INVASIVE CATFISH THREATEN MID-ATLANTIC FISH STOCKS--INCLUDING STRIPED BASS

 

Our coastal waters have endured invasions of foreign species for a very long time. 

European green crabs first began showing up on the U.S. Atlantic coast sometime during the 19^th Century, probably hitching a ride in the ballast water of cargo ships; they have more recently appeared on the Pacific coast, and now range as far north as Alaska.  Green crabs have been here so long that many anglers, who use them as bait, don’t realize that they’re not a native species, but an invasive, which can cause considerable damage to shellfish beds and inshore habitats, and out-compete native crustaceans.

Ballast water is suspected as the vector by which more recent invasive crustaceans, such as the Asian shore crab and the Chinese mitten crab, reached North American shores although, because the latter species is also a traditional food source, intentional releases into coastal waters may have played a contributing role.

Off the south Atlantic and Gulf coasts, invasive lionfish, most likely dumped into coastal waters by private aquarists ridding themselves of unwanted specimens, have become a serious threat to native fish populations.  Fortunately, because lionfish are a tropical species, they seem unable to overwinter farther north than the Carolinas, sparing the northeast from their ill effects.

But now, native marine life in the Chesapeake Bay is facing a new threat, and that threat could impact fisheries throughout the northeast.  It is the blue catfish.

Unlike most invasive species along our coast, the blue catfish didn’t arrive in the Chesapeake accidentally.  It didn’t hitch a ride in a ship’s ballast water, and it wasn’t unceremoniously dumped into the coastal sea by an aquarium hobbyist.  The blue catfish now threatening native fish stocks was intentionally introduced into the Chesapeake watershed by the state of Virginia, another in a long string of intentional, non-native fish introductions that span a spectrum ranging from European carp to brown trout, and have totally disrupted native North American ecosystems.

The story is always the same; some state natural resources agency decides that, for one reason or another, the local fish populations can’t keep anglers sufficiently entertained, so they go out and find some fish that lives elsewhere, and dump it into the state’s waters for anglers to, hoipefuylly, enjoy. 

Sometimes it works out pretty well for the anglers.  If you fish in fresh water, there’s a very good chance that the ancestors of the largemouth and smallmouth bass that you’re catching today were spilled out of a hatchery bucket.  The same is true of rainbow trout caught anywhere east of the Rockies; rainbows have such a long history of hatchery propagation that one book about them was titled “An Entirely Synthetic Fish.”  

Of course, such planned invasive-dumping doesn't always work out too well for native species, which have no natural defenses against the invader.  Brook trout are one example of a fish that has suffered, and suffered badly, from the practice.

Sometimes, it doesn’t work well for anyone, and the blue catfish introduced by Virginia appear to fall into that category.

It seems that Virginia failed to do its homework before dumping blue catfish into rivers that feed the Chesapeake Bay.  The state fisheries folk assumed that, because the catfish lived in fresh water, they would stay in the rivers where they were dumped.  

Like many assumptions, that one proved to be wrong.  It turns out that blue catfish can tolerate at least moderate levels of salt, and when heavy rains lowered the salinity of coastal waters, the catfish had no problem spreading out across the Bay and ascending other waterways.  The catfish are now found in just about every tributary of the Chesapeake Bay.

That’s not a good thing.

Last January, a video taken on a Maryland river was making the social media rounds.  It depicted a quiet night, and a school of blue catfish that seemed nearly as dense as a school of menhaden.  But unlike menhaden, the catfish don’t just eat plankton.  They feed on fish and crabs and just about anything else they can fit in their mouths.  And because blue catfish can, on occasion, weigh over 100 pounds, their mouths can get very large, and fit most things that live in coastal rivers.

There is now real concern that the Chesapeake Bay’s blue crabs, shad, river herring, menhaden, and even striped bass are at serious risk, because of the catfish explosion. 

No direct scientific link has yet been established between catfish predation and declines in important fish species in rivers flowing into the Bay.  However, Maryland has noted that seven of its most important commercial species, all of which share habitat with the blue catfish, have fallen into steep declines in recent years, with catches falling between 27 and 91 percent.  Blue crabs, striped bass, yellow perch, white perch and eels are among the species affected.

As a result, last week, Maryland governor Wes Moore called on the United States’ Secretary of Commerce to respond to not only the threat posed by blue catfish, but introduced flathead catfish and snakeheads—both of which, fortunately, lack the blue catfish’s tolerance for salt—as well, by declaring an ongoing commercial fisheries emergency.  If she does so, it will qualify Maryland fishermen for federal disaster assistance.

An article in Inside Climate News quoted Thomas Miller, a professor at the University of Maryland Center for Environmental Science, who noted that such fishery disaster payments

“usually provide relief that could be targeted to direct income support.”

However, they can also help fishermen impacted by a declining resource move into other fisheries.

“If you were a crab fisherman, for example, it’s not easy to become a straight bass fisherman because of the cost of the gear and the investment that you’ve made in a particular boat or particular licenses.  So, disaster relief has been used to do that.”

Of course, shifting fishing effort from one species that's been depleted by catfish predation to another species that's also on the blue cats' menu may not be a long-term solution.

A bill. passed by both houses of the Virginia legislature, more directly addresses the blue catfish problem.  Taking an “if you can’t beat ‘em, eat ‘em” approach to the issue, the legislation would authorize the Virginia governor to provide up to $250,000, in the form of both grants and loans, to improve and develop shoreside facilities that will support a ramped-up commercial blue catfish fishery.  The bill is now awaiting the governor’s signature.

Although it hasn’t yet been conclusively proven, it seems very likely that blue catfish are having a significant, negative impact on the Chesapeake Bay ecosystem.  But fishermen tend to be parochial, and neither a surfcaster up on Cape Cod nor a light tackle guide on Long Island Sound is likely to spend too much time worrying about whether blue catfish are causing real harm to yellow perch populations in Maryland’s tidal creeks.

Even so, such northeastern anglers ought to take some time to ponder just how the Bay’s blue catfish will impact them. 

After all, the Maryland portion of Chesapeake Bay is the single most important nursery area for striped bass on the entire coast.  And a Year 0 striped bass, six or eight inches long, would make a fine meal for a hungry blue catfish. 

At a time when striped bass recruitment is dismayingly low, a time when a changing climate may be making the Chesapeake watershed less likely to produce big year classes of bass, the last thing that we or the striped bass need is additional stress on the resource, whether that stress comes from increased recreational landings or from an increasing population of invasive, predatory blue catfish.

Unfortunately, it appears that, right now, we're going to be forced to deal with both.