Figure 3 - available from: Biological Invasions
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Typical hydroacoustic transects (dashed lines) in three backwater lakes (East Pit, West Pit and Rock Run) and in a section of the Starved Rock reach (with examples of main channel, tributary, side channel and harbor habitat). Note that hydroacoustic transects during the before and after harvest events in the three backwater lakes consisted of a single nearshore loop only, rather the multiple loops undertaken as part of the river-wide surveys (as shown). For all surveys, the acoustic beams were aimed outward from the nearest shoreline
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The threat posed by bigheaded carps (Hypophthalmichthys spp.) to novel ecosystems has focused efforts on preventing further range expansion; upstream progression in the Illinois River is a major concern due to its connection with the uninvaded Great Lakes. In addition to an electric barrier system, commercial harvest of silver carp (H. molitrix) an...
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... 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 (Stuck et al. 2015;Erickson et al. 2021;Broaddus and Lamer 2022), but mean maximum estimated lengths were consistent with those for long-established populations in portions of the Mississippi and Illinois rivers (Erickson et al. 2021;Broaddus and Lamer 2022) and within their native range (Nikolskii 1961). Silver carp growth and condition have been shown to be density dependent and can increase following large-scale commercial harvest and subsequent declines in population densities (MacNamara et al. 2016;Coulter et al. 2018b), but we do not have current density or relative abundance information on the Big Sioux and James river populations for comparison. Density-independent factors such as water quality and flow regimes may vary among the different river systems, which could impact silver carp bioenergetic requirements and subsequent growth. ...
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.
... Additionally, we observed that catch rates of silver carp were generally three times higher than bighead carp across all reported data. These differences in relative abundance are likely because silver carp outnumber bighead carp in many locations (e.g., Collins et al. 2015;Bouska et al. 2017;MacNamara et al. 2016MacNamara et al. , 2018. Overall, direct current electrofishing, gill netting, and trammel netting tended to score highest in our gear comparison when targeting adult life stages. ...
We conducted a review to summarize the settings, configurations, and capture data for an array of fisheries gear types used to capture invasive bigheaded carps (Hypophthalmichthys spp.) in North America. The goal of this paper was to synthesize patterns of bigheaded carp catch data across various gear types and capture methods. Data consisted of bigheaded carps captured among a variety of riverine habitats where their populations are well-established (e.g., lower pools of the Illinois River), as well as near the leading edge of their invasion front (e.g., Upper Mississippi, Upper Illinois, Upper Missouri, Red River). Our synthesis provides a summary of (1) capture gears and their settings/configurations, (2) catches (fish size, number captured, precision of estimates), and (3) assessment of gears that were robust (i.e., high precision, low cost, high catch, sample many habitat types) in riverine environments and impoundments. Across the 26 gear types used to target bigheaded carps, catch rates of silver carp were consistently higher than bighead carp, which may result from a combination of sampling inefficiencies, sampling biases, and spatial dynamics of their invasions. Gear performance matrices combining catch rate, precision, and labor cost indicated that DC electrofishing and herding fish into gill nets and/or trammel nets were the top-ranked capture methods. This review provides guidance for the development of detection, monitoring, and control programs that target bigheaded carp species, as well as identifies future research to fill critical data gaps.
... In this example, directing change is dependent upon interventions that transcend natural resources management and require a broad socio-economic coalition to address marketing (Keevin and Garvey, 2019), infrastructure and supply-chain bottlenecks to enable a regime shift. Questions remain whether a commercial fishery could suppress bigheaded carp biomass enough to weaken functional feedbacks while also sustaining a fishery market, but modelling efforts and empirical assessments have verified that increased fishing pressure (i.e., removal efforts) can effectively reduce population biomass (Tsehaye et al., 2013;MacNamara et al., 2016). Additional management efforts to enhance geomorphic complexity and broaden the range of habitat conditions are likely necessary to strengthen feedbacks of native fishes as bigheaded carp are often prolific in areas that have undergone habitat loss and degradation. ...
... Incorporating spatial dynamics and size-dependent movement into our model indicated that the best additional actions to take Removals focused on large individuals can have multiplying benefits on native ecosystem recovery and management outcomes (Love et al., 2018;Tamburello et al., 2019). Upper river harvest strategies near the invasion front continue to be effective (Coulter, MacNamara, et al., 2018;MacNamara et al., 2016) because they directly reduce abundance and upriver dispersal at or near the invasion front. Our model results support the need for continuing upper river harvest as a control strategy, recognizing that additional harvest efforts allocated toward lower river pools can have markedly stronger effects on their own, and in tandem may be the optimal scenario for managers. ...
