Water temperature drives variability in salmonfly abundance,emergence timing,and body size

Freshwater organisms are disproportionately impacted by climate change and human disturbance, resulting in shifts in species' distributions and life histories. We coupled contemporary and historical datasets documenting physical and ecological variables over four decades to quantify changes in the abundance, emergence timing, and body size of salmonflies (Pteronarcys californica) in the Madison River in southwest Montana. In contemporary surveys, water temperature was the main driver of salmonfly abundance, emergence timing, and body size. Salmonfly densities were negatively correlated with summer water temperature, which explained 60% of variation in larval density among sites, whereas substrate type played a negligible role. Emergence occurred 20 days earlier, and male and female exuvia length were 13.8% and 11.3% shorter, respectively, at the warmest site relative to the coolest site (4°C difference). These patterns were supported by historical data. For example, a 1.2°C increase in mean annual water temperature in the Madison River between 1977 and 2017 coincided with evidence for upstream range contraction. Between 1973 and 2017, emergence timing varied widely among years, occurring up to 41 days earlier in years when spring water temperatures were relatively warm. As climate change progresses, we predict that salmonflies could be extirpated from an additional 28 km of currently occupied habitat, representing a 22.6% reduction in suitable habitat along the Madison River. This study provides evidence of long‐term biological change of an aquatic insect and highlights the importance of combining spatial and historical datasets to better understand species' responses to environmental stressors across both space and time.     

Large‐scale spatial variability of riverbed temperature gradients in Snake River fall Chinook salmon spawning areas

In the Snake River basin of the Pacific northwestern United States, hydroelectric dam operations are often based on the predicted emergence timing of salmon fry from the riverbed. The spatial variability and complexity of surface water and riverbed temperature gradients results in emergence timing predictions that are likely to have large errors. The objectives of this study were to quantify the thermal heterogeneity between the river and riverbed in fall Chinook salmon spawning areas and to determine the effects of thermal heterogeneity on fall Chinook salmon emergence timing. This study quantified river and riverbed temperatures at 15 fall Chinook salmon spawning sites distributed in two reaches throughout 160 km of the Snake River in Hells Canyon, Idaho, USA, during 3 different water years. Temperatures were measured during the fall Chinook salmon incubation period with self‐contained data loggers placed in the river and at three different depths below the riverbed surface. At all sites, temperature increased with depth into the riverbed, including significant differences (p < 0.05) in mean hourly water temperature of up to 3.8°C between the river and the riverbed among all the sites. During each of the 3 water years studied, river and riverbed temperatures varied significantly among all the study sites, among the study sites within each reach and between sites located in the two reaches. Considerable variability in riverbed temperatures among the sites resulted in fall Chinook salmon emergence timing estimates that varied by as much as 36 days within a reach, depending on the source of temperature data used for the estimate. Monitoring of riverbed temperature gradients at a range of spatial scales throughout the Snake River would provide better information for managing hydroelectric dam operations, and would aid in the design and interpretation of future empirical research into the ecological significance of physical riverine processes. Published in 2007 by John Wiley & Sons, Ltd.     

Life‐History Plasticity of Riparian Annual Plants Adapted to Extreme Variations in Water Level: Mesocosm Experiments

The riparian zones of reservoirs associated with regulated rivers in China experience annual fluctuations in water level of up to 30 m that may vary in timing from year to year. Few plant species can tolerate such hydrological perturbation, but short‐lived riparian annuals might be evolutionarily pre‐adapted to such conditions. This study investigated plasticity of life history in four annual species: one typically associated with free‐flowing rivers (Panicum bisulcatum) and three that colonize reservoir margins (Cyperus michelianus, Fimbristylis miliacea and Eclipta prostrata). We found that all four species produced non‐dormant seeds that survived prolonged submergence; germination percentage was independent of the time of exposure by receding waters. Although growth was reduced as a result of shorter growing seasons, all four species completed their life cycles and produced seeds before winter. In addition, P. bisulcatum and C. michelianus allocated biomass to seed production, at the expense of roots and stems, in response to later establishment. All species responded to later establishment with a reduced vegetative growth period before seed production. C. michelianus, F. miliacea and E. prostrate could also delay the onset of flowering time by up to 2 months. P. bisulcatum, a plant that can flower only after exposure to short days, consequently had a fixed flowering time and could accommodate delayed establishment only with a progressively shorter period of vegetative growth. This lower flexibility might explain its absence from reservoir margins. The conceptual framework presented here offers a tool to predict the establishment of vegetation under hydrological disturbance in riparian environments and thereby provides insights into improved restoration practice. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of water withdrawals on macroinvertebrate emergence: Unexpected results for three holometabolous species

