density-dependent effects

Lake sturgeon ( Acipenser fulvescens) exhibit a complex life-history strategy where behaviour, including habitat selection, depends on ontogenetic stage. Protection or recovery efforts for one stage may not impact other stages. Stage-structured models have been used to explore the sensitivity of the population to changes in vital rates of individual stages. Recent research demonstrates that juvenile mortality may be lower than estimated in prior modelling efforts and density-dependent. We constructed a Lefkovitch matrix model to reflect an updated understanding of the prerecruitment stages of the lake sturgeon. We then compared the model to a population of lake sturgeon on the Ontario−Minnesota border. Our model predicts that population growth rate, time to equilibrium, and final population size were most sensitive to changes to the survival of early adults, followed by subadults and juveniles. Sensitivity to changes in age-0 survival was very low in contrast to earlier modelling efforts, while sensitivities to juvenile (ages 1–7 years) and subadult (ages 8–23 years) were higher than previously reported values.

Genomic Signatures of Freshwater Adaptation in Pacific Herring (Clupea pallasii).

Pacific herring (Clupea pallasii) is an essential target of commercial fishing in the North Pacific Ocean. Previous studies have suggested the existence of marine and lake ecological forms of this species within its range. The lake ecological form of herring has a shortened life cycle, spending the winter and spawning in brackish waters near the shoreline without long migrations for feeding; it also has a relatively smaller body size than the marine form. Genetic-based studies have shown that brackish water Pacific herring not only can be distinguished as a separate lake ecological form but possibly has its genetic legacy. Here, as part of an ongoing study, using ddRAD-sequencing data for marine and lake ecological forms from a total of 54 individuals and methods of comparative bioinformatics, we describe genomic signatures of freshwater adaptivity in Pacific herring. In total, 253 genes containing discriminating SNPs were found, and part of those genes was organized into genome clusters, also known as “genomic islands of divergence”. Moreover, the Tajima’s D test showed that these loci are under directional selection in the lake populations of the Pacific herring. Yet, most discriminating loci between the lake and marine ecological forms of Pacific herring do not intersect (by gene name) with those in other known marine fish species with known freshwater/brackish populations. However, some are associated with the same physiological trait—osmoregulation.

Sea Lamprey Alarm Cue Comprises Water- and Chloroform- Soluble Components

A diversity of aquatic organisms manage predation risk by avoiding waters activated with conspecific alarm cues, a chemical mixture released from injuries. The sea lamprey (Petromyzon marinus) is a nocturnal migratory species that relies on its alarm cue to navigate around areas of predation risk when moving through river channels. Identification of the cue’s chemistry would allow managers to harness this innate behavioral response to guide migrating sea lamprey to traps (invasive population in the Laurentian Great Lakes) or to fish passage devices where dams block migrations in their native range. We pursued isolation of the sea lamprey alarm cue through behaviorally guided fractionation, fractionating the alarm cue into water-soluble and chloroform-soluble fractions, each of which elicited a substantial avoidance response. Recombining the two fractions restored full reactivity, suggesting the alarm cue mixture contains components that exhibit high solubility in water (e.g., nitrogenous compounds), chloroform (e.g., lipids), or perhaps materials that dissolve readily in either solvent. We further screened 13 individual compounds or pure isolates and 6 sub-fractions from the water-soluble fraction and found one of the pure isolates, isoleucine, evoked an avoidance response on its own, but not consistently when found in other mixtures. In a third experiment, we observed no behavioral response after recombining 32 compounds isolated and identified from the water-soluble fraction. These results confirm other suggestions that the process of elucidating alarm cue constituents is challenging. However, we suggest the pursuit is worthwhile given the strong evidence for the utility of alarm cues for use in the conservation and management of fishes and other aquatic organisms.

High-density genomic data reveal fine-scale population structure and pronounced islands of adaptive divergence in lake whitefish (Coregonus clupeaformis) from Lake Michigan.