... MacNamara et al., 2016). ...
Invasive species management can benefit from predictive models that incorporate spatially explicit demographics and dispersal to guide resource allocation decisions.
We used invasive bigheaded carps (Hypophthalmichthys spp.) in the Illinois River, USA as a case study to create a spatially explicit model to evaluate the allocation of future management efforts. Specifically, we compared additional harvest (e.g. near the invasion front vs. source populations) and enhanced movement deterrents to meet the management goal of reducing abundance at the invasion front.
We found additional harvest in lower river pools (i.e. targeting source populations) more effectively limited population sizes upriver at the invasion front compared to allocating the same harvest levels near the invasion front. Likewise, decreasing passage (i.e. lock and dam structures) at the farthest, feasible downriver location limited invasion front population size more than placing movement deterrents farther upriver.
Synthesis and applications. Our work highlights the benefits of adopting a multipronged approach for invasive species management, combining suppression of source populations with disrupting movement between source and sink populations thereby producing compounding benefits for control. Our results also demonstrate the importance of considering metapopulation dynamics for invasive species control programs when achieving long‐term management goals.
... The advancement of split-beam echosounder techniques, however, provides a useful tool to managers interested in evaluating pelagic fish populations (Lyons, 1998;Gerasimov et al., 2019). Mobile echosounder surveys can cover large spatial areas (Baroudy and Elliott, 1993;Parker-Stetter et al., 2009;MacNamara et al., 2016) and effectively collect data in areas difficult to sample using traditional fisheries gears (e.g., flowing waters with steep banks; Casselman et al., 1990;MacNamara et al., 2016). These characteristics make echosounders a potentially effective tool for evaluating pelagic fish populations in large rivers. ...
... The advancement of split-beam echosounder techniques, however, provides a useful tool to managers interested in evaluating pelagic fish populations (Lyons, 1998;Gerasimov et al., 2019). Mobile echosounder surveys can cover large spatial areas (Baroudy and Elliott, 1993;Parker-Stetter et al., 2009;MacNamara et al., 2016) and effectively collect data in areas difficult to sample using traditional fisheries gears (e.g., flowing waters with steep banks; Casselman et al., 1990;MacNamara et al., 2016). These characteristics make echosounders a potentially effective tool for evaluating pelagic fish populations in large rivers. ...
... This phenomenon decreases fish abundance beneath the vessel, reduces fish encounters with vertically deployed transducer beams, and biases density estimates (Draštík and Kubečka, 2005;Godlewska et al., 2009). To mitigate this depth limitation and increase sample volume, transducers are often deployed using a side-looking orientation which facilitates data collection perpendicular to the survey platform (Duncan and Kubečka, 1996;CEN European Committee for Standardization, 2014;MacNamara et al., 2016). The horizontal deployment of transducers increases sample volume during surveys in shallow water where vertically deployed transducers are ineffective (Burwen et al., 2003;CEN European Committee for Standardization, 2014) and effectively detects pelagic fishes difficult to detect with down-looking transducers and conventional fisheries gears (gill nets, boat electrofishing) in large rivers (MacNamara et al., 2016;Gerasimov et al., 2019). ...
... Monitoring of adult bigheaded carp has generally relied on gillnet gear, although alternative methods including electrofishing, hydroacoustics, eDNA, and herding are under investigation (Erickson et al. 2016;MacNamara et al. 2016;Bouska et al. 2017;Hammen et al. 2019;Butler et al. 2019;Ridgway et al. 2020). Sampling with sinking, monofilament, experimental gillnets was standardized across the study area. ...
Bigheaded carp Hypophthalmichthys spp. are invasive species native to Asia expanding in the Mississippi River Basin in North America. An understanding of spatiotemporal distribution and aggregation of invasive carp is key to establishing when and where to focus surveillance designed to monitor expansion, and to managing harvest programs designed to curb population densities. We applied a two-stage hurdle model to assess three aspects of bigheaded carp ecology: distribution, relative abundance, and aggregation. Stage 1 was a binary 0/1 model that represented fish presence (p), and stage 2 was a truncated count distribution that had no zeros and included counts ≥ 1 only (C).