Small, low‐head diversion dams are capable of withdrawing much of the flow of a river, often resulting in elevated water temperatures. Accelerated growth and development of aquatic invertebrates has been demonstrated in warmer temperatures, suggesting that the timing of insect emergence and adult body size may be significantly altered by water withdrawals. To examine the influence of summer water withdrawals on aquatic invertebrate life histories, emergence timing and adult body mass of three holometabolous species were monitored continuously for 9–10 weeks on the Umatilla and Walla Walla Rivers in arid northeastern Oregon. On each river, multiple sample sites were located along gradients of decreasing discharge and increasing water temperatures caused by successive diversions. Despite reductions in discharge of up to 93% and increases in average water temperature of up to 4.6°C from upstream to downstream, timing of median emergence was unaltered for Helicopsyche borealis, Petrophila confusalis and Glossosoma traviatum. However, in a laboratory experiment, higher temperatures led to earlier emergence for H. borealis. Water temperature in the field study was not significantly correlated with reduced adult body size of these species, though female P. confusalis were 31% smaller at the warmest sample site. Holometabolous life histories and high temperature tolerances are possible explanations for the observed resistance of these species to life history alteration. Copyright © 2010 John Wiley & Sons, Ltd.     

Quantifying the influence of cold water intrusions in a shallow,coastal system across contrasting years: Green Bay,Lake Michigan

We present water column thermal structure for two climatically different years: 2012, which experienced abnormally warm spring and summer air temperatures preceded by a relatively low ice winter and 2013, which experienced cooler than average spring and average summer air temperatures and preceded by average ice conditions. Mean bottom water temperatures for the season and during cold water intrusions were significantly warmer in 2012 than 2013 leading to a significantly reduced stratified season in 2012. Cold water intrusions were driven into southern Green Bay by southerly winds while intrusions were terminated when winds switched to persistent northerly winds. 2012 observed a significant increase in northerly winds relative to 2013, decreasing cold water intrusion presence and duration but winds did not fully explain the difference in thermal conditions for southern Green Bay. These cold bottom waters drive stratification in polymictic southern Green Bay while dimictic waters were found to have significantly warmer bottom temperatures during 2012 and a deeper mixed layer. Our observations suggest that relatively shallow (<20?m), seasonally stratified systems may not increase in stratification strength and duration under a warming climate; rather, changing wind climatology and surface heat flux can inform the degree to which the mixing regime can be expected to change and impact stratification and thermal structure of coastal systems. We discuss the biogeochemical implications of different thermal regimes, particularly within the context of multiple drivers of physical water column structure in eutrophic, stratified coastal systems.     

Larval fish catches in the lower Milk River,Montana in relation to timing and magnitude of spring discharge

Larval fishes were sampled in the Milk River, Missouri River drainage, Montana from May to August 2002, 2003 and 2004 to describe temporal spawning distribution in relation to spring discharge. Total larval catch‐per‐unit‐effort (CPUE) in 2002 (28.9 fish/100 m³) was an estimated 29 times greater than in 2003 (0.99 fish/100 m³) and 16 times greater than in 2004 (1.78 fish/100 m³). In 2003 and 2004 more than one third of the total catch occurred before 12 June whereas in 2002, only 5% of the total catch occurred before 12 June. Marked differences in larval species composition were also observed between years, suggesting that a later peak in discharge may benefit some species and an earlier peak others. In 2002, when flows peaked later (at 77 m³ s^?1), common carp Cyprinus carpio represented 37% of the total larval catch. Common carp were proportionally less abundant in 2003 (7.2%) and 2004 (1.4%) than in 2002. In 2004, when flows peaked (at 163 m³ s^?1) 32 days earlier than in 2002 but only 15 days earlier than in 2003 (at 73 m³ s^?1), shorthead redhorse Moxostoma macrolepidotum and suckers Catostomus sp. were the numerically dominant taxa. These results indicate that the timing, not necessarily the magnitude, of peak spring discharge may influence spawning success in the lower Milk River, as indicated by larval fish catches. Copyright © 2008 John Wiley & Sons, Ltd.     

