Stream Sampling 3

by Carl Strang

Today I finish reviewing my initial catch-and-release session with the animals in the little stream that runs through the north half of Mayslake Forest Preserve. I was impressed by the diversity turned up with only a small sampling effort. I wasn’t surprised to find some crayfish, but the two that washed into the net were very small.

Perhaps a centimeter long, these had only tiny front claws.

They were colorfully marked, but I wasn’t sure how to identify such young ones. I’ll hope to catch their mom or dad in a future sampling session. Near the stream’s origin I caught a couple isopods.

These aquatic sowbugs have terrestrial relatives in our forests.

According to my reference these are omnivores, but get most of their nutrition by consuming dead organic matter.

The biggest surprise in the sample was a fish.

This green sunfish was less than 2 inches long.

Green sunfish can turn up anywhere, and I suppose this one washed in from May’s Lake. I doubt that there is a self-sustaining population in this tiny stream.

I’ll close with snails. Three different families were represented in the sample. Most abundant in the downstream end of my sampling area were tiny snails that appear to be ram’s horns, family Planorbidae.

They were only 2-3mm in diameter. Perhaps when larger they will prove to belong to a different family.

There were pointy snails, too (such adjectives underline my lack of sophistication, here). Some had the open end oriented to the left when the point is up. These belong to family Physidae.

To perceive the left-handedness, you have to imagine rotating this snail so the shell opening faces you.

Others belong to one of several families with a right-handed orientation.

In order to place this snail in its proper family I would need to see its operculum, the little door which covers the shell’s entrance when the snail withdraws. Some snails don’t have them, however.

Some of the snails were beautifully patterned.

I look forward to studying these pretty little things further.

This was an encouraging start. Maylake seems like such a mundane forest preserve at first glance, but the more I look, the more diversity I find in it.

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2 Comments

  1. Marie said,

    April 22, 2011 at 10:41 am

    I’ve heard that the number of right vs left handed snails is an indication of water quality.

    • natureinquiries said,

      April 25, 2011 at 6:13 am

      I have heard the same, though my main reference doesn’t say they are much more tolerant than some other families. In any case, the right-handed ones much outnumbered the left-handed ones, so that seems a positive indicator as does the diversity in general in that stream.


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