The dogs had a significant impact. When the team analyzed its samples in the lab, measuring the concentrations of E. coli, Enterococcus, and other contaminants, it detected the presence of potentially pathogenic bacteria like Salmonella and Campylobacter (a species that includes C. jejuni, a common cause of gastroenteritis) for 7 of the 11 pre-dog sampling days. But during the 9 gull-free days, the team couldn't detect the bacterial pathogens at all, and the levels of E. coli and Enterococcus species dropped dramatically and rapidly: A reduction of half the gull population decreased E. coli and Enterococcus species by 29 percent and 38 percent, respectively, the researchers report this month in Environmental Science & Technology.
Although technically called "gull harassment," Converse says the dogs provide a humane and effective deterrent method, albeit one that can be costly, if the dogs were brought in daily throughout the summer (oiling nests, in contrast, is a one-time expense). Airports and other sites can set up nets or set off shotguns, but those methods wouldn't be a good idea at a public beach. And while oiling gull eggs brings long-term results, they are not as immediate as simply chasing away the gulls. The "critical next step," she adds, is to show that those pathogens are actually infective strains that could get humans sick.
Connecting gull poop to actual human illness is difficult, however, cautions Richard Whitman, a research ecologist and station chief of the U.S. Geological Survey's Lake Michigan Ecological Research Station in Porter, Indiana. Other birds -- including Canadian geese -- and mammals could be sources of poop-borne bacteria, Whitman says, as could algae that incubate E. coli and other critters in the right conditions. Even so, he says the new study shows just how effective controlling seagulls can be on improving water quality.
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This is adapted from ScienceNOW, the online daily news service of the journal Science. http://news.sciencemag.org