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A Seal’s Whiskers Record a History of Foraging, Motherhood, and Stress

May 11, 2021

Through collaborative research, scientists are learning vital information about fur seal and sea lion biology and ecology from a surprising source.

Photo of a female northern fur seal's face and whiskers. Female northern fur seal. Credit: NOAA Fisheries.

Northern fur seals and Steller sea lions are iconic marine mammals that play important roles in healthy Alaska and North Pacific marine ecosystems. Both species have shown widespread, unexplained population declines in recent decades. The Pribilof Islands population of northern fur seals is considered depleted under the Marine Mammal Protection Act. The western population of Steller sea lions is listed as endangered under the Endangered Species Act.

Under federal law, NOAA Fisheries is responsible for providing the science needed to support the conservation of these marine mammals. Together with our partners, Alaska Fisheries Science Center scientists study northern fur seals and Steller sea lions to provide information essential to effectively manage and protect their populations.

But collecting information from large, free-ranging marine mammals is not easy. Many live in remote areas. They spend much of their time in the water, where it is difficult to observe them directly. To aid in collecting data, biologists may attach data recorders to animals to observe their movement patterns or diving behaviors. They may collect tissue samples to examine an animal's physiology, health, or diet. These samples need to be collected with minimal disturbance to the animals.

Adult fur seals and sea lions, especially territorial males, may strongly object to sampling.

Photo of a male northern fur seal's face, open mouth and whiskers.
Male northern fur seal. Credit: NOAA Fisheries.

Collaborative, innovative research is expanding possibilities to learn more about fur seals and sea lions in effective and efficient ways. Scientists across multiple disciplines are developing new ways to unlock a wealth of biological and ecological information—all recorded in a whisker.

Whiskers Record a Biological Timeline

A whisker’s unique properties make it a valuable chronicle of an animal’s history.

Fur seal and sea lion whiskers don’t shed—they grow continuously from before a pup’s birth until the end of its life. Once formed, their chemical makeup does not change. And whiskers can be collected with minimal disturbance to animals—you need only one!

“A whisker potentially represents the entire lifespan of an individual,” said Tony Orr, biologist at NOAA Fisheries’ Alaska Fisheries Science Center Marine Mammal Laboratory. “Even if the tip eventually abrades away, a whisker represents a long period, across seasons and years. With a single whisker, we can take advantage of a time series of data for an individual animal.”

To access these records, scientists analyze the chemical composition of a whisker along its length. The most recent history is at the root and the oldest is at the tip.

“Tracking the long-term behavior of these animals from the chemical footprint in a whisker gives us a better understanding of the conditions they experience when we’re not able to directly track or sample them. It is especially valuable to cover periods when they are at sea or move long distances,” said colleague Brian Fadely.

Partnerships Expand Possibilities

Photo of a northern fur seal pup, face close up.
Northern fur seal pup. Credit: NOAA Fisheries.

This innovative research is possible through efforts of many scientists from multiple organizations working together, each with particular expertise, equipment, and capabilities.

Our marine mammal biologists play a number of roles in this research. They help design the studies, access the animals (sometimes in very remote locations), and collect the biological samples used in collaborative studies. Working closely enough to collect a whisker takes experience and expertise to keep both humans and animals safe, and requires a scientific research permit. In this way NOAA Fisheries scientists can provide samples to other scientists while achieving their own research goals.

“We could not get this information any other way. No one person or group has the ability to do all aspects of this research,” said Fadely. “Collaborating with colleagues is a powerful way to use these tools. By combining our understanding of chemistry, physiology, biology, and ecology, our insight into the behavior of these animals is increasing by orders of magnitude.”

What We Can Learn from a Whisker

Recent studies showcase examples of new knowledge gained through collaborative, innovative research—and whiskers.

The Individuality of Foraging Northern Fur Seals

Understanding how top predators respond to environmental change in the marine environment is essential for their effective long-term management. A recent study provides a new understanding of northern fur seal foraging behavior and how to monitor it.

The research was conducted on San Miguel Island, California, where northern fur seal populations are increasing.

“Northern fur seals primarily reside in Alaska’s Pribilof and Bogoslof Islands, but their range extends to two islands off California,” said Orr, a coauthor on the study. “Studying the San Miguel Island population can help us understand what environmental factors are helping them increase while Alaska populations are stable or decreasing.”

The chemical composition of a whisker is influenced by the prey consumed at the time that the whisker is formed. Previous studies showed that a pup’s whiskers, which begin forming before birth, reflect its mother’s foraging habits.

“We wanted to see if pup whiskers also reflected the diets of unrelated mothers,” said Tanner Howard, biologist from the University of California, San Diego, who led the study. “That would mean we could sample just a few pups to see what the whole population is doing.”

Photo of a northern fur seal mother and pup sleeping on sand.
Northern fur seal mother and pup. Credit: NOAA Fisheries.

Instead, their findings underscore the complexity and diversity of northern fur seal foraging dynamics.

“There were no correlations between unrelated pups and mothers. Even though pups have very similar lives, the foraging habits of mothers are highly variable,” said Howard. ”Our research shows that it is important to have an adequate sample size to account for this variability to provide the information needed to manage and conserve this population.”

“When we talk about a species, we need to think of them as an aggregation of individuals,” said Orr. “There isn’t just this one behavior they are all doing. Each individual has her own patterns of behavior and some of them are similar enough that they can be grouped. However, there is enough variability in the population that examining a few does not reflect what the population is doing. ”

Reproduction and Stress in Retrospect

Another new study explores the potential for using whiskers to track reproductive histories and potential stressors in female northern fur seals and Steller sea lions.

