FEATUREPeces endémicos amenazados en la región florística de Cabo en Sudáfrica: un nuevo comienzo en el Río Rondegat RESUMEN: en muchos ríos a lo largo del mundo, las comunidades ícticas nativas se ven amenazadas por peces foráneos. En la región florística de Cabo, en Sudáfrica, la depredación ejercida por peces foráneos ha impactado severamente las poblaciones nativas de peces y más de 17 especies endémicas de peces están amenazadas. Con el fin de preservar la fauna íctica endémica, se le dio prioridad a la remoción de especies foráneas en las áreas de conservación en esta región. En febrero de 2012, la primera erradicación de peces no nativos mediante el uso de rotenona, se dio lugar en el Río Rondegat, un pequeño cuerpo de agua que ha sido invadido por la lobina boca chica (Micropterus dolomieu). El tratamiento fue exitoso y culminó después de un proceso de diez años facilitado por la colaboración de las autoridades de conservación de Sudáfrica (CapeNature), el Instituto Sudafricano de Biodiversidad Acuática y el subcomité de Manejo de Químicos de La Sociedad Americana de Pesquerías. Se anticipa que el incremento casi instantáneo de la biodiversidad tras la remoción efectiva de peces foráneos invite a tomar nuevos esfuerzos para restaurar más poblaciones de peces endémicos en Sudáfrica. ABSTRACT: Nonnative fishes threaten native fish communities in many rivers of the world. In South Africa's Cape Floristic Region, predation by nonnative fishes has severely impactednative fish populations and more than half of the 17 endemic fish species are endangered. To preserve the unique endemic fish fauna, removal of nonnative fish from conservation areas is a priority in this region. In February 2012, South Africa's first nonnative fish eradication using rotenone took place in the Rondegat River, a small headwater stream that had been invaded by Smallmouth Bass (Micropterus dolomieu). The successful treatment culminated from a decade-long process that was facilitated through collaboration among a South African nature conservation authority (CapeNature), the South African Institute for Aquatic Biodiversity, and the American Fisheries Society Fish Management Chemicals Subcommittee. The successful removal of alien fish and almost instantaneous increase in biodiversity is anticipated to encourage more endemic fish restorations in South Africa.

The piscicide rotenone has been used for over 70 years to eradicate unwanted fish, but controversy exists regarding its impacts on nontarget organisms, particularly aquatic invertebrates. We evaluated the toxicity of synergized Nusyn‐Noxfish and nonsynergized CFT Legumine rotenone formulations in 4‐ and 8‐h exposures to rainbow trout Oncorhynchus mykiss and six species of mountain stream caddisflies, mayflies, and stoneflies. We then compared these results with historical treatment data and aquatic invertebrate collections surrounding rotenone treatments in the 1990s that were designed to restore Paiute cutthroat trout O. clarkii seleniris to the Silver King Creek basin in Alpine County, California. The toxicity of rotenone was greatest to the trout; the synergist piperonyl butoxide appeared to have no effect on the toxicity of rotenone to the trout but did increase the toxicity to the invertebrates. The mean 8‐h concentrations (as rotenone) lethal to 50% of the rainbow trout were 5.3 μg/L for CFT Legumine and 6.2 μg/L for Nusyn‐Noxfish; the mean values for invertebrates ranged from 34 to 174 μg/L for CFT Legumine and from 13 to 74 μg/L for Nusyn‐Noxfish. These findings corresponded to that observed in Silver King Creek, where three annual treatments of 16–23 μg/L for 6–18 h were successful in extirpating rainbow trout hybrids but caused little change in aquatic insect assemblages. To lessen the impacts of rotenone treatment in mountain streams, project planners should (1) use the lowest rotenone concentration and duration needed to accomplish the treatment objective (we suggest 25–50 μg/L for <8 h) and (2) avoid using formulations containing the synergist piperonyl butoxide.

