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Eric Weimer

Publications and source records attributed to Eric Weimer.

4 recordsLinked to original sources
USGS2025

First-year survival of Lake Sturgeon reintroduced to the Maumee River

Objective Lake Sturgeon Acipenser fulvescens have experienced large population declines due to overfishing, habitat degradation, and pollution. Due to these factors, Lake Sturgeon were extirpated from the Maumee River watershed (Ohio, United States). In 2018, a 20-year reintroduction program began that aims to establish a self-sustaining population in the Maumee River. To understand the potential success of the reintroduction program, our objectives were to estimate poststocking survival of reintroduced Lake Sturgeon from age 0 to age 1. We also wanted to understand whether survival differed between age-0 Lake Sturgeon reared in a streamside facility and those reared in a traditional hatchery. Methods Lake Sturgeon from the two facilities were surgically implanted with acoustic transmitters; tagged fish ( n = 40 per year) were released into the Maumee River in 2018, 2019, and 2021, and their movements were monitored by the Great Lakes Acoustic Telemetry Observation System. Results Approximately 75% of Lake Sturgeon were detected at 100 d after release and 50% were detected at 200 d after release. We found no differences in tag attrition between the two rearing strategies. Monthly survival estimates for Lake Sturgeon were 0.87 (95% CI = 0.81–0.92) in 2018, 0.97 (95% CI = 0.89–0.99) in 2019, and 0.95 (95% CI = 0.90–0.97) in 2021. No differences in survival between rearing strategies within release years existed. Annual survival estimates ranged from 0.19 to 0.71 among the three release years. Conclusions Our results, along with known survival rates for adult Lake Sturgeon, suggest that achieving the goal of 1,500 naturally reproducing individuals in the Maumee River is possible if reintroduced fish return to the Maumee River to spawn as adults.

Ohio↗
USGS2025

Dead giveaway: Rising mortality rates suggest effectiveness of Lake Erie grass carp (Ctenopharyngodon idella) response

Grass carp ( Ctenopharyngodon idella ) are large, invasive fish that threaten Lake Erie’s economy and ecosystem. Incidental catches of grass carp have occurred since the 1980s in Lake Erie, while multi-day removal events were carried out in 2014 and 2017. To mitigate ecosystem impacts, a large-scale, multi-agency response to remove as many grass carp as possible from the Lake Erie basin (“strike teams”) began in 2018 and has increased every year. To date, total annual removals of fish has been the primary measure of progress; however, total annual removals do not indicate how efforts are affecting the grass carp population. Population vital rates, such as mortality rate, can indicate population demographic changes and may provide an alternative approach to measure how removals have impacted the grass carp population. We estimated annual mortality rates using 553 grass carp, representing 82.9 % of all grass carp removed in the Lake Erie basin, using a hierarchical catch-curve model and catch-at-age data from 2014 to 2022. Annual average mortality rates were initially low (4.3 %) and increased between 2017 and 2022 with the highest mortality (13.6 %) observed in 2021. Positive correlations between mortality and the number of fish harvested per year suggest that removals may be driving increases in the grass carp mortality rate. This increase in mortality rate shows promise for controlling the spread of grass carp within the Lake Erie ecosystem. This research supports the needs of fishery managers to better understand grass carp population dynamics and the adaptive management framework identified in the Lake Erie Grass Carp Adaptive Response Strategy.

Lake Erie↗
USGS2021

Validation of the model-predicted spawning area of grass carp Ctenopharyngodon idella in the Sandusky River

Spawning of grass carp, Ctenopharyngodon idella, in the Great Lakes basin was verified when eight fertilized eggs were collected in the Sandusky River, a tributary to Lake Erie, in 2015. Using a fluvial drift model (FluEgg) and simulation modeling, researchers predicted the fertilization location for those eggs was 3.8 ± 1 km (95% credible interval, CI) downstream of Ballville Dam. In June 2018, simultaneous collection of fertilized eggs and adults within the model-predicted spawning area provided the opportunity to verify the fertilization location. We used estimated developmental time (Dt) of eggs calculated from developmental stages, water temperature, and an equation that predicts Dt from cumulative thermal units experienced by developing eggs, in two analyses. First, we regressed Dt versus location of capture and solved that equation for developmental time of 0 hrs (Dt 0 ) to estimate fertilization location. Second, we used Dt in the Fluvial Drift Simulator (FluEgg) to simulate 23 scenarios representative of drift conditions throughout the spawning event using the model-predicted spawning area and the site of Ballville Dam as potential spawning locations. Regression analysis placed the mean fertilization location 3.36 km (95% CI 2.27, 4.24) downstream of the site of Ballville Dam, within the model-predicted spawning area. Drift models demonstrated the model-predicted spawning area was best supported. Histograms of fertilization times overlapped with capture times by boat electrofishing of diploid adult grass carp in the model-predicted spawning area. This suite of analyses confirms the model-predicted spawning area and validates the methodology used to locate it.

Ohio↗