This week's announcement that dogs help to reduce gull congregations on recreational beaches has heated up the debate as to whether or not dogs should be allowed to go off leash at beaches.

On the pro side, when trained border collie beach patrols chase away gulls, they help to prevent Esherichia coli -- present in gull droppings -- from leaching into beach waters, according to a study presented at this week’s annual meeting of the American Society for Microbiology.

The avian poop problem has resulted in swim advisories and beach closings, so dog patrols potentially mean more fun in the sun for people and their pets.

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Biologist Elizabeth Alm of Central Michigan University, who co-authored the study, told Discovery News that border collies on patrol at Great Lakes region sites repelled gulls “while at the same time not detracting from the beauty and tranquility of the beaches.”

She was quick to add, however, that “the dogs used in this study were not pets, but highly trained professional working dogs under the control of a handler. They were off leash only briefly and only while actively chasing gulls.”

Gulls are protected under the Migratory Bird Treaty act, but their populations have risen in certain places, such as the Great Lakes area. Alm attributes that to the protection provided by the act as well as to the gulls’ adaptability to humans. Easy food sources, such as landfills and beaches strewn with food remains left behind by beachgoers, can be gull magnets.

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Border collies have the instinct to chase, but not to catch, gulls, which are capable of flying to other locations and doing their business.

Not all birds and beach wildlife are so flexible, however.

Alm said, "We made sure that our beach sites were not nesting areas for sensitive bird species such as piping plover, and our beach sites were approved prior to the study as not being piping plover nesting sites."

A border collie patrols the beach as part of a study on reducing E. coli contamination. Elizabeth Alm

Piping plovers, small birds that breed on beaches or sand flats, are listed as “near threatened” by the International Union for Conservation of Nature. Off-leash dogs have attacked these birds from Maine to Oregon, prompting renewed efforts to encourage owners to leash and better monitor their dogs.

It's a challenge to protect some birds while chasing off others. Robert Johns, spokesperson for American Bird Conservancy, told Discovery News that "certainly, non-lethal approaches for avian control are preferred," so at least the border collie patrols aren’t intentionally killing birds.

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"That said," he continued, "the use of dogs presents another problem and that is the potential disturbance of non-target birds that might be using the beaches for rest and feeding during migration stopovers. Furthermore, there is potential for chicks from non-target birds to be fatally trampled in the process, so we recommend that adequate surveys be conducted to identify the kinds of birds that seasonally use the beaches in question and that particular care be used when migrant shorebirds and beach-breeding birds are present."

Off-leash dogs at beaches can be a threat to humans too. This is National Dog Bite Prevention Week, sponsored by the American Veterinary Medical Association. AVMA spokesperson Michael San Filippo said that an estimated 4.5 million dog bites happen every year in the United States. The vast majority involves off-leash dogs.

Then there is the problem of dog waste. Dog excrement can contain dangerous pathogens, such as the parasitic worm Toxocara, which can cause abdominal pain and even loss of sight in infected humans, according to Eric Morgan and colleagues from the University of Bristol's School of Veterinary Sciences.

Responsible dog ownership can help to alleviate that problem. Whether a dog is a sand and surf loving mutt or an elite border collie on patrol, the actions of the owners and handlers are usually what make or break a canine beach visit.