Harbor Seals, Glacial Ice and Tour Ships in Alaska's Disenchantment Bay

In Disenchantment Bay, near Yakutat, Alaska, harbor seals give birth and nurse their pups on floating ice calved from Hubbard Glacier, and tour ships come to see the glacier. NOAA Fisheries and the National Park Service's Glacier Bay Field Office have been working out whether the ships are harming the seals.

Harbor seals in Disenchantment Bay. NOAA Fisheries.

Tagging the pups

In June 2016 and 2017, biologists from the two agencies caught and sampled seals hauled out on the glacial ice and fitted satellite-linked transmitters to 73 pups and two mothers. Early results surprised them: pups tracked from the bay travelled more than 300 nautical miles, to Prince William Sound and Southeast Alaska.

At the same time, a vessel tracking station on Haenke Island recorded the route and speed of every ship entering the study area. Putting the ships' tracks together with the seals' positions and behaviour lets the researchers model how close, and for how long, vessels came to seals, and match that against when each pup was on the ice or in the water. The next step is to compare pups with and without ships nearby, in and out of the ships' path, to see whether ships make them spend more time underwater.

A pup netted for sampling and tagging. NOAA Fisheries, permit 19309.

Fitting a satellite-linked transmitter. NOAA Fisheries, permit 19309.

Taking samples in the boat. NOAA Fisheries, permit 19309.

Why time in the water matters

A pup knocked off the ice by a passing ship has to spend extra time in water chilled by the glacier. Earlier energy models suggested that even a modest increase in time submerged could force pups to trade body mass for body temperature, burning the blubber they need to get through their first months on their own. Over time that could cut survival and lead to a decline in the population.

A tagged pup ready to go back into the bay. NOAA Fisheries.

A long history

Tour ships have sailed into Disenchantment Bay to see Hubbard Glacier for more than a hundred years. NOAA Fisheries began surveying the seals on the glacial ice in the early 1990s. Within ten years the Tlingit Tribe of Yakutat raised concerns: tour-vessel visits to the seals' ice had grown tenfold in 30 years, hunters were finding fewer seals, and they feared the ships were to blame, especially while mothers were nursing pups on the ice, with consequences for their tradition of seal hunting.

• From the early 2000s, NOAA Fisheries developed ways to count the seals accurately from the air across a huge and shifting ice field, so the population could be followed over the long term. So far the counts show no marked change in numbers or in where seals gather, but reliable counts came only after the suspected decline may already have happened.
• Biologists made thousands of observations from tour ships, and found seals diving off the ice as far as ¼ mile from a ship.
• Applying the energy models to whole groups of seals showed that a single ship can send up to 14% of them into the water, an effect likely to add up when as many as four ships visit in a day.

A cruise ship near Hubbard Glacier. NOAA Fisheries.

These results, together with work by the Alaska Department of Fish and Game, the National Park Service and the Alaska SeaLife Center, led NOAA Fisheries in 2015 to develop guidelines for vessels in glacial areas to keep disturbance to a minimum.

The vessel tracking station on Haenke Island. NOAA Fisheries.

What comes next

With major funding from the National Park Service, the team put out 75 tags over two years. In the fall of 2017 it brought the tracking station's data back from the bay, while the last tagged pups headed out into the Gulf of Alaska, some of them, the scientists hope, to return one day to the ice to breed. The analysis is meant to help resource managers and tour operators decide whether more protection is needed and what form it should take, and to learn more about seals that live on glacial ice.

A harbor seal hauled out on glacial ice. NOAA Fisheries, permit 19309.

A tagged pup back in the water. NOAA Fisheries, permit 19309.

The face of Hubbard Glacier. NOAA Fisheries.

Sources

• NOAA Fisheries, "Multi-Year Study Seeks to Understand Potential Impact of Tour Vessels on Harbor Seals in Alaska's Disenchantment Bay"; rewritten in hubnx's own words. Photographs: NOAA Fisheries, taken under permit 19309 issued to the Alaska Fisheries Science Center's Marine Mammal Laboratory.
• NOAA Fisheries, Alaska Harbor Seal Approach Guidelines in Glacial Fjords 2015.