Changing Tides 2017 Midseason Update

The Changing Tides project is a three-year study examining the link between the marine and terrestrial environments, specifically between coastal brown bears, clams and mussels, and people. It is a cooperative project of the National Park Service, U.S. Geological Survey, Alaska Sealife Center, and Washington State University.

A brown bear looks towards the photographer
A brown bear watches the researcher’s camp briefly before moving on. NPS Photo/M. Bradburn

Bear Field Observation
Researchers completed the third and final season of brown bear observation in June. Washington State University graduate student Joy Erlenbach observed brown bear activity at three additional intertidal locations. Bear diets, habitat use, and daily activity were recorded around low tide at Amalik Bay, Swikshak Lagoon, and Cape Douglas. Bears were classified by age and sex to study differences in preferences among these categories. Bite counts per minute were logged to reveal nutritional and caloric values of forage activities.

A small bear is illuminated in morning light
A bear rests near an alder thicket near Cape Douglas. Photo Courtesy of J. Erlenbach

So far, bears have shown an impressive array of strategies to acquire food from coastal environments. Researchers have recorded them digging for clams, foraging for barnacles, and fishing for flounder. During other components of the project, bears were also sighted hunting seals and sea otters, scavenging on whale carcasses, and foraging on small crabs. It is not yet known how common these behaviors are across the coast. Intertidal use was most prevalent at Amalik and less evident at other sites where sedge was readily available.

A woman looks out towards a green field and glacier
Joy Erlenbach scans for bear activity at the viewing point chosen at Cape Douglas. In this location, bears showed a high preference for sedge as a food source. NPS Photo/C. Augustson

Current findings are preliminary. However, field observation suggests that the key resource for early season diets at many locations lay in the coastal sedge meadows, with many bears grazing on grass-like sedge for the majority of their food during times observed. Sedges are easy to acquire and digest in the early season. Further research is needed to measure what environmental stressors might impact this valuable resource.

The data collected from these observations will be analyzed in the months ahead to produce refined understandings of how bears use various coastal resources. Combined with a nutritional analysis of materials collected from the field, this will reveal which resources are most crucial for bear survival.

researchers weigh a bear in a sling
Researchers weigh a bear near Swikshak Lagoon, supporting the head while the bear is lifted. NPS Photo/M. Bradburn

Bear Health Exams
In July of 2017, biologists successfully recaptured and checked up on nine female brown bears collared in May in order to assess their health and collect samples of fur and blood for further analysis. In addition, two more bears were collared, taking advantage of favorable weather. As in past years, the entire process for each bear takes under 30 minutes, with care taken to ensure discomfort is minimized both before and after examination. Bear weights ranged from 270 to 492 lbs and their estimated ages ranged from 4 to 19 years old. The bears had 5-20% body fat, with an average of 15%. Each bear was in good health and had gained between 33-106 pounds, with an average gain of 81 pounds.

a leather and cloth collar is secured around a bear
The GPS collars are outfitted with canvas spacers designed to wear away over time in the unlikely event that the collars cannot be otherwise detached. NPS Photo M. Bradburn

Each bear examined has been outfitted with GPS collars to accurately track their movements across the park. This data will help inform researchers which habitats and resources brown bear prefer while also providing a rich set of data on bear movements over time. Maps of this season’s movements will be made available after the data has been collected. Researchers will remove the collars in October. The collars are programmed to detach remotely in the unlikely event a bear cannot be located.

hair is cleaned and sorted in plastic tubes
Researchers clean bear hair in chloroform-methanol to remove surface oils and store it in vials before isolating the carbon and nitrogen isotopes that reveal the signatures of a bear’s diet over time. Photo Courtesy of J. Erlenbach

Researchers will collect additional samples and measure mass and body fat in October, which will allow them to note changes in condition before and after the salmon runs that feed bears in late summer and early autumn. Samples collected will be processed to indicate individual bear diet and health across the season. Combined with observation, remote camera recordings, GPS movement records, collar-mounted video cameras, mussel and clam monitoring, and nutritional analysis, this complex study will highlight many of the links between intertidal environments and the lives of bears. It will also guide us in deciding how to protect bear habitat in the face of numerous environmental challenges.

For more information:

Questions or comments? Contact:

Kelsey Griffin, Coastal Biologist

Katmai National Park, King Salmon, AK

(907) 246-2104

Grant Hilderbrand, Wildlife Biologist

Alaska Science Center, Anchorage, AK

(907) 786-7076

Last updated: August 30, 2017