Estimation of pesticide runoff from paddy fields to rural rivers.

The runoff characteristics of pesticides from paddy fields to rural rivers were investigated over a period of three years in Hokkaido Prefecture, Japan. High pesticide concentrations were usually observed in rivers during pesticide application periods. In one year, the growth of rice seedlings slowed down after transplantation owing to low temperatures and lack of sunshine, and many farmers delayed herbicide application. In that year, high-concentration runoff of herbicides in rivers was observed 1-3 weeks later than in average years. The pesticide runoff rates ranged from 0.3% for fenthion to 42% for benfuresate. The runoff rates of pesticides applied post-flood were large. Furthermore, the larger the water solubility of the pesticide, the larger the runoff rate. The highest concentrations of herbicides in paddy water were observed on the day of application or 1-2 days later, and the concentrations decreased exponentially afterwards. The half-lives of the herbicides ranged from 1.2 days for pretilachlor and esprocarb to 5 days for simetryn; the concentrations of the herbicides in paddy water had decreased to 1/10 of their initial concentrations by about 7 days after application. Therefore, the runoff amounts of pesticides from paddy fields could be decreased by improving irrigation-water management.     

SPAWNING OF THE ENDANGERED AUSTRALIAN LUNGFISH (NEOCERATODUS FORSTERI) IN A HEAVILY REGULATED RIVER: A PULSE FOR LIFE

The Australian lungfish is an endangered native species currently protected under various state, federal and international agreements. Scarce information on their early life history is available due to the absence of juveniles collected in the wild. This has led to concerns about the sustainability of the species and become a driver for the conservation effort for Australian lungfish. This study aimed to consolidate knowledge on the critical hydraulic habitat requirements of this species within a water resource management context. In this study, spawning of Australian lungfish was found to be a seasonal strategy that is highly reliant on a variable low‐flow regime within riverine habitat. Suitable conditions for spawning were characterized by small flow events in early‐to‐mid spring when water temperatures are between 18 and 28 °C, leading to oviposition on short dense macrophytes in shallow water. Importantly, many of the key environmental factors driving the ecological response are manageable through existing water resource infrastructure. Specifically, releases from water storages within the current distribution of Australian lungfish should mimic the natural inflow and temperature regime within the spawning period, and also provide suitable riverine habitat within projected full supply limits. Copyright © 2012 John Wiley & Sons, Ltd.     

Warming of the lower Columbia River, 1853 to 2018

Water temperature is a critical ecological indicator; however, few studies have statistically modeled century-scale trends in riverine or estuarine water temperature, or their cause. Here, we recover, digitize, and analyze archival temperature measurements from the 1850s onward to investigate how and why water temperatures in the lower Columbia River are changing. To infill data gaps and explore changes, we develop regression models of daily historical Columbia River water temperature using time-lagged river flow and air temperature as the independent variables. Models were developed for three time periods (mid-19th, mid-20th, and early 21st century), using archival and modern measurements (1854–1876; 1938–present). Daily and monthly averaged root-mean-square errors overall are 0.89°C and 0.77°C, respectively for the 1938–2018 period. Results suggest that annual averaged water temperature increased by 2.2°C ± 0.2°C since the 1850s, a rate of 1.3°C ± 0.1°C/century. Increased water temperatures are seasonally dependent. An increase of approximately 2.0°C ± 0.2°C/century occurs in the July–Dec time-frame, while springtime trends are statistically insignificant. Rising temperatures change the probability of exceeding ecologically important thresholds; since the 1850s, the number of days with water temperatures over 20°C increased from ~5 to 60 per year, while the number below 2°C decreased from ~10 to 0 days/per year. Overall, the modern system is warmer, but exhibits less temperature variability. The reservoir system reduces sensitivity to short-term atmospheric forcing. Statistical experiments within our modeling framework suggest that increased water temperature is driven by warming air temperatures (~29%), altered river flow (~14%), and water resources management (~57%).     