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In September 2007, Lake Davis (near Portola, California) was treated by the California Department of Fish and Game with CFT Legumine, a rotenone formulation, to eradicate the invasive northern pike (Esox lucius). The objective of this report is to describe the fate of the five major formulation constituents-rotenone, rotenolone, methyl pyrrolidone (MP), diethylene glycol monethyl ether (DEGEE), and Fennedefo 99-in water, sediment, and brown bullhead catfish (Ameiurus nebulosus; a rotenone-resistant species) by determination of their half-lives (t(1/2)) and pseudo first-order dissipation rate constants (k). The respective t(1/2) values in water for rotenone, rotenolone, MP, DEGEE, and Fennedefo 99 were 5.6, 11.1, 4.6, 7.7, and 13.5 d; in sediments they were 31.1, 31.8, 10.0, not able to calculate, and 48.5 d; and in tissues were 6.1, 12.7, 3.7, 3.2, and 10.4 d, respectively. Components possessing low water solubility values (rotenone and rotenolone) persisted longer in sediments (not detectable after 157 d) and tissues (<212 d) compared with water, whereas the water-miscible components (MP and DEGEE) dissipated more quickly from all matrices, except for Fennedefo 99, which was the most persistent in water (83 d). None of the constituents was found to bioaccumulate in tissues as a result of treatment. In essence, the physicochemical properties of the chemical constituents effectively dictated their fate in the lake following treatment.

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The mysid Neomysis mercedis was examined as a test organism for use in acute toxicity tests at intermediate salinities characteristic of estuarine waters. Several sensitive invertebrate species are available for marine assessments (mysids) and freshwater tests (cladocerans), but few are available for estuarine toxicity tests. Observations in the laboratory indicate that Neomysis mercedis can be reared successfully at a temperature of 17°C, a salinity of 2‰, and a population density less than 5/L. Brine shrimp nauplii Artemia salina, algae, and commercial foods were used to sustain mysid cultures. Neomysis mercedis is viviparous and can complete its life cycle in 3–4 months. Neomysis mercedis is as sensitive as or more sensitive to toxicants than the marine mysid Mysidopsis bahia and the freshwater cladocerans Daphnia magna, Ceriodaphnia dubia, and Simocephalus serrulatus. The mean 96‐h LC50 values (concentrations lethal to half the test animals) for N. mercedis, in increasing order, were 0.20 μg/L for methyl parathion, 2.2 μg/L for malathion, 14 μg/L for carbofuran, 150 μg/L for copper sulfate, 280 μg/L for thiobencarb, and 1,600 μg/L for molinate. Neonates (5 d postrelease) were generally more sensitive than older juveniles. Coefficients of variation (100·SD/mean) of LC50 values varied from 21 to 35%.

In September 2006, Diamond Lake (OR, USA) was treated by the Oregon Department of Fish and Wildlife with a mixture of powdered and liquid rotenone in the successful eradication of invasive tui chub Gila bicolor. During treatment, the lake was in the middle of a phytoplankton (including cyanobacteria Anabaena sp.) bloom, resulting in an elevated pH of 9.7. Dissipation of rotenone and its major metabolite rotenolone from water, sediment, and macrophytes was monitored. Rotenone dissipated quickly from Diamond Lake water; approximately 75% was gone within 2 d, and the average half-life (t½) value, estimated by using first-order kinetics, was 4.5 d. Rotenolone persisted longer (>46 d) with a short-term t½ value of 16.2 d. Neither compound was found in groundwater, sediments, or macrophytes. The dissipation of rotenone and rotenolone appeared to occur in 2 stages, which was possibly the result of a release of both compounds from decaying phytoplankton following their initial dissipation. Fisheries managers applying rotenone for fish eradication in lentic environments should consider the following to maximize efficacy and regulatory compliance: 1) treat at a minimum of twice the minimum dose demonstrated for complete mortality of the target species and possibly higher depending on the site's water pH and algae abundance, and 2) implement a program that closely monitors rotenone concentrations in the posttreatment management of a treated water body.