Understanding patterns of genetic structure and adaptive variation in natural populations is crucial for informing conservation and management. Past genetic research using 11 microsatellite loci identified six genetic stocks of lake whitefish (Coregonus clupeaformis) within Lake Michigan, USA. However, ambiguity in genetic stock assignments suggested those neutral microsatellite markers did not provide adequate power for delineating lake whitefish stocks in this system, prompting calls for a genomics approach to investigate stock structure. Here, we generated a dense genomic dataset to characterize population structure and investigate patterns of neutral and adaptive genetic diversity among lake whitefish populations in Lake Michigan. Using Rapture sequencing, we genotyped 829 individuals collected from 17 baseline populations at 197,588 SNP markers after quality filtering. Although the overall pattern of genetic structure was similar to the previous microsatellite study, our genomic data provided several novel insights. Our results indicated a large genetic break between the northwestern and eastern sides of Lake Michigan, and we found a much greater level of population structure on the eastern side compared to the northwestern side. Collectively, we observed five genomic islands of adaptive divergence on five different chromosomes. Each island displayed a different pattern of population structure, suggesting that combinations of genotypes at these adaptive regions are facilitating local adaptation to spatially heterogenous selection pressures. Additionally, we identified a large linkage disequilibrium block of ~8.5Mb on chromosome 20 that is suggestive of a putative inversion but with a low frequency of the minor haplotype. Our study provides a comprehensive assessment of population structure and adaptive variation that can help inform the management of Lake Michigan's lake whitefish fishery and highlights the utility of incorporating adaptive loci into fisheries management.

Demographic resilience of brook trout populations subjected to experimental size-selective harvesting.

Sustainable management of exploited populations benefits from integrating demographic and genetic considerations into assessments, as both play a role in determining harvest yields and population persistence. This is especially important in populations subject to size-selective harvest, because size selective harvesting has the potential to result in significant demographic, life-history, and genetic changes. We investigated harvest-induced changes in the effective number of breeders ( ) for introduced brook trout populations (Salvelinus fontinalis) in alpine lakes from western Canada. Three populations were subject to 3 years of size-selective harvesting, while three control populations experienced no harvest. The decreased consistently across all harvested populations (on average 60.8%) but fluctuated in control populations. There were no consistent changes in between control or harvest populations, but one harvest population experienced a decrease in of 63.2%. The / ratio increased consistently across harvest lakes; however we found no evidence of genetic compensation (where variance in reproductive success decreases at lower abundance) based on changes in family evenness ( ) and the number of full-sibling families ( ). We found no relationship between and or between / and . We posit that change in was buffered by constraints on breeding habitat prior to harvest, such that the same number of breeding sites were occupied before and after harvest. These results suggest that effective size in harvested populations may be resilient to considerable changes in Nc in the short-term, but it is still important to monitor exploited populations to assess the risk of inbreeding and ensure their long-term survival.

Biomonitoring Legacy and Emerging Contaminants and Local Fish Consumption in Susceptible Great Lakes Populations, 2010-2020

Biomonitoring Legacy and Emerging Contaminants and Local Fish Consumption in Susceptible Great Lakes Populations, 2010-2020

Freshwater adaptation in prickly sculpin (Pisces: Cottidae): intraspecific comparisons reveal evidence for water pH and Na+ concentration driving diversity in gill H+-ATPase and ion regulation

Phenotypic divergence is a hallmark of adaptive radiation. One example involves differentiation in physiological traits involved in ion regulation among species with contrasting lifestyles and living in distinct environments. Differentiation in ion regulation and its ecological implications among populations within species are, however, less well understood. To address this knowledge gap, we collected prickly sculpin (Cottus asper) from distinct habitat types including coastal rivers connected to estuaries, coastal lakes and interior lakes, all from British Columbia, Canada. We tested for differences in plasma Na+ and Cl-, gill Na+/K+-ATPase and H+-ATPase activity and protein abundance as well as changes in body mass and arterial blood pH in fish sampled from the field and acclimated to two different freshwater conditions in the laboratory: artificial lake water (ALW) and ion-poor water (IPW). We also tested for links between environmental water chemistry and the physiological characteristics associated with ion regulation. Transfer to IPW resulted in upregulation of gill Na+/K+-ATPase and H+-ATPase activity as well as increases in gill H+-ATPase protein expression level in each habitat compared with that in the common ALW treatment. Despite the presence of population-within-habitat-type differences, significant habitat-type effects were revealed in most of the ion regulation characteristics examined under different acclimation conditions. Significantly lower plasma Cl- was detected in fish from coastal rivers than in fish from the other two habitat types during the IPW treatment, which was also significantly lower compared with that in ALW. Similarly, gill Na+/K+-ATPase activity was lower in the coastal river populations in IPW than in fish from coastal and interior lakes, which was not in accordance with the protein expression in the gill. For gill H+-ATPase, fish from interior lake populations had the highest level of activity across all habitat types under all conditions, which was related to the protein levels in the gill. The activity of gill H+-ATPase was positively correlated with the combined effect of water Na+ and pH under the ALW treatment. Our results suggest that variation in habitat may be an important factor driving differences in gill Na+/K+-ATPase and H+-ATPase activity across populations of C. asper. Further, the combined effect of water Na+ and pH may have played a key role in physiological adaptation in C. asper during post-glacial freshwater colonization and dispersal.