Estimates of p and C varied temporally and spatially, but not in harmony and sometimes in opposing directions, indicating temporal and spatial swings in fish distributions and aggregations. Intense fish aggregations in channels in spring shown by low p’s and high C’s, eventually scattered by summer and fall as shown by high p’s and low C’s. An alternative but complementary interpretation of our observations is that p indexes incidence of aggregations and C indexes size of aggregations. Partitioning catch into its zero and nonzero components provided insight into population ecology that can inform development of monitoring and management of harvesting programs targeted at lessening potential effects of the invasion.
... Study sites and fish collection.-The Illinois River flows southwest from its origin at the confluence of the Des Plaines and Kankakee Rivers until its confluence with the Mississippi River, USA, and is divided into reaches by a series of locks and dams (Fig. 1) Department of Natural Resources (IDNR) has been harvesting Silver Carp from the Starved Rock Reach since 2011, but the catch-per-unit effort has generally been low in this reach compared to middle and lower reaches of the Illinois River as population density declines near the leading edge of the species' range MacNamara et al., 2016;Coulter et al., 2018). On one day per month between April-October 2018, commercial fishermen contracted by the IDNR collected Silver Carp from the Starved Rock Reach (RM 231.2-271.4) ...
Invasive species threaten ecosystems with destruction of native habitat, introduction of novel diseases, and enhanced competition with native wildlife subsequent to reduced predator control, leading, in many cases, towards efforts to actively remove individuals. While these effects are frequently studied, minimal research has investigated the individual or population health of the invasive species themselves. In this study, we describe multiple health outcomes of Silver Carp (Hypophthalmichthys molitrix), an invasive species in the Illinois River, as a component of a long-term monitoring and removal program using electrofishing, gillnets, and trammel nets. Between April–October 2018, Silver Carp were collected from two reaches of the Illinois River, examined, blood was collected for hematologic measurements, and cranial kidneys collected for histologic examination of melanomacrophage centers. Collection location impacted body condition, as Silver Carp closer to the leading edge of invasion were heavier than those from more established populations. Silver Carp caught by nets had lower packed cell volumes than those caught by electrofishing. The Health Assessment Index (HAI) showed that 52% of livers and 53% of kidneys were grossly abnormal. The HAI comes with a caveat that validation protocols are required to implement this technique effectively. Hematology and histology are more likely to be useful in species for which reference ranges exist. Overall, invasive species contain a wealth of information on health outcomes that could be used to monitor ecosystem health, but techniques used for monitoring must be adapted to the species, management needs, and removal methods.
... In our assessment of general resilience, we focused on physical and ecological attributes of resilient systems, whereas this transformation emphasizes the importance of having a broader understanding of social and governance adaptability and transformability (Chaffin et al. 2016). Questions remain whether a commercial fishery could suppress biomass enough to weaken functional feedbacks while also sustaining a fishery market, but modeling efforts and empirical assessments have verified that increased fishing pressure (i.e., removal efforts) can effectively reduce population biomass (Tsehaye et al. 2013;MacNamara et al. 2016). Further understanding of whether ecosystem and economic objectives could be jointly met under such a transformation may be beneficial to assess risks and trade-offs of directing change. ...
As anthropogenic influences push ecosystems past tipping points and into new regimes, complex management decisions are complicated by rapid ecosystem changes that may be difficult to reverse. For managers who grapple with how to manage ecosystems under novel conditions and heightened uncertainty, advancing our understanding of regime shifts is paramount. As part of an ecological resilience assessment, researchers and managers have collaborated to identify alternate regimes and build an understanding of the thresholds and factors that govern regime shifts in the Upper Mississippi River System. To describe the management implications of our assessment, we integrate our findings with the recently developed resist-accept-direct (RAD) framework that explicitly acknowledges ecosystem regime change and outlines management approaches of resisting change, accepting change, or directing change. More specifically, we developed guidance for using knowledge of desirability of current conditions, distance to thresholds, and general resilience (that is, an ecosystem’s capacity to cope with uncertain disturbances) to navigate the RAD framework. We applied this guidance to outline strategies that resist, accept, or direct change in the context of management of aquatic vegetation, floodplain vegetation, and fish communities across nearly 2000 river kilometers. We provide a case study for how knowledge of ecological dynamics can aid in assessing which management approach(es) are likely to be most ecologically feasible in a changing world. Continued learning from management decisions will be critical to advance our understanding of how ecosystems respond and inform the management of ecosystems for desirable and resilient outcomes.
