Devils Lake Research Articles

Water-level changes impact angler effort in a large lake: Implications for climate change

Climate change is expected to influence aquatic habitats and associated fish populations, yet we know little about the impact on recreational anglers. Our goal was to explore whether interannual fluctuations in waterbody surface area and other explanatory variables could be used as indicators of changes in angler fishing effort. Our approach leveraged a combination of remotely sensed waterbody surface area, environmental and fish population data, and onsite angler survey monitoring data for Devils Lake, North Dakota, USA during the open-water fishing period (May 1st to August 31st) for 9 years (1992–2021). The information was used to develop a dynamic waterbody size-angler effort model. Changes in waterbody surface area reliably predicted changes in angler effort (r2 = 0.60). Increases in waterbody surface area led to increases in angler effort, and decreases in waterbody surface area led to decreases in angler effort. Our findings show promise that remotely sensed fluctuations in waterbody surface area could be used as an indicator of interannual angler effort dynamics. Dynamic waterbody size-angler effort models could provide managers the ability to predict changes in angler effort via climate-related hydrological cycles that affect the size and distribution of waterbodies on the landscape.

Correlating chlorophyll movement with wind speed and direction using satellite imagery: A case study of Devils Lake, North Dakota

Estimating the locations of high concentrations of Chlorophyll-a (Chl-a) is essential for accurate analysis of Harmful Algal Blooms (HABs). This paper focused on identifying the locations of higher concentrations of Chl-a in Devils Lake, North Dakota via satellite images by applying different segmentation techniques. The segmentation evaluation metrics indicate that Random Forest (RF) yielded better accuracy than other methods. The segmented images were validated with ground-sampled Chlorophyll data (location matching) and provided a matching percentage of 88.14% on August 08, 2023. The centroids of the contours from the segmented images acquired between 2017 and 2021 were analyzed to study the shift of chlorophyll against the average wind direction. The results indicate that there was a positive correlation of Chl-a against the wind direction. The wind velocity for the same periods was compared against the percentage change of the total area of Chl-a concentration. The results proved that the days having wind velocity greater than 3 m/s had a decrease in the area of Chl-a concentration.

Remotely sensed surface water variations during drought and deluge conditions in a Northern Great Plains terminal lake basin

Study regionNorthern Great Plains (NGP) region, North Dakota, USA Study focusUnderstanding climate change impacts on surface water dynamics of permanent and seasonal water areas under drought to deluge conditions in the Devils Lake Basin (DLB) utilizing a high-resolution global surface water dataset (GSWD). New hydrologic insightsFour phases of dry and wet conditions were experienced in the DLB during the 1990–2018 study period: wetting (1990–1999), stable (2000–2003), recent wetting (2004–2013) and recent drying (2014–2018). A substantial transition from bare land to permanent and seasonal water area is observed during the wetting period (1990–99) while during the stable period (2000–2003), changes are barely observed despite NGP-wide drought. In the recent wetting period (2004–2013), a noticeable gain of permanent water from seasonal and bare land is observed. During the recent drying period (2014–2018), a significant loss of seasonal water area to bare land occurred. The difference between the spring and summer surface water areas is high during the recent wetting period (e.g., 2009, 2011, 2013), but much lower as the DLB approaches a drought condition. The inter-annual and intra-annual water dynamics of permanent and seasonal water areas show different rates of change and varying hydrological lags to changing hydroclimatic drivers and these changes are sensitive to basin antecedent conditions.