Performance and ecological impacts of benthic barriers for the control of an invasive plant in a small urban lake

Yellow Floating Heart (YFH), Nymphoides peltata, is a rooted aquatic plant that is not native to North America, and can quickly establish nuisance populations in shallow lakes, rivers, and wetlands. There are few documented methods for effectively eradiating or controlling YFH. Little Albro Lake is a small (3 ha), shallow (<5 m deep) meso-eutrophic lake in Dartmouth, Nova Scotia, Canada that experiences an annual YFH infestation covering >50% of the lake during the growing season. A pilot study was conducted during the 2021 growing season to: (i) assess the feasibility of using benthic barriers to control YFH growth, and (ii) investigate the potential impacts of benthic barriers on ecosystem components. Two commercially available benthic barriers (Aquascreen, a permeable barrier, and Lake Bottom Blanket, an impermeable barrier) were tested in shallow (1 m water depth) and deep (3 m water depth) areas of the lake. A total of 18 test plots (6 permeable, 6 impermeable, 6 control), each measuring 3 m × 3 m, were established in early May 2021, and monitored throughout the growing season (May–September). Both types of barriers were effective in reducing YFH growth, with barriered plots possessing significantly less YFH coverage than control plots. Inspection of the permeable barriers after their removal from the lake, however, revealed that YFH had been able to grow through this type of barrier material. Several maintenance issues were also noted with both barriers including: (i) gas build-up under the barriers, which caused billowing, and (ii) an accumulation of sediment on top of the barriers and growth of YFH through these sediment layers. Both issues would need to be managed during a full-scale benthic barrier application program. An environmental effects monitoring program was also undertaken to understand the lake ecosystem and impacts of the barriers on the chemical and biological properties of the lakebed. The barriers had measurable impacts on the lakebed and generated lower oxidation reduction potential (ORP) in sediments, as compared to control plots with no barriers. Reduced ORP in lake sediments could facilitate the mobilization of redox-sensitive metals, such as arsenic and iron. There were only minor differences in benthic macroinvertebrate populations when comparing barriered and control plots. The bacterial alpha-diversity of the lakebed sediment was shown to differ by depth, with the shallow zone having higher observed ASVs and diversity levels. However, within the two depth zones, the barriers did not appear to have a large impact on bacterial community composition and potential functionality. In conclusion, benthic barriers can be used to prevent YFH growth, however barrier installations require maintenance and may reduce sediment ORP, potentially leading to release of redox-sensitive metals and nutrients.

Production and specific diversity of fish at the level of the Taabo dam lake (Ivory Coast, West Africa)

The management of fishery resources is a concern for managers of the fishing sector. The insufficiency of statistics in this sector is an obstacle to the sustainable management of fish. This study aimed at determining the fishing techniques, production and biological indices that characterize fishing in Taabo Lake. Data was collected from July 2019 to June 2020 in the Taabo-village station from surveys and analysis of fishermen's catches. Each identified specimen was weighed. The results of the study indicate seven fishing gears including conical fishing basket, castnets and gillnets with meshes smaller than the regulatory mesh. Purse seines and bamboo traps were specifically more selective (1 species). The seines have the annual catches (23,140 kg); CPUE (14.51 kg / exit); highest utilization (29%) and performance (46%) rates. An annual effort of 5501 fishing / trips for 50334.3 kg of fish caught characterized the fishing on Taabo Lake. This production is made up of 44 species belonging to 18 families. The Claroteidae family (47%) and the species Chrysichthys nigrodigitatus (46%) dominate the fish population of Taabo lake. This study provides our governments informations in their quest for the sustainable management of fishery resources.

