While in the field, we are routinely approached by members of the general public, who usually ask the questions below. The media buzz surrounding northern snakeheads has been a mixed blessing. On one hand, it has helped put invasive species on the map in the public’s perception of environmental issues. At the same time, the media has continued to report false information about northern snakeheads, inducing irrational fears about personal safety and potential impacts. If people end up viewing the initial reports as false alarms, the increased awareness of invasive species issues brought about by the media may turn to skepticism. It is my hope that the following answers will help to dispel the many myths surrounding northern snakeheads.
Do snakeheads walk on land and breathe air?
Northern snakeheads do not walk on land. Their pectoral fins (on the sides of the fish, just behind the head) lack spines, and have only soft rays. Thus, they have no ‘legs’ to propel them forward. Some species of snakehead (there are close to 30) are known to travel short distances over flat, muddy ground, but the northern snakehead is not among them. A northern snakehead placed on a gently sloping bank can probably wiggle back down into the water (and thus all snakeheads caught in the Potomac River should be killed by removing the head or viscera), but couldn’t have made it up the bank in the first place without assistance. Other native fishes, such as American eel, are far more able to travel across land than northern snakeheads.
In my many hours on the water, spent tracking radio-tagged northern snakehead and electrofishing, I have only seen two fish on land. Both were hiding in weed beds in less than a foot of water next to a very gently sloping muddy bank. Both exploded out of the water onto the bank as the electric current from the shocking boat approached them, and sat for a second on the shoreline, inches from the water line. Both then wiggled back into the water and were immediately stunned and captured. I have seen nothing to suggest that northern snakeheads do this naturally, or even when approached by boats that aren’t shocking the water.
Northern snakeheads do breathe air. Unlike many other air-breathing fishes, they have a series of spaces in the rear portion of their head called the suprabranchial chamber. These spaces are filled with folded tissues that have a high surface area, and allow oxygen exchange to occur directly between air and their blood. Unlike humans, they lack a diaphragm, and use water to exchange old air with fresh air each time they take a breath. Thus, their ability to breathe air when out of the water is limited. Northern snakeheads could survive out of the water for several days if they are kept moist, but would desiccate and perish in minutes if placed on dry land in direct sunlight. Northern snakeheads also have gills, and breathe water like any other fish. They breathe air to supplement their demand for oxygen, and appear to breathe air far more frequently when they are actively swimming, much like a runner gasps for breath compared to someone who is sitting and reading.
Do snakeheads bite or attack people or pet dogs?
No= northern snakeheads are a very shy fish and I have seen no evidence that they would attack anything larger than they are. Every radio-tagged fish that we tracked was hidden when we approached, and we saw very few fish in the turbid, weedy waters of the Potomac River, despite being within 1 m of most. Two of our radio-tagged fish were found guarding young, and I approached each nest once per day for a period of two weeks, netting a few of the young each day to determine their growth rate. I was never attacked by the adults. In fact, I rarely saw the guarding adults, who would emerge only after I remained perfectly still for over 10 minutes. Yet, a man honestly asked us one day if it was safe for his five year old son to play on his lawn, beside a retaining wall that was several feet above the water line.
I’m hesitant to say definitively that there is no danger of a snakehead biting a human. Northern pike and muskellunge are known to occasionally bite feet or hands being dangled over the side of a dock or boat. These large, predatory fish do not see the rest of the person attached to the appendage, and mistake it for a smaller animal that they are able to swallow. People bit by pikes will often require medical attention, and it seems plausible that a snakehead could similarly confuse an appendage with a small animal, particularly if the fish was guarding young. However, in my experience pikes are far more aggressive and less shy than northern snakehead, despite not guarding nests themselves. All things considered, I personally wouldn’t hesitate to dangle my feet in waters that had northern snakeheads, even though I’m cautious about it when muskie are present
Are snakeheads hurting the ecosystem? Will they eat every other fish in the river?
The lower Potomac River is a heavily altered ecosystem. Although many native fish species still exist in the river, most of the fish that we see while electrofishing are non-native, including carp, goldfish, catfish and largemouth bass. Additionally, shoreline and riverine habitats have been heavily altered, and the river is loaded with sediments, nutrients and chemicals from our activities. This makes it hard for a single additional species to have a major impact. The river is large and complex, with a high diversity of species. Although smaller, more indirect impacts are probably occurring as a result of the northern snakehead introduction, these are very difficult to detect in the face of other impacts. Blue catfish are another recently introduced piscivorous (fish-eating) species that have grown to immense size and abundance in the deep waters of the main channel. Detecting changes in population levels of other channel-dwelling species that coincide with the introduction of blue catfish is probably more likely than detecting specific impacts of the northern snakehead introduction at this time.