Automatic Calibration for CE-QUAL-W2 Model Using Improved Global-Best Harmony Search Algorithm

CE-QUAL-W2 is widely used for simulating hydrodynamics and water quality of the aquatic environments. Currently, the model calibration is mainly based on trial and error, and therefore it is subject to the knowledge and experience of users. The Particle Swarm Optimization (PSO) algorithm has been tested for automatic calibration of CE-QUAL-W2, but it has an issue of prematurely converging to a local optimum. In this study, we proposed an Improved Global-Best Harmony Search (IGHS) algorithm to automatically calibrate the CE-QUAL-W2 model to overcome these shortcomings. We tested the performance of the IGHS calibration method by simulating water temperature of Devils Lake, North Dakota, which agreed with field observations with R2 = 0.98, and RMSE = 1.23 and 0.77 °C for calibration (2008–2011) and validation (2011–2016) periods, respectively. The same comparison, but with the PSO-calibrated CE-QUAL-W2 model, produced R2 = 0.98 and Root Mean Squared Error (RMSE) = 1.33 and 0.91 °C. Between the two calibration methods, the CE-QUAL-W2 model calibrated by the IGHS method could lower the RMSE in water temperature simulation by approximately 7–15%.

Hydrological basis of the Devils Lake, North Dakota (USA), terminal lake flood disaster

Devils Lake, a terminal lake in northeast North Dakota (USA), has experienced catastrophic flooding since 1993. From January 31, 1993, to December 31, 2014, lake level rose from 433.62 to 442.44 m, lake area expanded from 179.9 to 653.5 km2, and lake volume increased from 0.70 to 3.80 km3. More than $1 billion ($USD) has been spent in government payments to mitigate direct, primary, tangible flood damages. This paper provides a case study of the hydrological basis of the Devils Lake flood disaster. The unique geomorphic setting, paleoclimatic record, and hydroclimatic conditions of the region are summarized, and a wide range of hydroclimatic data is examined to provide a broad understanding of the physical basis of the flood disaster. The primary cause of the disaster was a transition to a sustained wetter climate that resulted in a dramatic response in basin hydrological variables in 1993. The transition from a long-term dry period to a long-term wet period caused the lake water budget to begin to change from an atmosphere-controlled water budget dominated by precipitation input to an amplifier lake water budget dominated by surface runoff input to the lake. Other important hydrological factors include a nonlinear precipitation–runoff relationship following the long-term drought, fill-spill and fill-merge hydrological behavior that is characteristic of wetland complexes, an increase in the lake area-to-basin area ratio, and the critical role of frozen soils in controlling infiltration and runoff production of spring snowmelt. Engineering works to manage lake volume through two outlets have reduced, but not entirely eliminated, future flood risk.

Impacts of cold region hydroclimatic variability on phosphorus exports: Insights from concentration-discharge relationship

In lakes of the Northern Great Plains, algae blooms are of great concern due to the recent increase of streamflow resulting in influx of nutrients, particularly phosphorus (P). The cold sub-humid climate and snowmelt hydrology exert strong controls on P concentration, export and supply in the basin. To date, few studies have explored the impacts of hydroclimatic conditions on P concentration, export and concentration-to-streamflow relationships in cold region agricultural basins, and particularly in the headwater catchments of the Devils Lake Basin. This study gains a better understanding of the impacts of hydroclimatic variation on concentration-to-streamflow relationships between two headwater catchments (Mauvais Coulee: 1032 km2 and Tributary 3: 160 km2) draining to Devils Lake during the 2017–2018 period. High-resolution P observations during the first flush of snowmelt runoff are presented. The controlling factors of P exports using both field observations and hydroclimatic variability detected by physically-based hydrologic simulations are investigated. Total P is dominated by dissolved P, with little contribution from particulate P, which is presumed to be locked in an ice matrix in frozen soils. The Mauvais Coulee Basin expresses near chemostatic concentration-to-streamflow relationships in the rising limb of the hydrograph, while concentration correlates positively to streamflow in the descending limb. Our study period has two contrasting water years; a wet year (2016–17) and a dry year (2017–18). The wet year experienced high SWE, snowfall, maximum frozen soil conditions and a thick basal ice layer resulting in high snowmelt streamflow, while the dry year is characterized by lower SWE and absence of frozen soil/basal ice causing very little streamflow. During the wet year lower mean P concentration are observed compared to the dry year due to the presence of frozen soil/basal ice during melt period. However, the P export is much higher in wet year due to large snowmelt streamflow volume. Both chemostatic and flushing streamflow-to-concentration relationships are observed in both years. Thus, the impacts of hydroclimatic conditions to the concentration-to-streamflow relationship are inconclusive. Field observations of more extended time periods will be useful to better understand the influence of hydroclimatic variability on the concentration-to-streamflow relationship.

