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Conservation - Invasive Species Management

Preventive measures to help fight the battle against invasive species by Musky Mike.

How-To On the Water
Conservation - Invasive Species Management

One of the biggest threats to our precious fisheries and aquatic resources is the spread of invasive species. Invasive species management is one of the toughest sectors because the immediate discovery of foreign species requires an investigation of their previous native range, understanding of their biology and ecology, and implementing protocols to eradicate them. Protocols for managing and eradicating invasive species cost agencies up to a billion dollars annually.  Common logic once previously assumed was that the introduction of a foreign fish species to a lake or river system would increase diverse angling options for the public. Yet, research has simply demonstrated that foreign competitors always outcompete native fishes in terms of food, resources, and space. In this conservation article, Mercury Marine provides a comprehensive updated list of potentially invasive species, current ramifications, and a list of preventive solutions to stop potential widespread introductions of foreign invaders into new waterways.

Zebra Muscles

The introduction of Zebra mussels into the Great Lakes in the 1980s occurred through the discharge of ballast water of European merchant ships and others. Zebra mussels are foreign mollusks that are finger-length sized native to the freshwaters of Eurasia. In the 1980s, zebra mussels were introduced through the discharge of ballast water from European merchant and cargo ships in harbors/ports of the Great Lakes. Populations eventually spread into freshwater lakes inland from attachment to props, the bottom of hulls, sides and bottoms of trailers.  Upon their introduction, they seemed to positively impact the Great Lakes as they cleaned up turbid water conditions in nearshore areas of harbors, river mouths, and shallower breakwater. Biologists discovered however, that in the 1990s that zebra muscles negatively impacted the ecosystem through the consumption of large amounts of phytoplankton and zooplankton that alewives, smelt, and other main forage fishes depended on for their diet. Additionally, zebra mussels also filter out algae that native species require for food.

Preventive Solution: Completely drain and thoroughly clean livewells after trailering boat out of the water. Establish a convenient location near watershed operating out of and rinse sides boat, the bottom of the hull, and interior compartments with low-pressure hot water (around 120oF). The temperature of the water for rinsing and cleaning your boat is critical because cold water typically does nothing to invasive species. Warm water removes attached critters while hot water kills them. After thorough rinsing of the vessel, immediately wipe down with a towel in case of fishing another lake or river system that day or the next day. Allow for several days to dry until the next fishing expedition. Never use chemicals to clean boat such as bleach for example because its bad for the environment, cause damage to boat compartments and parts, and harms human health.

New Zealand Mud Snail

 An uncommon introduction of invasive species into a native ecosystem can also be through angler's footwear. An example of this invasive situation occurred with the New Zealand mudsnail. New Zealand mudsnails are tiny aquatic crustaceans around 1/8 inch in length when full-grown and exhibit a light to dark brown shell, featuring 5-6 spirals. A distinct feature of its shell is a retractable cover called an operculum, which thus allows the snail to seal itself inside when threatened from predators or exposed to pollutants. Its rigid operculum allows for unharmed detection when digested through a fish or birds digestive system after consumption. Original populations were initially introduced into fisheries of the United States through contaminated ship ballast water and transportation of live fish or eggs for the commercial aquaculture industry. Long distance dispersal of the sneaky invader has occurred by attaching to landing nets, bottom and sides of wading boots, waders, and trailers. Evidence suggests that New Zealand mudsnails can move 10 feet per hour, which is incredibly fast for such a small organism. Worse characteristics associated with these invasive critters are that the females exhibit a parthenogenetic reproductive lifestyle meaning that the populations are self-cloning, so no fertilization is required. The average brood size of individual females ranges from 20-120, each of which can potentially produce up to 230 offspring per year. The main ecological threat from New Zealand mudsnails is that they displace native insects, snails, and mollusks that native fish are dependent on. Thus, this results in significantly reduced growth rates of native fish and lower populations of economically important sport-fish species.  

Although the use of felt-sole waders is still legal in some states, it is recommended to purchase waders from companies that use alternative soles that contain scientifically-tested material known for not spreading aquatic hitchhikers. Wader companies such as Patagonia, Simms, Hodgman, and Korkers are utilizing Vibram outer soles to assist in preventing the spread of aquatic hitchhikers. Vibram is a vulcanized rubber that is explicitly designed to provide a high degree of resistance and excellent traction on rocky substrates yet restricts organisms like the mudsnail from clinging onto the bottom of the wading boot. Look for this material when purchasing wading boots for your next fishing expedition. Thorough rinsing with warm to hot water, your waders and wading boots will assist in not transporting them to other watersheds. An additional prevention step is to implement a 10-minute soaking of gear into an undiluted Formula 409 bath except for Goretex waders. Dry waders by hanging vertically onto a closer hanger. Store gear at room temperature.


