Research Article |
Corresponding author: Justin D. Harms ( justin.harms@jacks.sdstate.edu ) Academic editor: Darragh Woodford
© 2024 Justin D. Harms, Kenny R. Jimerson, Josh M. Schmidt, David O. Lucchesi, Benjamin J. Schall, Alison A. Coulter.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Harms JD, Jimerson KR, Schmidt JM, Lucchesi DO, Schall BJ, Coulter AA (2024) Progression along the invasion curve: silver carp growth slows temporally in two Missouri River tributaries. Aquatic Invasions 19(1): 109-120. https://doi.org/10.3391/ai.2024.19.1.116040
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Silver carp (Hypophthalmichthys molitrix Valenciennes, 1844) have been invading North American rivers for decades, often altering zooplankton community structure and impacting native fishes. Silver carp invaded eastern South Dakota tributaries of the Missouri River in the early 2000s. Changes in dynamic rate functions can occur as invasive populations move to the latter stages of the invasion curve, but direct temporal assessments of silver carp populations are limited. Our objectives were to compare current growth of silver carp 1) between the Big Sioux and James rivers in South Dakota and 2) with previous growth recorded from the early stages of invasion (2009–2012) in these rivers. We collected silver carp in May and June of 2020–2022 using boat electrofishing and cast netting. We extracted lapilli otoliths for consensus aging from 99 and 82 silver carp from the Big Sioux and James rivers, respectively. We evaluated growth for each population using Bayesian von Bertalanffy models and compared posterior mean length at ages 2–5 to determine the probabilities of differences between rivers and with estimates from the introduction stage. Posterior estimated mean L∞ values were similar between the Big Sioux (714 mm) and James rivers (709 mm); however, the probability that the posterior mean K estimate was greater for silver carp in the James River (0.271) than the Big Sioux River (0.248) was >99.9%. Estimated mean lengths at age 2 were larger in the Big Sioux and James samples than during the introduction stage, but mean lengths at ages 3–5 were smaller. Changes in growth characteristics indicate that growth has slowed in the current establishment stage of invasion from the earlier introduction stage.
bigheaded carp, invasion stages, growth, rivers, invasive carp, establishment, von Bertalanffy growth
Invasive species are an ever-increasing problem worldwide and are considered one of the biggest threats to native habitats and biodiversity. Nonnative species move through a progression of stages as they become invasive, but the timing of this progression can vary considerably spatially due to local differences in resources. The invasion curve is the theoretical timeline of progression following a new invasion and consists of four different invasion stages: transport, introduction, establishment, and spread (
Silver carp (Hypophthalmichthys molitrix Valenciennes, 1844) have been widely introduced around the world and have become a prevailing issue in the U.S. since escaping into wild waterways the 1970s (
Long-term monitoring of invasive carp populations will allow evaluation of temporal trends as invasive carp become established throughout the U.S. Growth in silver carp is commonly faster close to the leading edge of invasion for expanding populations (
The Big Sioux and James rivers are two mid-sized rivers and are the largest tributaries to the Missouri River in eastern South Dakota (
Silver carp were primarily collected using daytime boat electrofishing in 2021 and 2022. Electrofishing was performed in a downstream direction with a Smith-Root GPP 7.5 electrofishing boat using pulsed direct current (170 V; 11–14 A; 120 pulses/s). Silver carp were also collected opportunistically as by-catch during electrofishing sampling events for other species. In June of 2020, juvenile silver carp (n = 13) were collected on the Big Sioux River below the falls at Sioux Falls and below the Sioux Falls spillway using a 2.44-m diameter cast net with 6.4-m mesh.
All silver carp were measured for total length (TL; mm). Silver carp were euthanized with either a lethal dose of MS-222 or by pithing, and lapilli otoliths were extracted for age estimation. Lapilli otoliths were used for aging based on the recommendation of
We modeled silver carp growth using the von Bertalanffy growth equation:
Lt = L∞ (1 − e−K (t − t0))
where Lt is the TL at time t, L∞ is the mean asymptotic TL, K is the Brody growth coefficient, and t0 is the theoretical time when TL is zero. We ran the model using a Bayesian framework with a Gaussian probability distribution for each waterbody, denoted with a subscript j, as follows:
Lt ~ Normal(µ, σ)
µ = L∞ j (1 − e−K j (t − t0 j))
L ∞ [Big Sioux] ~ Normal(900, 100)
L ∞ [difference] ~ Normal(0, 50)
K [Big Sioux] ~ Normal(0.2, 0.1)
K [difference] ~ Normal(0, 0.2)
t 0 [Big Sioux] ~ Normal(0, 1)
t 0 [difference] ~ Normal(0, 1)
σ ~ Exponential(0.25)
Bayesian modelling allows for the incorporation of prior knowledge in the form of a prior probability distribution and can improve the estimates of von Bertalanffy growth parameters when year classes are missing or older ages are underrepresented in the sample, making the results more biologically realistic (
We sampled from the posterior from ages 2 to the maximum observed age for both rivers to evaluate parameter trends. We compared posterior parameter estimates for L∞ and K between the Big Sioux River and James River population samples. We determined the probabilities that the L∞ and K values were greater for the Big Sioux River population than for the James River population. We calculated 90% prediction intervals (PI) for TL at ages 2–5 and calculated the probabilities that posterior estimated PI TL values were larger for silver carp in the Big Sioux River than the James River. We estimated mean length at ages 2–5 for silver carp in the introduction stage using the von Bertalanffy equation provided by
We performed a sensitivity analysis to ensure that our prior distribution values did not negatively impact model fit. The sensitivity analysis utilized the same data and model specifications as the original model, except all prior standard deviation sizes were doubled for L∞, K, and t0 parameters, and the σ prior value was halved. We assessed model fit using the same methods as for our original model and compared the difference in posterior parameter estimates between the sensitivity and original models.
