After hundreds of studies, it has been difficult to link fish predation by cormorants (Phalacrocorax auritus) to the reduction of fishing quality in Minnesota lakes. It appears that game fish such as walleye and northern pike make up from less than 1% to nearly 3% of the bird’s diet. They eat only small fish. Many of the fish they eat are perch, which prey on walleye, and it is even possible that by culling small walleye or northerns, they increase the growth rate for those fish in two way. One is by reducing competition between fish for food, and the other is by exerting selective pressure for faster growth.

When cormorants were heavily culled on Leech Lake a few years ago, the Walleye fishing got better. The fishermen and resort owners hailed the killing of the birds as a great thing and attributed the improved fishing to the culling policy. However, the lake simultaneously underwent a very aggressive restocking, and slot limits had been imposed at the same time. The fisherman and resort owners are, sorry to say, being stupid about this, rejecting the science, and possibly shooting themselves in the foot.

Two Minnesota Congressmen have been behind changing federal law to allow widespread killing off of cormorants in the state. This, I believe, is unbecoming of a member of Congress who have the responsibility of paying attention to the science, and of being stewards of our national resources at a level greater than a few local whiny mayors and resort owners.

This issue has been brewing for a few years and will continue. I am hoping that the recent focus on the importance of science in developing public policy will mean a more intelligent, less immature and misinformed cormorant policy in Minnesota over the next few years.

Sources and resources on Cormorants (Phalacrocorax auritus):

Comments

  1. #1 Russell
    November 23, 2012

    Another leap for the political jugular of the great white north !

    Next, is acid rain increasing swan predation by pike ?

  2. #2 Daniel J. Andrews
    November 24, 2012

    If members of Congress were paying attention to science, they’d be trying to do something about climate change.

    We had similar cull programs for cormorants in the Great Lakes. I was given an “opportunity” to conduct a study where we’d spray oil on cormorant eggs instead of destroying them. If eggs are destroyed, the cormorants may renest. If the eggs are just sprayed (and the young die in the egg), the cormorants continue to nest and by the time they realize the eggs won’t hatch, it is too late to renest.

    Despite having a chance to work with some good scientists who would have been a boon to my not yet started career, I turned it down. My advisor, who had been neutral to that point, smiled and said, “I didn’t think you’d go for it–good for you”.

    A few years later, I started hearing some of the same arguments for shooting loons(!). Fortunately, that didn’t gain much traction, at least in our area.

  3. #3 John Meagher
    Ireland
    November 25, 2012

    Cormorants are destroying wild fish stocks all over Ireland ,despite efforts from angling clubs to maintain spawning beds ,these birds are destructive and should not be procted by some anti blood sport body,anglers should take the law into their own hands and go out and cull these birds, look at the revenue that would be collected on cartridges, who gave this body of people that power, at least there should be an open season of 3 months for culling. Will cormorants eat dead fish on the bank of the river?. Regards, John

  4. #4 Greg Laden
    November 25, 2012

    John, I’d appreciate any scientific research you have to back up your suggestion that people carry out criminal acts!

  5. #5 Markk
    November 27, 2012

    Cormorants make a fascinating story of how funding and issues like this interact. Some of the few large scale waterfowl surveys out in Lake Michigan and Green Bay hve been fully funded only because of fishing groups wanting data on Cormorants supported them. To justify killing them really, although they never say that out loud. On the other hand just looking at the islands off the Door County Peninsula that have been devastated and essentially ecologically destroyed by Cormorants gives even serious birders pause. Then again, Cormorants seem to eat a lot of lousy fish in Lake Michigan, perhaps they are even improving the game fish situation. Hard to tell! So that is why it’s a fascinating story, with a lot of seemingly rational responses with different plusses and minuses and nothing close to simple.

  6. #6 Greg Laden
    November 27, 2012

    I think we need to be asking ourselves, “what eats cormorants?”

  7. […] Can we please have a scientific cormorant policy in Minnesota? [Greg Laden's Blog] (scienceblogs.com) Share this:TwitterFacebookLike this:Like10 bloggers like this. This entry was posted in Biology, Birds, Environment and tagged Argentina by petrel41. Bookmark the permalink. […]

  8. #8 Lisa Gelvin-Innvaer
    MNDNR
    October 3, 2013

    The MN DNR has updated its webpage for double-crested cormorants.
    http://www.dnr.state.mn.us/birds/doublecrestedcormorant.html

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