Invasive Fish Species Update
By Christopher Smith, Principal Fisheries Biologist
The terms non-indigenous and non-native refer to species introduced by people, either intentionally or unintentionally, into areas in which they do not naturally occur. Non-native species are all around us, and many go unrecognized in our daily lives.
Many species of fish that anglers believe to be native to our region, such as Largemouth and Smallmouth Bass, are actually non-native species introduced long ago.
While non-native species can have negative effects, not all non-natives are necessarily invasive species. NJ Fish & Wildlife uses the terms "potentially dangerous" and "invasive species" for non-native species whose introduction causes or is likely to cause harm to the environment, economics, or human health. Examples of impacts include:
- Predation — Large Snakeheads and Flatheads indiscriminately consume any fish species small enough to fit in their enormous mouths.
- Competition — Food, spawning areas, and habitat are sought after by invasive fish; therefore, less is available for desirable species.
- Habitat Loss — Plants like Purple Loosestrife or Common Reed (Phragmites) can take over a wetland making it less suitable for native wildlife.
- Loss of Recreation — Silver Carp threaten recreational boating in the Mississippi River Watershed as these large fish, when startled, leap high enough to intercept passing boaters.
- Decreased Property Value — Beautiful lakefront property can be transformed into a weed-choked monoculture once Eurasian Water Milfoil or Water Chestnut establish themselves.
- Economic Impact — Zebra Mussels cause millions of dollars of damage each year in the Great Lakes alone.
Before we delve deeper into the world of Aquatic Invasive Species (AIS), let's look at two terrestrial insect invaders that most people in New Jersey have encountered. The impact of the Emerald Ash Borer can be seen as millions of ash trees across 30 states have been decimated. This destructive insect exemplifies the definition of an invasive species with a well-documented arrival, establishment, spread, and significant impact to the forests of our region. More recently, the Spotted Lanternfly has arrived. It has the potential to cause significant impact, and the New Jersey Department of Agriculture recently launched the "Join the Battle, Beat the Bug! Stomp it Out!" campaign to encourage residents to do their part.
New Jersey's freshwater ecosystems have been invaded in recent decades as well. The Flathead Catfish, first caught by an angler in the D&R Canal in 1999, is now all too common throughout the Delaware River and a few of its tributaries, in addition to being found across the state in the Millstone and Raritan Rivers. Approximately 10 years later, in 2008, the Northern Snakehead and Asian Swamp Eel were first documented in NJ. The Asian Swamp Eel, fortunately, remains rather limited in its distribution, but the Snakehead population took off like the Spotted Lanternfly, spreading quickly throughout the region.
In New Jersey, thirteen species or groups of fish are regulated as potentially dangerous, and the possession of live individuals or their release when caught is prohibited. These species include Asian Swamp Eel, Bighead, Grass (diploid), and Silver Carp, Blue and Flathead Catfish, Round Goby, Brook Stickleback, Green Sunfish, Oriental Weatherfish, Snakehead, Warmouth, and all black bass except for Largemouth and Smallmouth Bass.
Since its introduction, the Snakehead is probably the most recognized invasive fish species. NJ Fish & Wildlife biologists have actively monitored and documented the growth and spread of the species throughout the Delaware River basin since first documented. New and emerging species, like the Snakehead, are fascinating to study, especially those that have the potential to reshape the ecological interactions of species and habitat. Studies ranging from age and growth, population growth and distribution, and diet studies are currently being utilized to ascertain the long-term impacts of the species. Today's technological advances, such as eDNA (environmental DNA), have provided fish and wildlife agencies with the tools to detect emerging threats more efficiently. Environmental DNA is the detection of DNA released by an organism into the environment through feces, mucous, skin, and carcasses. Through eDNA, species presence can be detected from a water sample.
As previously mentioned, not all non-native species are considered invasive. Although non-native, recreationally important species such as Largemouth Bass, Channel Catfish, Bluegill, and Rainbow Trout are not considered invasive species. They have been around for more than a century with widespread reproducing populations (naturalized) and/or are considered a valuable natural resource in most waters of the state. There is an emphasis on the word most, as there are places where they do not belong. There are certain interactions between these naturalized non-native species and sensitive native species that NJ Fish & Wildlife prefers to minimize or prevent. One example is the competition and/or predation exerted upon our native Brook Trout by other non-native salmonids such as Brown or Rainbow Trout. A second example is found within the sensitive and naturally acidic waters of the Pinelands. Although widely protected from development, this fragile landscape is a refuge to a suite of unique native flora and fauna (such as Blackbanded Sunfish). Non-native and invasive species introductions here would cause irreparable harm to these areas. Therefore they are generally not managed for or stocked with non-native species, even those that have become naturalized.
Transferring any fish species into any waterbody can have serious consequences. Regardless of whether a fish is regulated as an invasive species or not, it is important to recognize that the action of moving fish is illegal and most often irreversible. The damage can take many forms including harm to both game and nongame species populations. Fisheries management strategies can be undermined with the best of angler intentions. Native Brook Trout populations suffer and are at times lost when Brown Trout move or are moved into native Brook Trout waters. Highly predatory species can deplete forage bases. Species such as Alabama Bass and Spotted Bass have been deemed invasive outside of their native range due to the severe impacts they have on Largemouth and Smallmouth Bass. In fact, they are known to dominate a fishery, outcompete more desirable species, and are prone to stunting, meaning they become overabundant and remain smaller than anglers generally enjoy fishing for.
For NJ Fish & Wildlife, the species officially regulated as potentially dangerous can cause severe impacts and are unwanted in all waters. Not all species pose the same threat level and are at different stages of invasion. Some species, like the Green Sunfish, are widely distributed throughout the state. Others, like the Snakehead, are confined to the Delaware River and tributaries. A Blue Catfish has recently been caught by an angler and the Round Goby has not yet been encountered. Protecting native species and their habitat is of utmost importance to the agency.
What Can You Do?
The angling community plays an important role in protecting New Jersey's native species and recreationally important non-natives by following the guidelines established under the Potentially Dangerous Fish regulations.
- The possession or release of live, potentially dangerous fish IS PROHIBITED.
- Anglers must destroy all species encountered and must not return them to the water.
- Specimens or photos should be reported to a NJ Fish & Wildlife Bureau of Freshwater Fisheries biologist for verification. To reach a regional biologist, call 908-236-2118 (north), 609-223-6076 (central) or 856-629-4950 (south).
Although an invasive species, Common Carp are NOT regulated as Potentially Dangerous as they are already found in the vast majority of waters throughout the state. As such, carp do not have to be destroyed when caught by anglers.
Unfortunately, a portion of the angling community continues to release invasives back into the water, which is to the detriment of New Jersey's freshwater resources. Invasive species are likely to cause environmental harm to the state's fisheries resources by outcompeting preferred game fish species. Some invasives' presence and impact are obvious when one sees a stand of dead ash trees due to the Emerald Ash Borer or hundreds of Spotted Lanternflies littering your backyard and feeding on trees. What lies beneath the water is far less tangible to most, and species like the Snakehead continue to spread at alarming rates. The long-term effects of practicing catch-and-release are yet to be seen, and only time will tell how much of an impact these invasive predators will have on the aquatic ecology of the state. Do your part, and please do not release the potentially dangerous invasives!
Regardless of whether or not a fish is regulated as an invasive species, NEVER relocate or stock ANY FISH without an approved Fish Stocking Permit regardless of species. Please help us manage and protect our waters for future generations to enjoy!