Frankenfish may be having a big impact on other fish, says new study – PennLive

The northern snakehead, the invasive fish species that some refer to as the frankenfish, may be more damaging to native fish populations than previously thought.

A recent study by the U.S. Fish and Wildlife Service and Maryland Department of Natural Resources for the first time found major shifts in a fish community following establishment of northern snakehead.

The study of Marylands Blackwater River and Little Blackwater River, where the snakehead showed up in 2012, determined that of 21 fish species captured both before and after the arrival of the snakehead 17 declined with the invader in their river.

The decline varied species to species and ranged from 30 percent to 97 percent.

The main difference in fish communities was a reduction in overall biomass of most fish.

Species dominance during the post-snakehead period was significantly higher for both Blackwater River and Little Blackwater River. Pre-snakehead surveys were more evenly distributed and dominated by white perch, black crappie and brown bullhead, while post-snakehead surveys were less even and dominated by common carp and gizzard shad.

The researchers had an existing pre-snakehead dataset from 2006 and 2007 surveys of fish populations. They replicated those surveys in 2018-19 to come up with the post-snakehead data.

While the trends shown in the study are troublesome, the researchers say further investigation into ongoing fish community changes, and continued vigilance in minimizing spread and population growth of the northern snakehead is needed.

Snakeheads were first documented in the U.S. in 1977, in California, and subsequently in southeastern states. They were found in Maryland in 2002, and shortly after its discovery in Potomac River in 2004, the species gained a foothold in tidal waters. Since then it has spread to every major tributary of the Chesapeake Bay.

They were first confirmed in Pennsylvania in July 2004, when 2 were caught in Meadow Lake in Philadelphia. The lake, part of a maze of interconnected bays and tidal slough, led the commission to believe the fish were likely present in the Schuylkill and Delaware rivers.

A snakehead was caught in May 2017 in Bernhardt's Dam in Berks County and 2 were caught in Octoraro Creek in Lancaster County in July 2018.

In spring of this year, 81 snakeheads were caught in the fish lifts at Conowingo Dam on the Susquehanna River, about 5 miles downriver of the Pennsylvania state line, according to MDNR.

Only one snakehead a predatory species that can grow to nearly 5 feet in length was found in the lifts in 2017, and none were found in the lifts last year.

The Conowingo Pond, the reservoir upriver of the dam, extends upriver 8 miles into Pennsylvania.

All the snakeheads were destroyed before moving upriver of the dam, but the MDNR described the spike in numbers seen in the lifts as dramatic and expressed concern over a possible northern expansion by the aggressively invasive species.

The 2 fish lifts were installed on the east and west sides of the Conowingo Dam decades ago to allow passage of migratory fish such as American shad and river herring. They operate during the spring migration as part of restoration efforts for those migratory fish species. Spring is also when snakeheads are known to travel longer distances in the watershed.

After the snakehead was observed in the east fish life in 2017, an agreement was established between the Conowingo Dams owner, Exelon, and the Susquehanna River Anadromous Fish Restoration Cooperative to implement voluntary, adaptive best management practices that reduce the spread of northern snakeheads while still allowing migratory fish passage, according to the DNR.

Smaller dams upriver of Conowingo Pond, which include Holtwood, Safe Harbor and York Haven, in Pennsylvania, may help to slow the northward spread of snakeheads.

However, snakeheads can breathe air from the atmosphere using an air bladder that works like a lung and are known to travel short distances on land.

The Northern Snakehead Working Group of the U.S. Fish and Wildlife Service notes, Although the northern snakehead can survive up to four days out of the water, overland migration is only possible for juveniles. The rounded body of the adult northern snakehead is not as conducive to overland migration as observed in more horizontally flattened snakehead species.

In late September an angler caught a 28-inch snakehead in the Monongahela River at Pittsburgh, killed the fish and notified the commission.

Its the first sighting of the species in western Pennsylvania.

After examining the snakehead from the Monongahela, Kris Kuhn, chief of the fisheries management division for the commission, told TribLive.com that the fish was likely released illegally into the river. She noted that there are no connecting populations of snakeheads.

In Pennsylvania its unlawful for anyone to possess, sell, buy or trade live specimens; to introduce or import them into Pennsylvania waters; or to transport them in or through the state.

Kuhn and Gary Smith, area fisheries manager for the commissions southwest region, said the fish is being treated as a single fish find because there is no evidence of an established group of fish.

Its not total panic mode, Smith said. Were not too alarmed at this point, as we dont know if they are established.

According to the working group, northern snakehead likely arrived in U.S. waters by importation for the live food fish market. Unauthorized intentional release from this trade, as was the case in the founding individuals of the Crofton pond population in Maryland, continues to be the major mechanism for introduction. The northern snakehead has become widely popular in ethnic markets and restaurants over the last two decades.

Recognized as a highly injurious species, importation and cross-border transport of northern snakehead was prohibited in the U.S. by a 2002 listing under the Lacey Act. Nevertheless, cases of northern snakehead for sale in areas where possession is illegal are not uncommon.

These predatory fishes may compete with native species for food and habitat. Juveniles eat zooplankton, insect larvae, small crustaceans and the fry of other fish. Adult snakeheads feed almost exclusively on other fishes, with the remainder of their diet composed of crustaceans, frogs, small reptiles and sometimes small birds and mammals. Adult snakeheads show significant diet overlap with largemouth bass.

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Frankenfish may be having a big impact on other fish, says new study - PennLive