Potential Impact of Rusty Crayfish in New Environments



     Rusty crayfish may cause a variety of negative environmental and economic impacts when introduced to new waters.  This aggressive species often displaces native or existing crayfish species.  Rusty crayfish displace other crayfish species through three primary mechanisms:

    

     1.) Crayfish to Crayfish Competition

Rusty crayfish are better able to exclude other crayfish from shelters and better able to compete for limited food resources.

     2.) Increased Fish Predation

Rusty crayfish can increase fish predation on native crayfish in a variety of ways. They force native species from the best hiding places. As the native crayfish try to swim away from a fish or rusty crayfish attack, this makes them more vulnerable to capture by fish. Rusty crayfish, on the other hand, assume a claws-up defensive posture that reduces their susceptibility to fish predation. Also, rusty crayfish are larger and have larger claws than most native species, which results in fish preying upon native species over rusty crayfish.

     3.) Hybrdization

While rusty crayfish do not hybridize with Orconectes virilis, they do hybridize with Orconectes propinquus. This hybridization results in fertile and vigorous offspring, but ultimately results in the decline of Orconectes propinquus. The competitive superiority of the hybrids helps exclude genetically pure Orconectes propinquus faster than Orconectes rusticus would without hybridization.

     The destruction of aquatic plant beds is perhaps the most serious impact. Rusty crayfish have been shown to reduce aquatic plant abundance and species diversity.   This can be especially damaging in relatively unproductive northern lakes, where beds of aquatic plants are not abundant. Submerged aquatic plants are important in these systems for:

• habitat for invertebrates (which provide food for fish and ducks),
• shelter for young gamefish, panfish, or forage species of fish,
• nesting substrate for fish, and
• erosion control (by minimizing waves)

     Although other crayfish eat aquatic plants, rusty crayfish eat even more because they have a higher metabolic rate and appetite.  They also grow larger, hide less often from predators – and therefore feed longer – attaining high population densities.
     Rusty crayfish are more likely to compete with juvenile game fish and forage fish species for benthic invertebrates than are native crayfish species. Displacement of native crayfish by rusty crayfish could result in less food for fish. Crayfish are eaten by fish, but because of the higher ratio of their thick exoskeleton (shell) relative to soft tissue, their food quality is not as high as many of the invertebrates that they replace. Less food or lower food quality means slower growth, which can reduce fish survival.
     Rusty crayfish can harm fish populations by eating fish eggs, reducing invertebrate prey, and through loss of habitat (aquatic plants). Male bass and sunfish protect their nests until the eggs hatch and the advanced fry swim away.  It was also found that total zoobenthos, larval midges, mayflies, dragonflies, and stoneflies decline as rusty crayfish populations increase.  Walleye reproduction dropped after a rusty crayfish invasion.
Observations and circumstantial evidence gathered by Wisconsin fishery managers suggest that bluegill and northern pike populations frequently decline following the introduction of rusty crayfish.  Impacts on other fish species are not as obvious.  The cause of bluegill, bass, and northern pike declines is probably reduced abundance and diversity of aquatic plants.  Reduced food (such as mayflies, midges, and stoneflies) and egg predation may also play a role.
     Cabin owners on heavily infested northern Wisconsin and Minnesota lakes have even stopped swimming because large numbers of "rustys" occupy their favorite swimming area throughout the day. They fear stepping on them and getting pinched by their large claws. Other crayfish species, even if abundant, are less conspicuous during daylight hours.

Control and the Prevention of the Spread of Sea Lamprey



http://www.glsc.usgs.gov/main.php?content=research_lamprey&title=Invasive%20Fish0&menu=researchinvasive

     The sea lamprey is one of the few aquatic invasive species that is being successfully controlled. In the late 1940s the State of Michigan began investigations into the biology of sea lampreys. In 1950, this became a federal program. In 1955, the Great Lakes Fishery Commission (GLFC) was created under a convention between the United States and Canada for the purpose of restoring fisheries. One of the GLFC’s primary duties was the control or eradication of sea lampreys. It currently manages sea lamprey populations across the Great Lakes to about 10% of their former levels. Control is delivered through its control agents, the U.S. Fish and Wildlife Service and the Department of Fisheries and Oceans, Canada.

     Control depends on breaking the life cycle. The first control efforts attempted to do that by blocking access to the spawning areas in streams. This was only partially successful because the weirs used to do this were impossible to maintain 100% of the time. There were attempts to use electric fields alone or in conjunction with the weirs, but that was eventually abandoned as too dangerous. A second vulnerable point in the life cycle is during the larval stage, when sea lampreys spend at least three years burrowed in the stream sediment. During the 1950s, over 6,000 chemicals were screened before finding one that was selectively toxic to sea lampreys. That chemical, TFM, has been carefully applied to infested streams, beginning in Lake Superior in 1958. Treatments quickly decreased sea lamprey numbers to 10% or less of their former numbers. Reduced lamprey numbers allowed native and stocked lake trout to survive and the lake trout populations to rebound. Recently, the restoration of lake trout in Lake Superior was declared a success and federal stocking of lake trout was stopped. Lake trout stocks in Lake Superior are once again selfsustaining.

Locations of dams preventing the spread of spawning sea lamprey.

     Treatments with TFM start with electrofishing surveys of the Great Lakes tributaries known to potentially produce sea lampreys. Based on estimates of the number of metamorphosed sea lampreys to be produced and on treatment costs, a list of streams to be treated is made each year. Because of the duration of the larval stage, streams are treated at intervals of 3 to 5 years or longer.