In Silico Screening and Development of Microsatellite Markers for Genetic Analysis in Perca fluviatilis.

Simple SummaryPerca fluviatilis is an economically important species of freshwater fish that has flavorsome meat with a high nutritional value. Microsatellite markers are widely used in the genetic structure analysis of aquatic animals due to their abundance, high polymorphism, and codominance. In this study, we screened, tested, and developed polymorphic markers and evaluated the genetic diversity of the main wild P. fluviatilis populations in China. From the P. fluviatilis genomic data, 98,425 pairs of microsatellites were identified. A total of 200 primer pairs for tetranucleotide microsatellites were synthesized and tested in randomly selected wild individuals. Among them, 152 microsatellite markers were found to be polymorphic. A total of 29 markers with clear amplified bands and high polymorphism were selected for the genetic analysis of the four populations. The results indicated a high level of genetic diversity in P. fluviatilis populations in Wulungu Lake, Jili Lake, and the Wulungu River and a medium level of genetic diversity in the Kalaeerqisi River. There was moderate genetic differentiation among the populations in Xinjiang. The results of this study provide important information on the genetic diversity and genetic population structuring of P. fluviatilis in China as well as a scientific basis for the protection and molecular marker-assisted breeding of P. fluviatilis.Perca fluviatilis is an economically important species of freshwater fish. To understand the genetic structure of P. fluviatilis in China, 268 samples were collected from Wulungu Lake (WL), Jili Lake (JL), the Wulungu River (WR), and the Kalaeerqisi River (KR). These samples were then analyzed using microsatellite markers. A total of 98,425 microsatellite markers were developed based on the genomic data, and 29 polymorphic microsatellite markers were selected to analyze genetic diversity in this study. The number of alleles (Na) and observed heterozygosity (Ho) per population ranged from 4.621 (KR) to 11.172 (WL) and from 0.510 (KR) to 0.716 (JL), respectively. The results of the polymorphic information content (PIC) showed that the WL, JL, and WR populations were highly polymorphic (PIC ≥ 0.5) and that the KR population was moderately polymorphic (0.25 ≤ PIC < 0.5). The genetic differentiation coefficient (Fst) among the four P. fluviatilis populations was 0.074, indicating moderate genetic differentiation among the populations in Xinjiang. The reason for the significant difference between the rivers and lakes could be the presence of a dam blocking the flow of P. fluviatilis. The development of microsatellite markers provides support for population genetics in the future. The evaluation of the genetic structure of P. fluviatilis in Xinjiang provides a reference for the reproduction and conservation of P. fluviatilis.

Anthropogenic influences on genetic diversity and differentiation of the clearhead icefish (Protosalanx hyalocranius), as revealed by mitochondrial and microsatellite DNA markers

The clearhead icefish, Protosalanx hyalocranius, is an economically important fishery species in China. For the past few decades, the wild resources of P. hyalocranius have markedly decreased due to human activities such as overfishing, hydro-projects and water pollution. Meanwhile, P. hyalocranius has been widely introduced into lakes and reservoirs of northern China and some have become established, invasive populations, leading to detrimental effects on ecosystems. Using mitochondrial control region sequences and nine microsatellite DNA markers, the aim of this study was to assess to what extent human activities could impact the genetic diversity and population structure of P. hyalocranius, and explore the sources of the invasive Heilong River population based on genetic characterization. Based on mitochondrial DNA, the average haplotype diversity and nucleotide diversity among six populations were 0.737 and 0.0029 respectively. Based on microsatellite markers, the observed (HO) and expected (HE) heterozygosities in each population ranged from 0.481 to 0.565 and 0.478 to 0.565, respectively. Both mitochondrial and microsatellite markers indicated the genetic diversity in Chaohu Lake was the lowest. HO and HE of the two anadromous populations (Liao River Estuary and Yalu River Estuary) were close to Chaohu Lake and relatively low among all populations. The pairwise Dest values showed high and significant genetic differentiation between Taihu Lake and other populations. There was no evidence of genetic differentiation between Chaohu Lake and the two anadromous populations. No significant reduction of genetic diversity was observed in the Heilong River population. Bottleneck analysis showed that the two anadromous populations may have experienced a recent genetic bottleneck. DIYABC analysis suggested that the sources of the invasive Heilong River population were Taihu and Hongze lakes, with a greater genetic contribution from Hongze Lake. Therefore, the anadromous populations of P. hyalocranius may have suffered more impacts from human activities than the strictly freshwater populations. Among freshwater populations, Chaohu Lake should also be paid more attention in fisheries management. In addition, our study demonstrated that multiple introductions can give rise to high genetic diversity in an invasive population.