 Although Alaska is recognized as one of the classic examples of pristine wildernesses remaining in the natural world, it has received introductions of invasive aquatic vegetation that threatens the native vegetation as well as the complexity of fish-holding habitats and structure in Alaska's rivers and lakes. Discovery of an invasive aquatic plant called Elodea occurred in Interior Alaska around a decade ago in shallow backwater sloughs connecting to mainstem rivers around Fairbanks. Elodea is commonly found in goldfish tanks. Residents from the North Pole and Fairbanks emptied goldfish/tropical fish tanks into the waterway, which resulted in the widespread takeover of the local ecosystem. Potential ramifications of Elodea include reduction of salmon-spawning and rearing habitat, prevention of motorized watercraft into shallow areas, particularly those with densely concentrated areas of vegetation, and increased cost for eradication and management implications.  An additional concern for the spread of Elodea to remote freshwater lakes and rivers in Alaska pertains to floatplanes.  As floatplanes travel back and forth to remote lakes and rivers, any remaining signs of Elodea attached will get transported. The current eradication strategy in Alaska for Elodea involves the development of the aquatic pesticide called flouroidone. When exposed to small concentrations, it destroys the plant from spreading yet inflicts minimal harm to native aquatic and terrestrial vegetation.  The function of the herbicide is to prevent the plant from making a protective pigment that keeps chlorophyll from breaking down in the sun.

Preventive Solution: Dispose of Elodea from fish tanks into the garbage can appropriately. If reusing fish tanks for future pet fishes, always thoroughly clean out tanks with hot water and never dispose of wastewater into waterways or terrestrial vegetation located near shorelines that contain riparian vegetation. Proper disposal of pet fishes should be immediately discarded into the trash at all times. The identical protocol also exists for throwing away Elodea or other aquatic plants used in fish tanks for pet fish.

Highlighted above are some of the recent ecological threats experienced as a result of the spread of invasive species into our lakes and rivers we fish over the past two decades. Most importantly, if presence invasive terrestrial or aquatic vegetation is detected, please report immediately through calling the U.S. Fish Wildlife Service or local Department of Natural Resources (DNR). Provide a thorough explanation of the location of where the sighting was so that habitat biologists can act fast to manage or completely eradicate the invasive threat. If witness anyone engaging in acts of illegal stocking, please call local law enforcement or conservation game wardens so justice is served and native ecosystems remain wild and pristine as they should. Illicit stocking of fish and/or vegetation is a reckless act that eventually hurts all of us anglers in the long run.

Introduction of Invasive Fishes through Illegal Stocking

The fundamental objective of this subsection is to explain the ramifications of illegally stocking invasive predatory fish into a natural lake or river system. Anglers of all types have an interest in targeting specific species they prefer over others, yet in some scenarios, anglers feel the only way to fish a species not present in a lake or river is to introduce them undetected surprisingly. Over the past several decades this has been a problematic situation that needs attention. Examples of this activity include (1) illegal stocking of northern pike into non-native trout lakes of the Rocky Mountain states and Southcentral Alaska, (2) introduction and unlawful transportation of muskellunge into lakes of the Kenai Peninsula in Alaska, and (3) common or grass carp into shallow watersheds to manage vegetation or create trophy carp fisheries. The illegal introduction of predatory fishes like muskies and pike into a native fishery can lower native fish populations, lower forage fish biomass, and increase competition between foreign and native fishes for food, resources, and habitat use.

Preventive Solution – Never under any circumstances introduce non-native fishes to a lake or river system. If anglers are interested in establishing a fishery for a specific species, the responsible protocol is to write to your local legislature and submit a handwritten or typed submission with recommendations of interest in developing a sport fishery for a species of fish of choice. Biologists will highly consider the comments and perhaps develop a new fishery. Many great fisheries have been established through simple communication between agencies and the general public compared to non-native stocking fishes by the elements of surprise. Stocking fish illegally poses detrimental consequences on native fish stocks, affects predator/prey balance, and costs taxpayers annually millions of dollars to reverse the damages inflicted from these illegal acts.

 As responsible stewards of the land and waters we fish, it is our job to ensure populations of fish flourish, as well as to promote conservative approaches to safeguard our ecosystems operate naturally. Please follow the outlined steps in this conservation special on preventing the spread of invasive species across our precious nationwide waterways. Each of us has a responsibility towards educating those not environmentally aware of the situations that could potentially occur as a result of not being alert. While many of us are in a hurry to vacate the boat launch so the next group of anglers can launch or retrieve their vessel, take a few extra minutes to implement the steps as outlined in this article, so our waterways will continue to produce fish-catching Kodak moments for generations to come. Our precious wild fisheries are one of the most important things that give the human population a sense of hope that wild adventures and places still exist in today's highly industrial, advancing world.

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