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Wild Thursday: Asian carp and bald eagles

Some days, things just converge, like questions and speculation on Asian carp and bald eagles.

First Bill Anderson of CatchPhotoRelease.com, who had earlier sent a photo link and speculation that maybe eagles are finding it easier to forage around the warm water discharges on the Des Plaines than below the Starved Rock dam, posed this:

I also read on your blog that they attribute it to lack of shad. When you take that and combine it with the fact I talked to a friend who fishes a lot of walleye tournaments, and he said that overall weights are down at all the weigh ins… Maybe those Asian carp are effecting the Eagles too?? They think the carp are causing a decline in the shad that the walleye eat.

And an hour or so later this morning, by coincidence (and you have to love it), Phil Willink, fish curator for the Field Museum, sent this set of speculation:

Dale,

Your comments the other day about missing Bald Eagles and Gizzard Shad are interesting. I do not pay too much attention to Bald Eagles, but I have been thinking a lot about Gizzard Shad lately. They eat plankton, which is what Asian Carp eat. So it is assumed that Asian Carp and Gizzard Shad have similar ecological roles. When we look to see if Asian Carp are having a negative impact on the environment, we often look at Gizzard Shad. And when we conduct ‘thought exercises’ to see where Asian Carp may live (such as the Great Lakes), we often look at Gizzard Shad.

There is some evidence that Asian Carp are outcompeting Gizzard Shad in the Mississippi. Fishermen are reporting drops in Gizzard Shad numbers as Asian Carp numbers go up, but I am not sure if this is quantified or just observations.

If Asian Carp are increasing, and Gizzard Shad are decreasing, and Bald Eagles eat Gizzard Shad, then this is bad news. There is no scientific proof, but it is disturbing to think that our National Symbol is getting taken out by an invasive fish. This is also an elegant example of how this problem is not just restricted to aquatic systems.

It should be noted that none of this has been proven, as far as I know. Bald Eagles may not actually be down permanently. Bald Eagles may start eating something else, like Asian Carp. And Gizzard Shad numbers may just be fluctuating naturally because they are having a bad winter. Hard to tell at the moment. But definitely something to keep an eye on.

I also find it hard to believe that nobody else has connected these dots.

Oh well. The madness continues.

Phil

It’s worth pondering. Not that it makes me feel better.