By PAULA DOBBYN
Anchorage Daily News
March 29, 2006
But whether harbor seal numbers are declining because of ship traffic remains unknown.
Scientists with the National Oceanic and Atmospheric Administration released a report on Monday on seal behavior in Disenchantment Bay, a Southeast Alaska fjord that cruise ships take passengers to for close-up views of Hubbard Glacier.
The study found that when the large ships got closer than 1,600 feet, seals were more likely to jump off the ice floes they haul out on. The closer the ships got, the more likely the seals were to dive into the water.
When a ship was about 300 feet away, a seal was 25 times more likely to jump into the water than when the ship was 1,600 feet way, the study found.
"It really confirms what has been known for some time: that as ships get closer to seals, the seals will get off the ice floes. As a result of that, we have operating practices in place" to minimize disturbance to the animals, said John Hansen, president of the North West CruiseShip Association.
The ships try to maintain at least 1,600 feet of distance from seals, he said.
But that's not always possible because of weather, navigational and other reasons, including not being able to see the seals, which sometimes appear like glacial debris on the ice floes, said John Jansen, the study's lead author. During the study, biologists documented many times when the ships got within 300 feet of seals, he said.
A concern is that if seals are routinely disturbed, it will drain their energy reserves, possibly resulting in lower reproduction or reduced survival, the researchers said.
The study also found that the more time ships spend in Disenchantment Bay, the closer the seals come to one another. Such huddling behavior is common among animals that feel threatened, said Jansen.
The research, which began in 2002, also compared harbor seal numbers in Disenchantment Bay with those of Icy Bay, a nearby glacial fjord with similar natural characteristics. The only major difference between the two bays is that cruise ships do not visit Icy Bay, Jansen said.
Icy and Disenchantment Bays started out with roughly the same number of seals in May, between 1,000 and 1,500, Jansen said. The study found that seal populations in Icy Bay increased from May to August, while in Disenchantment Bay, they peaked in June and then declined slightly. Icy Bay ended the summer with 5,400 seals while Disenchantment Bay had only 1,800.
Whether the seals are leaving Disenchantment Bay and heading to the quieter waters of Icy Bay is unknown because scientists have yet to track the movements of individual seals with radio transmitters. Hopefully that will be the next phase of the research, Jansen said.
The study was a cooperative effort involving NOAA, the cruise industry and the Yakutat Tlingits.
As cruise traffic increased in Disenchantment Bay since the 1970s, the tribe had become concerned about whether ships were disturbing the seals, especially during pupping season in May and June.
"We feel strongly that they do affect the seals during those months," said tribal member Bert Adams Sr., a charter captain and former president of Yakutat's tribal council.
"The local people are saying that the seals are moving from Disenchantment Bay to Icy Bay because there is less disturbance there," Adams said.
Answering that question with certainty will take longer-term research, Jansen said.
Biologists do not have accurate long-term data on seal populations in Disenchantment Bay like they do at nearby Glacier Bay National Park, he said. At Glacier Bay, however, harbor seal numbers have declined by 50 percent since 1992. During that time, the number of boats, including cruise ships, has increased steadily, according to NOAA.
Scripps-McClatchy Western Service, http://www.shns.com
Publish A Letter on SitNews Read Letters/Opinions