      Ineffective and labor-intensive screen weirs have been replaced with low-head barriers that block sea lampreys but allow jumping fish to pass.  A combined low-head and electrical barrier was constructed on the Ocqueoc River, which functions effectively as a low-head barrier but also blocks sea lampreys during high water on this flood-prone stream. This combination of proven technologies allows effective blockage of migrating sea lampreys and passage of jumping fishes under a much broader range of stream flows. Under normal flows, the low-head barrier is functional, no current flows to the electrical barrier, and jumping fish can pass. During flood conditions, when the low-head barrier is inundated, the electric barrier automatically turns on and blocks sea lampreys.

Impact of Sea Lamprey on the Great Lakes

The Correlation Between the Number of Sea Lampreys and Lake Trout in Lake Superior



Sea Lamprey feeding on a native lake trout in Lake Superior.

http://www.glsc.usgs.gov/main.php?content=research_lamprey&title=Invasive%20Fish0&menu=researchinvasive

     Sea lampreys quickly devastated the fish communities of the Great Lakes.  Sea lampreys probably entered Lake Ontario in the 1830s via manmade locks and ship canals. Improvements to the Welland Canal in 1919 allowed sea lampreys to bypass Niagara Falls and enter Lake Erie. After sea lampreys were discovered above Niagara Falls (in Lake Erie in 1921 and Lake Huron in the early 1930s), they spread throughout the upper Great Lakes by 1939. The lake trout was the main predatory species at that time and the sea lamprey’s preferred host. Although early declines in lake trout abundance in the 1940s are suspected to have been caused by overfishing, sea lampreys are believed to be responsible for the very rapid decline in the later 1940s and 1950s. Lake trout actually became extinct in Lakes Ontario, Erie, Huron (except a few inlets of Georgian Bay), and Michigan. Only remnant native stocks remained in Lake Superior. Two factors contributed to the devastating effect of sea lampreys. First, sea lampreys lacked effective predators. Second, the Great Lakes probably have as many miles of tributaries and as many acres of larval habitat as the native range of the sea lamprey along the Atlantic Coast. Host fishes in the Great Lakes are much smaller than those attacked in the Atlantic Ocean and are more likely to be killed by a sea lamprey attack. Between 40% and 60% of lake trout attacked by a sea lamprey will die from loss of blood. These attacks were a major cause of the collapse of lake trout, whitefish, and chub populations in the Great Lakes in the 1940s and 1950s. Lake trout harvests in the U. S. and Canada averaged 15 million pounds per year before the sea lamprey, but declined to record lows within 20 years of the sea lamprey’s appearance.
     Other equally important secondary effects were caused by cascading changes in the fish communities. After the elimination of predators like lake trout, the populations of invasive prey species like the rainbow smelt and alewife increased rapidly in the absence of predation. Those invasive species then out competed native species or preyed on their young. Extinctions of sculpin and deepwater cisco species have been suspected of being linked to extended periods of high abundance of smelt and alewives. The massive annual die offs of alewives that fouled the beaches in Michigan during the 1950s and 1960s were due to overcrowding and poor condition and were a secondary effect of the invasion of the sea lamprey. Alewives also prey heavily on zooplankton. Because zooplankton graze on phytoplankton, the density of phytoplankton increased and the color and clarity of water were affected, particularly in the lower Great Lakes.
     Human activities were affected first through the loss of sport and commercial fisheries across the Great Lakes. Following those losses, came other, equally important economic effects caused by the disappearance of fishery-related jobs and the loss of fishing tourism. With the beaches fouled with dead alewives, there were also losses of tourism associated with beach use.

Impacts of Goby in the Great Lakes



http://el.erdc.usace.army.mil/ansrp/neogobius_melanostomus.pdf

-Populations of native sculpin and logperch have exhibited a substantial decline in the Saint Clair River where the round gobies were first introduced.

-Round Goby eat darters, sculpins, logperch, the eggs and juveniles of trout and the eggs of lake sturgeon.

-Transfer of contaminates in the food cycle.

-Round gobies interfere with the actions of anglers.  For example, gobies eat the bait off hooks and anglers catch gobies instead of coveted sports fish.

-Round gobies interfere with habitat restoration projects in the Great Lakes and other regions.

-They behave aggressively toward other fish and drive native species from prime spawning areas.

-Round gobies tend to out compete native fishes for food partially due to an ability to feed in complete darkness and to the presence of a suctorial disk located on their pelvic fin which allows them to attach to rocks and remain fixed on the bottom in fast currents.

Some positive impacts include:

-Gobies eat zebra mussels, another Great Lakes invader.

-They also serve as a food source for larger predatory fishes and water snakes.

 

Prevention of the Spreading of Asian Carp into the Great Lakes



http://www.erikorganic.com/green/stakes-are-raised-for-asian-carp-prevention-in-great-lakes/

-The Obama administration made a 2011 commitment to increase Asian carp prevention measures for the Great Lakes in December of 2010.

-The plan calls for $47 million in funds to be applied to Asian carp detection, removal, and prevention.

-At the top of the amped-up policy initiative, stands environmental DNA (eDNA) detection methods, which will be used to more accurately direct prevention and removal measures.

-Great Lakes protective measures against Asian carp are incredibly important because the invasive species threatens the multi-billion dollar Great Lakes fishing industry, as well as the Great Lakes ecosystem.

-Some of the efforts already in place include electronic fish barriers and fences, as well as elimination of Asian carp that are already in waterways that connect to the Great Lakes.

-The eDNA programs that will be implemented will be used to help better focus such migratory prevention and numbers management.

-Many environmentalists argue however, that the only surefire way to keep Asian carp from thoroughly invading the Great Lakes is by closing the Chicago locks. Illinois and Chicago business leaders stand in strong opposition to this option, due to the economic impact it would have on waterway commerce for their economies. Even so, the Army Corps of Engineers is currently investigating such options, and will release a comprehensive report on the matter in 2015.