The Rusty Crayfish
by Thomas Farley
BIOL/WATER 361, Fall 2013
The setting is Lake Vermillion near Tower, Minnesota. The year is 1962 and the first rusty crayfish were being dumped into the lake by fisherman who brought them up as bait. Little did they know, with just a few buckets of leftover crayfish, they had laid the groundwork for serious detrimental changes to the future of Lake Vermillion. I have lived on Vermillion for over half my life, and a home owned by extended family has been there since the 1950’s. The rusty crayfish is an invasive species that has completely colonized the lake and destroyed what used to be a pristine fishery.
Invasive species are a wildlife manager’s worst nightmare. The universal solution to get rid of most invasives is to keep them from ever showing up in the first place. Any number of reasons can explain why a species is invasive. The species may have been brought for food, bait, cultivation, or even as predator on a different invasive. Whatever the reason, an invasive species is usually brought by humans intentionally (or by accident) to a new habitat and out-competes the local fauna. The rusty crayfish is such a species. Orconectes rusticus is native to the lakes, rivers, and streams of Ohio and Kentucky (Mather & Stein, 2013). Rusty crayfish were brought to the upper midwest in the 1960’s as bait for fishing. The population grew slowly over the next three decades but exploded onto the scene in the early 1990’s. Now some of the pristine northern lakes of Minnesota and Wisconsin are overwhelmed with O. rusticus.
The rusty is a well-known aggressive invasive species. It is unmatched by its ability to invade and decimate a northern lake habitat. It out-competes native crayfish species in a multitude of ways. Able to grow larger than the native species, it is able to bully its way to food sources and shelter. Orconectes rusticus has a voracious appetite and consumes more plant and animal matter and at a higher rate than the native crayfish species, O. virilis. Getting rid of this feisty decapod is no easy task and the likelihood of eradicating it from a large lake is next to zero. Understanding the biological characteristics of O. rusticus is vital to developing a protocol to eradicate this introduced species.
Thinking back to those first crayfish to enter Lake Vermillion… What allowed them to establish a population and exponentially increase until “the bottom is a crawling carpet of rusty crayfish” — Gary Tisovich, my great uncle and longtime scuba diver? One thing Orconectes rusticus would have to be after being dumped into a lake full of smallmouth-bass-infested rock piles is tough. The rusty is equipped with two massive claws used for attracting mates, fighting, and feeding (Szela & Perry, 2013). Even when matched up against same-sized males of the native crayfish, the rusty will win competitions over food and shelter nine times out of ten (Szela & Perry, 2013). When the rusty bullies a native crayfish out of its prime hiding spot, the native crayfish is more likely to be eaten. This could explain the short amount of time it took for a bucket of crayfish to displace the entire native population.
Aggressiveness has also allowed the Rusty Crayfish to avoid predation by certain fish species. When threatened, instead of fleeing when the smallmouth comes knocking, the red spotted decapod raises its claws up and out like a football referee proclaiming ‘Touchdown!” The menacing large claws of the rusty are enough to deter predation (Szela & Perry, 2013). In Lake Vermillion however, our only “native” answer to the invasion is the smallmouth bass. Where the more passive walleye sees dangerous pinchers, the smallmouth sees an all you can inhale seafood buffet. My great grandmother would always tell us how the lake was famous for its trophy northern pike and walleyes. With the introduction of the rusty crayfish and the detrimental effects it has had on the lake’s aquatic vegetation and the not-so-well guarded walleye eggs, the fishery has transitioned in the matter of a decade to a prime muskellunge and smallmouth bass based fishery with hardly any northern pike or walleyes.
Orconectes rusticus is a generalist when it comes to diet, feeding on anything it can grab in its claws. Not only is the rusty able to consume more during one feeding, it also consumes more rapidly than the native species (Morse et al., 2013). This presents an obvious advantage when competition for food is a limiting factor on a population. When food is scarce, the rusty crayfish is able to feed upon what little there is to offer (Morse et al., 2013). This can have devastating results when the rusty invades and the population is not kept in check.
The results of this study are seen firsthand on the battlefield of Lake Vermillion. Ten years ago, native aquatic vegetation used to be seen floating among the waves in the majority of bays big and small. Now, the only vegetation it seems are thick stands of invasive cattails on the water’s edge. The effects of the red spotted monster are also hidden where only few can see. Those that used to troll for fish down deep would often hook “weedfish” and “plantbass”. This was not at all the intent, but at least there was some excitement hooking into something. Hooking weeds was also helpful in steering the boat to deeper water to get out along the weed edge where the walleyes are. This practice would allow the weed-bed to be slowly traced out by the end of the night. However, thanks to the never-ending appetite of Orconectes rusticus, there are no weeds to be found anymore (nor fish it would seem). Where once the anticlimactic event of hooking into a weed had had us on the edge of our seats, now we are constantly snagging a freshwater lobster and usually losing our leech or worm. Neither hooking weeds nor crayfish is ideal, yet the weeds meant that the walleyes had food and cover. Plus, the vegetation did not eat our bait while being reeled in.