Northern snakeheads do eat primarily fish. They have a similar diet to largemouth bass, but largemouth eat considerably more crayfish and other species such as frogs, turtles, snakes, etc. In comparison, northern snakeheads are almost completely piscivorous (unpublished data). However, there is nothing to suggest that they are any more voracious than the bass that already exist in greater numbers in the river. If anything could eat all the fish in the river, bass would have already done so. Northern snakehead do often select shallower, weedy habitats than bass, where they feed extensively on small banded killifish and mummichog. In the long run, increased predation on such fishes may have indirect effects on the food web of the Potomac River, but there is no evidence for such effects yet.
The same may not be said for more pristine systems. Northern snakeheads are hearty fish, able to survive in diverse freshwater environments. Their release in a small ecosystem, particularly one with rare species and lacking a top piscivore, could be disastrous. Even in the Potomac River, the story is still being written. Invasive species can be viewed as a ticking time bomb, and changes in the ecosystem from habitat alterations, climate change, or from the introduction of additional non-native species can result in previously unexpected population explosions of existing invasive species. Plus, this northern snakehead population is very young and may still be growing (see below).
Where are snakeheads from and how were they introduced?
Northern snakeheads are native to northern China and eastern Russia. Most snakehead species are native to China, though a genus (Parachanna) is found in Africa. Of the nearly 30 snakehead species, the northern snakehead is the only species predicted to be able to survive the North American climate north of Florida and Mexico, though they could survive as far north as Hudson Bay (Herborg et al. 2007).
The population in the Potomac River was probably released by an individual who purchased them from a live food market. Although the possession of live snakeheads (all species) has been banned in North America since 2002 (the year a population was discovered in Crofton Pond, MD), the population in the Potomac River was probably released before this data. Analysis of the age structure of fishes captured in 2004 suggests that the population was released around 1998 (Odenkirk and Owens 2005). Genetic analysis of these specimens suggests that few individuals were originally released; 19 of the 20 fish came from the same ancestral mother or group of sisters (Orrell and Weight, 2005).
Are snakeheads good to eat?
Snakeheads are a popular food fish in Asia, and are regularly raised in aquaculture settings and sold in fish markets. Most North Americans seem to agree, despite disagreeing with Asians about the palatability of carps. Anglers should be warned that there are consumption advisories for most Potomac River species (e.g. no more than two meals per month, no consumption by pregnant women) because of contaminant levels, though to my knowledge tests have not been done for contaminant levels in snakehead muscle tissue. It may be possible to refer to consumption advisories for largemouth bass, though snakeheads are on average a larger fish, and larger individuals have the highest contaminant levels. It is common to find large curled red parasite worms in the flesh of northern snakeheads from the Potomac River, and though unappetizing they are not harmful to humans if they are cooked or cut out of the flesh prior to cooking.
Are snakeheads a good sport fish?
It depends. Many people are concerned with their potential impact on the largemouth bass fishery, while others see northern snakeheads as an emerging sport fishery. It is true that they are a large, predatory fish with a reputation as a strong fighter, but these factors alone don’t make a fish popular for sport. Longnose gar already exist in the river in great numbers, and despite sharing all of these characteristics (and being a prized food fish in the southern states), they are not considered a sport fish.
Perhaps the fact that longnose gar are very shy and difficult to hook has kept them from becoming a popular sport fish. It’s no accident that bass have become the most popular freshwater sportfish in North America- they appeal to North American anglers because they are easy to catch; even if only the pros land several five orsix-pound fish in a day, most people can catch at least a few small bass each time they go fishing. On the other hand, despite talking with many anglers over the past couple of years on the Potomac River, I haven’t run into anyone who reliably claims to have caught more than a dozen fish. The bottom line is, you can’t create a fishery with people only landing six fish a year. Even if some anglers are doing slightly better than this, I don’t expect a tournament any time soon where people fill their livewells and have to cull smaller fish. Catch rates may rise if the northern snakehead population increases and North American anglers become more experienced with the techniques required to land this new species, but I doubt that they will ever become as popular as the standard North American sport fishes.