The effects of cool and variable temperatures on the hatch date,growth and overwinter mortality of a warmwater fish in small coastal embayments of Lake Ontario

Little is known about the ecology of warmwater fish in small coastal embayments (< 32 ha) where temperatures are lowered by exchange with the adjacent lake. Using pumpkinseed (Lepomis gibbous) as a model warmwater fish, we compare hatch dates and overwinter survival in two embayments with higher and lower amounts of cold-water input from Lake Ontario, in a warmer and cooler year. In 2007, the embayments differed by approximately 2–5 °C until late-July. In that year, temperatures in the cooler embayment delayed hatching times until July 18–August 20, approximately eight weeks later (May 24–August 20) than in the warmer embayment. Almost all offspring in the cooler embayment were likely too small to survive the winter. In 2008 both embayments had similar temperatures. In that year, pumpkinseed started hatching in early-June, and most were likely large enough to survive the winter. The findings from the two intensively sampled embayments were confirmed with a 21-year fish monitoring dataset; adult pumpkinseed were captured in the littoral zone of warm embayments 6–8 weeks earlier than in cooler embayments. Relative to pumpkinseed in the small inland lakes of eastern and central Ontario, spawning is delayed by at least two weeks in coastal embayments. Using water temperatures as a surrogate for growth, we calculated that only 5 of the 17 embayments for which we have temperature records were able to consistently produce successfully overwintering age-0 fish. Nevertheless, we found pumpkinseed age ≥ 1 in embayments too cold to produce age-0 pumpkinseed, suggesting immigration from warmer embayments.     

Possible Impacts of Projected Temperature Change on Commercial Fruit Production in the Great Lakes Region

Commercial fruit production is a primary revenue source for many locations within the Great Lakes region. Projected climate change may have a profound impact on this highly climate sensitive activity, which owes its existence to the moderating influence of the Great Lakes. Downscaled daily maximum and minimum temperature series provided by the U.S. National Assessment were utilized to evaluate 1) possible changes in the frequency and timing of several agronomically-relevant temperature threshold events and 2) potential interactions between crop phenology and a commercially-important insect pest (Cydia pomonella (L.)). The analyses are for the two future decades of 2025 to 2034 and 2090 to 2099. The assessments for 2025 to 2034 suggest that fruit-growing areas in the Great Lakes region will experience a moderate increase in growing season length and seasonal heat accumulation and a decrease in the frequency of freezing temperatures. In addition, important growth stages will occur earlier in the calendar year than at present. Very large changes in the temperature threshold parameters are projected for 2090 to 2099. However, it is unclear for both assessment decades whether fruit production will be more or less susceptible to damage from cold temperatures after critical growth stages are reached. Projected warming may also result in increases in the number of generations per season of a primary insect pest and the number of necessary pesticide applications.     

鄱阳湖南矶湿地典型植被对水深和淹没频率的响应分析

水文要素是控制湿地生态过程发展与演替的主要驱动因子,在湿地形成、发育、演替直至消亡全过程中起重要作用。湿地植被群落是湿地生态系统重要组成成分和主要初级生产者,其结构、功能和生态特征综合反映着湿地生态环境的基本特点和功能特性。本文以鄱阳湖南矶湿地国家级自然保护区为例,运用植被群落—水文要素丰度直方图和敏感性指数,分析探讨了保护区内5种典型湿地植被群落对水深和淹没频率两种水文要素的耐受性和敏感性。结果表明:不同植被群落对水深、淹没频率的耐受性和敏感性不同。其中:(1)虉草和蓼子草2种群落对水深的耐受性最强,南荻群落最弱;苔草群落对淹没频率的耐受性最强,蓼子草群落最弱。(2)相较于淹没频率,5种典型植被群落对水深的敏感性更强;(3)南荻群落对水深和淹没频率变化的敏感性最强,而蓼子草群落对水文要素变化的响应最不敏感。     

Variability of Water Resource in the Yellow River Basin of Past 50 Years, China

We use Mann–Kendall trend test and Lepage method to study spatial and temporal variations of the streamflow series over the past 50 years based on daily hydrologic data from six gauging stations in the Yellow River basin. Research results indicate that: (1) The streamflow of the Yellow River basin is decreasing and water resource deficit tends to be more serious from the upper to the lower Yellow River basin; (2) Zero-flow days are observed after 1970 and overwhelmingly prevail during 1990–2000. Moreover, zero-flow events are observed mainly during spring and summer; (3) Low flow events are more sensitive to climatic changes and human activities when compared to the high flow events, which is mainly reflected by larger fluctuation of timing of change points. Furthermore, the timing of change point of hydrologic events tends to be earlier from the upper to the lower Yellow River basin, indicating more intensive impacts of human activities on water resource in the lower Yellow River basin. The current research will be greatly helpful for sound and effective water resource management in the Yellow River basin, being characterized by serious water deficit.     

