Abstract
The common carp has been highly problematic in North American ecosystems since its introduction over a century ago. In many watersheds, its abundance appears to be driven by source-sink dynamics in which carp reproduce successfully in peripheral ponds that lack egg/larva micro-predators which then serve as sources of recruits for deeper lakes. This manuscript describes how carp were sustainably reduced in two chains of lakes by disrupting source-sink dynamics in three steps. First, we ascertained whether lakes had problematic densities of carp that could be explained by source-sink dynamics. Second, ways to control recruitment were developed and implemented including: (i) aerating source ponds to reduce hypoxia and increase micro-predator abundance, (ii) blocking carp migration, and (iii) locating and removing adults from sinks using targeted netting guided by Judas fish. Third, we monitored and adapted. Using this strategy, the density of carp in 3 lakes in one chain was reduced from 177 kg/ha to ~100 kg/ha in 3 years and held constant for a decade. Similarly, adult density was reduced from 300 kg carp/ha in 2 lakes in the other chain to 25 kg/ha. Once carp densities were low, aluminum sulfate treatments became reasonable and once conducted, water quality improved.
Highlights
The common carp, Cyprinus carpio, is one of the world’s most invasive fishes and likely to become more as our climate warms [1]
During the course of this 10 year study/ management effort, three major sources of young carp were controlled, and nearly 6000 adults removed. This integrated effort caused the carp biomass in lakes Kohlman–Gervais–Keller to fall from an average of about 177 kg/ha to a minimally-damaging level of about 40 kg/ha in 2016 from which it rose to ~100 kg/ha in 2018
While CPUE estimates in 2018 suggested a possible slight increase in adult density, recent anecdotal reports of juvenile captures in Lake Gervais suggest this likely was caused by a few adult carp entering Gervais Mill Pond to spawn during high water events
Summary
The common carp, Cyprinus carpio, (hereafter “carp”) is one of the world’s most invasive fishes and likely to become more as our climate warms [1]. Adult carp are seasonal spawners and migrate, on the local environment, mature at 2–5 years age and wetlands, can live ponds to be or over 60 years of age, sometimes greatcarp distances, into shallow waters of (floodplains, shallow lakes) where release million eggs each onto submersed vegetation [15,16]. In shallow lakes in Midwestern North America, correlations between adult carp density, a threshold foraquatic unacceptable ecological damage,and andwater which almost always is associated with a shift plant community composition, clarity, show that when adult carp densities reachin stable state and cyanobacteria blooms along withreduction decreased in water. For a population of fish to become highly abundant and invasive, its recruitment rate must on inter-connected glacial lakesitsinmortality the Midwestern America, variety evidence this average, exceed and emigration rates. We describe our overarching strategy (which we developed over the course of this study), and how it was implemented, and our results
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