Evaluation of the Marine Bacterial Population in the Great Bitter Lake, Egypt, as a Source of Antimicrobial Secondary Metabolites

The ecological uniqueness of the Great Bitter Lake ecosystem makes its bacterial population interesting for investigation. Here, we present the first trial to evaluate the biosynthetic capacity of the bacterial population at the lake as a source of novel antimicrobials. We collected different samples from various locations throughout the lake including the oxic sediment, anoxic sediment, shore water, and off-shore water. We modified a molecular approach to compare and choose the samples with the highest bacterial biosynthetic capacity by quantifying the polyketide synthase gene clusters in their total community DNA. Furthermore, we screened the bacterial isolates recovered from these samples and their metabolic extracts for antimicrobial activity. We tried to tentatively investigate the identity of the active metabolites by PCR screening and LC–MS. The bacterial population in the oxic sediment had the highest biosynthetic capacity compared to other sample types. Four active Bacillus isolates were identified. The isolated Bacillus species were expected to produce numerous probable bioactive metabolites encoded by biosynthetic gene clusters related to the polyketide synthases (either individual or hybrid with non-ribosomal peptide synthetase), such as Bacillomycin D, Iturin A, Bacilosarcin B, Bacillcoumacin G and Macrolactin (N and G). These results suggest that the under-explored bacterial community of the Great Bitter Lake has a prospective biosynthetic capacity and can be a promising source for novel antibiotics.

Türkiye'nin güneybatısındaki istilacı Coptodon (Perciformes: Cichlidae): Dizi verileri kullanılarak tür tanımlaması

Nonnative cichlids (Coptodon zillii) have established populations in the Köyceğiz and Koca Lakes, located on the west coasts of Mediterranean Turkey. Conflicting species names in these lakes have been reported for many years. We studied samples from current populations of Coptodon in these lakes and the Pecenek canal concerning existing GenBank data. We estimated the possible ancestral population using sequence data in the mitochondrial D-loop segment. Inter and intra-population morphological variations of Coptodon were examined using 25 morphological and six meristic characters. Haplotype analysis revealed three unique haplotypes in three populations of Coptodon, indicating poor genetic diversity. Both maximum likelihood and Bayesian trees showed that these three haplotypes constitute a distinct subclade within the Coptodon zillii clade. This phylogenetic pattern indicates that populations of both lakes were founded by a single invasion of C. zillii and belong to a single species. Consistent with phylogenetic data, the populations of both lakes do not exhibit significant phenotypic divergence, though the Pecenek population is slightly divergent. Intra-population morphological variability may be due to phenotypic plasticity in response to habitat heterogeneity within the lakes.

Variation in growth, length and age characteristics of estuarine Acanthopagrus (Sparidae) populations in New South Wales, Australia

Knowledge of spatial variation in growth and demographic characteristics of exploited teleost populations is informative for understanding levels of resilience and susceptibility to environmental and anthropogenic perturbations and for resource management. This study investigated variation in length- and age-compositions, length-at-age and growth, longevity and mortality of Acanthopagrus (A. australis, A. butcheri and their hybrids) population complexes across seven estuaries spanning seven degrees of latitude in eastern Australia. Populations were sampled using two gears according to standardised fishery-independent survey protocols. Populations within each estuary displayed considerable variation in length-at-age, with sex-specific growth attributes evident in some estuaries but not others. Nevertheless, females dominated populations, and on average, the mean lengths and ages of females were greater than males within each estuary population. Estuary type and location appeared to influence the estuary-specific growth characteristics of both sexes, with populations in the southern coastal lakes having, on average, greater mean lengths at age and faster growth than those in the northern riverine estuaries. Length and age compositions of populations did not vary accordingly, with observed longevities and estimated natural mortalities varying among estuaries, most likely reflecting estuary-specific environmental conditions and anthropogenic activities. In general, populations across all estuaries primarily comprised fish <25 cm fork length (FL) and 10 years of age. Given their potential to reach FLs up to 50 cm and ages >20 years, populations across most estuaries appeared length and age truncated. Ecological relationships and resource management implications are discussed.