Land Cover and Land Use Change in the US Prairie Pothole Region Using the USDA Cropland Data Layer

The Prairie Pothole Region (PPR) is a biotically important region of grassland, wetland, and cropland that traverses the Canada-US border. Significant amounts of grasslands and wetlands within the PPR have been converted to croplands in recent years due to increasing demand for biofuels. We characterized land dynamics across the US portion of the PPR (US–PPR) using the USDA Crop Data Layer (CDL) for 2006–2018. We also conducted a comparative analysis between two epochs (1998–2007 & 2008–2017) of the CDL data time series in the North Dakotan portion of the US–PPR. The CDL revealed the western parts of the US–PPR have been dominated by grass/pasture, to the north it was spring wheat, to the east and southern half, soybeans dominated, and to the south it was corn (maize). Nonparametric trend analysis on the major crop and land cover types revealed statistically significant net decreases in the grass/pasture class between 2006 and 2018, which accounts for more than a quarter of grass/pasture area within the US–PPR. Other crops experiencing significant decreases included sunflower (-5%), winter wheat (-3%), spring wheat (-2%), and durum wheat (-1%). The combined coverage of corn and soybeans exhibited significant net increases in 23.5% of its cover; whereas, the individual significant net increases were 5% for corn and 11% for soybeans. Hotspots of increase in corn and soybeans were distributed across North and South Dakota. Other crop/land covers with huge significant increases include other hay/non-alfalfa (15%), and alfalfa (11%), which appear to be associated with the sharp increase in larger dairy operations, mostly in Minnesota. Wetland area increased 5% in the US–PPR, due to increased precipitation as well as inundation associated with Devils Lake in North Dakota. Hotspots of decreasing grass/pasture area were evident across the study area. Comparative trend analysis of two epochs (1998–2007 vs. 2008–2017) in North Dakota revealed that grass/pasture cover showed a negligible net trend (-0.3 %) between 1998 and 2007; whereas, there was a statistically significant decrease of more than 30% between 2008 and 2017. Combined coverage of corn and soybeans experienced statistically significant net increases in both epochs: 11% greater during 1998–2007 and 17% greater during 2008–2017. Recent sharp losses of grasslands and smaller wetlands combined the expansion of corn, soybeans, and alfalfa bode ill for wildlife habitat and require a re-examination of agricultural and energy policies that have encouraged these land transitions.

Mitigating Impact of Devils Lake Flooding on the Sheyenne River Sulfate Concentration

AbstractDevils Lake is a terminal lake located in northeast North Dakota. Because of its glacial origin and accumulated salts from evaporation, the lake has a high concentration of sulfate compared to the surrounding water bodies. From 1993 to 2011, Devils Lake water levels rose by ~10 m, which flooded surrounding communities and increased the chance of an overspill to the Sheyenne River. To control the flooding, the State of North Dakota constructed two outlets to pump the lake water to the river. However, the pumped water has raised concerns about of water quality degradation and potential flooding risk of the Sheyenne River. To investigate these perceived impacts, a Soil and Water Assessment Tool (SWAT) model was developed for the Sheyenne River and it was linked to a coupled SWAT and CE‐QUAL‐W2 model that was developed for Devils Lake in a previous study. While the current outlet schedule has attempted to maintain the total river discharge within the confines of a two‐year flood (36 m3/s), our simulation from 2012 to 2018 revealed that the diversion increased the Sheyenne River sulfate concentration from an average of 125 to >750 mg/L. Furthermore, a conceptual optimization model was developed with a goal of better preserving the water quality of the Sheyenne River while effectively mitigating the flooding of Devils Lake. The optimal solution provides a “win–win” outlet management that maintains the efficiency of the outlets while reducing the Sheyenne River sulfate concentration to ≤600 mg/L.

