Harvest removal of fish from populations is often biased toward larger, older individuals, which affects population responses. The harvest strategies evaluated during 2010 through 2012 were (1) an ongoing contracted harvest program in the upper Illinois River, (2) a “fisher-side” incentives program that offered select commercial fishers progressive economic rewards for participating (i.e., sharing harvest data) and harvesting increasing amounts of bigheaded carp for direct-consumption markets, and (3) a “market-side” incentives program that set a quota-based harvest of bigheaded carp for indirect-consumption markets of fish meal. Although the likelihood of reducing bigheaded carp to extinction in such a large, open system is low, the capacity for population suppression and reducing further expansion may be high. If reliable moderate- to high-value markets can be developed for bigheaded carp in the lower river, exploitation should remain high and reduce upstream migrants via invasivorism. In the lower Illinois River from where bigheaded carp in the upper Illinois River derive, commercial harvest is legal. Removal at this range edge is expected to be agency funded for the foreseeable future and has likely prevented upstream range expansion toward Lake Michigan. Since 2010, contracted removal of greater than 3200 tons of bigheaded carp has occurred near the CAWS in the upper Illinois River, where commercial harvest is prohibited.
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Removal of bigheaded carp is included in all eight management strategies for stopping interbasin movement of these fish, and non-structural control plus harvest is the only strategy that can be initiated immediately. Establishment of bigheaded carp in the Great Lakes may jeopardize fisheries valued at $7 billion USD per year. These species invaded the lower Mississippi River basin of the US in the 1970s, expanded northward, are now more abundant in the Illinois River than anywhere else globally, and may invade the Laurentian Great Lakes via Lake Michigan. nobilis (Richardson), collectively known as bigheaded carp. Potential candidates for invasivorism are silver carp Hypophthalmichthys molitrix (Valenciennes) and bighead carp, H. This consumer-based control of invasive species is popularly called invasivorism. Whereas government assistance is necessary to control invasive species that have low market value such as sea lamprey, Petromyzon marinus (Linnaeus ), fishes with commercial value could be marketed to reduce financial burden on government agencies. Yet, factors such as time, effort, and expense often limit success. Thus, controlled harvest may help control invasive populations of fish and other taxa. For example, humans routinely overharvest fish stocks. Invasive species threaten biodiversity worldwide, costing $120 billion USD annually in the United States. Given the geographical scale of this invasion and complicated harvest logistics, concerns about economic dependence on invasivorism that encourage stock enhancement are likely unmerited. However, lack of processing infrastructure and supply chain bottlenecks could constrain harvest, particularly at low commodity prices. With sufficient market demand, harvest may control bigheaded carp. Total density declined in one river reach, and harvest may reduce upstream movement toward the invasion fronts. Larger, older fish were disproportionately harvested, which may hinder the ability to suppress population growth. The “market-side”, set-quota approach removed >1.3 million kg of bigheaded carp in less than 6 months. However, participation was low, perhaps due to reporting requirements for fishers. “Fisher-side” removals totaled 225,372 kg in one year. Contracted removal was effective for suppressing small populations at the edge of the range but cannot support a market. We quantified the efficacy of these approaches and potential population impact in the Illinois River. To explore the efficacy of a consumer-based market (i.e., invasivorism) to manage them, we developed a conceptual model and evaluated three harvest approaches-direct contracted removal, volume-based incentives (“fisher-side” control), and set-quota harvest (“market-side” control). Invasive bigheaded carps, genus Hypophthalmichthys, are spreading throughout the Mississippi River basin.
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