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Environmental groups have highlighted that loss of fish habitat is leading to hundreds of North American fish species being endangered. A highly invasive water plant called Eurasian milfoil is rapidly spreading across North America, and is significantly contributing to fish habitat loss. Eurasian milfoil can completely displace fish spawning habitats as deep as 25 feet (7.6M). Milfoil threatens to cause damage to the North American 50+ Billion-dollar freshwater sport fishing industry.
The US Fish and Wildlife Service have stated that “America’s fisheries are facing a conservation crisis. Nearly 40% of North American fishes, 700 species in total, are imperiled. More than two-thirds of these are listed as threatened or endangered under the Endangered Species Act. Habitat alteration is the principle factor in this conservation crisis”.Other groups, including the World Wildlife Fund2 and the Canadian Department of Fisheries and Oceans3, support this conclusion; that damage to fish habitats will negatively affect fish populations and that habitats must be protected. A significant percentage of popular game fish such as trout, bass, crappy, catfish and salmon spawn in the shallows of lakes and rivers down to 12-feet-deep.
Eurasian milfoil, as the name implies is, from Europe and Asia. In North America it does not have any natural predators to keep it in check since it is an exotic plant. What makes this plant most threatening is that it can spread extremely quickly. Milfoil is a fragile plant that spreads by stem fragmentation. As such, if a plant is cut into 10 pieces those fragments will grow 10 more plants. A fishing boat idling through an infestation for only a few minutes can create thousands of new plants from the propeller clippings. Even a canoe paddle can create hundreds of clippings.
When milfoil infests an area, it can form thick underwater strands of tangled stems and vast mats of vegetation at the water's surface. The dense growth of the milfoil (up to 250 plants/yd2, or 300/m2) completely displaces the indigenous plants and aquatic wild life as well as eliminating fish spawning habitats. It reduces local oxygen content and pumps phosphates into the water that support the growth of blue green algae, a toxic bacterium. It makes recreational use in those areas difficult or impossible and creates a safety hazard for swimmers (figure-1).
Milfoil can sit almost dormant in a body of water for years without any issue. However, once it gets into high boat traffic areas it spreads quickly, sometimes doubling and tripling in size in two or three years. Milfoil can easily spread in all types of lakes, whether they are nutrient rich (eutrophic) or mineral rich (oligotrophic). Although milfoil can grow as deep as 25 feet, it is most dense between 1 to 12 feet deep (the littoral zone of a lake), a common fish spawning area.
ABV des 7 is a non-profit environmental group responsible for the 7 watersheds North of Gatineau, Québec. Its 2015 milfoil survey of 13 lakes indicated that milfoil can cover from 30% to 45%4 of the lake littoral zone. In extreme cases, milfoil can cover 80%.
The rate at which milfoil spreads depends on many variables including: nutrient levels, temperatures, boat traffic, days of sun, etc. Trying to remove milfoil by cutting also increases the rate at which it spreads, since it is very difficult to collect all the cuttings. Harvesting (industrial cutting) is sometimes used to gain an immediate trimmed result in large areas. However, mechanical cutting of milfoil can produce a disastrous effect the following year from the large number of fragments left behind.
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Figure-1/ Typical Eurasian Milfoil infestation
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Figure-2: Map created by the Early Detection and Distribution Mapping System (EDDmapS)6 |
The map (Figure-2) shows the distribution of Eurasian milfoil (Myriophyllum spicatum L.) by county, across the United States. This is not a complete map, but only what has been reported to that website and does not show the thousands of locations in Canada, specifically in Ontario, Quebec and British Columbia. Note: The states showing very little Milfoil are also the states with very few lakes, except for Florida.
In summary:
- Eurasian Milfoil has already spread to well over 10,000 documented locations across the US and Canada. Thespread in many more locations is still undocumented;
- Milfoil is continuing to spread rapidly since there is no continental approach to controlling it. It is also spreadingin regions with very high densities of lakes and popular fishing destinations;
- Milfoil can cover a high percentage of the fish spawning habitats of the infested lakes; and,
- Environmental groups have drawn a clear link between fish habitat loss and the reduction of the related fishpopulations.
Therefore, a logical conclusion is that Eurasian Milfoil will create significant losses to the 50+ billion-dollar7,8 sport fishing industry in North America.
Milfoil must be controlled to stop it from spreading! It is not realistic to completely eradicate it. The spread of milfoil has been ABV des 7’s number one environmental concern over the last decade. After analysing all the various methods to control the spread of milfoil and not finding an adequate solution, it decided to look at other options. In 2008, an environmental group, Inland Fisheries Ireland, tested the use of burlap on Lagarosiphon major, an invasive water plant in that region9. Many other studies since then have also shown that the burlap can kill off certain invasive aquatic plants in 4 months. In 2012, ABV des 7 then ran their own 3-year study10 to test the burlap process on Milfoil, which proved highly successful.
The process involves laying biodegradable burlap on top of the milfoil and holding it to the lake bottom with local sand. The burlap kills off the milfoil in the first season and biodegrades in 1 to 3 years after installation, providing an ideal environmental solution (Figure-3).
However, to stop Milfoil from coming back or spreading, the Milfoil must be killed off in high traffic areas to stop the fragmentation. A holistic approach must be taken to control the Milfoil in a specific lake or river. This includes targeting public passageways and private docks. Measures also need to be taken to clean boats, trailers and aquatic equipment when removed from a lake or river, to remove all Milfoil fragments. This will prevent the Milfoil from spreading between bodies of water.
Figure-3: The edge of a treated section showing an untreated v.s. treated area. The area on the right was treated with burlap in 2012 in the ABV des 7 study8
Local, regional and federal authorities need to take action. They should support sustainable solutions which have been tried and tested, such as the laying of biodegradable burlap. Inaction will cost the North American economy billions!
Governments and fishing federations should be doing further research to better understand the relationships between the spread of milfoil, the damage of fish habitats, and the resulting impact on game fish populations in North America. This includes quantifying the spread of Milfoil in lakes to understand how severe the problem is. A problem cannot be properly controlled unless it is fully understood and measured.
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