On the molecular identity of Paratylenchus nanus (Nematoda: Tylenchida).

In this study, molecular characterization of Paratylenchus nanus collected from the type locality in Four Mile Run, Fall Church, Virginia using COI, D2-D3 of 28 S rRNA and ITS rRNA gene sequences was provided. We molecularly also characterized, Paratylenchus specimens collected from grasses in Devils Lake, Ramsey County, North Dakota indicated as the type locality in the original description of P. nanus by Cobb (1923). These nematodes were identified as representatives of the species P. projectus. Populations of P. nanus belonging to the molecular types A and B, and previously designated by Van den Berg et al. (2014) should be now identified as P. nanus and P. projectus, respectively.

Wetland loss impact on long term flood risks in a closed watershed

Flood control is one of the most important ecosystem services provided by wetlands. Large-scale loss of wetlands, combined with more intensive precipitation under changing climate, increases flood risks, to which closed watersheds are particularly susceptible. In the Devils Lake (North Dakota, USA) watershed, a prolonged wet condition since early 1990s has caused a nearly 10 m rise in water level, resulting in over $1 billion losses. While studies have shown the changing climate is the major driver of this flooding, it is still unclear how much contribution could be due to the historical conversion of wetlands in the upper basin. We developed a Soil and Water Assessment Tool (SWAT) model for the Devils Lake watershed and simulated various scenarios representing present and possible past and future wetland area. We estimated the changes in flood risks under the historical and CMIP-5 future climates with these wetland scenarios. We found that while currently wetland restoration does not significantly change flood risks, under the modified climate it presents a good complementary measure reducing the negative impacts of current flood management strategies.

Managing the wicked problem of Devils Lake flooding along the US–Canada border

ABSTRACTThe flooding of Devils Lake, North Dakota, is a multi-decade, multi-billion-dollar, and yet unsolved water management issue along the US–Canada border. In this study, we define this situation as a ‘wicked problem’ and suggest a ‘green paradiplomacy’–based framework that fosters multiactor, multiscale collaboration across jurisdictions as a management strategy. We interviewed stakeholders and combined their perceptions with currently employed management strategies to assess the potential for green paradiplomacy to address the Devils Lake problem. This study may encourage further discussion of green paradiplomacy as a strategy to manage other transboundary watershed problems along the US–Canada border and elsewhere.

A volumetric water budget of Devils Lake (USA): non-stationary precipitation–runoff relationships in an amplifier terminal lake

ABSTRACTDevils Lake, a terminal lake in eastern North Dakota, rose more than 9 m between 1992 and 2013, producing a 286% increase in lake area, and causing more than US$1 billion in direct damages. An annual volumetric lake water budget is developed from monthly hydroclimatological variables for the period 1951–2010 to investigate the rapid lake expansion. The lake is an amplifier terminal lake in which long-term climatic changes are amplified by positive feedback mechanisms, causing the lake to transition from a precipitation-dominated to a runoff-dominated water budget. Factors specific to the Devils Lake Basin further amplify this positive feedback relationship. These include principles of fill–spill hydrology that operate between individual sub-basins within the closed basin, and between the innumerable wetland complexes within each sub-basin. These factors create a pronounced non-stationary precipitation–runoff relationship in the basin during both long-term wetting and drying phases.

Comparing CMIP-3 and CMIP-5 climate projections on flooding estimation of Devils Lake of North Dakota, USA.

