Data from: Invasive Eurasian minnow alters the trophic niche and growth of brown trout in high-latitude lakes
Data files
Nov 12, 2025 version files 100.69 KB
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Kangosjarvi-etal-FishData.csv
82.40 KB
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Kangosjarvi-etal-SCAdata.csv
12.62 KB
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README.md
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Abstract
Invasive species pose a major threat to aquatic ecosystems, particularly in high-latitude lakes which are characterised by low biodiversity. In northern Europe, Eurasian minnow (Phoxinus phoxinus) has colonised lakes historically dominated by salmonids, raising concerns about the impacts of invasive cyprinids on native fish populations and food webs. We compared the trophic niche, growth, and maturation of brown trout (Salmo trutta) in lakes with and without minnow and assessed dietary overlap between the two species using stomach content and stable isotope analyses. Stable isotope analysis revealed that in lakes with minnow, trout exhibited more pronounced ontogenetic niche shifts from pelagic to littoral feeding and towards higher trophic positions compared to lakes with only trout. The isotope data also showed that small trout overlapped in trophic niche with minnows. Stomach content analysis revealed a shift in trout prey use, with reduced consumption of Eurycercus lamellatus and Gammarus lacustris, increased use of surface insects and a transition towards partial piscivory (prevalence of piscivory 5.5 %). Despite potential resource competition at early life stages and shifts in diet, when coexisting with minnow, trout grew faster and females showed a tendency to mature earlier. Overall, the presence of invasive minnow does not appear to negatively affect native trout. This is likely due to a combination of flexible resource use and the opportunistic piscivory exhibited by trout. Since our study systems were recently invaded, the findings provide new insights into how native salmonids respond to invasive species shortly after their establishment in small high-latitude lakes.
Dataset DOI: 10.5061/dryad.7d7wm3871
Description of the data and file structure
This data was collected to estimate the impact of invasive Eurasian minnow (Phoxinus phoxinus) on the trophic niche and life history traits of native brown trout (Salmo trutta) in small, subarctic lakes located at the Abisko area, Northern Sweden. Data is used in the manuscript titled "Invasive Eurasian minnow alters the trophic niche and growth of brown trout in high-latitude lakes" by Kangosjärvi et al. 2025.
Files and variables
File: Kangosjarvi-etal-SCAdata.csv
Description: Results of the stomach content analysis. Each row present one fish individual.
Variables
- Lake: Name of the study lake.
- Community: Community type of the lake, either allopatric (Salmo trutta only), or sympatric (Salmo trutta and Phoxinus phoxinus).
- Tlmm: Total length of fish in mm.
- Size: Size class of the fish; small (<181 mm), medium (181–280 mm) or large (>280 mm).
- Species: Scientific name of the fish species name.
- Fish: relative amount (percentage) of fish prey (trout, minnow and burbot) in the stomach content.
- Gammarus: relative amount (percentage) of Gammarus sp. in the stomach content.
- PSM: relative amount (percentage) of predator sensitive macroinvertebrates (larvae of Plecoptera, Trichoptera, Ephemeroptera and Sialis, and Coleoptera and Hymenoptera) in the stomach content.
- Chironomids: relative amount (percentage) of Chironomidae sp. in the stomach content.
- Molluscs: relative amount (percentage) of molluscs (Planorbidae sp., Lymnae sp. and Pisidium sp.), in the stomach content.
- Eurycercus: relative amount (percentage) of Eurycercus lamellatus in the stomach content.
- Zooplankton: relative amount (percentage) of pelagic zooplankton (Polyphemus sp., Copepoda sp., Bosmina sp., Daphnia sp., Bythotrephes longimanus and unidentified zooplankton remains) in the stomach content.
- Surface_insects: relative amount (percentage) of surface insects in the stomach content.
- Other: relative amount (percentage) of other gut content (unidentified content, Hydrachnidia sp., and plant material) in the stomach content.
File: Kangosjarvi-etal-FishData.csv
Description: The dataset includes location and fish data, with detailing characteristics of the study lakes and individual fish. Each row represents a single fish.
Variables
- lake: Name of the study lake.
- country: Country where lake is located at.
- lakeID: Swedish national lake ID, according to https://vattenwebb.smhi.se/svarwebb/ .
- WGS84N: Location of the lake, WGS84 northern.
- WGS84E: Location of the lake, WGS84 eastern.
- day: Sampling day.
- month: Sampling month.
- year: Sampling year.
- altitude: Altitude of the lake, meters above sealevel.
- areakm2: Surface area of the lake, km2.
