New Studies Will Improve Abundance Estimates for Ice 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 two studies on bearded, ribbon, and spotted seal haul-out behaviorand the spring "emergence" of ringed seals. This research provides critical information on the percentage of seals hauled out on sea ice to those remaining in the water. It also describes how 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 or hidden in snow-covered dens. 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 spring 2025, scientists conducted a large-scale aerial survey of the Bering, Chukchi, and Beaufort seas of Alaska. They photographed and counted 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, not all seals haul out on the ice at the same time. These new studies allow scientists to produce better overall abundance estimates. They can better estimate how many seals are in the water, and thereby missed by the aerial counts.

Multi-Year Study Provides Important Biological and Behavioral Information

The first 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 sensors that measure conductivity. Because saltwater is more conductive than air, they can determine whether the device-and therefore the seal-is in or out of the water. When on the surface, the device transmits the seal's haul-out behavior data to researchers through the Argos satellite network. Satellite transmission is essential for the research given the extremely remote location.

We have deployed 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 with batteries that can last 1-2 years. Importantly, they stay attached to the seal during the molt period. These deployments provide location information when the seal is out of the water and can transmit up to several months of data indicating the portion of each hour the tag was out of the water.

Ice Seal Study Findings

Ice-associated seals rely on sea ice for 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. Warming of Arctic ecosystems could decrease the quantity and quality of suitable habitat. 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 NOAA Fisheries Research Permit #23858 and NOAA NIF #N24-17.

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. 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 spring, haul-out behavior is centered around solar noon-when the sun is at its highest point in the sky. 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.

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.

A Hidden Challenge: Ringed Seals in Snow Lairs

Ringed seals present a unique challenge. They build snow-covered dens ("lairs") on the sea ice. This means a ringed seal can be out of the water, but still remain hidden from aerial surveys.

Lairs provide a warm, dry place for ringed seals to rest during the winter and to have their pups in March and April. Later in the spring, ringed seals switch from using lairs to basking on the surface of the ice, a transition called "emergence." Understanding the timing of this behavioral switch is important for estimating what fraction of the seal population is visible to aircraft.

The second study, published in Ecology and Evolution, focuses on this puzzle. Researchers also used biologger data to estimate when emergence occurs. "We found that adult ringed seals typically emerged in mid-May, and that the likelihood of emergence increased substantially with warmer temperatures and longer days," said Jessica Lindsay, lead author of the paper and biologist at the Alaska Fisheries Science Center. After emergence, ringed seals spent more time out of the water and centered their haul-out behavior around solar noon. Authors on this study included NOAA scientists and co-authors from:

• Alaska Department of Fish and Game
• North Slope Borough Department of Wildlife Management
• University of Washington

The study also revealed that timing varies by latitude; seals farther north in the Beaufort Sea emerge later than those in the Bering Sea. Understanding when this transition happens geographically will help scientists time their surveys to get the most accurate counts in the different regions.

Benefit to Future Survey Efforts

Scientists will integrate information from these studies with data collected during aerial surveys to predict what portion of the seal population is on the ice and available to count. Together, these pieces of information allow researchers to estimate current abundances of bearded, ribbon, spotted, and ringed 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.