A look at "Back from the Brink" - Hard Science or Lopsided Observation?

Photo Credit:  NCSU AWCP

In recent weeks, a story of tragedy followed by triumph has circulated among aquatic scientists, the media, and the general public.  "Back from the Brink - How Lake Ellwood, Once Doomed Is Being Rescued", although written as a blog posting, has found its way into various social outlets, professional discussions, and even into mainstream media.  Let’s be honest, with a title as strong as this, how could anyone shy away from reading?  The two words "doomed" and "rescued" alone insight a primal need in all of us to find out what wrong is being done, and who exactly the hero is that saved the day?

 The problem here, however, is a problem that only the most critical of readers, or those most familiar with the science, would catch.  Are we REALLY looking at someone's scientific findings, or merely an opinion expressed as such?  We'll let you be the judge.  Prior to continuing here on the Aquatics Update, we suggest you take the time to read "Back from the Brink..." before you form your own opinion of the matter.  

Back with us now?  Great.  Now let’s get started. 

Did you get a feel for the who will play the role of villain that "doomed" Lake Ellwood?  How about the subsequent "rescue" of the Lake?  We can almost bet that the villain, in this case a herbicide known as 2,4-D, is obvious to most of us.  The "rescue" may not be as clear, but a call for halting all aquatic herbicide use in the Lake is likely a good fit.  Fisheries data and aquatic plant observations seem to drive home the story.... but wait.... let’s take a good, hard look at the data and especially the rather strong inferences made from that data, and apply the scientific method.

A Typical EWM infestation.  Photo Credit:  NCSU AWCP

 First a little background.  For those of you not familiar with aquatic herbicide use, 2,4-D is an herbicide labeled for aquatic use which controls various broadleaf plants.  The plant toted as the "savior of the lake", Eurasian watermilfoil (a very aggressive invasive aquatic plant might we add) is controlled regularly through the use of 2,4-D.  Unlike some other aquatic herbicides, 2,4-D is actually selective, meaning that it can remove broadleaf plants like EWM, and open up habitat for native monocots to flourish. Furthermore, the removal of EWM would likely INCREASE diversity of other native plants rather than denuding all of Lake Ellwood.... So why the decline in fish???  Looking at the report, there seems to be a thriving adult fish population - so what about predation?  2011 and 2012 were very dry and hot summers in midwest, so what about lake levels? Could low DO and high temperatures have killed smaller fish or roe, and/or inhibited reproduction?  What about other lakes that use 2,4-D for control of EWM?  If the herbicide alone is to blame, then why is this the first time in decades of 2,4-D use would such declines be observed?  What percentage of the lake was infested by EWM, and how much of that percentage was treated each year? We would hope that these and other causes be investigated or cited, but it seems this work was either limited in investigative scope, or the "suspect had already been booked, tried, and sentenced" prior to the first survey. Let's keep moving.

EWM in situ.  Photo Credit:  NCSU AWCP

So what about surveying aquatic plants?  The process of estimating aquatic plant presence, coverage, density, and distribution is one of the most technical aspects in aquatic plant science.  Although new advancements in data collection and methodology have greatly improved a means by which to make such estimates, aquatic plant surveys require a great deal of time and effort to complete.  Timing is also extremely important as aquatic plants are not permanent structures and will change in coverage and biomass throughout the course of a year.  The report makes several qualitative guesstimates regarding plant community structure using such words as "sparse" and "rare", but what do these words really mean?  Sparse compared to a stand of hydrilla in southeastern reservoir or sparse as sago pondweed in native stand of seagrasses?  There are standards used in measuring aquatic plant biomass and coverage, however this report makes no attempt at actual quantification of plants over time in Lake Ellwood.  Just as an example, let’s use the line stating "Aquatic vegetation has never been considered to be abundant in Lake Ellwood. During a comprehensive fisheries survey conducted during 2002, aquatic vegetation was listed as “sparse” (Young 2002)."  In 2012, the report states that "Bluegill abundance has dropped drastically over the last 10 years".  So how exactly is fish decline caused by a decline in aquatic vegetation when Lake Ellwood has never been known as a lake driven by aquatic vegetation?  A claim of more fish in 2013 also had us raising our eyebrows.  A rebound in fry was observed in 2013 (a year when EWM was not treated), however no estimation of plants, whether invasive EWM or native, was made before or after such an event. So how exactly can claims that a decline in EWM, or vegetation in general be understood without actual data to support such claims?  Lastly, where does the fish population data from ’04, ’06 and ’08 come from that is mentioned in the original report, after the statement that prior to 2012 the last survey was conducted in 2002?

The issue regarding Lake Ellwood's fish population is as dynamic as the habitat in which these species (both fish and plant) call home.  Scientific conclusions are built upon the investigation of various parameters which may, or may not, contribute to the outcome observed.  Adequate collection of data within ALL of these parameters is needed to more fully understand the cause of an observed phenomenon.  The main problem here is that the author is jumping to conclusions without data to support their claim, and apparently dismissing any other possible cause or collection of causes.  As one takes a deep read into this article, and the report, hard science begins to hide behind biased and assumptive conclusions about the association of fish reproduction to aquatic vegetation and herbicide use. There should be no discredit to the fisheries data presented here, however such conclusions cannot be drawn without adequate survey of the other side of the equation - the aquatic plant community.  Rather than painting 2,4-D (and by association all weed control) as the sole cause of the problem, the author should have posed such an assumption as a POTENTIAL explanation rather than THE culprit. While we understand that the authors of the report in question, and of the subsequent blog posting, are individuals who study fish, it only seems necessary or even just for that matter, to take into account all potentially contributing factors in such a unique occurrence as that on Lake Ellwood.   

For more information on the intricate relationship between fish and aquatic plants, visit our Best Management Practices Handbook, Chapter 2:  Impact of Aquatic Invasive Plants on Fish written by Dr. Eric Dibble of Mississippi State University.  For more information on Aquatic Herbicides, visit Appendix C:  A Discussion to Address Your Concerns: Will Herbicides Hurt Me or My
Lake?

For the original report entitled "Comprehensive fisheries evaluation of Lake Elwood, Florence County, Wisconsin 2012", click HERE.