- secchi: Secchi depth of the lake, m.
- surfaceTemp: Surface temperature of the lake, celsius degrees.
- TOC: Total organic carbon of the lake, mg/L.
- TN: Total nitrogen of the lake, µg/L.
- totP: Total phosphorus of the lake, µg/L.
- nroSpecies: Number of fish species in the lake.
- speciesPresent: Common names of the fish species present in the lake.
- community: Community type of the lake, either allopatric (Salmo trutta only), or sympatric (Salmo trutta and Phoxinus phoxinus).
- CPUEtrout: Number of caught brown trout per 100 m2 of gillnets per night.
- CPUEminnow: Number of caught Eurasian minnow per 100 m2 of gillnets per night.
- BPUEtrout: Biomass of caught brown trout in grams per 100 m2 of gillnets per night.
- BPUEminnow: Biomass of caught Eurasian minnow in grams per 100 m2 of gillnets per night.
- fishID: The identification of each fish individual.
- scientificName: Scientific name of the fish.
- age: Age in years, estimated from otoliths.
- totalLength_mm: Total length of fish in mm.
- weight_g: Wet weigth of fish in grams.
- size_class: Size class of the fish; small (<181 mm), medium (181–280 mm) or large (>280 mm).
- sex: Sex of the fish (female, male, juvenile).
- maturity: Maturity of the fish, mature = 1, immature = 0. Females were classified as mature if the gonads occupied at least three-quarters of the abdominal cavity and the eggs had a minimum diameter of 3 mm. Males were defined as mature if minimum half the length of the gonads appeared visibly swollen.
- d13C: Carbon stable isotope value from fish muscle tissue, δ13C.
- d15N: Nitrogen stable isotope value from fish muscle tissue, δ15N.
- lit_d13C_max: Maximum δ13C value recorded from littoral-benthic invertebrate baseline samples.
- lit_d15N_mean: Mean δ15N value recorded from littoral-benthic invertebrate baseline samples.
- pel_d13C_min: Minimum δ13C value recorded from pelagic zooplankton baseline samples.
- pel_d15N_mean: Mean δ15N value recorded from pelagic zooplankton baseline samples.
- LR: Littoral reliance of fish, estimated according to linear two-source mixing models (Post, 2002), with Δ¹³C = 1.4 ‰ and λ = 2.
- TP: Trophic position of fish, estimated according to linear two-source mixing models (Post, 2002), with Δ¹⁵N = 4.0 ‰ and λ = 2.
References: Post, D. M. (2002). Using stable isotopes to estimate trophic position: models, methods, and assumptions. Ecology, 83(3), 703–718. https://doi.org/10.1890/0012-9658(2002)083[0703:USITET]2.0.CO;2
We sampled six subarctic lakes in Abisko, northern Sweden, comprising three allopatric trout lakes and three sympatric lakes with trout and minnow. Fish were caught using standardised multi-mesh gillnets set at multiple depths to cover all major habitats. In the laboratory, trout were measured, sexed, aged (from otoliths), and assessed for maturity. Maturity was treated as a binary variable. Females were classified as mature if the gonads occupied at least three-quarters of the abdominal cavity and the eggs had a minimum diameter of 3 mm. Males were defined as mature if minimum half the length of the gonads appeared visibly swollen. Muscle tissue and stomachs were dissected from all fish for stable isotope (SIA) and stomach content (SCA) analyses.
Baseline samples for SIA were collected from each lake: littoral benthic invertebrates using kick net and benthic sledge, and pelagic zooplankton using vertical hauls with a plankton net. Water samples were collected for chemical analyses of TOC, TP and TN. All isotope samples were freeze-dried, homogenised, and analysed using isotope-ratio mass spectrometry, with δ¹³C and δ¹⁵N values used to infer trophic position (TP) and littoral reliance (LR) via baseline-corrected two source mixing models (Post et al., 2002).
SCA was conducted on 2023 samples using the relative fullness method (see Amundsen & Sánchez-Hernández, 2019). Prey items were identified to the lowest feasible taxonomic level.
References:
Amundsen, P.-A., & Sánchez-Hernández, J. (2019). Feeding studies take guts – critical review and recommendations of methods for stomach contents analysis in fish. Journal of Fish Biology, 95(6), 1364–1373. https://doi.org/10.1111/jfb.14151
Post, D. M. (2002). Using stable isotopes to estimate trophic position: models, methods, and assumptions. Ecology, 83(3), 703–718. https://doi.org/10.1890/0012-9658(2002)083[0703:USITET]2.0.CO;2