New Study Will Improve Abundance Estimates for Bearded, Ribbon, and Spotted Seals in Alaska

An adult female ribbon seal looks around among ice floes in the Bering Sea. Animals are much harder to detect during aerial surveys when they are in the water. Credit: NOAA Fisheries / Josh M London / Photo taken under authority of NOAA Fisheries Research Permit #23858.

NOAA Fisheries scientists recently published a study on bearded, ribbon, and spotted seal haul-out behavior. This research provides critical information on the percentage of seals hauled out on sea ice compared to in the water. It also looks at how this seal behavior changes with the weather and time of day. This information enables us to account for seals that are not photographed because they are in the water during surveys. As a result, we can use a "correction model" to improve the accuracy of abundance estimates along with efforts to conserve and manage seal populations.

In the spring of 2025, scientists will conduct a large-scale aerial survey of the Bering, Chukchi, and Beaufort seas of Alaska. They will photograph and count the number of ringed, bearded, ribbon, and spotted seals (collectively called "ice seals") hauled out on ice. Ice seals rely heavily on sea ice for resting and nurturing their pups. But, all seals do not haul out on the ice at the same time. This new study will allow scientists to produce better overall abundance estimates. They will know how many seals are in the water, and thereby missed by the aerial counts.

Multi-Year Study Provides Important Biological and Behavioral Information

The study, published in PeerJ, relies on data from electronic devices known as biologgers attached to seals. The results provide insights on when seals are more likely to be hauled out on the ice. They also show how that behavior is impacted by season, time of day, and weather.

Researcher Skyla Walcott prepares to release a subadult female ribbon seal after a successful sampling procedure. The transmitter adhered to the top of the seal's head will provide data on her location, diving, and haul-out behavior. Credit: NOAA Fisheries / Jessica Lindsay, Photo taken under authority of NOAA Fisheries Research Permit #23858.

"We found that seals are more likely to haul out on ice in the middle of the day and when wind speed is low and temperatures are higher," said Josh London, lead author of the paper and marine mammal biologist at the Alaska Fisheries Science Center. "Haul-out behavior increased through March and April, peaking in May and early June before declining again."

This season matches the period during which seals are nursing their pups, breeding, and molting, when they benefit from more time out of the water. The specific timing and frequency of haul-out behavior also differs across age and sex.

A ribbon seal mother and pup rest on pack ice in the Bering Sea. Credit: NOAA Fisheries / Jessica Lindsay, Photo taken under authority of NOAA Fisheries Research Permit #23858. An adult female ribbon seal with a newly applied transmitter on the top of her head. The transmitter will provide data on her location, diving, and haul-out behavior. Credit: NOAA Fisheries / Jessica Lindsay, Photo taken under authority of NOAA Fisheries Research Permit #23858.

"Before the study, these daily and monthly patterns were generally understood, but the biologgers allowed us to precisely quantify them for the first time," said London.

The biologgers in the study rely on special conductivity sensors (saltwater is more conductive than air) that determine whether the device is in the water or out. The haul-out behavior data is transmitted from the device through the Argos satellite network to researchers. Satellite transmission is essential for the research given the extremely remote location.

NOAA Fisheries has deployed the biologgers on seals in several studies that have spanned 15 years. We partnered with the Alaska Department of Fish and Game and the North Slope Borough Wildlife Management. We also worked in close collaboration with Alaska Native community members.

Adult female spotted seal heads back to the water after two biologgers have been glued to its hair and attached to its flipper. These biologgers help researchers understand her spatial and temporal foraging behavior. Credit: NOAA Fisheries / Skyla Walcott, Photo taken under authority of NOAA Fisheries Research Permit #23858.

For this study, researchers used two types of biologgers. The first type is glued to the seal's hair and provides location and behavioral (e.g., diving and hauling out) information via satellite until it falls off. These devices usually fall off during the molt, which also happens during our study period. We attach a second biologger device to the webbing of the seal's rear flipper. Biologgers attached to the flipper are much smaller, transmit for 1-2 years, and stay attached to the seal during the molt period. These deployments provide location information when the seal is out of the water. They transmit up to several months of data indicating the portion of each hour the tag was out of the water.

Ice Seal Study Findings and Benefit to Future Survey Efforts

Ice-associated seals rely on sea ice for a variety of activities, including pupping, breeding, molting, and resting. In the Arctic, many of these activities occur in spring (April through June) as sea ice begins to melt and the edge of the pack recedes northward. Rapid acceleration of warming of Arctic ecosystems is therefore of concern as the quantity and quality of suitable habitat is forecast to decrease. Robust estimates of seal population abundances are needed to properly monitor the impacts of these changes over time.

Female spotted seal nurses her pup on an ice floe in the Bering Sea. Photo taken while working under authority of NMFS Research Permit #23858.

Results from the study also provide a clearer picture of how reliant these seal species are on sea ice in the Bering Sea during the spring months of March through June. Sub-adult ribbon seals start increasing their time hauled out on the ice in early April followed by adult females who are about to give birth at that time. Adult males increase their use of the ice a short time later, in early to mid-May. In the early part of the season, haul-out behavior is centered around solar noon. As the season progresses, though, seals use the ice throughout the day. During their molt, seals shed their hair and grow an entirely new coat. This requires a lot of energy, and the seals benefit from extended hours resting, out of the water and in the warmer sun.

Scientists will integrate information from this study with data collected during aerial surveys to predict what portion of the seal population is on the ice and available to count. Together, these two pieces of information allow researchers to estimate current abundances of bearded, ribbon, and spotted seals in Alaska. Accurate abundance estimates are essential for conservation of these species and co-management with Alaska Native communities. Over time, researchers will also be able to better monitor how these populations are responding to environmental changes in the ecosystem.

Research team prepares to release a weaned spotted seal after successfully sampling it. The Norseman II support vessel and crew can be seen in the background. Credit: NOAA Fisheries/Skyla Walcott, taken under authority of NOAA Fisheries Research Permit #23858.