Effects of Water Temperature on Breeding Phenology,Growth, and Metamorphosis of Foothill Yellow‐Legged Frogs (Rana boylii): A Case Study of the Regulated Mainstem and Unregulated Tributaries of California's Trinity River

Many riverine organisms are well adapted to seasonally dynamic environments, but extreme changes in flow and thermal regimes can threaten sustainability of their populations in regulated rivers. Altered thermal regimes may limit recruitment to populations by shifting the timing of breeding activities and affecting the growth and development of early life stages. Stream‐dwelling anurans such as the foothill yellow‐legged frog (Rana boylii) in the Trinity River of northern California are model subjects for examining associations between water temperature and the timing of oviposition, hatching, and metamorphosis, and body condition and size of tadpoles and metamorphs. Breeding activity, hatching success, and metamorphosis occurred later, and metamorphs were smaller and leaner along the regulated and colder mainstem relative to six unregulated tributaries of the Trinity River. Persistently depressed summer water temperatures appear to play a seminal role in inhibited tadpole growth on the regulated mainstem and may be a causative factor in the pronounced decline of this population. Environmental flow assessments should account for the influence of the thermal regime on the development of vulnerable embryonic and larval life stages to improve outcomes for declining amphibian populations. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Forecasting impacts of climate change on Great Lakes surface water temperatures

Temperature influences the rates of many ecosystem processes. A number of recent studies have found evidence of systematic increases in Great Lakes surface water temperatures. Our study aims to construct empirical relationships between surface water temperatures and local air temperatures that can be used to estimate future water temperatures using future air temperatures generated by global climate models. Remotely sensed data were used to model lake-wide average surface water temperature patterns during the open-water period in Lakes Superior, Huron, Erie, and Ontario. Surface water temperatures typically exhibit linear warming through the spring, form a plateau in mid-summer and then exhibit linear cooling in fall. Lake-specific warming and cooling rates vary little from year to year while plateau values vary substantially across years. These findings were used to construct a set of lake-specific empirical models linking surface water temperatures to local air temperatures for the period 1995–2006. Hindcasted whole-lake water temperatures from these models compare favourably to independently collected offshore water temperatures for the period 1968–2002. Relationships linking offshore water temperatures to inshore water temperatures at specific sites are also described. Predictions of future climates generated by the Canadian Global Climate Model Version 2 (CGCM2) under two future greenhouse gas emission scenarios are used to scope future Great Lakes surface water temperatures: substantial increases are expected, along with increases in the duration of summer stratification.     

Size and age distributions of juvenile Connecticut River American shad above Hadley Falls: influence on outmigration representation and timing

Age‐ and size‐based habitat use and movement patterns of young‐of‐year American shad in rivers are not well understood. Adult females reach their natal rivers at different times and ascend the river at different rates, which may lead to variation of hatch dates at a single location. Also, shad are serial spawners, so eggs of the same female may be released at different distances from the river mouth. It has long been hypothesized that juvenile shad emigration is a function of size or age, and not necessarily keyed only to a decrease in water temperature during the fall. We seined three sites in the Connecticut River biweekly to collect pre‐migrant shad during river residence (spring to fall). During emigration, samples were also collected weekly at two hydroelectric facilities. Otoliths were removed from ～20% of the fish to obtain age and growth rate information. We found increases in length and age over time until late in the season, after which such increases were mostly insignificant. Cohorts collected early in the year as pre‐migrants were never sampled as migrants later in the year at the hydroelectric projects. Cohorts collected late in the year as migrants were never collected earlier in the year as pre‐migrants. Only during a narrow window of time were fish collected as both pre‐migrants and migrants. Fish that were hatched later in the season exhibited higher growth rates than fish that were hatched earlier in the season. Copyright © 2008 John Wiley & Sons, Ltd.     

