Wednesday, December 1, 2010


As fly anglers we are often confronted with invasive species and rightly so. Invasives present one of the greatest threats to aquatic environments worldwide. When non-native species are introduced either accidently or intentionally they can alter habitat and/or the food web. This has been shown time and again. Let me cite a few examples of invasive fish species:
Nile Perch- not a perch though- a sibling of the snook in reality
-Lake Victoria Africa. The Nile perch (Lates niloticus) was introduced as a source of protein for local villagers. Unfortunately the 300+ species of native cichlids quickly became food items. Most of these colorful endemic fish were less than 6 inches in length. They stood no chance against a 6 foot long, 200 pound predator. And the local fishermen?  Their nets were designed to catch 6” cichlids. Didn’t work.
Silver carp leaping in the Mississippi
-Mississippi Drainage. Asian carp (technically the bighead carp (Hypophthalmichthys nobilis) and silver carp (.Hypophthalmichthys molitrix). These fish were imported to help improve water quality by removing excess phytoplankton in sewage treatment plants and aquaculture facilities. They escaped, got into the Mississippi. There they are competing, very successfully, with native species and in areas they are more numerous. Now the carp are threatening to get into the Great Lakes where they would be an incredible threat to native species and the sport fishing industry.
Large school of blue tilapia
-Florida. Aquaculture and the pet trade in the peninsula state have allowed many species of non-native species to become naturalized. The blue tilapia (Oreochromis aureus) is now the most common mid-sized percoid fish in Florida. Fish and Wildlife officials introduced peacock bass (Cichla sp.) into canals in South Florida to consume the tilapia. Didn’t work well- the peacock bass don’t do well in cold weather and don’t attain the sizes they do in their natural habitat in South America. There are at least 73 invasive fish species in the Sunshine State many of which successfully reproduce.

These are a few examples of invasive species that have caused problems. Obviously they present a lot of big problems. There are so many other examples- Lake Davis in California has been treated with rotenone to remove northern pike twice now, lake trout are strictly catch to kill in Yellowstone Lake, Atlantic salmon are showing up and spawning in Pacific tributaries because of escapes from fish farming… I could go on.
Stocked brown trout from the Winooski River
I am going to throw out a couple of interesting local situations that I think about now and then. In Vermont some of the most popular gamefish are brown trout, rainbow trout, largemouth bass, and smallmouth bass. Only one of these three species is a native- the smallmouth. The rainbow and brown tend to outcompete native brook trout in rivers and the brook trout tend to be limited to smaller rivers and streams in the state. Granted that many of the larger rivers have habitat that has been degraded to a point where our native char will not survive. Thinking on a grander scale, anyone that claims a rainbow trout or a brown trout anywhere in Eastern North America is a “native” doesn’t know much about the history of trout on this continent. Wild perhaps, but these fish not native by any means.

All three of these species have special regulations in Vermont. They are popular gamefish. The common carp, another introduced species, has no such protection. Contrary to popular belief the carp has little impact on native species. Yes they do muddy up areas of Lake Champlain and its tributaries. Have they had an impact on the numbers and diversity of the shallow wetland areas they live in? I spend a lot of time in those areas and have not seen that. I see many native species like yellow perch, bowfin, many minnows, pike, pickerel, and sunfish in those areas. But on Lake Champlain carp are more likely to be targeted with a bow rather than a rod and reel. Many of those shot are left in the water to rot. Really cool huh?
Want a kiss?
How about one of the biggest fisheries issues Lake Champlain has had to contend with: the sea lamprey (Pteromyzon marinus)? It is entirely possible that this species is a native to the lake. WHAT????? A lot of people aren’t familiar with this. It is possible that the fish we have been trying to eliminate for years is a native. There were sea run Atlantic salmon in Champlain when Europeans first came to the area. There are sea run lampreys in other St. Lawrence tributaries near the mouth of the Richelieu River (which drains Lake Champlain). Sea lampreys do not return to a natal stream like salmon do- they use whatever stream they come across. Any reason they would not have travelled up the Richelieu historically? Nope.

When did the lamprey become a problem? When we fed them. Seriously. In the 1970’s the Lake Champlain Salmonid Restoration Program started. This is awesome- Champlain with lake trout and landlocked salmon again. And lets restore steelhead and brown trout too. Huh? Restore two non-native species… Let’s get back to the original story. Millions of salmonids put into the lake. Lots of prey species for lamprey. The lamprey population booms. Classic predator/prey relationship. Definitely a problem that needed to be addressed and the Sea Lamprey Control programs have done a great job with it. (I won’t get into non-target species with treatment now). But we do need to be aware of how things got to be the way they are.

I guess the biggest concept I am trying to get at with all this is that as anglers we need to be cognizant of the history of the fisheries we enjoy fishing in, especially the history of the species we target. Many of the species we target didn’t get to where they are on their own. I love chasing carp, bluegill, and largemouth on Lake Champlain and brown trout and steelhead in Champlain tributaries. Hell, I am happy to see stronger runs of steelies and would not be upset to see better runs of browns. But I am aware that they are not natives.
King salmon fresh out of the Salmon River
I go to fish Lake Ontario tribs a lot. I target king salmon, Coho salmon, brown trout and steelhead. All introduced. Mostly to deal with alewives that got into the lake thanks to the Erie Canal. Yea, again, let’s introduce another species or two to deal with a previous introduction. I do enjoy it. It is a cool fishery and provides a lot of income for folks around the Great Lakes. A great deal of the fishery is supported by hatcheries- just another reality to be aware of (natural reproduction for most species does happen frequently though).  If the Asian carp gets into the Great Lakes this could be a big problem to this fishery. Just another paradox to be aware of: the latest non-native threat is a menace to the introduced species that were established to consume another invasive.

There are a lot of other examples that I could get into now, but I will save them for later. Bait bucket biology with alewives, yellow perch, black crappie, largemouth bass, and channel catfish is another interesting topic to get into. And I will at some point.

So next time you are out fishing, where ever you fish, just be aware of how those fish got there. Are they a native species? Are they supported by hatchery stocking? Are your target species having adverse impacts on the natives? I am not trying to take away any enjoyment of fishing for these fish, I fish for them just like everyone else, I just think it is good to be aware of how we as a species have really changed the face of fish locally and globally.


  1. Amen - I don't mind catching exotics, especially in degraded systems or manmade lakes but it drives me nuts that people believe they deserve to have trout/salmon/walleye in every lake or river or when people think that it is ok that exotics are replacing natives (almost completely) in the upper Colorado River basin.

  2. What's funny is how some exotics like brown trout are held in a higher esteem than other exotics like carp, or even other natives like brookies or buffalo. I loathe the double standard.