What’s Behind the Fish Kills on the Shenandoah?

Photo by Tusik Only

Now that the summer has officially arrived, everyone wants to know how the fishing is doing on the Shenandoah River. Unfortunately, for this season, I am afraid it will be a bit of a slog, but there are a couple of encouraging signs that bode well for the fishery in future seasons.

In 2014, a quiet fish kill took out a significant number of fish (anywhere from 30 to 70 percent) in the 13″ – 17″ range. Virginia Department of Game and Inland Fisheries (VDGIF) biologists are still trying to assess the extent of the fish kill, but it was significant.

In addition, persistent algae blooms are still appearing on the Shenandoah and are affecting both forks of the river as well as the main stem. These algae blooms are the result of excessive amounts of nutrients (primarily phosphorous and nitrogen) entering the river from the over fertilization of agricultural fields and even private residences. The long strands of filamentous algae make paddling and rowing difficult as each stroke of the blade is wrapped with what looks like a mop head of green hair. Even worse, we have found evidence of blue/green algae coating parts of the river bottom threatening bottom dwelling creatures that cannot tolerate the toxins released from the algae.

Of the two forks, there is anecdotal evidence that the North Fork has experienced a more significant reduction of smallmouth bass and red-breasted sunfish over the past year. While Paul Bugas, VDGIF aquatics manager, and his team of biologists have not completed their sampling efforts for this year, their preliminary findings are suggesting the same thing. Angling results being experienced on the South Fork are achieving only marginally better results. It actually appears that the main stem may have been spared the most and as a result could provide the best fishing on the Shenandoah for 2015.

Due to heightened awareness of the presence of blue/green algae, the South River Science Team (SRST), who monitors and assesses the presences on mercury in the Shenandoah, is now collecting liver samples of smallmouth bass to ascertain the presence of microcystins (also known as cyanoginosins). Microcystins can be produced in large quantities during algal blooms and pose a major threat to drinking water, as well as the environment at large. The presence of microcystins in fish liver will prove that toxins are entering the fish and possibly contributing to the periodic fish kills we have been experiencing on the Shenandoah.

In April 2015, we met with USGS Dr. Vicki Blazer and doctoral candidate Ryan Braham to discuss their upcoming study in the Potomac watershed. In addition, USGS is conducting research on the two forks of the Shenandoah, collecting water samples for further analysis involving atrazine (common pesticide used on corn and is banned in Europe) and glyphosate (found in the pesticide Roundup). We are collaborating with USGS on this effort by helping to collect samples.

So what’s the good news? VDGIF Naturalist, Paul Bugas said the 2014 spawn was the second highest recruitment class in the last 18 years. And 2010 and 2012 also saw good recruitment years. The 2010-year class is responsible for most of the 11”-12” smallmouth bass that are currently in the river. Moreover, if you keep your fingers crossed and the creek doesn’t rise – literally – the 2015 spawn has the potential to produce an outstanding recruitment class but those fry need to get through the month of June before the fisheries biologists will exhale a sigh of relief.