BackgroundWater level fluctuations in endorheic lakes are highly susceptible to even slight changes in climate and land use. Devils Lake (DL) in North Dakota, USA is an endorheic system that has undergone multi-decade flooding driven by changes in regional climate. Flooding mitigation strategies have centered on the release of lake water to a nearby river system through artificial outlets, resulting in legal challenges and environmental concerns related to water quality, downstream flooding, species migration, stakeholder opposition, and transboundary water conflicts between the US and Canada. Despite these drawbacks, running outlets would result in low overspill risks in the next 30 years.MethodsIn this study we evaluated the efficacy of this outlet-based mitigation strategy under scenarios based on the latest IPCC future climate projections. We used the Coupled Model Intercomparison Project CMIP-5 weather patterns from 17 general circulation models (GCMs) obtained under four representative concentration pathways (RCP) scenarios and downscaled to the DL region. Then, we simulated the changes in lake water levels using the soil and water assessment tool based hydrological model of the watershed. We estimated the probability of future flood risks under those scenarios and compared those with previously estimated overspill risks under the CMIP-3 climate.ResultsThe CMIP-5 ensemble projected a mean annual temperature of 5.78 °C and mean daily precipitation of 1.42 mm/day; both are higher than the existing CMIP-3 future estimates of 4.98 °C and 1.40 mm/day, respectively. The increased precipitation and higher temperature resulted in a significant increase of DL’s overspill risks: 24.4–47.1% without release from outlets and 3.5–14.4% even if the outlets are operated at their combined full 17 m3/s capacity.DiscussionThe modeled increases in overspill risks indicate a greater frequency of water releases through the artificial outlets. Future risk mitigation management should include providing a flood warning signal to local resource managers, and tasking policy makers to identify additional solution measures such as land use management in the upper watershed to mitigate DL’s flooding.

Modeling Water Quantity and Sulfate Concentrations in the Devils Lake Watershed Using Coupled SWAT and CE‐QUAL‐W2

AbstractDevils Lake is an endorheic lake in the Red River of the North basin in northeastern North Dakota. During the last two decades, the lake water level has risen by nearly 10 m, causing floods that have cost more than 1 billion USD in mitigation measures. Another increase of approximately 1.5 m in the lake water level would cause spillage into the Sheyenne River. To alleviate this potentially catastrophic spillage, two artificial outlets were constructed. However, the artificial drainage of water into the Sheyenne River raises water quality concerns because the Devils Lake water contains significantly higher concentrations of dissolved solids, particularly sulfate. In this study, the Soil and Water Assessment Tool (SWAT) was coupled with the CE‐QUAL‐W2 model to simulate both water balance and sulfate concentrations in the lake. The SWAT model performed well in simulating daily flow in tributaries with ENS > 0.5 and |PBIAS| < 25%, and reproduced the lake water level with a root mean square error of 0.35 m for the study period from 1995 to 2014. The water temperature and sulfate concentrations simulated by CE‐QUAL‐W2 for the lake are in general agreement with the field observations. The model results show that the operation of the two outlets since August 2005 has lowered the lake level by 0.70 m. Furthermore, the models show pumping water from the two outlets raises sulfate concentrations in the Sheyenne River from ~100 to >500 mg/L. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.

Gendered entanglements: Dakotas and Scandinavians at Spirit Lake, 1900–1930

ABSTRACTIn this article the author explores the interconnections between the social and the material—as people move to a space on the land, coexisting with one another. By focusing in on one specific place—the Spirit Lake Dakota Indian Reservation (formerly called the Devils Lake Sioux Indian Reservation) in North Dakota—the author analyzes what happened when white immigrants came to homestead and live on land historically reserved for Dakotas. Against the backdrop of Native dispossession, this illustrative case reveals the ways everyday interactions created entanglements through landownership, the gendered division of paid work, neighboring practices, and leasing land. It challenges us to uncover gendered processes, probe denials, and interrogate silences.

