March 23, 2010
The northern snakehead has become a widespread invader in the United States. Due to this species’ ability to survive and thrive in many different environments, control efforts for this species must implemented. Poison is one of the various methods being explored. In laboratory testing, several different concentrations proved lethal to the snakehead . Lazur et. al determined that the smallest lethal dose was 0.075mg/L of rotenone, a commonly used aquatic poison. Such a dose killed all test subjects within 1 hour of administration, and proved incredibly effective in a pond setting in Crofton, MD as 8 adult and 834 juvenile snakeheads were recovered. These results demonstrate a susceptibility of this species to known control methods. However, all other aquatic fauna in the affected region succumbed to the poison as well. Additionally, the affected area remained toxic for at least one week after treatment. It is suggested that this method only be utilized in clearly defined and isolated areas.
(North American Journal of Fisheries Management 2006; 26: 628-630)
February 4, 2010
Expansion of a Northern Snakehead Population in the Potomac River System
Transactions of the American Fisheries Society 136:1633–1639, 2007 doi: 10.1577/T07-025.1
Northern snakeheads (Channa argus) are illegal to posses in the states of Maryland and Virginia. After finding several of these fish in a Maryland pond in 2004, both states created an initiative in order to quantify and eliminate the snakehead “threat.” By way of electrofishing (a system of creating an electrical blast radius in a water body) and traditional hook and reel fishing, a large number of snakeheads were accounted for. The amount of snakeheads caught increased between the years of 2004 and 2006, either by way of informed anglers, or increased breeding.The study came to several conclusions. The majority (>80%) of the fish caught originated from a single point, showing a central nest location. They then began to migrate downstream in an attempt to find more food and nesting grounds. As the population matured over the years, the average length and mass of captured snakeheads increased. In addition, these fish fed primarily on the local aquatic fauna population, decreasing the amount of game fish for local anglers.
January 23, 2010
Myriophyllum, more commonly known as “water milfoil”, is an aquatic invasive species originating in Eurasia. This species has recently been discovered in some of the rivers that run through the Adirondacks, very popular spots for fly-fishermen. The most reasonable explanation for the migration of this species from the Eastern to the Western hemisphere is that of ballast-water transportation. Before embarking on a journey, large ships take in a certain amount of water called “ballast water”. This water is used as a type of counterweight – the addition of it to the ship’s weight helps to stabilize the ship and provide proper buoyancy. Upon reaching their destination, these ships release this water into the surrounding bay, dock, inlet, etc. Biologists have concluded that this is the most justifiable reason for the discovery of water milfoil in the United States – particularly the New York area, as it is such an epicenter of the coming and going of ships. One way environmentalists are attempting to reduce the water milfoil population in upstate New York water parks is with devices called “benthic barriers”. This form of eradication is fairly simple – gigantic plastic sheets are taken to the bottom of the lakes and pinned down, covering water milfoil colonies. This prevents sunlight from reaching the plants, and eventually leads to their death. Another method is called “biocontrol”, where certain fish and small marine life are introduced to these ecosystems in order to feed on the watermilfoil population and keep it under control. A curious fact about these plants is that it is seen as a valuable source of biofuel, especially in our day and age where everybody is struggling to “go green”. The battle of whether to kill off milfoil or to try and control it for human use is currently underway.
The mute swan – generally seen as a majestic creature and one that inspires peace and tranquility, this large waterfowl is not understood to be an aquatic invasive species by most of the general public. What makes this bird so destructive? It is typically known as one of the most aggressive species of waterfowl, and it consumes large amounts of underwater vegetation. This vegetation is important to the rest of the ecosystem in that it helps to hide baby crabs, fish, etc. who need the protection of the grass before they are big enough to make it alone in open water. This over consumption of underwater grasses is leading to a decline in those native populations, and a 10% increase in mute swan populations every year (meaning that the population doubles every 7 to 8 years). Right now, officials in the Maryland/Chesapeake Bay area are considering several methods for the reduction of the mute swan population. The least violent of these methods is a process where mute swan eggs are covered with oil which prevents them from hatching. Although reluctant to resort to such a measure, killing the swans (either by shooting or breaking their necks) is provided for as a last resort option. While animal rights activists claim that the mute swans do not have a great effect on bay grasses, studies have shown that the average adult mute swan eats up to 8 lbs of bay grass every day.
Although I could not find any direct information on aquatic invasive species in Texas, I did find this interesting website that lists many of the invasive species found in the state. Some of the more unique ones are electric eels, freshwater sting rays, and piranhas.