Building a Better Snakehead Trap

April 15, 2010

The northern snakehead (Channa argus) is a delicacy in its Asian homeland.  In the United States however, it is a highly feared invasive species whose spread has not been successfully slowed.  When the snakehead first emerged as an ecological threat in 2002, media reports first described the fish as being capable of surviving weeks out of water and walking miles from one body of water to the next.  In reality, the snakehead’s unusual physiology allows it to survive approximately one day on dry land, possibly up to four in moist muddy areas.  Furthermore, it is the more mundane aspects of this species’ life history, and not the biological rarity of being able to breathe both underwater and on land, that make it such a nuisance species. 

Snakehead are efficient carnivores whose group hunting tactics can rapidly deplete native fish populations.  However, more important to their spread throughout the United states is their ability to tolerate a wide range of water temperatures.  This general diet and wide thermal tolerance have led some experts to estimate that the northern snakehead could invade all of the lower 48 states.

Current efforts at controlling snakehead populations focus on the use of piscicides (poisons designed to eradicate fish) to wipe out the invasive species.  The current piscicide of choice is the toxin rotenone, which is derived from the jicama plant.  Rotenone is 100% lethal to the northern snakehead; however it also kills all other fish in the target area and is rather expensive.   This combination of collateral environmental damage and high cost is what led Duke University research Evan Schwartz to try and develop alternative piscicides for use in slowing the spread of the northern snakehead.

Schwartz and his team of researchers are looking at three new toxins obtained from other plants with known poisonous properties (Nerium oleander, Canabium sativum, and Strychros nux vomica) to determine if a cheaper, and greener, piscicide can be produced.  Their research will include expansive field testing that compares the efficacy of these newly derived poisons to that of rotenone as well as other control techniques such as electro-shocking and netting.  Schwartz says that his research should pose little threat to surrounding populations because rotenone decomposes in sunlight and is also inherently less toxic to humans and other mammals.

From these field experiments, Schwartz hopes to assemble data on how each of the new plant-based toxins compares to rotenone in terms of both snakehead mortality as well as the effect on the native fish populations.  Ideally, one of the tested poisons would retain the same high lethality towards the snakehead as rotenone, but would cause much less collateral damage to the native species.  Yet, this is unlikely and so a more realistic outcome would be to find a plant based poison with both positive and negative effects similar to rotenone that can be more cheaply produced.  This would allow for the broader implementation of snakehead control policies throughout the contiguous United States, hopefully leading to a halt of the spread of this aquatic invader.


No Rotenone, No Problem?

April 15, 2010

Ben Berg

The ongoing fight against invasive species has bred several unique strategies for eradicating the harmful foreign species that now inhabit many ecosystems worldwide. In the case of aquatic species, one such strategy has been the use of the piscicide rotenone, a poison that when dumped into rivers, streams, and lakes kills most living organisms within a given radius.

Besides the ecological concerns associated with the use of such a poison, rotenone is both expensive and in increasingly short supply. An extract of the jicama plant, rotenone has recently been synthesized in a laboratory setting, creating a cheaper and more effective version of the poison, which has higher solubility in water in its synthesized form than its naturally occurring state.

A proposed study by researcher Alex Groszewski, however, highlights the issues associated with the development of synthetic rotenone, and aims to solve these problems through the use of new and different chemicals. “Cheaper and more deadly forms of rotenone only amplify the problems that exist with naturally occurring rotenone.” Groszewski said, commenting on the increased number of native species that will be affected by the more available and effective synthetic rotenone.

Building on existing research by Ashraf et al., Groszewski hopes to uncover chemicals that are equally accessible, yet better than rotenone in their ability to specifically target undesirable species in a given area. No scientific investigation has provided a comprehensive look at such chemicals or their ability to affect certain species more than others. The answers to these questions will thus be important goals of the proposed research.

Groszewski plans to test the effects of extracts of three herbs, Nerium Oleander, Cannabium Sativum, and Datura Alba, which are informally recognized as piscicides by “ artisanal fishermen” surveyed in the Ashraf et al. study. The effects of these extracts will be tested on the Northern snakehead (Chana Argus), sea lamprey (Pertomyzon Marizon), and ruffe (gymnocephalus cernuus).