Evapotranspiration Mapping with METRIC to Evaluate Effectiveness of Irrigation in Flood Mitigation for the Devils Lake Basin

Abstract. A period of excess precipitation since 1993 in the Devils Lake basin in northeastern North Dakota has caused extensive flooding of agricultural land and has raised the question of whether irrigation of agricultural crops to increase evapotranspiration (ET) might be an effective way to remove water from the basin. The objectives of this study were to compare ET estimates derived from application of the Mapping ET at High Resolution with Internalized Calibration (METRIC) algorithm for North Dakota conditions (METRICND) under irrigated and rainfed conditions and to assess the potential for irrigation to increase crop ET as a flood mitigation strategy. Weather data, land use maps, and Landsat 5 Thematic Mapper imagery from 2006, 2007, and 2008 were used as inputs to the METRICND model. The ET for irrigated crops (ETIrrigated) was estimated at five test sites from the Devils Lake Basin Water Utilization Test Project (DLBWUTP). The ET for the predominantly rainfed study area (ETRainfed) was estimated using land use maps to identify locations of the same crops as were present on the test sites. The METRICND model was compared to ET values derived from an eddy covariance (EC) system for approximately two months in 2007 at an irrigated alfalfa test site in the DLBWUTP; the mean absolute error between METRICND and the EC system for the comparison period was 0.51 mm d-1. Linear regression of ET (in mm) for the test sites and the larger study area yielded ETIrrigated = 1.23 × ETRainfed + 4.77 with R2 = 0.96, and a t-statistic indicated that the slope was greater than 0 at p = 0.001, indicating the potential for increased ET under irrigation. However, addition of large volumes of irrigation water to the predominantly poorly drained soils in the basin will cause waterlogging and trafficability problems. Installation of subsurface drainage may help alleviate waterlogging, improve crop productivity, and increase ET, but subsurface drainage brings its own complications of disposal of the drained water, salinity of the drainage effluent, and possible sodicity problems on some soils. Keywords: Drainage, Evapotranspiration mapping, Irrigation, METRIC, Landsat 5, Remote sensing, Satellite imagery, SEBAL.

Mean hydroclimatic and hydrological conditions during two climatic modes in the Devils Lake Basin, North Dakota (USA)

AbstractProxy variables from palaeolimnological studies of lakes in the Prairie Pothole Region of North America have been used to infer large oscillations during the late Holocene between longer periods of high‐salinity–dry conditions and shorter periods of low‐salinity–wet conditions producing a normative pattern marked by the absence of hydrological stability. Studies of the historical rise in lake level at Devils Lake have identified 1980 as a transition point between two such hydroclimatic modes. This study uses multiple datasets to characterize the mean hydroclimatological and hydrological conditions of these two climatic modes. Mode 1 is a cool and dry phase, and mode 2 is a warmer and wetter phase. Precipitation onto the lake increased by 24% from mode 1 to mode 2. This small, but sustained, increase produced significant changes in the mean hydroclimatic and hydrological states for the basin, including a 383% increase in surface run‐off to the lake, and a 282% increase in the basin run‐off ratio. Devils Lake Basin is located along a hydrotone (region of strong hydroclimatic gradients) where small changes in hydrological drivers are amplified into large changes in regional moisture. The effects of the fluctuating climatic modes and strong hydroclimatic gradients are probably further amplified by the unique fill–spill hydrology of the northern glaciated plains, which can result in nonlinear precipitation–run‐off relationships. This natural pattern of extreme hydrological variations for Devils Lake produces enormous challenges for lake management.

Can land-use change mitigate long-term flood risks in the Prairie Pothole Region? The case of Devils Lake, North Dakota, USA

The combined effects of climate and land-use change have changed both the hydrology and management of endorheic watersheds globally. Devils Lake (DL), North Dakota, USA, has risen nearly 10 m since 1991, resulting in a costly, lengthy and litigious water management issue in the region. With more than 1 billion US dollars already spent in mitigation, DL is less than 2 m from its uncontrolled overspill to the nearby Sheyenne River, which could lead to mounting economic, environmental and social costs. While previous studies have generally attributed the changes in the hydrology of DL to the current wet spell, the impacts of land-use changes have not been investigated. Using a hydrological model, here we develop four land-use alternatives driven by market and policy conditions in the DL watershed and investigate their effects on DL hydrology and overspill probability under historic and changed climates. Land-use scenarios under an ensemble of statistically downscaled general circulation model projections indicate a higher overspill risk (7.4–17.0 vs. 0–2 %) under historical climate. Incentivized grass and alfalfa scenarios were able to moderate the hydrological implications to DL under a changed climate, indicating their potential companion roles in DL flood mitigation strategies.