Population genetic dynamics during colonisation and establishment of an obligate parthenogenetic Daphnia pulex population in a small lake of a continental archipelago

Abstract Population genetic diversity and structure are known to influence successful colonisation and establishment of a population in a novel habitat. However, our understanding of actual population genetic changes in the early stage of colonisation and detailed time‐series of genetic changes during the establishment of a new population is still limited due to the difficulty of making long‐term direct observations of a colonising population. Using a paleolimnological approach, we revealed the long‐term genetic dynamics of an obligate parthenogenetic panarctic Daphnia pulex population during the early stage of colonisation and subsequent establishment in Lake Fukami‐ike of Nagano, Japan. We collected diapausing eggs in ephippia of D. pulex from layers of sediment core samples (c. 370 cm long; dated 1662–2017) and then the mitochondrial DNA was sequenced using the markers designed for the NADH dehydrogenase 5 (ND5) gene and the control region. Daphnia pulex colonised and established a population in the early 2000s. Population genetic analysis showed that one colonising haplotype predominated in the population throughout the study period. Genetic diversity was consistently limited and there was no recovery of genetic diversity after colonisation. Clearly limited genetic diversity did not hamper population growth, possibly because phenotypic plasticity was used to cope with changes in predation pressure. Analysis using multivariate auto‐regressive models showed that responses to environmental and ecological factors varied depending on the haplotype, which may have contributed to successful colonisation of the lake by the different haplotypes. The present results suggest that an obligate parthenogenetic population can establish in a new habitat and be maintained for generations even though it has limited genetic diversity. We found that two independent lineages (JPN1 and JPN2) successfully established and coexisted toward the end of the study period. Although limited genetic diversity did not impede colonisation success, how the later colonising JPN1 lineage has successfully invaded a population consisting solely of the early colonising JPN2 deserves future attention to understand the population genetic dynamics revealed in this study.

Dysfunctional information feedbacks cause the emergence of management panaceas in social-ecological systems: The case of fish stocking in inland recreational fisheries

