Monday, February 18, 2008

Snakes! Interception, or search-and-destroy? A million-dollar question.

Brown tree snakes may already be establishing a population in Hawai'i, but could be undetected.

That's because they are very secretive, and because while we are actively watching ports to prevent their arrival, nobody's actively looking for them.

(Photo: A brown tree snake in hand. Courtesy Coordinating Group on Alien Pest Species-Hawai'i.)

A new study suggests it is more cost-effective to add a search-and-destroy function to existing brown tree snake prevention efforts, than to expand the prevention alone.

The study compares current efforts to a drunk who only looks for lost car keys under the streetlight, rather than where he may have dropped them. Current tree snake monitoring is done primarily at places where cargo arrive, like airports. Once a snake slithers out of these areas, nobody's looking.

The paper, “Beyond the lamppost: Optimal prevention and control of the Brown Tree Snake in Hawaii,” was published in the journal Ecological Economics. Its authors are economists Kimberly Burnett of the University of Puget Sound in Tacoma, and Sean D'Evelyn, Brooks Kaiser, Porntawee Nantamanasikarn and James Roumasset, all with the University of Hawai'i at Mānoa. Kaiser is also associated with Gettysburg College in Pennsylvania.

The costs of getting the tree snake issue wrong are significant.

“Actively searching for a potential population of snakes rather than waiting for an accidental discovery may save Hawaii tens to hundreds of millions of dollars in future damages, interdiction expenditures, and control costs,” the paper says.

The losses from uncontrolled snake population in Hawai'i could run to billions of dollars.

Take the case of Guam, a comparatively small island where brown tree snakes became established in the 1950s. Today, the island has densities of 12,000 snakes per square mile. The paper lists thousands of hospital visits for snake bites each year, 90-minute power outages (the snakes span power lines, shorting them out) every other day, and the killing off of 11 of the island's 18 bird species.

Because of the large and growing amount of military and civilian travel between Guam and Hawai'i, it is considered the most likely source of a Hawai'i snake invasion.

Christy Martin, who heads Hawai'i's Coordinating Group on Alien Pest Species, conceded that Hawai'i has teams of snake hunters trained in Guam, but that they only come out after someone has made a confirmed snake sighting.

“I think it would be very prudent to do more searching, particularly around the ports of entry,” Martin said.

Since 1981, eight brown tree snakes have been caught in Hawai'i, mostly at the point of entry—near shipping containers or aircraft. What's the likelihood that some got away uncaught?

“Because interdiction is imperfect, we do not know how many snakes may have arrived without discovery. Given the abundance of local prey base (think birds, geckos, etc.) a small number of escaped snakes have a good chance of establishing,” Burnett said.

Martin said that's a valid concern.

“There have already been a few very credible sightings, with no snakes recovered,” Martin said.

Burnett said her study of the situation concludes “that more funds should be directed towards search, early detection and removal of the brown tree snake in Hawaii.

“While current interdiction efforts are impressive and agencies have done a remarkable job in this area with extremely limited funds, our results show that more attention needs to be given to searching for snakes that may have evaded detection at ports of entry,” Burnett said.

Current interception spending, the paper said, is at $2.6 million, and the scientists assume that even at that, there is a 90 percent chance of a snake arriving within 10 years. Increasing that to $9 million could cut the potential of a snake getting through to one in five.

The economists argue that there's more bang for the buck in expanding the scope of brown tree snake programs than simply beefing up port-of-entry monitoring.

““When the population has not been identified but there is a substantial probability that one exists, early detection is the appropriate strategy,” the paper says.

And there's good reason for doing it, they say.

“Based on Guam's experience, an established population has the potential to do millions of dollars in damage through disruptions to the state's power infrastructure, lost biodiversity, and medical damages due to snakebites.

For more information, see the Hawaii state brown tree snake site:

Or the U.S. Department of Agriculture brown tree snake site:

© 2007 Jan W. TenBruggencate