Eel Eradication

February 6, 2010

North American Journal of Fisheries Management 2006; 26: 949-952

doi:  10.1577/M06-023.1

The Asian swamp eel, which has already colonized four major locations in the southeastern US, has been labeled as a “major threat” to the nearby fragile ecosystems in the Everglades.  Methods to control or potentially eradicated the Asian swamp eel (Monopterus albus) are being pursued with little success.

One of the characteristics that has contributed to the eel’s widespread invasion is the species’ ability to obtain oxygen through surface air.  This trait rules out the option of using piscicides (fish poisons) to control the eel population.  However, a study conducted by Thomas Reinert and collaborators sought to determine if poison could be used to affect very young eels that still absorb oxygen through their skin.  Eels and control fish were exposed to different concentrations of Atimycin-A; however, the juvenile eels were unaffected, even at high concentrations.  Unfortunately, eradication through toxicants is probably not the answer to stopping the invasive eels, and other methods of biological control need to be studied.

Et tu, Weevil?

February 6, 2010

J. Aquat. Plant Manage 38: 78-81 (2000)

A study led by Robert P. Creed, Jr., of Appalachian State University investigates the use of biological control to restrain the spread of Myriophyllum spicatum, better known as the Eurasian watermilfoil. This aquatic plant has invaded lakes across North America, and scientists are examining the effects of the North American weevil (Euhrychiopsis lecontei) on watermilfoil on 4 environmental levels ranging from the individual plant to entire geographic regions. On the smallest scale, that of an individual plant, weevil larvae damage meristems, which hinders stem growth, and both larvae and pupae injure vascular tissue, preventing roots from getting nonstructural carbohydrates. Also, scientists found that weevils can make watermilfoil beds collapse in lakes, but the precise weevil density to cause this is uncertain. More research concerning aquatic predators, the nutrient content in sediment, and the regional climate is necessary. Creed concludes that further investigation is crucial at all four spatial levels to determine the efficacy of weevil biocontrol on watermilfoil.

Weevil Wonder

February 6, 2010

Journal of Aquatic Plant Management 44: 115-121 (2006)

Giant salvinia (Salvinia molesta) is a noxious aquatic fern native to Southern Brazil that has threatened many freshwater ecosystems. Giant salvinia reproduces rapidly by fragmenting part of their stems to create a new plant. Its overgrowing has replaced native vegetation, altering the food web of the aquatic ecosystems, and also reduced dissolved oxygen levels, which eventually asphyxiates all aquatic life. It hinders irrigation, clogs waterways and promotes diseases in the stagnant waters the fern creates.

Daniel Flores and J.W. Carlson of the USDA introduced the salvinia weevil (Cyrtobagous salviniae) to control the fern. Herbicides usually exacerbate the situation or are not effective. The places where the researchers introduced the weevils have a significant decrease of the fern and an increase in dissolved oxygen levels. The giant salvinia population has remained constant and the weevils have shown to only consume the fern and nothing else. The authors say more research is needed, but biocontrol has shown to be an effective option.

SW3: Starvation helps chances for survival?

February 6, 2010

Environmental Biology of Fishes volume 50: 391-403 (1997).

Red Lionfish (Pterois volitans) are an invasive species of spiny fish that have invaded the US Atlantic coast for about the past fifteen years. Their voracious predation on smaller fish and lack of many predators has facilitated their rapid spread as far north as the coast of New York.

A published study suggests another possible reason for the Red Lionfish’s successful spread- its ability to last up to eight weeks without food. Red Lionfish were kept in tanks during this period and dry-weighed each week. Unlike some other species, the Red Lionfish lost less and less weight each week. Overall they lost a smaller percentage of their original body mass (10%) compared to the other species of lionfish discussed in the study. This versatility probably explains how the Red Lionfish adapted so well in Atlantic waters when it was initially released.