Shedding Light on Molting Ice Seals

By Juliana Kim, Mammalogist and PHOCAS research trainer

We previously posted a blog about the PHOCAS project, a research program at the Alaska SeaLife Center that exemplifies how science and animal training can intersect to achieve conservation goals. The Training for Science’ blog showcased several different ways in which our resident ringed and spotted seals are trained for data collection and how cooperative relationships between the researchers and their study animals can improve not only the process of data collection, but also the quality of data that is collected. In this post, we expand on an important component of the larger PHOCAS project—the characterization of molt—and explain how understanding this important process helps us to learn more about the unique biology and physiology of ice seals.

Growing a new fur coat

Arctic seals rely on sea ice as a platform for rest during a number of critical life stages, and one of the most physiologically taxing of these is their annual molt. Every spring, individuals of both sexes and all developmental stages replace several layers of epidermis and regrow a new fur coat through the process called ‘molting’. The process is different from the regular ‘shedding’ of some land mammals because the seals, like many birds, complete this process in a short period of time. This often leaves them vulnerable during the molting period.

Patterns of molting—including timing, duration, and dynamics—appear to exhibit species-specific differences. These differences among ice-dependent Arctic seals are still poorly understood. Arctic seals, or ‘ice’ seals, are difficult to observe in the wild over time—and it is currently impossible to track a single wild  individual across the full duration of molt in order to learn how their molt progresses. For this reason, documenting the molting patterns of seals living in human care can provide novel and urgently needed data pertaining to this important life-history event. This information in turn can help us learn about potential health-related consequences that ice seals may experience as a result of sea ice loss. 

A bearded seal rests on an ice floe while it begins its molt. Notice the old coat (the light brown fur) covering most of the animal and the emergence of the new silver coat on its chest and flippers. photo: NOAA

As a result of projected sea ice loss—and likely associated disruptions of routine haul-out patterns—ice-dependent seals may exhibit changes in their annual molt and incur increased energetic costs associated with molting. Our general understanding is that ice seals molt in the spring and early summer. The duration of their molt is species-specific, but for ringed and spotted seals, generally lasts between 4 to 5 weeks. Molting their coat doesn’t seem to affect a seal’s thermal insulation, as the seals rely primarily on a thick layer of blubber to stay warm. When seals molt, they spend a significant amount of time outside of the water hauled out. They prefer to rest for extended periods on ice floes or land-fast ice, which allows them to escape land-based predators quickly by fleeing to the water when necessary. When hauled out, seals vasodilate (open up) their peripheral blood vessels. This allows warm, nutrient-rich blood from their core to reach the surface of the body and promote regeneration of epidermis and fur. If seals were forced to remain in water during this time, they would either need to reduce blood flow to their periphery or lose a dangerous amount of their core body heat to the surrounding water. Neither scenario bodes well for hair and skin growth.

How do we collect molt data?

Arctic seals living in the wild can be difficult to study due to their wide distribution in remote and difficult-to-access areas. In addition to this, molting seals are on high alert, and easily spook into the water if they are disturbed or feel threatened. Instruments glued onto wild seals usually fall off when hair is lost during the molting period, making data collection in free-ranging animals difficult. Luckily, we have the chance to study this process in individual ice seals living here at the Center. Their specialized training and daily contact with humans provides us with a rare opportunity to closely monitor the molting patterns, body condition, and behavioral changes that occur during the molt, and to track fine-scale changes in individuals over time and across years that would be impossible to study in the wild. 

Since ringed seals and spotted seals molt around the same time each year, we have an idea of when the beginning signs of molt may appear. The animal care staff here at the Center examine the seals for changes in pelt coloration, evidence of hair loss, and changes in behavior such as spending extended periods of time hauled out of the water. Once we observe active hair loss and confirm the start of molt for each animal, we can then take regular photographs and make observations to quantify the percentage of new hair growth each day.

Ringed seal Pimniq hauled out during the month of May; this is one of the only times of year that we see the seals at the Alaska SeaLife Center hauled out and completely dry. Photo: PHOCAS – NMFS 18902.

