Cormorants: The heart of the problem

The level of animosity toward the federally protected cormorant has escalated in the past decade. 

Double-crested cormorants don't get much respect these days. While I don't expect to generate much sympathy for the cormorant, I do wonder about the recent level of disdain and disgust often associated with the mere mention of this fish-eating bird's name.

Cormorants never were all that popular. While people might speak highly of a great blue heron or pelican or common loon — all birds that also eat fish — cormorants seldom receive that same kind of admiration.

But the level of animosity has certainly escalated in the last decade, during which cormorant populations all across the Midwest have increased significantly. These birds have become so numerous that they've been blamed — sometimes rightly so — for reductions in fish populations in many locales.

The cormorant is just one of many natural predators that eats some of the same fish, birds or mammals that anglers and hunters pursue. Great-horned owls eat pheasants. It's hard to say if there are more owls now than 100 years ago, but I do know the pheasant population has increased. To blame owls for eating pheasants is like taking exception to the guy grabbing a sofa off the boulevard during city clean up day, only because you wanted that gem for yourself.

The historic cormorant increase is linked to a combination of events. Nationally, scientists point to the federal ban on the chemical DDT as a turning point for cormorant populations, which had dwindled into the 1970s.

In the Midwest, biologists point toward a wet cycle that began more than a decade ago as a major factor. Since 1993 in North Dakota and other nearby states, water levels in thousands of wetland and lake basins have increased, flooding and killing mature trees that had grown up around previous shorelines.

Cormorants nest and roost in bare, dead trees within or next to water. Within a few years, cormorants had a lot more nesting habitat available. In addition, the high water that flooded the trees in the first place began to support fish, so there was also much more food available.

It's a classic example of how nature's predator-prey cycle has a built in lag. The prey in this case is the fish inhabiting the bodies of water. For several years, anglers in North Dakota happily enjoyed the bounty of dozens of "new" fisheries before the cormorants started to become noticed as a major competitor.

Someday, when all those dead trees finally fall to the ground, and those flooded water basins shrink, the cormorant population will naturally decline. In the meantime, there are considerable ongoing discussions about whether people should step in and begin cormorant population control now.

The heart of the matter

Cormorants eat fish like a deer eats alfalfa. One study showed a single cormorant can eat a dozen fish in a day.

While cormorants would be hard pressed to swallow the same size fish that anglers typically target, they can eat a whole bunch of smaller fish. And they don't differentiate if the fish is a walleye fingerling, next year's keeper perch, or a fathead minnow. A study in Minnesota showed cormorants do feast on walleye and perch, but also in the diet are less desirable species, namely ling and sucker.

Cormorants influence more than just fish and fish populations. Their colonies are known to exclude other bird populations that rely on the same type of habitat, and there are even concerns in some areas of the United States that cormorants could be detrimental to federally threatened or endangered fish species.

Cormorants are migratory birds under protection of the U.S. Fish and Wildlife Service. The North Dakota Game and Fish Department has petitioned the service, so far unsuccessfully, for broader tools for decreasing the cormorant population.

Some groups have called for cormorant population reduction via shooting in areas where dozens, if not hundreds of these birds congregate to feed. Fish and Wildlife Service research in the Great Lakes region has shown that cormorants will avoid such danger by just moving to another area where they are not harassed. While that might immediately reduce pressure on an individual body of water, control measures over an entire region would be necessary for effective population reduction.

Am I an advocate for the cormorant? Not necessarily, but they do have a place in the world.

And that place may be the same secret fishing spot to which you're headed, for the same reason: To catch some fish.

Leier is a biologist for the Game and Fish Department. He can be reached by email: dleier@state.nd.us