How Anglers Can Help Prevent the Spread of Exotic Species

You Have An Obligation to Help Prevent Aquatic Hitchhikers

This poster for boaters appears at a launch ramp on Lake Lillinonah in Connecticut. Photo © Ken Schultz

The problem of foreign plant or animal species - also called invasive species or exotic species - is almost a daily news item. Much of these problems are manifest in or around water bodies, and anglers see examples all the time, whether they realize it or not. Anglers are also sometimes part of the problem in the spread of these species, and should certainly be part of the solution.

About Exotics and Their Occurrence

In the simplest sense, exotic species are organisms that have been introduced into habitats where they are not native. This has occurred around the world both intentionally and accidentally. 

Occasionally exotic species occur in new places through natural means, but usually, the agent is some action of man. That includes transportation of fish or larvae via the ballast of ocean freighters and the bait buckets of small-boat anglers, passage of new species via newly constructed canals, the introduction of plants by using them in packing shellfish that are shipped trans-continent, the dumping of aquarium plants and fish into local waterways, the experimental stocking of predator and prey species by scientists and non-scientists, and many other means. Exotic species can be transported by and with animals, vehicles, commercial goods, produce, and even clothing.

The Problems Caused

Exotic species often are agents of severe local, regional, and even worldwide habitat alteration. Also referred to as non-indigenous, non-native, alien, transplant, foreign, and introduced species, they can be the cause of biological diversity loss, and greatly upset the balance of ecosystems.

While some exotic introductions are ecologically harmless, many are very harmful and have even caused the extinction of native species, especially those of confined habitats. Freed from the predators, pathogens, and competitors that have kept their numbers in check in their native environs, species introduced into new habitats often overrun their new home and crowd out native species. In the presence of enough food and a favorable environment, their numbers explode. Once established, exotics rarely can be eliminated.

Beneficial Fisheries Examples

Sometimes the introductions of exotic species have generally beneficial results. Anglers consider the importation of coho and chinook salmon from the Pacific Ocean into the Great Lakes, for example, to be a highly successful introduction of a non-native species. Certainly in terms of providing recreation, and controlling what were once unchecked populations of alewives (also not native in the upper Great Lakes), this is true. 

The same can be said for brown trout, first imported from Germany to the United States in the 1880s, and also spread to many countries on others continents. Hugely popular species like rainbow trout and largemouth bass, though native to many parts of the U. S., were introduced into many locales and waters where they were not originally found, mostly with popular results from an angling point of view.

Harmful Fisheries Examples

But the same cannot be said for carp, imported in the late 19th century and spread throughout North America, resulting in the destruction of spawning habitat for other species and the alteration of many environments into which they were placed. Likewise, the introduction of Nile perch into Lake Victoria in Africa is generally viewed as one of the most destructive exotic introductions of all time, having resulted in the apparent extinction of hundreds of small native tropical species. 

Other Aquatic Examples

Exotic species include other aquatic animals and plants as well as fish. These include such organisms as zebra mussels, the spiny water fleaEurasian watermilfoil, hydrilla, and water hyacinths. Many exotic introductions have been especially harmful. Several examples from the Great Lakes reflect this. 

The zebra mussel invaded the Great Lakes from its native habitats in Europe and has become a nuisance by clogging the intakes of water pipes and outboard boat engines. It has received much attention because it can be common in shallow water near shore and is large enough to be easily seen.

During the 1980s, the 1-centimeter-long zooplankton called spiny water flea entered the Great Lakes and has had a profound effect. The sea lamprey, aided by overfishing in the early- to mid-1900s, severely depressed lake trout, which used to reproduce naturally in all of the Great Lakes, and now reproduce naturally primarily in Lake Superior, with isolated occurrences in the other lakes.


Anglers and boaters have an obligation to make sure they do not assist in transplanting any organisms. This pertains to the known problem exotics, and also to not-so-obvious ones, such as yellow perch being introduced into a small trout pond, or didymo ("rock snot") being carted into an uninfested waterway. This obviously starts with not deliberately planting or stocking species from one environment to another, which is illegal in many places

However, since many introductions are accidental, and many of the organisms moved are so small they cannot be readily seen (like larvae), anglers must be diligent at all times. These are the primary precautions to take:

  • Empty a bait bucket on land before leaving the water.
  • Do not transport bait from one water body to another.
  • Inspect boat, motor, all parts of a trailer, and all boating equipment that gets wet, and remove any plants and animals that are visible before leaving the water body; hose down in a safe place. Some water-control or other environmental agencies require high-pressure heated water cleaning of boat hulls.
  • Inspect the soles of your boots, waders, wading shoes, and other footwear, and remove any substances that are visible before leaving the water body; hose off in a safe place.
  • Drain livewells, bilge water, and transom wells at the access site before leaving the water body.
  • Where zebra mussels and spiny water fleas are known or suspected, wash and dry your boat, tackle, trailers, and other equipment with hot water when you get home. Flush water through the motor’s cooling system and other parts that get wet. If possible, let everything dry for at least three days before transporting the boat to another water body. Flushing with chlorinated tap water may be helpful.

In some states, you are required to inspect your boat and trailer. Connecticut state law, for example, says that no person shall transport a vessel or trailer without inspecting, properly removing, and disposing of all vegetation and animals deemed invasive, including zebra mussel, quagga mussel, Chinese mitten crab, Asian clam, New Zealand mud snail, and rusty crayfish. Most people wouldn’t recognize all or most of these species, nor other exotics that may be present wherever they do their boating and fishing, so it’s imperative that a thorough cleaning be done and everything removed. You have to be vigilant, or you’ll become part of the problem.