What is Trophic Status, and How Does It Affect Fishing?

David K. asks:

Hey Joel I was wondering what the differences are between a lakes trophic status and how that affects the fishery as far as being eutrophic, mesotrophic and so on and so forth.

Hi David – there’s some really great book resources to learn more on this, I’m thinking specifically from a Limnology course in my past.  Of course there are some online sources as well, and this was the first hit on Google.

Without getting too detailed regarding the science, and focusing more on the fishing and fishery aspect, remember these are general guidelines helpful for discussing similarities among lakes of similar type.  Consider trophic status as an indicator, among other things, of fertility.  Eutrophic lakes are highly fertile, often dominated by shallow weed growth, and thus extremely productive systems.  They can be prone to winterkill because of their shallow nature, and can also be warmer bodies of water in general.  Bass and panfish communities tend to be the dominant species groups here, but many more species can exist depending on other factors.  Oligotrophic lakes on the other end of the spectrum are rock-controlled, deep-water, and minimally fertile lakes.  You’ll find these in Canadian shield areas, with their gamefish species composition being often consisting of lake trout, pike, and walleye.  Mesotrophic lakes describe a very large swath in the middle, often with sand and gravel controlled middle-depth features.  A large host of species can live here.

The Minnesota Department of Natural Resources goes a bit further in regards to classifying their fisheries by specific chemical and physical characteristics.  They divide the lakes in Minnesota into 43 distinct classes that help serve to compare sampling averages and general population statistics among other lakes within the same class.  Spend any time in the MN DNR Lakefinder App, and you’ll discover that many of the same walleye lakes well-known to hold quality populations or trophy fish, often are of a handful of lake class numbers.  The same is true for other species throughout the state.  Without giving up too many secrets, I’ll leave it up to you to do the research to discover which ones are which, but these are just a few hints to finding similar lakes that produce compared to lakes of a known quantity. 

Joel

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