We collected and aged 99 silver carp from the Big Sioux River and 82 silver carp from the James River. Silver carp age estimates ranged from 2–14 years for the Big Sioux River and 2–11 years for the James River. The posterior mean (95% credible interval) von Bertalanffy growth parameter estimates were L∞ = 714 mm (683–753 mm), K = 0.248 (0.190–0.314), and t0 = -1.299 (-2.149 – -0.610) for the Big Sioux River population and L∞ = 709 mm (646–774 mm), K = 0.271 (0.191–0.393), and t0 = -1.314 (-2.702–0.067) for the James River population (Figure
Mean total length (mm) for ages 2–5 silver carp estimated from von Bertalanffy growth models for fish collected in 2020–2022 in the Big Sioux and James rivers, South Dakota (this study) and for fish collected in 2009–2012 in the Big Sioux, Vermillion, and James rivers, South Dakota (
Study | Age 2 | Age 3 | Age 4 | Age 5 |
---|---|---|---|---|
Big Sioux | 394 (321–467) | 465 (391–539) | 519 (447–591) | 561 (489–635) |
James | 416 (339–486) | 484 (407–557) | 536 (466–609) | 577 (506–650) |
|
358 | 495 | 611 | 708 |
Von Bertalanffy growth curves and 90% prediction intervals (shaded) for Silver Carp collected in the Big Sioux and James rivers, South Dakota from 2020–2022. Circles represent individual length-at-age estimates and are randomly offset to reduce overlap, and the dashed line represents the combined von Bertalanffy growth curve across the observed ages from the early stages of invasion (2009–2012) in the eastern South Dakota tributaries to the Missouri River (
Mean posterior estimated TL values in the Big Sioux River and the James River were lower than the introduction stage estimates after age 2 (Table
Our model successfully converged, with R̂ values being <1.01 for all parameter estimates. Traceplots exhibited full mixing of the Markov chains, and posterior predictive check plots showed that the posterior estimates for the model closely matched the observed values. Additionally, all parameter estimates in the sensitivity analysis were within 5% of the original model parameter estimates, indicating low sensitivity to prior value selection.
Our study demonstrates that growth has slowed after a 10-year period as silver carp became established in two eastern South Dakota tributaries to the Missouri River. The substantial reduction in growth potential suggests that silver carp in the Big Sioux and James rivers have transitioned to the establishment stage of the invasion curve. Comparisons of length at age estimates indicated that mean TL at ages 2–5 were lower than mean estimates during the introduction stage (
The Big Sioux and James rivers exhibited similar silver carp growth characteristics. The probabilities that silver carp in Big Sioux River had larger posterior estimated L∞ (61.6%) and TL at ages (all approximately 40%) than in the James River demonstrated substantial overlap in estimated values. The similarity among populations may be a result of population mixing between the Big Sioux, James, and Missouri rivers, as silver carp are known to make large-scale movements in other free-flowing (
Due to low water conditions, we were unable to sample the Vermillion River in areas upstream of the confluence, so we were not able to include the Vermillion River population in our comparison of growth.
Growth of silver carp in the Big Sioux and James rivers was slower than in low-density, leading-edge populations in the Wabash, Mississippi, and Ohio rivers (
The larger length at age 2 during this study can likely be attributed to the reduction in the mean asymptotic length and the lack of age-1 silver carp among our aged individuals. The Brody growth coefficient (K) is a measure of how quickly fish will achieve their asymptotic length, so K and L∞ values tend to be negatively correlated (
The transition of silver carp from introduction to establishment stages on the invasion curve has likely caused ecosystem shifts in the eastern South Dakota tributaries to the Missouri River. Changes in silver carp growth have been linked to shifts in the zooplankton community (
JDH, KRJ, JMS, and BJS contributed to research conceptualization, sampling, and data analysis, and all authors contributed to writing and revision of this manuscript.
All research was performed in accordance with the Guidelines for the Use of Fishes in Research by the American Fisheries Society.
We would like to thank all the graduate and undergraduate students from the University of South Dakota and South Dakota State University as well as the full-time, seasonal, and intern staff with the Game, Fish and Parks for assistance with field sampling and otolith extraction. We also thank two anonymous reviewers for improving the manuscript. Code used in statistical analysis available in the GitHub repository, https://github.com/bjschall/South-Dakota-Silver-Carp-Growth.