There has been a lot of "bug talk" around here lately and at least one Forum Poll on seining, so I thought I would share some of the processes used to determine the health of coldwater streams and rivers.
The projects are called Benthic Macroinvertebrate Bioassessment Studies
, or "Macro Studies" for short and the collection methods are surprisingly primitive. After samples are collected is where the amateur nerd anglers (like me) separate from the Professional Biologists. The angler samples to see "what kind" and "how many" different insects are present that the trout may be feeding on (or may be hatching), thus they simply examine what has been caught in the net (streamside) and then move on from there. The Biologist will return the net contents to a laboratory where an applied methodology is employed to closely examine the contents and determine the overall "health" of the coldwater environment.
Sounds simple enough, but if you're extra nerdy (like me) you can be a bit of a hybrid and employ some of the lab methods and calculations to accomplish both (although not to perfection… which is basically the difference between doing it for fun, and getting PAID to do it).
I've done a few Macro studies back east on behalf of small conservancies that just don't have the funding to pay for such a study. I got as much - if not more - out of it than they did and my daughter usually joined me which always made for an interesting day afield. Below are some of the things you would have to take along, how you would use them, and (optionally) what to do with the results.
Things You Will Need
--Pitchfork: Just a simple “garden variety” 4-pronged type, used for dislodging rocks and gravel from the stream bed during sampling.
--Sein: Fiberglass screening (as that used to repair screen windows) fastened to a pair of wooden broom handles, used for catching the dislodged organisms.
--Stream thermometer: Used for recording water temperature (optional)
--Yard stick: Used for measuring current speed (optional)
--Thin-bladed knife or spatula: Used for coaxing specimens off of the screen.
--3-ring Binder: Used for recording data… we keep our tally sheets in here, as well as some “cheat sheets” (pictures of various nymphs), maps, notes, and other reference material.
--Several small jars: These can be used to take specimens home for further analysis or identification.
--Other misc. items: Camera, hand towels, magnifying glass, reference books, and a small shallow dish (for photographing specimens streamside).
Method of Collection
We sampled riffle areas where surface speeds exceeded 0.3 ft/sec using a “kick/screen” method where as my daughter would position herself in the current flow facing upstream with the broom handles held firmly to the stream bed and net stretched between them… then I would disturb the substrate from approximately 4 feet upstream down to the base of the net using the pitchfork as well as my wading shoes. Once the clouded water filtered through the screening area my daughter would raise it in with slow, upstream scooping motion.
Back on the shoreline I would spread the net out and sweep back and forth from top-to-bottom examining and identifying the contents. I would call out the organisms as I removed them from the net while my daughter recorded them on a pre-prepared tally sheet.
As per methods used on other studies of this nature, we ONLY sampled riffle areas as the species that live here are typically the least tolerant of poor water quality. While sampling deep runs and pools (in addition to riffles) would give a better indication of the overall insect diversity, it does change the results as many of the organisms found here are highly tolerant of poor water quality.
Here are some of the areas that are of high importance to Biologists, and also moderate to high importance for Anglers (depending on your love of – or tolerance for - this kind of stuff).
Biotic Index (BI)
Most aquatic species have a number assigned to them which represents their tolerance to organic pollutants. The BI scale is 0-10 with lower numbers representing lower tolerances for pollutants. The overall Biotic Index for each sample station is calculated by multiplying the numbers of individual species by their assigned BI number... the sum of these numbers is then divided by the total number of organisms for that station. The resulting Biotic Index is judged against the table in Figure 1 below indicating the quality of the water and degree of organic pollution.
Interestingly enough, the aquatic insects of most interest to anglers and trout, are also the insects of most interest to sampling Biologists. The insect orders of Ephemeroptera
(Stoneflies), and Trichoptera
(Caddisflies) are grouped together for an EPT Index. These insects are generally considered to be pollution sensitive, thus higher totals of EPT’s among the total numbers of species collected represents healthy biotic conditions.
Many environmental agencies view the percent contribution of mayflies in collection samples as an indication of high water quality. Mayflies are one of the least tolerant orders with regards to pollution. The "percent mayflies" is calculated by taking the total number of mayfly species collected divided by the total number of organisms collected.
Whether you're an aspiring Biologist or just an over-curious angler, there is much to be learned from simply researching and reading Macro studies performed by others (let alone getting out there and doing it yourself). And speaking strictly from an angler's perspective, it can often reveal populations on your local waterway that you didn't even know existed.
For example; the table below shows the results from a study that we did on a fairly small freestone stream back in PA. We sampled 7 stations with 1 being close to the mouth where it emptied into a large river and 7 being just below a warm water reservoir spillway near the headwaters. I had fished that stream for years and thought that I knew it quite well, but I had only really fished the areas from station 1 up to station 4.
When doing the macro study my daughter and I visited new sections further upstream than we had gone before and discovered that it had a very healthy Drunella lata
(Blue-winged Olive) population. I fished this hatch on that stream from that spring until we relocated to Utah… all alone nearly every time!
Tight lines and happy seining!