DNR to continue mute swan reduction

Invasive species a threat to bay health

Friday, June 12, 2009

Mute swans consume about eight pounds of submerged aquatic vegetation (SAV) daily and, back when their population neared 4,000, annually consumed nearly 10 percent of the bay's SAV, according the committee's majority recommendation. SAV is a critical food source for a variety of bay wildlife, including other waterfowl, fish and crabs.

While most waterfowl consume SAV, most are seasonal animals and do so after the plants have already seeded. The mute swan is different in that it feeds on SAV year-round, lowering the amount of SAV growth and expansion. The bay's current SAV levels are only 10 to 15 percent of what they were 60 years ago.

Reduction of the region's mute swan population has been a major component of the state's efforts to clean up the bay since 2001. Methods used are killing adult mute swans via gunshot or breaking of the neck and addling eggs – the process of killing an egg's embryo without alerting the mother by coating the egg with corn oil, depriving the embryo of oxygen.

"While the swans may be beautiful, they continue to pose a serious threat to the Chesapeake Bay and its native wildlife, and non-lethal controls have proven insufficient for reducing the population," said DNR Secretary John Griffin in a press release. "For these reasons, we are unfortunately compelled to continue Maryland's mute swan control efforts, through both non-lethal and lethal means."

The 12-member committee did not reach a consensus. Ten members recommended a continued reduction of mute swans in the region, while the remaining two members argued to maintain the current population of mute swans.

In their recommendation, the two dissenters accused the majority of portraying the mute swan as a scapegoat for the bay's ills. But John McKnight, the DNR's associate director of habitat conservation and a member of the committee's majority, rejected that characterization.

"At this point the SAV damage from mute swans is 20 percent of what it was a few years ago. In my opinion the main cause of the SAV decline is nutrient runoff and sediment runoff," McKnight said. "I've heard this thing about how we're blaming the mute swans for everything, and that's not accurate. The mute swans are part of the problem, but they aren't the biggest problem."

The mute swan is also extremely aggressive and protective during breeding season, according to the majority recommendation, and is a threat to native wildlife, including the tundra swan.

"This was clearly the right call for the resource and I'm impressed that DNR moved quickly to make this decision," said Dr. Wayne Bell, president of the Maryland Ornithological Society, in a press release. "Maryland has achieved an unparalleled 80 percent reduction in the population of this invasive species, so to stop now would have made little sense."

The mute swan is one of six invasive species that have been identified as harmful to the bay. The other five are: nutria, a rodent native to South America; the zebra mussel, which is native to Russia; and three plants –purple loosestrife, phragmites and Asian water chestnuts. Efforts are being taken to reduce populations of all six, McKnight said.

The cost of reducing the nutria population is nearly $1 million per year, according to the majority recommendation. Reducing the mute swan population has yet to exceed $100,000, and McKnight hopes to bring that number down substantially.

"With the mute swan the goal is to bring it down to a very low level. We don't think eradication is likely. But it's pretty much the same thing as the nutria — we want to bring it down to as low a level as possible," McKnight said. "There will probably always be some people that won't let us onto their property. Certainly eradication in the natural areas of the Chesapeake [is a goal]."

jnewman@somdnews.com