A hostile takeover is going on in the waters of Pennsylvania, and most people don't even know it's happening. To make matters even more grim, humans are the main cause.
Pennsylvania's native crayfish species are being threatened by aggressive invaders, said Dave Lieb, an aquatic invertebrate zoologist with the Western Pennsylvania Conservancy and the state Fish and Boat Commission.
Four exotic species - the red swamp, calico, virile and rusty crayfish - have been introduced to Pennsylvania waters and literally can wipe out native populations, Lieb said.
"We know for sure that they are eliminating the native crayfish," he said. "We know for sure that humans are the cause."
Native vs. exotic
About 11 native species of crayfish live in Pennsylvania. They eat a variety of plant matter, other invertebrates, snails, algae and insects that hatch out of the water, such as mayflies, caddisflies and midges.
Some native crayfish only live in certain parts of the state, while others are found throughout it.
Leib said the term "exotic" is synonymous with non-native. If a species is exotic to a particular water body, then it is not naturally found there; rather, it has been introduced.
"Other crayfish are native to parts of Pennsylvania but have been introduced to areas where they do not naturally occur, such as the Allegheny crayfish, the White River crayfish and the big water crayfish," he said.
"Lycoming County has one native crayfish species (the common crayfish)," Lieb said. "One other species has been introduced to the county - the Allegheny crayfish. There could be other exotic species in the county that we do not know about because not every water body has been thoroughly surveyed."
Big and bold
Exotic crayfish tend to grow much larger than Pennsylvania's native crayfish, but identifying specific species is difficult, Lieb said, and usually takes an "expert's" eye.
He has studied several sites where exotics now live. They range throughout the Susquehanna River basin, nearby streams and in parts of what Lieb called the "Delaware drainage area."
Even though crayfish usually only live about two years, an exotic species, or a native that has invaded new territory, can do a lot of damage, he said.
For example, the Allegheny crayfish is a native species in the western part of the state. It can grow fairly big, he said, and has large claws.
"The exotics use their claws to crush natives. I have seen cases where natives' faces have been removed," Lieb said.
Alleghenies have moved from the west to east and now can be found in and around the Philadelphia area, hundreds of miles away from their native stomping grounds.
The large populations of non-natives and exotics and their tendency to colonize new areas are beginning to affect Pennsylvania's fisheries.
"From the food web studies I have done, they (native crayfish) have a really important central role in aquatic systems," Lieb said.
The fish that normally would eat crayfish often have trouble eating the exotics because of their size, he said.
"When you have exotics, they often get too big too fast to be eaten by fish species and they aren't as good for the fish," Lieb said.
In addition, exotic species will eat fish eggs and other foods that the fish normally eat.
"If they were as easy to eat as the natives, it wouldn't be a problem for fish," Lieb said. "They often grow so quickly ... they are not small for long."
Without population control, the exotics quickly can grow in numbers.
The fish commission has said that non-natives can exceed 18 individuals per square foot, populations higher than their native counterparts.
Blame it on people
Humans probably are at the root of the problem, the commission zoologist said.
"We have problems with people moving natives around the state and bringing in exotics," Lieb said.
Whenever species of crayfish are moved around, he said, there is a great potential that the act will have a negative impact on a waterway.
Anglers may transfer crayfish by catching them and using them for bait.
It is much safer to use crayfish that are caught in the specific area where an angler wants to fish.
Unfortunately, Lieb said, fishermen take crayfish elsewhere to use as bait and then let them go.
Crayfish bought from pet stores usually are exotics, he added.
Originally purchased for pets or to use as food for other pets, these crayfish sometimes will find a home in the wild when their owners discard them.
Classrooms and laboratories also have been known to introduce exotics.
In some places where exotics were introduced, Lieb said he has come back five or six years later and not found one native in that water.
Exotics can breed with the natives, creating hybrids, which also negatively affects the native population, he added.
Avoid live crayfish
Because people are the primary reason for the exotics' expansion, they can help stop it.
"It's the individual fisherman or teacher in the classroom or the buyer at the pet store (who can) decide if we have another introduction or not," Lieb said.
Lieb recommends that anglers not buy live crayfish from bait stores and refrain from collecting them in the wild. Or, if the latter is not an option, then only use the crayfish in the exact stream where they were captures.
If someone goes out and collects a pretty-full bucket or discovers that it is easy to find crayfish, it is likely they aren't natives, he said.
"The natives are less abundant and (it is) more difficult to collect a lot of them," he said.
Artificial crayfish catch a lot of fish, Lieb said.
"They are great," he said. "I have always used artificial crayfish for smallmouth bass and I think they are more efficient. Why risk your fishery by using live crayfish when you have so many alternatives?"
Solution evades specialists
The Fish and Boat Commission is looking into this problem and trying to find solutions.
Lieb said his studies need to involve more waterways so he can examine the impact across the state.
Right now, everything just is in talks, but anglers or residents can help by not moving crayfish at all.
"We have already lost native crayfish from large areas of the state," Lieb said. Still, "there are a lot of areas exotic crayfish have not invaded."
Something, he said, needs to be done now. If Pennsylvania waits 10 years, Lieb added, much of the state may be without native crayfish.
