Each year, thousands of people set sail from Cape Ann aboard whale-watch tour boats with hopes of catching an up close glimpse of one of the planet's largest mammals, but the long-term effects of such substantial whale watch exposure had been relatively unknown — until now.

New research published by scientists at the Gloucester-based Whale Center of New England suggests that heavy whale watch exposure is not having harmful effects on the calving intervals, or calf survival, of humpback whales in local waters.

The findings are published in a new issue of "Biological Conservation," a peer-reviewed research journal.

"What we wanted to do was to look at whether whale watching was impacting whales in the long run, not whether it was causing short-term disturbance," said Mason Weinrich, chief scientist at The Whale Center and senior author of the study. He noted that, while whale watching has become one of the busiest tourism industries, it is not heavily regulated.

Whale watch boats in the Gulf of Maine operate under a voluntary code of conduct, or guidelines, that are officially endorsed by the National Marine Fisheries Service, the federal agency in charge of managing whale populations in U.S. waters.

"Since we have a long-term database on individual whales," Weinrich said, "we thought we could examine whether whales that were watched more often had a compromised reproductive success over time."

A 2007 study had shown that whale watch boats were not always good at following the federal guidelines, particularly when it came to speed, Weinrich noted. Some whale watch captains were not acting responsibly and that had raised concern, he said.

The Whale Center, based at Harbor Loop, has been studying humpback whales, using both whale watch boats and research boats, since 1979. Each humpback whale can be identified using natural markings on both the underside of their tail flukes and their dorsal fin, Weinrich said. Using three decades worth of data collected each year from naturalists aboard whale watch boats out of Gloucester and Boston, scientists could assess how often each whale was "watched."

"Obviously, some whales had lots of exposure to boats, while others had relatively little, giving us a good range of whales to examine," Weinrich said. "We then compared this with the frequency that those whales had calves, and what percentage of those calves survived to at least two years after weaning."

Naturalists and data collectors from The Whale Center regularly work with Capt. Bill and Sons Whale Watch and Seven Seas Whale Watch in Gloucester, as well as Boston Harbor Cruises. However, Weinrich emphasized that the data analysis was not biased "in any way" and that The Whale Center is "independent" and not "tied financially" to any whale watch companies.

The study database contained almost 300 reproductive females and more than 500 calves. Their behavior was observed in the southern Gulf of Maine, primarily around Stellwagen Bank and Jeffreys Ledge off Gloucester and waters southwest of Gloucester Harbor between April and November from 1980 to 2006. Both areas are submerged glacial deposits that, combined with local currents, create "substantial upwelling and nutrient productivity," Weinrich wrote in his report.

Results of the comparison showed no negative effects of whale watch exposure on any of the parameters that were examined. In fact, those females more heavily exposed to whale watching within a year were found to be more likely to return with calves, and those calves most heavily watched were most likely to survive.

"This doesn't mean whale watching is good for whales," noted Weinrich, "but it does suggest it is not having negative effects. It really shows how important a healthy environment in the Stellwagen Bank National Marine Sanctuary is for whales, and how that seems to supersede any long term effects that boats may have."

Since Stellwagen Bank and Jeffreys Ledge are sites where there is significant boating, fishing and shipping traffic in addition to whale watching, Weinrich said that using measurements of whale watch exposure alone may not be as important as they would be in understanding impacts as in other more pristine areas such as Shark Bay, Australia, or Doubtful Sound, New Zealand.

Just last year, incidents involving whales and commercial vessels off the Massachusetts coastline prompted federal charges against two fishermen. And in September, Robert J. Eldridge Jr., of West Chatham, paid a $500 fine for illegally untangling a humpback whale caught in his fishing gear, a violation of the federal Endangered Species Act and the Marine Mammal Protection Act.

Fishermen are required to call a licensed marine mammal rescue worker in such cases rather than disentangling the animal themselves. Such disentanglement teams carry special permits issued by NMFS.

Federal charges have also brought against Christopher Jacques of Gloucester for an incident where he allegedly hit two whales while on the fishing vessel Lisa Rose inside the Stellwagen Bank National Marine Sanctuary on July 23, 2008. Jacques is scheduled back in court in two weeks. And a National Oceanic and Atmospheric Administration research boat struck a right whale off Scituate this past April.

The Whale Center researchers caution that their findings don't necessarily mean that whale watching should continue unsupervised.

"There are a number of caveats to our conclusions," Weinrich notes, "and short-term disturbance of an endangered species, if it is happening, is both illegal and a bad practice. Managers need to decide what they want to manage for, short-term or long-term effects. But it is reassuring to note that we can't find life history impacts on the whales we in New England care so much about.

"Despite the 'long-term' nature of this study, we only examined the potential impacts of whale watching on humpback whales over a fraction of their lives," he added.

Humpbacks are thought to live for 50 or more years.

"So, this study at best addresses the effects for approximately half their lives," Weinrich said. "It is possible that long-term exposure to whale watching, and to other vessel traffic, may eventually impact individuals through causing hearing damage or chronic stress, leading to an eventual decrease in fitness."

However, a 1999 study of the acoustic interaction of humpback whales and whale watching boats off the coast of Hawaii published in Marine Environmental Research concluded it was "unlikely that the levels of sounds produced by the boats in the study would have any grave effects on the auditory system of humpback whales."

Whale watching tours began in New England in 1975, and within a decade the regional whale watching industry became the largest in the United States and one of the largest in the world.

Whale watching in New England primarily targets humpback whales, which use the waters off Gloucester, Cape Ann and elsewhere in the Gulf of Maine as a feeding ground from April through December, then spend winter months breeding in the Caribbean waters.

Jonathan L'Ecuyer can be reached at 978-283-7000, x3451 or jlecuyer@gloucestertimes.com.