Informing Common Carp (Cyprinus carpio) Removal and Submerged Aquatic Vegetation Restoration in Lake Mattamuskeet
Creators: name: Lamb, April
Publisher: name: Zenodo
Year: 2020

description: Globally, shallow lakes and wetlands are experiencing unprecedented declines in the abundance and biodiversity of submerged aquatic vegetation (SAV). This loss is detrimental, as SAV increases ecological resilience, provides unparalleled foraging and refugia habitat for fish and waterfowl, and limits eutrophication. Declines in SAV abundance are frequently driven by changes in nutrient loading and turbidity, which disproportionately impact closed systems with high residence times and a limited capacity to self-regulate inputs. Shallow inland lakes therefore exist in one of two alternative ecological states: a clear-water state dominated by SAV, or a turbid-water state dominated by phytoplankton. These states are generally stable; however, high biomasses of invasive Common Carp (Cyprinus carpio, hereafter “carp”) resuspend sediment, uproot SAV, and increase nutrient availability during foraging, and can contribute to shifts from the clear to turbid-water state. Carp removal has been shown to reverse state shifts, but this has historically been limited to smaller systems and may be short-lived as carp are resilient to eradication. Thus, when considering management in large systems where repeated system-wide removals are costly, it is important to understand baseline population characteristics that may impact success. Our first objective is to inform carp management in Lake Mattamuskeet, a 16,314-ha shallow, hypereutrophic lake in eastern North Carolina that has undergone widespread declines in water quality and a total loss of SAV. Specifically, we characterize baseline population characteristics, estimate biomass, and simulate population-level responses to harvest using age-structured models. We found that carp are young (mean age = 3.7), short lived (maximum age = 7 years), and fast growing (K = 0.68). Annual mortality rate (A = 0.50) was higher than expected, possibly due to the extreme environmental conditions that occur annually in this system, including sustained periods of hot water temperatures (&gt; 30°C) and high pH (8 – 10), which encroach and exceed the maximum physiological tolerance of carp, respectively. Using an in-lake mark-recapture arena, we estimated a carp biomass of 124 kg · ha-1, which is above the reported threshold for ecological impairments due to carp presence. Finally, we ran a Beverton-Holt yield-per-recruit model to evaluate the population response to exploitation given our estimated range of natural mortality. We found that yield does not decline with increased exploitation, indicating that a population crash is unlikely from removal alone. The growing consensus is that an adaptive, multifaceted approach that increases ecological resilience in addition to reducing stressors is needed for successful restoration. Transplanting SAV following carp removal offers one strategy that can help reestablish native species in systems where seed banks have been depleted. Our second objective is to inform SAV restoration efforts in Lake Mattamuskeet. Specifically, we evaluate the establishment, overwinter survival, and growth potential of three native, macrophyte species [Vallisneria americana (submerged), Najas guadalupensis (submerged), Nymphaea odorata (floating-leaf)] when planted alone and together, and measure localized water quality parameters that may impact transplantation success. All three species successfully established, despite several water quality parameters that failed to meet median SAV habitat requirements. Submergent taxa exhibited the highest survival (N. guadalupensis = 92%; V. americana = 83%) followed by N. odorata (=75%). By far, V. americana exhibited the greatest upward and outward growth, expanding outside of the planting area in every enclosure it was detected in. We observed only one instance of vegetation (V. americana) growing outside of an enclosure. Total biomass of V. americana captured outside of the planting area averaged 126.0-g and was significantly higher in the all species treatment (V. americana + N. guadalupensis + N. odorata) than when planted alone or with only N. odorata after we corrected for