17 April 2020

Michigan considering prohibiting Marmorkrebs

Yesterday, there was a conference call meeting of the Michigan Natural Resources Commission that included discussion of adding Marmorkrebs to the state’s list of invasive species.

The presentation slide deck makes some... interesting statements.

Slide 14 in the deck says, “No native range, presumed product of captive breeding”. This implies that someone deliberately set out to create an asexual crayfish, and that’s misleading at best. There is zero evidence I am aware of that anyone deliberately set out to create an asexual crayfish. Marmorkrebs may have originated in captivity, but nobody planned it. Nobody thought an asexual crayfish was even possible. Nobody was “breeding” for it

Slide 15 says, “Threat to natural resources: Aggressive behavior traits”. This is an odd item to list first. There is no evidence that Marmorkrebs are more aggressive than other crayfish species. The papers on Marmorkrebs fighting to date have shown that they are competitive in when they are facing size-matched individuals from other species. The qualifier is important, because Marmokrebs are smallish crayfish. Many other species get larger, and large animals win. Further, Marmorkrebs have only been compared with a couple of other crayfish species.

The same slide lists another threat as “Introduce disease”. Maybe? Disease has been a big problem with introduced crayfish in Europe, but last I looked at a map, Michigan is not Europe. In the US, disease has usually not been a significant problem with crayfish impacts. It could be. But so far, this seems like one of the lower risks.

I would have inverted this list, and started with “Alter fish communities” and “Degrade water quality”.

The bottom line? The slide deck lists the “next steps” as:
  • Recommend listing Marbled Crayfish as prohibited to DNR-Director
  • Officially list in May, if recommendation is approved
So this process looks quite advanced and likely to happen.

If this went through, this would make Michgan the third North American jurisdiction to regulate Marmorkrebs specifically.

External links

16 April 2020 agenda of Natural Resource Commission (PDF)
Presentations given to the NRC - 16 April 2020, Fish (PDF)

Join in this week’s NRC meeting online or by conference call

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