A team of scientists was led by Mandy Keogh, then at the Alaska Department of Fish and Game. They developed methods to measure reproductive and stress-related hormones in the whiskers of northern fur seals and Steller sea lions. These findings provide a new tool for research and management.

“Determining reproductive rates in free-ranging fur seals and sea lions is challenging and traditionally requires extensive field efforts and sampling events over multiple years,” said Keogh. ”Our study developed a method that uses one whisker to measure hormones associated with pregnancy and stress and allows us to identify previous pregnancies in Steller sea lions and northern fur seals. With one whisker we can estimate how many pregnancies a Steller sea lion had during the previous three to six years.”

Photo of adult male and female northern fur seals kissing.
Adult male and female northern fur seals. Credit: NOAA Fisheries.

Seasonal Shifts in Steller Sea Lion Diets

In another recent study, researchers used whiskers to examine diet diversity of adult female Steller sea lions in the Aleutian Islands. A team of scientists, led by Andrew Doll of the University of Colorado, found that food habits of adult females shifted significantly with the seasons. In the summer, they ate fish like walleye pollock, northern rockfish, and Atka mackerel, which are relatively low on the food chain. In winter, sea lions consumed a much more diverse diet with a greater proportion of higher-level predators like Pacific cod, octopus, and arrowtooth flounder.

Understanding seasonal diet shifts is important for planning the conservation and recovery of this endangered species as some populations continue to decline. Predictable diet shifts can also inform fisheries policies, allowing managers to identify potential competitive interactions with commercial fisheries.

Environmental Contaminants and Steller Sea Lions

A 2020 study looked at whiskers for insight into how the feeding ecology of Steller sea lion mothers affects mercury levels in their pups.

“We want to understand how significant contaminants are in driving changes in Steller Sea lion populations,” said Fadely, a coauthor on the project. “Aleutian Islands populations in the western areas are still declining. We are trying to understand why.”

The team, led by Lorrie Rea of the University of Alaska Fairbanks, collected pup whiskers to assess the trophic level their mothers were feeding at during gestation. Mercury has been shown to biomagnify moving up the food chain. This means that the amount of mercury obtained from a predatory fish is greater than that from a smaller fish lower on the trophic pyramid. Predators like sea lions that feed on higher trophic levels are therefore at higher risk of exposure to mercury.

Mercury adversely affects health, survival, and reproductive rates in wildlife. Any or all of these effects could lead to decreasing population trends.

The study found a wide range of mercury and feeding levels at each breeding colony, reflecting the different individual foraging habits and species eaten by Steller sea lion mothers.

Close up head photo of an adult male Steller sea lion.
Adult male Steller sea lion. Credit: NOAA Fisheries.

A Valuable New Tool

Scientists at the Alaska Fisheries Science Center conduct the research needed to effectively manage, conserve, and recover fur seals and Steller sea lions. These recent studies prove the analysis of whiskers to be a valuable new tool to complement and expand our understanding of these marine mammals.

Research highlighted in this article was conducted through collaborative efforts among the following individuals and organizations:

Comparison of temporally matched stable isotope values in whiskers from unrelated northern fur seal pups and adult females at San Miguel Island, California: University of California, San Diego (T. Howard, K. Narel, C. Kurle) and the Marine Mammal Laboratory, Alaska Fisheries Science Center, NOAA Fisheries (T. Orr).

Whiskers as a novel tissue for tracking reproductive and stress-related hormones in North Pacific otariid pinnipeds: Division of Wildlife Conservation, Alaska Department of Fish and Game (M. Keogh, currently at NOAA Fisheries’ Office of Protected Resources); Division of Wildlife Conservation, Alaska Department of Fish and Game (P. Chaparata, J. Waite); Baylor University (P. Chaparata); Marine Mammal Laboratory, Alaska Fisheries Science Center, NOAA Fisheries (B. Fadely, T. Zeppelin, V. Burkanov); University of Alaska Fairbanks (L. Rea, J. Waite, M. Wooller); Pacific Geographical Institute, Far East Branch of Russian Academy of Sciences (V. Burkanov);Texas A&M University (C. Marshall, A. Jones, C. Sprowls).

Regional variations and drivers of mercury and selenium concentrations in Steller sea lions: University of Alaska Fairbanks, Fairbanks (L.D. Rea, J.P. Avery, J.M. Castellini, T.M. O’Hara); Alaska Department of Fish and Game (L.D. Rea, M.J. Rehberg); Marine Mammal Laboratory, Alaska Fisheries Science Center, NOAA Fisheries (B.S. Fadely, V.N. Burkanov); Pacific Geographical Institute, Far East Branch of Russian Academy of Sciences (V.N. Burkanov); Texas A&M University (T.M. O’Hara).

Temporal records of diet diversity dynamics in individual adult female Steller sea lion (Eumetopias jubatus) vibrissae: University of Colorado (A.C. Doll, M. B. Wunder); Alaska Department of Fish and Game (B. D. Taras, L. D. Rea); U.S. Geological Survey (C. A. Stricker); University of Alaska Fairbanks (L.D. Rea, T.M. O’Hara, A. P. Cyr ; Alaska Fisheries Science Center, NOAA Fisheries (S. McDermott, B. S. Fadely); Ocean Peace Inc. (T. M. Loomis).