To collect these molt progression data, we train the seals with fish rewards to cooperate in regular assessments of their coat condition. We take photographs from pre-determined angles, and fill out detailed data sheets marking areas of new fur growth, areas of fur loss, and anything else that may stand out to us. We check the status of the seals’ nail beds, their whiskers, and record whether there is a presence or absence of waxy discharge from the ears. We also rely heavily on trainer-reported data. Using a daily husbandry log, trainers fill out any observed changes in animal behavior during sessions, as well as whether loose fur is noted on the seal or in their enclosure at the start of each day. Monitoring the amount of fur lost each day can help us chart the timing of molt, and how the speed of hair regrowth changes throughout the progression of the molt.

Detailed information about the molt collected each year reveals patterns related to development and to changes in the environment, such as temperature or photoperiod. In addition, we can overlay the molting period with other data obtained from the same individuals to infer connections between energy intake, metabolism, body condition, and behavior. 

Top: Spotted seal Kunik at the start of his annual molt — his brownish, dry coat is one sign that he is getting ready to go through the process! At this moment, you can just see the start of his silver coat emerging on his back Bottom: Kunik, 28 days later, with a complete new coat, at the end of his molt. Photo: PHOCAS – NMFS 18902.

What does new hair growth look like? Below is a picture of Spotted seal Sura displaying the process of coat replacement.

You can see the loose hair that she dropped sitting on top of her pelt. The silver line running down the center of her back is new hair growth. The new hair is often thicker, denser, smoother, and more silver than the hair that is molting off. Photo: PHOCAS – NMFS 18902.

Working with the seals during the molt takes a lot of patience from the trainers and the researchers. The animals must remain still in different orientations for extended periods of time while allowing a researcher to examine different parts of their bodies and take photos or collect shed hair. It does not sound like a daunting task, but this takes a lot of training with these skittish animals. During this time, there is a lot going on physiologically which also can make them nervous, sleepy, or uncooperative. Through consistent training and relationship building, we are able to successfully obtain needed photos during this sensitive time of their lives.

High-tech tools

Training animals to cooperate in exams and photo sessions is a one way to learn about the annual progression of their molt. We also use some high-tech gadgets to monitor how the behavior of our seals changes during the molting interval. Some of our seals are equipped with special electronic tags mounted on their rear flippers. These little ‘tidbit’ tags log the ambient temperature every 5 minutes, and researchers can download the data from the tag every few weeks using a handheld data shuttle with an optical reader. To provide a baseline to compare the flipper tag data to, we have temperature tags constantly recording water and air temperatures in each seal’s enclosure. When we compare the daily temperature records from the seal’s flipper tags to the baseline environmental data, we can figure out when each seal was either hauled out or in the water based on the relative temperature reading. 

Amak (left) and Tunu (right), two adult spotted seals hauled out at the Center during the molt. The small, orange ‘tidbit’ sensor Amak is wearing is visible if you look carefully at his rear flippers. Photo: PHOCAS – NMFS 18902.
Researcher Maddie Meranda easily downloads tag data from a spotted seal using a handheld data shuttle thanks to cooperative training. Photo: PHOCAS – NMFS 18902.

What does this molting data tell us?

The seals ramp up their time spent out of the water during the molt, with the most time spent dry around the 50% new coat date. During this period, the seals’ new fur coat is coming in fast. Hauling out of the water allows them to direct their blood flow to the skin’s surface to promote hair re-growth.  Understanding haul-out behavior during the annual molt is more important than you might think. Because the molting period is the time of year that wild seals spend the most time out of the water, it is the time of year they can be counted most accurately. Therefore, our haul out data can be used to support population estimates for these Alaskan species.

The information we have gathered at the Alaska SeaLife Center about the patterns of molt in ringed and spotted seals can be added to what we have learned about molt in bearded seals through our ongoing research at Long Marine Laboratory, in Santa Cruz, California. These data advance our understanding of a seal’s physiological and behavioral changes throughout the molt. In collecting these observations, we have been able to characterize the molting process in three of four Alaskan ice seal species. Most importantly, these data improve our ability to assess the resilience of these animals in the face of unprecedented climate change.

To learn more about this project, please visit: and

By Juliana Kim, Mammalogist and PHOCAS research trainer

Leave a Reply