Orconectes rusticus has shown what makes it invasive in Lake Vermillion. Is there something about Lake Vermillion that sings a beautiful duet with the rusty crayfish? Are humans the only ones complaining about the new neighbors? One simple search proved these questions wrong tenfold. Through the pages upon pages of research on O. rusticus invasions, a similar lake in Canada had identical problems. Effects of the rusty crayfish takeover were measured across three phyla over nineteen years. It covered the effects near introduction of the rusty to mass takeover. With an exponential explosion in the population of O. rusticus, came a dramatic decline in sunfish and pumpkinseed. An 80% decrease in aquatic snails and nearly wiping out all of the native crayfish were also noted (Wilson et al., 2004).
The decline in fish and native invertebrates is easily seen on Lake Vermillion by peering into the shallows on a sunny day. The revealed rocky flats and sandy shores will nearly crawl with rusty crayfish. Whether it is at ice melt or ice out, the rusty is thriving and surely any nook or cranny in the rocks that may have housed native invertebrates is inhabited by an aggressive invader we may never be rid of.
There may be hope for lakes infested with rusty crayfish. Like the recently deceased Nelson Mandela said, “It always seems impossible until it’s done.” One researcher set out to do the impossible and remove rusty crayfish from a small lake in Wisconsin. The DNR has no solution for lakes already filled with rusty crayfish. The only tips provided are to keep them out in the first place. With no manual on how to proceed, Gretchen Hansen and her team deployed 150 crayfish traps and removed any Orconectes rusticus caught in the trap every three days. Eight long years persisted before “significant” ground was broken. After removing nearly 100,000 rusty crayfish out of the small lake, the ecosystem had begun to show signs of recovery. 95% of the crayfish caught in that eighth year were native crayfish (Hansen et al., 2013).
With a large lake such as Lake Vermillion, Orconectes rusticus is safe from human “solutions.” Lake Vermillion is more than one hundred times larger than the lake in the Wisconsin study by Hansen et al. (2013). Instead of trying to swallow the entire pie in one go, there may be hope however of restoring small areas of the lake and evaluating the results there. With continuous trapping and removing, the scuttling lake bottom of Lake Vermillion could one day grow still. It would take a community effort or Batman to eradicate a bay over a number of years, but the hope persists.
Orconectes rusticus, the rusty crayfish, is exploding onto the scene in upper midwest lakes from crimes committed thirty years past before sensible law prohibited transporting exotic species from foreign ecosystems to new. A seemingly bottomless pit for a stomach and a shovel for a spoon, the rusty is constantly foraging or hunting. The red spotted crustacean’s aggressive behavior on top of its appetite, combine to make this invasive a serious threat to any lake ecosystem. If the misfortune of the rusty crayfish inhabiting your lake falls upon you, a minimum of 8 years of large-scale trapping is necessary to even significantly reduce the population. It may seem an extreme act to pursue this action but the consequences if the lake is not trapped heavily are serious degradations to quality of habitat. Vegetation, invertebrate numbers, fish population, and native crayfish will all suffer a decline in number.
All of these effects are felt on Lake Vermillion. The lake suffers from the invader and the community is damaged as well. What once was a famous fishery for walleye and pike has morphed into a mediocre smallmouth and musky one. Those who live and fish on the lake regularly have noticed it is harder to find the walleyes. They have also seen a number of constricting regulations emplaced by the DNR. Slot and limit sizes are continually changed to smaller and smaller sizes. The crayfish invasion will not be stopped by human intervention on Lake Vermillion. Following the DNR’s advice, the best hope for a treasured lake near you is to never let Orconectes rusticus invade in the first place. I challenge you to investigate any invasive species found in your waterways and research what can be done to contain and eliminate them before a quality fishery degrades forever.
- Hansen, G.J.A., Hein, C.L., Roth, B.M., Vander Zanden, J., Gaeta, J.W., Latzka, A.W. & Carpenter, S.R. 2013. Food Web Consequences of Long-Term Invasive Crayfish Control. Canadian Journal of Fisheries and Aquatic Sciences 70: 1109-1122.
- Mather, M.E. & R.A. Stein. 1993. Direct and indirect effects of fish predation on the replacement of a native crayfish by an invading congener. Canadian Journal of Fisheries and Aquatic Sciences 50:1279-1288.
- Morse, J.W., Baldridge, A.K. & Sargent, L.W 2013. Invasive crayfish Orconectes rusticus (Decapoda, Cambaridae) is a more effective predator of substrate nesting fish eggs than native crayfish (O. virilis). Crustaceana 86: 387-402.
- Szela, K. & W.L. Perry 2013. Laboratory competition hierarchies between potentially invasive Rusty Crayfish (Orconectes rusticus) and native crayfishes of conservation concern. American Midland Naturalist 169: 345-353.
- Wilson K.A, Magnuson J.J, Lodge, D.M., Hill, A.M., Kratz, T.K., Perry, W.L. & Willis, T.V. 2004. A long-term rusty crayfish invasion: dispersal patterns and community change in a north temperate lake. Canadian Journal of Fisheries and Aquatic Sciences 61: 2255-2266.