Natural hydroclimatic forcing of historical lake volume fluctuations at Devils Lake, North Dakota (USA)

Devils Lake, a terminal saline lake in eastern North Dakota, has experienced catastrophic flooding over the past two decades producing direct damages in excess of $1 billion ($USD). We use three long-term datasets to examine the temporal coherence between historical lake fluctuations and basic hydroclimatic drivers. Monthly precipitation and mean monthly air temperature data are used to characterize long-term precipitation delivery and evaporative demand. Monthly water balance data for a representative location are used to assess basin soil moisture conditions. A lake volume time series documents lake volume fluctuation in response to long-term precipitation and regional soil moisture conditions. Three variables are derived from the datasets, each characterizing a different aspect of the region’s hydroclimatology. A rescaling technique is applied to each variable to examine the temporal coherence and relative patterns of the variables and to identify distinct homogeneous hydroclimatic regimes during the historical period. The three rescaled variables show strong temporal coherence and confirm 1980 as an abrupt transition year between two distinct long-term hydroclimatic modes. Mode 1, a longer and drier phase, runs from 1907 to 1980, while mode 2, a shorter and wetter phase, extends from 1981 to the present. Multi-decadal and century-scale fluctuations between these two modes are the key drivers of long-term lake volume fluctuations, upon which interannual- and interdecadal-scale climatic variability are superimposed. The similar rates of change among the rescaled variables provides evidence in support of the conclusion that long-term natural hydroclimatological variability is the primary driver of observed lake volume changes at Devils Lake during the Twentieth Century and provides a foundation upon which to evaluate the potential contributing effects of anthropogenic climate change, and human alterations of the land use hydrology.

Persistence of Triploid Grass Carp in Devils Lake, Oregon

Abstract Grass carp Ctenopharyngodon idella are sometimes used as a biological tool for managing aquatic vegetation in reservoirs. Sterile, triploid fish were stocked in Devils Lake, Oregon, during 1986, 1987, and 1993 to control aquatic vegetation. We present a case study for using multiple measures on the same fish to determine whether illegal stocking of fertile, diploid grass carp occurred. An investigation into the estimated age of a dead grass carp found in Devils Lake suggested that it was significantly younger than would otherwise be expected, given the only stocking events occurred during 1986, 1987, and 1993. To determine whether illegal stocking or reproduction by presumed sterile grass carp had occurred in Devils Lake, we conducted a study that balanced the needs of lethally sampling grass carp for biological measures with the socially and politically sensitive sentiment of the pro–grass carp citizenry of Devils Lake. These considerations, in combination with a low catch per-unit effort, resulted in a modest sample size for grass carp. We sampled grass carp and recorded multiple measures for each fish. Ploidy testing of blood samples indicated the grass carp were all triploid. Based on gonadal histopathology, six fish were male, two were female, and two were sex-indeterminate with severe gonadal dysgenesis. Age estimates from lapillus otoliths were consistent with fish originating from the legal stocking events in Devils Lake. The grass carp were 21–30 y old, and we were unable to find published reports of grass carp anywhere else in the world that are older. The grass carp were significantly smaller than much younger fish from other regions. The small size of these grass carp relative to their age in Devils Lake suggests food limitations that stunted growth. The dead grass carp that was the impetus for this study was aged by anatomical structures that we have since found to be unreliable. This suggests that the dead grass carp was probably in fact older and originated from the legal stockings. The use of multiple biological measurements on a modest sample size of grass carp, combined with the knowledge that no juvenile grass carp have been observed since legal stocking occurred, lead us to conclude that the grass carp in Devils Lake are sterile fish that originated from legal stocking events.