Northern Clearwater Crayfish

2010 June 12

“The cray is certainly not a fish, [but] a handsome crustaceous animal” – J. J. Audubon[1]
I’ve been meaning to make an entry for crayfish for some time, so when we went down to Otter Lake in the third weekend of May, we made a point of finding one. This one was resting on the boat launch ramp just above the Otter Lake dam, and we were able to just drop the net right over it.

Crayfish are pretty big as Michigan arthropods go. We put it in a glass pan with water for photography[2], and the squares on the checked tablecloth that you can see under it are just about a centimeter across, so it was just over 7 cm across from nose to tail (almost 3 inches)

The eyes are slightly stalked, and there are actually four antennae rather than the two antennae that you find on insects. They normally move by creeping along the bottom, but when alarmed they can use their “telson” (the last body segment, which is modified to look like a fish tail) to rapidly scoot backwards, making them hard to catch unless you sneak up behind them with a net or bucket.

The underside of the tail is where the gills are located. As long as they keep their gills moist, most crayfish can actually survive on dry land for a time, and some of them will dig little pits in muddy areas where they can hang out and emerge briefly to find food.

Crayfish are “decapods” like lobsters, crabs and true shrimp, so they have ten legs. The two front legs are modified into grasping claws that they use to catch and cut up food (and also to fight with – they can give a pretty solid pinch if you handle them carelessly).

As for what particular kind of crayfish this is, I’m pretty sure that it’s one of the species in the genus Orconectes. After comparing it to the pictures in the Ontario Crayfish Identification Guide I think it is the Northern Clearwater Crayfish, Orconectes propinquus. I don’t think it is the closely-related Rusty Crayfish, Orconectes rusticus, because it lacks the rusty-brown spots on the sides of the carapace, and the black bands on the claw tips.

It is good to see that this was probably not a Rusty Crayfish, because the Rusty Crayfish is something of a problem. It is native to the Ohio River Valley, but has become established in the Midwest and Ontario due to people using it as bait[3]. The Rusty Crayfish is somewhat larger and considerably more voracious than the other crayfish species that are already in the area. It tends to first displace the other crayfish, and then eats larger quantities of water weeds and fish eggs/hatchlings, reducing fish populations and sometimes promoting erosion of riverbeds. In the case of the other Orconectes species, the Rusty Crayfish also hybridizes with them, basically eliminating the other species as distinct populations. So, even though it is a legitimate North American species, it is still considered to be an invasive.

Anyway, like their close relatives the lobsters, crayfish are perfectly edible. It’s just a matter of scale. While it is possible to eat a small crayfish, the amount you get isn’t that huge, so it is a bit hard to get enough to make a proper meal. The bigger species (which tend to live further south) can get quite large (the ones we sometimes see imported by the local stores are over five inches long). There is a thriving crayfish farming industry for the larger ones, but the local Michigan crayfish are small enough that they are mostly only commercially raised for fishing bait. Which is a shame, because I think crayfish are tasty, and I’d kind of like to raise them for food in our swampy area out back. Oh well.

[1] Technically, the full quote goes; “The cray is certainly not a fish, although usually so styled; but as everyone is acquainted with its form and nature, I shall not inflict on you any disquisition regarding it. It is a handsome crustaceous animal certainly, and its whole tribe I consider as dainties of the first order” [from Delineations of American Scenery and Character, J. J. Audubon, 1926], but the first time I saw it, it was in the shortened form, which is a bit “punchier” and easier to remember.

[2] I’m afraid I goofed a bit on the lighting here. The crayfish was so large that I actually had to stand back several feet from it to get it all into the picture, and as a result my flash wasn’t illuminating it as well as it should have. I should have opened up the aperture to get more light, it didn’t need to be choked all the way down to f/32 to maximize the depth of field when the subject was far away as that. As it is, the dark crayfish came out a lot darker than I would have liked. I’ll try to do better next time.

[3] The people who are trying to prevent the spread of invasive aquatic species are almost as exasperated by fishing as by oceangoing ships dumping ballast water. Between people dumping their unused fishing bait overboard, and boats getting pulled out of one lake and put into another along with all the adhering water weeds (and the things living in them), recreational fishing is a primary way that undesirables spread from one lake or river to another.

3 Responses
  1. June 13, 2010

    In 10 Books That Screwed Up The World, I just finished the chapter on Mein Kampf. Hitler would not have approved of this: “In the case of the other Orconectes species, the Rusty Crayfish also hybridizes with them, basically eliminating the other species as distinct populations.” He would have felt that the crayfish nation existed to support and strengthen the Rusty Crayfish as a race. I’m sure he would have told you that hybridizing only weakens this Aryan arthropod.

    On a different note, I had no idea the gills were on the tail. Awesome stuff as always!

  2. June 18, 2010

    I suppose that if we started a campaign to rename the “Rusty Crayfish” as the “Nazi Crayfish”, it might go a long way towards convincing people to stop spreading them around.

  3. jack permalink
    November 1, 2012

    hey i’v caught a lot of thees in the river now i actually know the name of them thanks again ,jack

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