Social-ecological systems are characterized by interconnections between social (e.g., angler communities) and ecological systems (e.g., fish populations in lakes and rivers). One means by which human actions feedback on ecosystems is through management actions, some of which are controversial due to the possible downsides for biodiversity and ecosystem functioning. In complex systems, sub-optimal management strategies may become entrenched. In such cases, leverage points must be identified to escape undesirable stable states. Based on a review of published and grey literature about the management practice of fish stocking in German inland recreational fisheries, we describe key pathways characterizing social-ecological interactions and resulting outcomes. The pathways we review suggest that missing or dysfunctional information feedbacks predispose privately governed fisheries-management systems typical of Germany to develop stocking as a panacea in operational management. Similar outcomes are likely in open access recreational fisheries. Three key feedback cycles reinforce each other to maintain stocking in the manager's toolbox. The first is that the lack of dedicated monitoring in many fisheries and ignorance of research results breaks a feedback signal from the management measure of stocking to the evaluation of outcomes. The lack of ability of those involved in stocking to conclusively learn when stocking works and when it fails to deliver additive effects reinforces personal norms by managers and anglers that stocking may be necessary to sustain fisheries. A related second feedback is that stocking may increase catch rates in the short-term, which increases angler expectations for catch and stocking as a safeguard of the catch, in turn fostering linear cause-and-effect mental models and the emergence of a pro-stocking social norm among anglers. A third key feedback is among hatchery operators and fisheries managers in fishing clubs, where hatchery operators are often key informants about stocking practices while concurrently having commercial interests to sell fish for stocking. This creates economic incentives that perpetuate stocking. The amount of resource investments by angler communities through stocking is additionally fostered and maintained by monetary resource availability, size and type of ecosystem that is managed and governance processes as well as political inertia. Thus, the maintenance of stocking as a panacea is intimately linked to a range of psychological, social, economic and governance drivers. We use our case study to illustrate how information-related feedback loops can trap natural resource management strategies into a suboptimal basin of attraction, and provide recommendations on leverage points to possibly break these loops. Collaborative active adaptive management of natural resources and reducing the temptation to rely on economic incentives by hatcheries may be needed to introduce possibilities for learning and thereby avoid the entrenchment of stocking and related activities as a panacea. The lessons learned around stocking are applicable to a range of social-ecological issues in recreation and planning whenever feedback flows of information are critical to direct management and when these flows are either distorted by disinformation, wrong incentives or not present at all. The study has several implications for fisheries and natural resource management:-Establishment of regular monitoring systems that are trusted by stakeholder can be recommended and is key to break dysfunctional information feedbacks and move social-ecological systems, such as recreational fisheries, on more sustainable trajectories.-Changing fish stocking under private fishing right systems can happen either through bottom-up approaches based on co-production of knowledge and using principles of adaptive management or from the top-down by implementing hard constraints on the possibility for self-organized stocking policies.-The former strategy will be more time-consuming and may fail in some situations, but is likely to create less conflicts and more durable outcomes from a social perspective.-Alternative to fish stocking, such as improvement of habitats or harvest constraints, should be considered whenever feasible. Establishment of regular monitoring systems that are trusted by stakeholder can be recommended and is key to break dysfunctional information feedbacks and move social-ecological systems, such as recreational fisheries, on more sustainable trajectories. Changing fish stocking under private fishing right systems can happen either through bottom-up approaches based on co-production of knowledge and using principles of adaptive management or from the top-down by implementing hard constraints on the possibility for self-organized stocking policies. The former strategy will be more time-consuming and may fail in some situations, but is likely to create less conflicts and more durable outcomes from a social perspective. Alternative to fish stocking, such as improvement of habitats or harvest constraints, should be considered whenever feasible.

Current genetic structure of European vendace Coregonus albula (L.) populations in Latvia after multiple past translocations

The European vendace Coregonus albula (L.), also known as the European cisco, is a widespread fish species in northern Europe, often regarded as an example of a glacial relict. It is an economically valuable fish and has been artificially propagated in Latvia since 1900. Despite past translocations of larvae and fry and its current protection status, it can be found in only 15 Latvian lakes. We used nine microsatellite markers to study vendace populations from nine Latvian lakes. A higher mean allelic richness and private allelic richness in Lake Riču suggest that this population may be indigenous. Three complementary clustering methods revealed similar grouping into three distinct genetic groups. According to the results, European vendace populations in the Latvian lakes studied may currently be a mixture of several other populations after multiple translocations.

Controlling invasive fish in fluctuating environments: Model analysis of common carp (Cyprinus carpio) in a shallow lake

AbstractClimate change can act to facilitate or inhibit invasions of non‐native species. Here, we address the influence of climate change on control of non‐native common carp (hereafter, carp), a species recognized as one of the “world's worst” invaders across the globe. Control of this species is exceedingly difficult, as it exhibits rapid population growth and compensatory density dependence. In many locations where carp have invaded, however, climate change is altering hydrologic regimes and may influence population demography and efficacy of human control efforts. To further evaluate these processes, we employed a modified version of an age‐based population model (CarpMOD), to investigate how hydrologic variability (change in lake area) influences carp population dynamics and control efforts in Malheur Lake, southeastern Oregon, USA. We explored how changes in lake area influence carp populations under three control scenarios: (1) no carp removal, (2) carp removal during low water years, and (3) carp removal during all years. Lake area fluctuations strongly influenced carp populations and the efficacy of carp control. Modeled carp biomass peaked when the lake transitioned from high‐to‐low levels, and carp biomass declined when lake area transitioned from low‐to‐high. Removing carp during low water periods—when fish were concentrated into a smaller area—reduced carp populations almost as much as removing carp every year. Furthermore, the effectiveness of control efforts increased with the prevalence and severity of low lake conditions (longer durations of very low lake area). These simulations suggest that a drier climate may naturally decrease carp populations and make them easier to control. However, drier conditions may also negatively affect aquatic ecosystems and potentially have a greater impact than non‐native species themselves.