by Brandon Peoples
The media likes to make a big deal about invasive species. We’ve seen plenty videos of jumping carp, documentaries about Red Lionfish, and photos of pipes choked by zebra muzzels. But what about the other aquatic invaders, the ones that sometimes sneak past the headlines…the species that may even be threatened in their native range? Today, I highlight a few of those–some of my favorites from the USGS Nonindigenous Aquatic Species database. Browse the database for yourself–you’re liable to find something surprising!
American shad have experienced massive population declines on the East Coast due to dams, habitat degradation, and overfishing. In fact, harvest of any American shad is illegal in many East Coast states. However, American shad have become established in several major Pacific tributaries, where they were stocked heavily the 1800s. High densities of American shad can compete directly with commercially important populations of salmon, sometimes drastically reducing food sources.
Smallmouth bass are one of the most popular sport fishes in the US, and are personally one of my favorite fishes. Smallmouth are native throughout the Mississippi River basin, and are carefully protected by fishing regulations in their native range. But popularity comes at a cost. These voracious predators have been introduced around the world, and have affected native fish communities from Japan, to South Africa, to Arizona.
Brook trout are heralded by angling purists as the gem of Appalachian streams. Brook trout are highly sensitive to temperature changes and sedimentation from deforestation. They are imperiled in several parts of their native range, and millions of dollars and work-hours have been devoted to restoring this charismatic clear-water beauty. But brookies are an unwelcome member of Rocky Mountain stream fish communities, often replacing and/or displacing native species of Cutthroat trout. Biologists in the East are fighting to keep Brook trout around, and biologists in the West are trying to get rid of them!
Pumpkinseed is a colorful and welcome addition to many a pond fishing experience. But these are one of the nastiest invaders in European waters, wiping out invertebrate food sources and out-competing native species.
Goldfish seem completely harmless in your home aquarium. But when you can’t take care of them anymore and release them into a nearby waterbody, these east-Asian natives can establish considerable populations. In some waterbodies of the American West, goldfish can grow to massive sizes and can have detrimental effects on native species.
The Fisheries Blog 
Building on the theme of unlikely invaders…If asked to name an introduced freshwater fish (species that weren’t here before European settlement), I expect most folks would come up with an exotic foreign transplant like snakehead or Asian carp. However, of the introduced fish species found in any given eastern US stream, the vast majority originated from North America, and most of these were transplanted from a neighboring river basin in their native range. For example, 83 species of fish are confirmed as established in the Virginia and North Carolina portion of the New River drainage. Of these, 46 (55%) were introduced (Yes, you read that right–introduced fish species outnumber natives in the New River drainage). The native range for all but five of the 46 introduced species (common carp, goldfish, brown trout, rainbow trout, and redear sunfish) is located within 100 miles of the New River drainage.
An aside: not all invaders were introduced. Due to human changes to the environment (deforestation, dams, climate change), both native and introduced species that thrive in human-altered streams have spread into areas where they did not occur a century ago, sometimes replacing natives less tolerant of the changes and thereby homogenizing local fish communities (Scott & Helfman, 2001). In the New River drainage, native bluehead chubs were found in just 36% of watersheds sampled prior to 1950, but are now found in 88%. Native mountain redbelly dace simultaneously expanded from 21% to 75% of New River watersheds. Brandon Peoples can tell you why (here’s a clue: Bluehead chubs construct nests and welcome guests). These native invaders kept pace with the fastest spreading introduced species, rock bass, which spread from 32% to 75% of New River watersheds during this time.
I meant to link to Brandon’s earlier post Bluehead Chubs Construct Nests and Welcome Guests