Unconvinced? At the turn of the century, North American fisheries agencies were busy spending taxpayer money to aggressively stock a sport fish across the continent. This fish was the epitome of European sportfishing. It was large, a strong fighter, and a popular food fish as well. Establishing populations of this species was notoriously difficult, and many millions of individuals had to be introduced, often in the same system, before a population would take hold. Eventually, human technology and persistence prevailed, and the species was stocked across North America. Did a sport fishery develop? The species I’ve been describing is the common carp, and although a few North American anglers target them, they are now widely considered a trash fish and even a nuisance. Common carp uproot vegetation while foraging for invertebrates in the substrate, increasing the turbidity of aquatic ecosystems.
It is my fear that North American anglers will imagine the potential for a northern snakehead fishery in their own backyard reservoir/lake/river, and will take it upon themselves to collect and release individuals in other ecosystems. Examples from the Potomac river include a guide charging $300 a day for snakehead fishing trips, and ‘snakehead’ fishing lures being sold for $25. These dollar signs may light up like light bulbs over the heads of anglers in other parts of the country but be warned that transporting a live snakehead over state lines is a violation of the Lacey Act and caries a fine of up to $200,000 and five years in jail, not to mention state laws prohibiting the release of species. A nightmare scenario would be a repeat of the common carp phenomenon, this time by individuals seeking to create profitable fisheries. Yet the sustainability of such fisheries is largely unknown, and the Potomac River fishery is too young to serve as an example. Northern snakehead may become a popular sportfish, or anglers may put in a great deal of effort to catch a few fish, then get bored with low catch rates and switch back to targeting bass. Besides, if we want to fish for an exotic-looking, large, air-breathing, hard-fighting, piscivorous species that is shy and a challenge to hook and land, we already have gar, and just how popular are they with North American anglers? Oh, and did I mention common carp?
Is the snakehead population increasing?
The short answer is, we don’t know. It is very difficult to estimate the size of a fish population in a large, open system, particularly without a detailed monitoring program in place. However, electrofishing catch rates increased significantly from 2004 to 2006, suggesting that the population is continuing to increase (Odenkierk and Owens 2007).
Additionally, northern snakehead continue to be captured at more distant locations, including as far upstream as above Little Falls and the Anacostia River and as far downstream as Aquia Creek in 2007. This may represent the maximum area of the river that snakeheads can colonize, with Great Falls as a potential upstream barrier, and downstream dispersal limited by saline conditions. However, many of these areas were probably colonized some time after the Dogue Creek area, and populations will continue to increase throughout the river. The C & O Canal is connected to the mainstem Potomac River in several locations, and may represent a pathway for northern snakeheads to colonize the upper Potomac River, above Great Falls. Dispersal may yet be possible further downstream. A large rainstorm event could push a freshwater plume further downstream than normal. If this were to happen when snakeheads are dispersing (early May, see Movement, Dispersal and Home Range section), individuals could follow the plume downstream and then back up tributaries or adjacent watersheds into permanently freshwater habitats.
As for the populations in Dogue Creek and the surrounding areas, they may still be increasing as well. Over the past two seasons, I have seen the average size of the largest northern snakeheads captured by boat electrofishing increase from around eight pounds to over ten. This suggests that we were capaturing the same age class, probably around six years old in 2008, each year. Larger fish tend to have a greater reproductive output, and it may be that the first numerous age class of this population is just now reaching its peak reproductive period. We may find that juveniles are more numerous than ever in 2008, and that they will reach their own reproductive peak another six years down the road. At some point, the population should level off as competition for resources such as food and habitat become limiting, but current data suggest this has not yet occurred.
Herborg L. M., N. E. Mandrak, B. C. Cudmore, and H. J. MacIsaac. 2007. Comparative distribution and invasion risk of snakehead (Channidae) and Asian carp (Cyprinidae) species in North America. Canadian Journal of Fisheries and Aquatic Sciences. 64:1723-1735.
Orrell, T. M., and L. Weigt. 2005. The northern snakehead Channa argus (Anabantomorpha : Channidae), a non-indigenous fish species in the Potomac River, USA. Proceedings of the Biological Society of Washington 118:407-415.
Odenkirk, J. and S. Owens. 2007. Expansion of a Northern Snakehead Population in the Potomac River System. Transactions of the American Fisheries Society 136: 1633-1639.