Seasonal Movements and Habitats of Brown Trout (Salmo Trutta) in Southcentral Lake Ontario

During 1980–82 the movements, seasonal locations, and habitat preferences of brown trout in southcentral Lake Ontario were examined using radio telemetry and vertical gill nets. In fall and spring 85% of the 28 brown trout tracked by radio moved east from tagging sites. Movements frequently centered around original stocking sites, streams, and power plant outflows. Fish moved farther in spring (4.4 ± 2.5 km/d) than in fall (2.4 ± 1.7 km/d) seasons, but short-term movement rates did not differ between seasons (0.4 ±0.1 km/h in spring vs. 0.4 ± 0.3 km/h in fall). Females moved farther and faster than males in the fall. Brown trout generally occupied shallow waters < 1 km from shore; 81% of temperatures occupied by trout were between 8–18°C in spring (10.6 ± 2.3°C) and fall (10.1 ± 3.9°C), but turbidity appeared to influence presence or absence of trout near shore on a daily basis. In summer 78% of the 75 brown trout netted were in 8–18° C water (12.6 ± 4.0°C); 88% were caught in or within ±3 m of the thermocline region. Brown trout occupied regions near the thermocline despite widely varying bottom depths and thermocline temperatures. All brown trout were netted within 3.2 km of shore in summer, most in water ≤ 30 m deep; 70% were caught more than 3 m off bottom. The strong association of brown trout with nearshore and thermocline regions may distinguish their distributions from other salmonid species in Lake Ontario.     

MASS OCCURRENCE OF BLOODSUCKING BLACKFLIES IN A REGULATED RIVER REACH: LOCALIZATION OF OVIPOSITION HABITAT OF SIMULIUM TRUNCATUM USING DNA BARCODING

In order to understand the factors giving rise to a stable and annual outbreak of the pest blackfly species Simulium truncatum (Lundström, 1911) (Simuliidae), the oviposition habitat has been localized and the egg density quantified at different contour levels in the studied regulated river channel bank. Larvae and adults of 12 blackfly species were identified to species based on morphology. As reference library for subsequent species identification of eggs and small larvae, these specimens were subsequently DNA sequenced for the barcode gene cytochrome c oxidase subunit I. Interspecific distance was large between species or species complexes (average nearest neighbour distance: 0.14; range: 0.09–0.20), while intraspecific distance was comparatively low except for the Simulium ornatum and Simulium tuberosum species complexes. S. truncatum was the only species located high up in the channel bank. The core oviposition habitat was a steep moist erosion edge with moss and dead roots and with a continuous supply of groundwater. Egg densities were estimated to 42 773–50 274 eggs cm^–2. Humid oviposition areas high up on the riverbank, but within the annual spring flood levels, seem to be the basis for annual outbreaks of S. truncatum. The mass occurrence of S. truncatum is a phenomenon probably created by man, directly related to the river regulation regime and the construction of a dam in 1936, which gave rise to the formation of the channel and the erosion edge. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal Influences on Life‐History Traits and Reproductive Effort of Introduced Pumpkinseed Sunfish Lepomis Gibbosus in the River Moselle Basin (Northeastern France)

The influence of local thermal regimes on juvenile growth rates, life‐history traits, and reproductive effort of introduced populations of pumpkinseed Lepomis gibbosus was examined in 11 water bodies in the River Moselle basin (northeastern France). Female pumpkinseed were collected during their reproductive period in mid‐June in 2009 and 2010, and water temperature was assessed over a 12‐month period in 2010. Annual thermal degree‐days above 10 °C varied from 1529 in a headwater site to 2722 in the Mirgenbach Reservoir, heated by cooling water from a nuclear power plant. Mean age at maturity varied from 1.3 to 2.2 and was inversely related to annual thermal degree‐days. The proportion of mature age‐1 females also increased with temperature, but neither mean total length at maturity nor gonadosomatic index was related to waterbody thermal regime. Body size at the end of the first year of life was unrelated to thermal regime, but the growth rate of immature age‐1 females in their second growing season was positively related to thermal degree‐days in the spring. Warmer water bodies showed elevated reproductive effort in age‐1 females when either early season gain in mass or mass at the beginning of the second growing season was controlled for; however, reproductive effort was unrelated to thermal regime in age‐2 and age‐3 females. Mean age at maturity was related to mean length at age 1 but not to mean length at age 2, in contrast to native North American and introduced European populations. We conclude that the life‐history response of pumpkinseed to warmer temperatures occurs primarily in age‐1 individuals and predict that climate warming will produce changes in pumpkinseed life‐history traits that will make the species more invasive in parts of Europe where the species is present but not actively spreading. Copyright © 2014 John Wiley & Sons, Ltd.