... BHC harvest was initiated in the upper Illinois River in 2010, an area that was previously closed to all commercial fishing. In the upper Illinois River, harvest reduced densities of BHC while limiting replenishment from adjacent habitats (MacNamara et al., 2016) and curbed the exponential growth of biomass as observed during the early years of invasion in the lower river (Fig. 2). ...
... Movement of BHC from the densely populated lower river to the intensely harvested upper river likely undermines efforts to suppress BHC abundance in the upper river (MacNamara et al., 2016). This Fig. 1. ...
... The lower Illinois River includes reaches 6-8 (river kilometers 0-372), and the upper Illinois River includes reaches 3-4 (river kilometers 372-460). problem is compounded by sporadic but successful BHC reproduction in the lower river (Gibson-Reinemer et al., 2017a) and relatively open river conditions during high water periods (MacNamara et al., 2016). Nonetheless, we suggest that the upper river is indeed benefiting from the suppression of BHC, because a greater proportion of the population is being harvested, and this harvest was initiated prior to the population of BHC reaching an exponential growth phase as occurred in the lower river. ...
Large riverine systems are diverse and dynamic and are made up of multiple habitat types of lentic and lotic water. They are also heavily modified by humans and today nearly all habitats in many large rivers have been drastically altered. These modifications often include disconnecting lentic habitats either permanently or intermittently from the main channel. The Merwin Preserve at Spunky Bottoms (Merwin) began as a connected backwater that was leveed and drained for agriculture in the 1920s and restored in 1999, with restoration allowing it to become a disconnected backwater habitat. This status changed in 2013 when record flooding on the adjacent Illinois River overtopped and breached the levee creating an unmanaged and intermittent connection allowing the river access at moderately high river stages. During the past 20 years, the fish community at Merwin has undergone several changes that follow three drought events pre-breach, the exchange of fishes from the mainstem following the breach in 2013, and subsequent low water conditions of much of the area as river levels drop. Long term data and more intensive sampling efforts during the drought of 2012 showed relative abundance of sport fishes declined during, or immediately following, pre-breach drought events and post-breach low water conditions while relative abundance of non-sport and non-native fishes remained stable. The unique story of Merwin can provide a case study for other large river restoration projects on the effects of drought, climate change, and impacts of an unmanaged connection of a previously disconnected habitat to an adjacent large river.
... molitrix; hereafter referred to collectively as bigheaded carps) are examples of in-vasive species that have spread rapidly across the Mississippi River Basin, setting off a cascade of interactions (Jennings 1988;Chick and Pegg 2001;Lu et al. 2002;Sampson et al. 2009). Bigheaded carps arrived in the Illinois River, a highly productive tributary to the Mississippi River, in the mid-1990s and subsequently achieved among the highest recorded population densities anywhere in the global range of either species (McClelland et al.2012;Sass et al. 2010;MacNamara et al. 2016). One of the keys to the success of bigheaded carps as invasive fishes is their ability to switch between zooplankton, phytoplankton, and detritus as food resources, and the rapid increase of bigheaded carp populations has dramatically reduced zooplankton abundance in the Illinois River (Sass et al. 2014). ...
Since their arrival in the 1990s, invasive bighead carp (Hypophthalmichthys nobilis) and silver carp (Hypophthalmichthys moli-trix) have attained exceptional population densities and growth rates in the Illinois River. Standardized monitoring encompassing the duration of the invasion provides a rare opportunity to examine changes in the size distribution of age-0 and adult (age-3+) cohorts as biomass expanded dramatically. Biomass of bigheaded carps sampled expanded 150-fold, from just over 3,000 kg in 2000 to over 490,000 kg in 2013. Over the period of invasion, size distributions within both age-0 and adult cohorts have consistently fallen as population densities increased, strongly implying constraints on individual growth rates. Between 2000 and 2014, the mode of total lengths of age-0 bigheaded carps fell by 67%, whereas the 50th and 75th percentiles of adult silver carp lengths declined by 25%. Declines in zooplankton abundance and native planktivore condition suggest density-dependent competition for food likely has driven the decline in the size at age for both age groups. The trends observed in this study may provide useful information on how size distributions can vary across densities, particularly during the exponential growth phase of invasions.
