This nutshell is based on a recently published paper:
Hoover-Miller and Armato. 2017. Harbor seal use of glacier ice and terrestrial haul-outs in the Kenai Fjords, Alaska. Mar Mamm Sci.
Background: Where ice meets the sea
Many people come to Alaska to see the impressive tidewater glaciers in the fjords of southeastern and southcentral Alaska. These towering walls of ice are breathtaking, creating a thunderous cacophony when they calve. To most visitors, we view the calving and might think of the power of nature. It might remind us how climate change is having real, tangible impacts on our ecosystems.
Video from the National Park Service, Kenai Fjords National Park
To harbor seals, the sound of glacier ice crashing into the ocean is the sound of home.
While harbor seals are most commonly sighted on beaches, rocks, and piers, in Alaska, 15% of harbor seals use ice as their preferred habitat for resting, raising their young, and molting. On the Kenai Peninsula, ice associated seals experienced an 85% decline from 1980-1994—sparking an intense research interest. One site that was monitored was Aialik (pronounced: Eye-al’-ick) Bay — the fjord just over the mountain range to the west of the ASLC. There the decline persisted at least 15 years beyond the time when elsewhere in southcentral Alaska numbers appeared to be recovering.
In Aialik Bay and the surrounding Kenai Fjords region, seals use both ice and terrestrial habitats. This provided an opportunity for researchers to look at how habitat use has changed over time between multiple tidewater glacier and terrestrial haulouts.
Planes, boats, and cameras
In order to study how habitat use changed over time, researchers at the ASLC monitored seal attendance on tidewater glacial ice, tidally influenced glacial lakes, and terrestrial sites like beaches and coves for over 10 years. They did this via aerial surveys, boat surveys, and by using remotely controlled cameras. Using all three methods, adults and pups were counted.
Counting seals via remotely operated cameras, from boats (through a partnership with Kenai Fjords Tours), and from aerial surveys. Aerial survey image credit: NOAA Fisheries (original here)
While ‘counting’ animals sounds easy, it can be a very labor intensive task that requires a LOT of patience. Want to try your hand at counting animals from imagery? In Google Earth you can often find seals if you look closely! Here is an example from Northwestern Fjord–one of the fjords studied in the new paper.
How many seals can you see in the following image?
Patterns in the ice
Results of this long-term study showed from 2004-2012, the number of seals at glacier sites and terrestrial sites have changed. During the molt, seal numbers increased each year by 5.4% at glacier sites but by 9% at terrestrial sites. During the pupping season, the number of seals without pups showed the opposite trends (7.96% at glacial sites and 5.1% at terrestrial sites). Numbers of seals with pups showed a clear preference for tidewater glacial sites where more than 5 times more pups were born than at terrestrial sites. Furthermore, population recovery is more rapid at glacial sites where numbers of pups are increasing by 5% each year while numbers of pups at terrestrial sites increased by only 1.5% annually. The low number of pups counted at terrestrial sites also shows that seals in this region seem to strongly prefer ice for pupping.
These results show that not only is the population on the Kenai Peninsula beginning to recover, but that the patterns of recovery are different across habitats. It also highlights differences in the behavior of seals between pupping and molting periods. Population surveys, generally conducted during the molt in Alaska when seals rest and shed their coats, paints a different picture of habitat use than is apparent during pupping. Based on these findings, reliance on surveys conducted during the molt underestimate numbers of seals using glacial ice habitats and the importance of ice sustaining these populations.
This study has furthered our understanding of seal habitat use and highlighted areas where future work can continue. For example, seals may move between glacial and terrestrial sites in relation to ice availability as glaciers retreat. Tourism near glaciers also may impact their habitat and influence their movements. Monitoring such effects leads to decisions that are more informed, and better adaptive management strategies in the face of climate change and changing marine landscapes.
Written by: Anne Hoover-Miller and Amy Bishop