Rapid recovery of macroinvertebrates in a South African stream treated with rotenone

Abstract

South Africa's Cape Fold Ecoregion supports a unique freshwater fish assemblage with many endemics. To mitigate impacts of alien invasive fishes on this unique assemblage, nature conservation authority CapeNature used rotenone to remove smallmouth bass (Micropterus dolomieu) from the Rondegat River. We investigated whether the rotenone treatments had an adverse impact on the aquatic macroinvertebrate community over the long-term, the first study of its kind in Africa. We monitored macroinvertebrates within treated and untreated (control) sites on multiple sampling events for 2 years before and 2 years after two rotenone treatments. We analysed the difference in invertebrate abundance between treatment and control sites before and after treatment, using generalised linear mixed models with sampling event as a random factor to partition out natural fluctuations in abundances over time. Populations fluctuated widely in control and treatment sites over the study period, and we found no effect that could be clearly attributed to rotenone. We conclude that macroinvertebrates recovered rapidly after treatment, probably through drift from untreated areas upstream, with no long-term adverse effects. We recommend that the presence of uninvaded upstream refuges that may provide demographic rescue be used Handling editor: Verónica Ferreira

Ecosystem responses to the eradication of common carp Cyprinus carpio using rotenone from a reservoir in South Africa

“…Unfortunately, the possibility of this being a consequence of seasonal influences could not be investigated because the treated reservoir dried up in January 2018 owing to severe drought conditions, so collection of the 12‐month post‐treatment sample was not possible. The rapid recovery of macroinvertebrate communities in the present study is similar to findings by Bellingan et al (2019), who demonstrated the rapid recovery of macroinvertebrates in a South African stream treated with rotenone.…”

“…documented (Bellingan et al, 2019;Vinson et al, 2010). Here we demonstrated that the treatment of a small reservoir using rotenone resulted in the eradication of common carp and a decrease in turbidity, a shift in plankton and invertebrate communities and changes in water quality.…”

“…As a result, attempts to rehabilitate aquatic ecosystems through eradication of alien fishes are becoming common management interventions (Britton et al, 2010; Shelton et al, 2018; van der Walt et al, 2019; Weyl et al, 2014). Of the available methods, piscicides are the most effective at achieving fish eradications (see Rytwinski et al, 2019) but are also the most controversial as the collateral impacts on non‐target taxa have not been extensively documented (Bellingan et al, 2019; Vinson et al, 2010). Here we demonstrated that the treatment of a small reservoir using rotenone resulted in the eradication of common carp and a decrease in turbidity, a shift in plankton and invertebrate communities and changes in water quality.…”

Experience and Lessons from Alien and Invasive Animal Control Projects in South Africa

“…Micropterus dolomieu were successfully extirpated from this river following two rotenone treatments 1 year apart and upgrading of an instream weir to prevent reinvasion from downstream sources (Weyl et al 2014). Extensive post-treatment monitoring of non-target aquatic invertebrates illustrated that despite short-term negative effects, the invertebrate community recovered relatively quickly to pre-intervention levels (Woodford et al 2013;Bellingan et al 2015Bellingan et al , 2019. Native fish from upstream of the treatment zone successfully recolonised the treatment zone, resulting in an increased area of occupancy for these species in the absence of M. dolomieu (Weyl et al 2014;Marr et al 2019).…”

Trophic structure of a pond community dominated by an invasive alien species: Insights from stomach content and stable isotope analyses

“…At present, conservation efforts are focused on eradicating invaders, but those that are well established and strongly interspersed with natives cannot realistically be eradicated without affecting native species (i.e. with the use of rotenone; Bellingan et al, 2019). Accordingly, IAS removal may lead to unwanted and unexpected outcomes (Zavaleta, Hobbs & Mooney, 2001; Wallach, Ripple & Carroll, 2015).…”