Aquatic Invasive Species (AIS)

By: Chris Hamerla

What are they and why are they bad?

AIS are: plants, animals, and pathogens that can live at some point in the water, have been introduced to an area where they do not naturally occur (are not native), become established, and spread widely in the new location. In many cases the same invasive may have multiple modes of being transported. Originally it arrives by one mode, but then makes its way across the state through other modes. In Wisconsin, by definition, all non-native fish are considered invasive species. Though it can be debated, some non-native fish are very much appreciated (brown trout, chinook salmon, rainbow trout, coho salmon).

Invasives are able to spread widely because there are no natural controls in their new environment. Native species are not accustomed to competing with the invasives. Sometimes, over the course of time, native species will adapt to or begin utilizing the invasive. For example, in Lake Michigan may game fish species have started feeding on the abundant gobies.  Until that occurs, the invasives have little or no competition for food and space.  Simply put, two people with two sandwiches in a three person boat are happy and comfortable.  Six people with two sandwiches in a three person boat will not be as happy and comfortable.

Invasives establish easier in areas that are disturbed. These areas once had the native species occupying the space but something displaced them. This is why a healthy, diverse aquatic plant population is important.  Think of invasives as “weeds in your garden”. A new garden is put in. If not taken care of, “weeds” will show up first and take control.  After the invasives have become established they can change the environment and relationships within the environment.

Some invasives can have negative effects on human health and most have negative effects on the economical value of the areas they occur. The occurrence of one invasive may also make it easier for other invasives to become established. Rusty crayfish have the ability to “clear cut” weed beds. In doing that, these areas are susceptible to new, aggressive plants like Eurasian water milfoil and curly leaf pondweed.

How do aquatic invasive species get here?

The Great Lakes:
Two sources are the shipping industry and canals connecting the Great Lakes to the ocean. Ballast water in ships carries sediments and living organisms. Gobies, an invasive fish from the Black and Caspian Seas and VHS (viral hemorrhagic septicemia) have made their way across the ocean in this mode. Zebra mussels, from the Baltic and Caspian Sea regions, also arrived here in ballast water. Sea lampreys and alewife made their way into the Great Lakes through the Welland Canal that bypasses Niagara Falls.

Nurseries, Aquaculture, & Intentional Stocking:
Non-native fish and other species brought over to be raised for food, ornamental purpose, or other have escaped or been released and become established in the wild. Bighead and Silver carp, smelt, Chinese mystery snails, purple loosestrife, and Japanese knotweed are examples of this type of introduction. Impoundments stocked with fish sometimes flood or wash out into a near-by body of water allowing fish to escape.

Ornamental plants are given away or removed as they expand.  When not contained or cared for correctly the plants spread into the wild.  In some cases a person may want the species in a different location, maybe closer to their house. Smelt are a prime example of this.  A distribution map of smelt in Wisconsin clearly shows the spread along highway corridors. Introduction of invasive species is illegal in Wisconsin.

Many people have caught fish and stocked them in other bodies of water. This is also illegal in Wisconsin. This intentional stocking can lead to the spread of invasive species and diseases such as VHS. Stocking of this nature can also disrupt the balance of the ecosystem in that body of water.

Aquariums, Water Gardens, & Ponds:
The world is full of interesting and beautiful plants, animals, and fish. The aquarium trade has made it possible for anyone to experience these wonders in the convenience of their own home. The problem comes in when these things are no longer wanted due to growing too large or interest is lost. Whatever the reason, do not release the unwanted items into the wild!  It is believed that this may be how Wisconsin’s latest (August 2009) aquatic invasive species, the red swamp crayfish, became established.

Have you ever wondered how someone ends up catching a piranha or seeing an alligator so far from its native area?  They didn’t travel here all on their own. Similarly, water gardens and ponds have the potential to introduce invasives into the wild.  Examples of invasives that were or are commonly sold for stocking these areas include various plants (hydrilla, parrot feather, yellow floating heart, and water hyacinth), fish (western mosquitofish, goldfish, and koi), and non-native crayfish species (red swamp crayfish).

Special attention should be paid to what a person is actually buying.  Some species are sold using Latin names. Brazilian waterweed is commonly sold as Anacharis and fanwort is commonly sold as cabomba.  Both are listed as prohibited invasive species in Wisconsin. Before buying plants or animals check with local and state ordinances. Just because something is for sale though mail order or on the internet doesn’t mean it is legal.

Boating, fishing, hunting, ATVing, and almost any outdoor form of recreation can be a mode for invasives to be transported.  Mud on equipment and footwear can carry seeds, fragments of plants can be transported through clothing, trailers, anchor ropes, duck decoy cords, and anywhere else imaginable. Felt soled wading footwear can trap and hold invasives like New Zealand mud snails, didymo, quagga mussels, zebra mussels and VHS.

The felt can remain damp for weeks, keeping invasives alive, and is difficult to thoroughly clean. New Zealand has banned the use of felt soles and Trout Unlimited is urging manufactures of felt soled footwear to discontinue production by 2011. Water in live wells, bilges, ballast compartments, and engines of boats can transfer VHS and young zebra mussels.

With so many things to think about what can a person do?  Plain and simple, take the time to clean equipment off after each use. Drain all water from equipment, including live wells and containers with fish.

This leads into the question of bait.

Live & Dead Bait:
Live and dead baits are very effective for certain fish and during certain times of the year. Unfortunately, these baits can quickly spread VHS and introduce invasive fish to new bodies of water. A minnow bucket with water from a VHS infected body of water could easily spread  infected water to a clean  area.

As water is exchanged to keep minnows “fresh” or if a floating style minnow bucket is used, infected water and or minnows can spread VHS to new waters. Dumping unwanted bait into a body of water also increases the chance of spreading invasives. To prevent new infestations there are some precautions that should be followed. Buy bait from licensed bait dealers. Don’t move water and bait or other fish to other bodies of water. Each state may have their own laws regarding the use of bait.

Wisconsin Bait Laws:
All bait must be bought at a Wisconsin bait dealer. Leftover minnows can be taken away from any state water and used again on the same water. Unused minnows can be used on other waters if no lake or river water, or other fish were added to the container. A maximum of two gallons of water can be used to transport the minnows.  Suckers are considered minnows and fall under the same rules. In Wisconsin it is illegal to release unwanted bait into the wild.

Unwanted bait should be disposed of in the trash or on a compost pile. Dumping unwanted bait on the shore should be avoided because of the smell, appearance, and impression it leaves with other people. Dumping of unwanted bait on state lands is considered littering.  Smelt and other dead bait must be preserved in a way that does not require freezing or refrigeration. If the bait was alive when you started fishing or was caught in the water you are fishing it can be used as unpreserved dead bait. Example:  While out fishing, catching a sucker, cutting it up, and using it as unpreserved dead bait is legal.

Once you leave the water the dead bait needs to be preserved. So what about catch your own minnows?  On waters free of VHS minnows can be harvested and used on that body of water. The minnows can not be used on any other water. Minnows can not be harvested from VHS waters.


Chris Hamerla is the Aquatic Invasive Species Coordinator of Lumberjack Resource, Conservation, & Development Council serving Lincoln, Langlade, and Forest Counties in northern Wisconsin. As the Aquatic Invasive Species Coordinator, Chris focuses on implementing AIS prevention and control efforts through public awareness and education programs. For more information or have any questions contact Chris at 715-362-3690 e-mail


Learn more about each Aquatic Invasive Species (AIS) Click on the Links Below:

Eurasian Watermilfoil
Curly-leaf Pondweed
Rusty Crayfish
Asian Carp
VHS (Viral Hemorrhagic Septicemia)