In last quarter’s Limnology 101 we learned that the redox soils in the bottom of Devils Lake can produce a smell similar to rotten eggs when disturbed. This is from chemical reactions that lead to an environment with little to no oxygen. This affects plant growth on the bottom which can result in less habitat and food for other living things in the lake. Yikes!     

  

   This quarter we are going to talk about grass carp. We will learn why they were used in the first place, their costs and benefits, and why we are petitioning for more. 

   Devils Lake has had a unique history when it comes to vegetation management. Since Lincoln City started developing around the lake, the influx of phosphates and nitrates in the water fed the vegetation to an extremely overgrown state. The lake was so full of weeds that there was a limitation on lake recreation. The Devils Lake 100 Year History records what each year was like. Residents wanted to use the lake to it’s full potential. How lucky this area is to have a great body of water in their backyard, except few could use it. In 1984 The Devils Lake Water Improvement District formed. Their goal was to improve water quality. Two years later, the first batch of 10,000 grass carp were placed in the lake. 

         Bio-controllers are a tricky business. Biological control is a management strategy that reduces a population that has become burdensome by using its natural enemies to reduce its numbers. This can become controversial quickly. Most pest populations that grow too big for an environment are invasive. Often is the case is that they don't have natural predators in the environment, so besides competition and perhaps disease, there is no regulation on their populations. By introducing their predators, another potential invasive species will enter the environment. This can have unforeseen impacts. For example, in 1935 the poisonous Cane Toad was introduced to Australia as a bio control for the Greyback cane beetle. The beetle was destroying sugar cane crops, so the toads were introduced to reign in these populations as they had been successful in Hawaii. The problem ended up being that not enough research was done prior to the introduction and the toads ended up being a complete failure. The toads started to spread rapidly, and soon Australia had two major invasive species. It is hard to know exactly what is going to happen when a bio-control is introduced because each population can behave differently, and each situation is unique.

    The decision to put grass carp in Devils Lake was based on a number of things. They had been used as weed controller as they eat their own weight of plant material each day under the right conditions. The major concern was reproduction. Since the grass carp are non-native, they had no natural predators which could mean their populations could get out of control. The solution....sterile fish.  One year after the initial 10,000 fish were stocked, another 17,050 were put in the lake. The wanted results were still not being achieved so, in 1993 5,000 more carp were introduced. The following year there was a near total eradication of aquatic plants in the lake. Only the hardened stalked lily pads and emergent cattails remained.  This was unintended, as the original goals were to maintain some vegetation, but as population dynamics are rarely an exact science, the extra carp pushed the scales and nearly all the vegetation at the bottom of the lake was lost.   

  

   Consequently, the nutrient rich waters were still nutrient rich, and as nature abhors a vacuum, something was going to fill that niche.  All this time, the weeds had been feeding on the nutrients. With the weeds gone, the lake became the perfect breeding ground for blue-green algae, aka Harmful Algal Blooms (HABS),  to flourish.   While blue-green algae have been part of the Devils Lake ecosystem long before grass carp, with the weeds suppressed or basically mowed down by the grass carp, blue-green algae have become more prevalent.  

    After all the change to the lake, why is the District applying for more carp to be stocked in the lake? Simply because it remains the most cost effective means to manage vegetation in a lake this size.  Also the District wants to retain this tool in the toolbox as it  would cost many, many thousands of dollars a year to control weeds otherwise (e.g. weed harvesters, herbicides, dredging, etc.), all of which come with their own environmental issues.  

The carp did exactly what they were meant to do, control vegetation.  In fact they have been doing so for nearly three decades.  The Chinese Grass Carp actually have out lived even the best estimates of their longevity, causing some speculation that they may have not been infertile after all. To test that point, the Oregon Department of Fisheries & Wildlife have conducted fish surveys and in 2014 scientifically aged and tested a sample of these fish proving that in fact they are sterile and from those original stockings of either 1986, 1987, or 1993.  This makes the Grass Carp of Devils Lake likely some of the oldest, if not the oldest documented Grass Carp in the world.  

Eventually however, even these hardy souls will face their demise and without a new approval to stock additional fish the weed problems of the 60's, 70's and 80's will likely come roaring back.  The new application calls for the right to put in a modest one carp for every two acres in the lake needing weed control, every other year.  That is 277 fish on a bi-annual cycle.  The District would continue to monitor the weed population before stocking allowing some vegetation to grow back before releasing any new fish. This is a promising strategy because nothing quite like it has been done before. Controlling vegetation from a top down approach has been done.  Devils Lake is a prime example.  However controlling vegetation from a bottom up approach where the bio-control is introduced before wide-spread invasions have taken over is "new ground" or in this case maybe we should say, would be "testing new waters".  The District currently has an application into ODFW to allow this approach.  Should ODFW approve a new stocking plan, Devils Lake would continue to serve as an important experiment with biological controls and provide recreational access to thousands of people each year.  

The American Power Boat Association is holding power boat races on the "World's Fastest Lake". These races provide the viewers some fast action and hopefully some exciting speed records. Last year our own local boat builder Craig Selvidge debuted his new boat "The Spirit of Devils Lake" (shown here) which raced and record speeds.

To learn more about the races, visit the official website here or click on the picture!

Also enjoy a preview to the festivities by watching the video.  Zoom, Zoom!