Sea Grant focuses on harmful nonnative fish in local waterways

By Noah Zucker
Posted 3/3/21

A local organization is swimming upstream to stem the tide of invasive fish species that have made their homes in Delaware’s waterways.

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Sea Grant focuses on harmful nonnative fish in local waterways

Posted

A local organization is swimming upstream to stem the tide of invasive fish species that have made their homes in Delaware’s waterways.

Delaware Sea Grant, a nonprofit at the University of Delaware associated with the National Oceanic and Atmospheric Administration, has launched a campaign to raise awareness about these damaging, nonnative fish.

“The card that we created highlights some ways to identify these fishes” and features pictures and important details about these species, said Kate Fleming, DSG’s coastal ecology specialist.

She added that the cards will tell local anglers how to report their findings online to the Delaware Department of Natural Resources and Environmental Control.

“The Delaware State Invasive Fish Tracker is what (the reporting tool) is called. It’s going to ask you for some contact information and what fish you think you have,” Ms. Fleming said.

“They really like to see a photo,” she said. “That streamlines their ability to be able to confirm the report. Then, they’ll ask you a series of other questions about the fish.”

Unfortunately, this issue is far from unique to Delaware.

“Invasive species are everywhere,” Ms. Fleming said, but DSG is focused on the aquatic ones.

“(They) have lots of different vectors for getting around,” she said. “They can travel around the world in ballast water (of) ships, … so we have species that are coming from faraway places coming into brand-new places on a global scale.”

But recreational boaters can also spread these unwanted guests between different bodies of water by not properly cleaning their vessels, Ms. Fleming said. So can irresponsible pet owners, who have sometimes been known to release nonnative creatures into local habitats when they become inconvenient to care for.

Three species

Although there are many invasive species in Delaware, DSG has focused its efforts on three.

One species DSG has identified is the northern snakehead, which is native to east Asia and was first found in Maryland’s Potomac River in 2004.

“The population has expanded its range throughout much of the Chesapeake Bay watershed and has been introduced into Delaware waters in recent years,” said Ed Hale, a marine advisory service specialist with DSG.

“Northern snakehead have been suggested to pose one of the greatest threats to the aquatic ecosystems of the United States because of their aggressive (tendency to eat mostly or only fish), rapid growth rate and tolerance to low temperatures and ice coverage,” he said. “Further, this species has been found to prey upon native forage species and displace sportfishes that contribute millions of dollars to local economies.”

Ms. Fleming said these swimmers are notable for their length and coloration.
“It’s got these vertical splotches all over its body,” she said. “Then, some of the things we identified in the card for people to look at is that kind of squared-off tail and long anal and dorsal fins. It’s sometimes misidentified as the bowfin, which is a native species.”

The DSG is also keeping its eyes out for flathead catfish.

“Flathead catfish are a large catfish native to the southern Great Lakes and Mississippi drainage basins, as well as along waters of the Gulf of Mexico,” said Mr. Hale.

He said these transplants can get as big as 1 meter long and weigh as much as 110 pounds.

“In addition to the sizes that these fish can attain, flathead catfish have demonstrated a rapid dispersal and population growth rate that has led to their successful invasion within waterways of the Mid-Atlantic Bight,” Mr. Hale said.

“The relative size and population growth of this species has led to significant concerns within management agencies, particularly given the dietary habits of this species,” he said. “Flathead catfish feed extensively on native … fishes,” which navigate upstream from the sea to reproduce, like the American shad, blueback herring and other prey of significant economic concern, like blue crabs.

“With the catfishes, you can actually count the number of rays along their anal fin to try and help determine what kind of catfish you have. It can be a little bit difficult sometimes.”

Mr. Hale said the flathead’s cousin, the blue catfish, is also a problem in Delmarva. Although the species is native to the central and southern United States and the Gulf of Mexico, there’s now a stable population in the Chesapeake Bay and Delaware waterways like the Nanticoke River.

“This species was initially stocked in the freshwater reaches of several Chesapeake Bay tributaries in the 1970s and 1980s to establish new fisheries, since expanding to tidal portions of the estuary,” he said.

Although they can be as much as 50% longer than a large flathead, they do tend to be a little bit lighter. They’re also less harmful than their cousins but are still a detriment to ecosystems across the region.

“Blue catfish tend to have a more variable diet than flathead catfish, including immature insects, crayfish and freshwater mussels, shifting to larger invertebrate and fish prey concurrent with … development (over the course of its life),” Mr. Hale said.

“(For) the catfishes, we also included some identifying information (on the card), like coloration and the shape of the tail and jaw,” Ms. Fleming said.

Silver linings

Although these catfish are certainly an overall negative for Delaware, Mr. Hale did mention that it has opened opportunities for local fishers.

“There already (is) a commercial fishery for blue catfish in the Chesapeake Bay watershed, with millions of pounds being harvested per year,” he said. “So this is definitely something that I think is achievable in Delaware waters, particularly in the Nanticoke River, where these fish have been found.”

Mr. Hale said a new fishery “would expand the economic opportunity of our commercial fishers, thus diversifying their options of species to capture and enhancing the resilience of our coastal economies.”

Mr. Hale said he has “been told that the fish has a nice flavor profile that is dissimilar from farmed catfish.”

Regardless of if they get eaten, he said it’s important that local anglers euthanize these animals if they’re caught, after they’ve been properly identified through DNREC’s tracking tool.

“Upon correct identification, they should most definitely humanely euthanize these animals,” Mr. Hale said.

“Northern snakeheads have achieved some level of notoriety for their capability to crawl on terrestrial environments, so tossing a live northern snakehead onto the banks of a river may result in that animal crawling back to the water,” he said.

Ms. Fleming said the card is available online at bit.ly/3bbES5T. Physical copies are also available.

“We’ve got these cards at six state parks, then we’re also getting connected to some of our municipal parks,” in places like Milford and Seaford, she said.

“If you’re part of a fishing club or a group that may be interested in receiving these cards, we can probably make that happen,” Ms. Fleming said. “I can mail them out if you have a group to distribute them to.”

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