When asked about the choice of fish to be tested in the study, Groszewski responded, “These are three invasive species that currently threaten the Laurentian Great Lakes region. This is an area species invasion risk is a large concern and because of this they made logical choices as test subjects.” The plan is to dose these potential invaders with the extracts of the above plants as well as synthetic rotenone, and gather data that will allow a comparison of the effects of the respective chemicals. Aquatic species native to the Laurentian Great Lakes region will also be tested to try and find a chemical that is better at targeting invaders than the native ecosystem.

Groszewski is hopeful that his study could prevent the further use of destructive poisons in the elimination of invasive aquatic species. If a more target-specific poison is found, it could prevent some of the damage done by rotenone, which has left some native species’ populations reduced by as much as 21% after a period of five years. He also hopes to find a chemical that could act as a cheaper substitute to the naturally occurring rotenone and that would thus be feasible for large-scale use.

Such a poison would represent a huge leap forward for scientists who have otherwise resorted to using the harmful rotenone or other strategies such as electrified barriers whose effectiveness remains in question. Groszewski’s objectives appear simple yet important to the preservation of aquatic ecology, a combination that makes for compelling possible outcomes. All that remains to be seen is whether or not such a piscicide exists, and if it will be efficient enough to end the use of rotenone in invasive species control.


Not Exactly Pearls: An Examination of the Green Porcelain Crab’s Effects on Oyster Reef Restoration

April 15, 2010

DURHAM, N.C. – The green porcelain crab (Petrolisthes armatus) is an invasive crab hailing from South America. This filter feeder tends to reside in available oyster reefs, creating population densities of over 1,000 crabs per square meter. Such densities are unheard of anywhere in the world, even in the crab’s native environment.

First sighted in Florida in 1994, this crab has spread throughout the South Atlantic Bight, an area of coastline ranging from Cape Hatteras, N.C. to Cape Canaveral, F.L. Even though the blue crab (Callinectes similis), common mud crab (Panopeus herbstii), and mummichog (Fundulus heteroclitus), a small fish, readily consume this invader, nothing has truly slowed its movement. Researchers worriedly speculate about the environmental and commercial effects of such densities on American oyster reefs, a major fishery in the Southeast United States.

The green porcelain crab represents a double edged sword: increasing the population of oysters at current reefs, while decreasing their growth rate. Yet, the decreased physical growth offsets any oyster population growth. Thus, P. armatus represents a danger to all reef restoration efforts, as they remove nutrients and space required for reproducing oyster habitats.

P. armatus has demonstrated an affinity for hard substrates currently used in reef restoration projects. However, there is no research on whether this crab is likely to inhabit other substrates used in reef restoration efforts as well. Such information would prove useful in avoiding new crab colonies in future artificial reefs.

According to Wilber, “this study should tell us whether altering the method of oyster reef restoration will have an impact on this invasive species.  This can hopefully be compiled with data on oyster recruitment and material cost to generate the optimum strategy for restoring oyster reefs in the South Atlantic region.”

The research focuses on determining the effects of different substrates on populations of P. armatus. His proposal outlines the construction of four artificial reefs at five to eight intertidal sites chosen by the South Carolina Oyster Restoration and Enhancement program (SCORE), the targeted funding body.

The artificial reefs will consist of two naturally occurring substances (oyster and whelk shells), and two artificial substances (cinderblocks and cement treated crab traps). The oyster and whelk reefs will have a higher density due to the bagged shells in chicken wire, while the cinderblock and concrete reefs will have a lower density. After creating each artificial reef, the total area will be mapped and physically sectioned off. Every seven days during a two to three month summer period (as the crabs die in the winter, according to Wilber), a section will be chosen at random and removed at low tide. The inhabitants of the section will be identified and recorded. After acquiring data from the section, the inhabitants and section of the reef will be returned to their original location.

The SCORE reefs will be used as a control for the experiment, in order to determine the efficiency of the artificial reefs as opposed to the current ones.

Reef restoration efforts are often costly and manpower intensive. Wilber hopes to determine the most effective and most cost efficient material(s) for use in artificial reef construction. He notes that such information will allow resource managers to maximize ecological benefit and best utilize manpower in reef construction, by noting which materials prove the least desirable for P. armatus.

Further lines of suggested research include a determination for preference and avoidance of certain materials as indicated by avoidance of predators and an analysis of symbiotic relationships between the oysters and P. armatus over a longer period of time.

-By Evan Schwartz


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