DOI: 10.5061/dryad.7d7wm3871
title: Data from: Invasive Eurasian minnow alters the trophic niche and growth of brown trout in high-latitude lakes

description: 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.
description: 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. <em>Journal of Fish
 Biology</em>, 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. <em>Ecology</em>, 83(3), 703–718. https://doi.org/10.1890/0012-9658(2002)083[0703:USITET]2.0.CO;2
description: # Data from: Invasive Eurasian minnow alters the trophic niche and growth
 of brown trout in high-latitude lakes Dataset DOI:
 [10.5061/dryad.7d7wm3871](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 (&lt;181 mm), medium (181–280 mm) or large
 (&gt;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 (*Polyphemu*s 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/](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 (&lt;181 mm), medium (181–280 mm) or large (&gt;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](https://doi.org/10.1890/0012-9658\(2002\)083%5b0703:USITET%5d2.0.CO;2)