Q&A: Environmental Indicators to Determine Polar Bear Population Status
Declines in sea ice extent in the Arctic are impacting multiple facets of northern ecosystems. Loss of sea ice has significantly changed the way wildlife and people can access those ecosystems. Here, we talk with federal and state biologists about how declines in sea ice in the Chukchi Sea region are changing the way they must study the health and status of polar bear populations.
Return to USGS Alaska Q&A Series
USGS Alaska Science Center Karyn Rode has been studying polar bears in the Chukchi Sea for over a decade. This region lies off the coast of northwestern Alaska and is usually locked up with vast amounts of sea ice through the fall, winter, and spring. Karyn’s research typically involved working from a helicopter to collect information on the status of individual polar bears, their health and reproductive rates, and from these data, quantify the overall condition of the bears in the Chukchi Sea region.
However, since 2017, Karyn and her colleagues from the U.S. Fish and Wildlife Service and the Alaska Department of Fish and Game have been unable to continue research in their standard way due to substantial declines in spring sea ice cover in the Chukchi Sea. The sea ice that did occur has become thinner, more broken, and less safe to work on. So, they came up with some new ways to determine polar bear population status in the vast Chukchi Sea region.
Karyn and her colleagues recently completed a study that uses environmental data and indices of seal health (ecological data) to estimate the body condition and recruitment of polar bears in the Chukchi Sea during the period of poor spring sea ice conditions after 2017, when direct assessments of condition were not feasible. They found that some environmental and ecological data were available that accurately described past changes in polar bear population status (when field data had been collected) that could be used to predict population status in the years when direct data collection was not possible (2018 to 2022).
In this Q&A we talk with Karyn and her colleagues about how they devised and carried out this plan to still track the overall condition of Chukchi Sea polar bears using data on sea ice, atmospheric conditions, and indices of seal health instead of direct data collected from polar bears on the sea ice.
A capture-based polar bear research program that started in 2008 was forced to end in 2017 due to lack of sufficient spring sea ice needed to safely capture and sample bears, and although spring sea ice cover has partially recovered in recent years large areas of open water still make access to polar bear habitat hazardous.
Q: Hi Everyone. So, it sounds like poor ice conditions ended your field research efforts in 2017. Did you think that was the end of polar bear monitoring at that time?
Karyn: At the time I don’t recall thinking that we wouldn’t be coming back for 5 years. I thought we just had a combination of poor conditions that required us to end our field season early in 2017. The changes in the ice were obviously consistent with Arctic warming but at that point the primary focus was on declines in summer sea ice, not ice in March and April. I didn’t anticipate that we would see substantially reduced spring sea ice, the lowest recorded, in the years that followed.
Ryan: I wasn’t sure at the time if it would end our field research efforts, but I knew it was the beginning of a shift towards new sea ice conditions we had been anticipating that would make those efforts more challenging. Two more failed years of trying to get onto the sea ice in 2018 and 2019, however, solidified for me that we need to find new ways to monitor this subpopulation of polar bears.
Q: How did you start to explore other sources of data that could be used to predict aspects of population health for Chukchi Sea polar bears?
Karyn: From the start of our collaborative studies in 2008, we had an objective of identifying what factors (e.g., prey health, sea ice conditions, etc.) affected the abundance of polar bears in the Chukchi Sea. We knew that identifying these factors can help predict how a population will respond to environmental change. We had hoped to collect at least 10 years of data, but when we could no longer collect data in 2018 and 2019, we started to look at the 8 years of data we had in hand to see if we could identify whether various measures of prey and sea ice availability – as well as other variables – were related to the condition and reproduction of polar bears in the region. In 2022, we published a paper describing these relationships which led us to consider whether ice and prey information could help us estimate polar bear body condition and reproduction.
Lori: The Alaska Department of Fish and Game has worked with Alaska Native hunters of the region to sample the seal harvest for decades to monitor the status and health of ringed, bearded, and spotted seals (ringed and bearded seals are the primary prey of polar bears). Through the harvest surveys, we can monitor seal body condition, productivity, age at maturity, and proportion of pups in the harvest, annually. These metrics provide an index of the status of seal population health. If seals are doing well, it is more likely bears will also be doing well and vice versa.
Justin: Seal status and health was predicted to decline with changes in the Arctic ecosystem. However, while sea ice has decreased during the last two decades, indices of health suggest ringed and bearded seals in Alaska are healthy and producing pups that are successfully weaned.
Karyn: The data collected by Alaska Department of Fish and Game was critical to being able to predict how polar bears may be responding to sea ice loss. The resilience of ringed and bearded seals to sea ice loss in the Chukchi Sea seems to be an important aspect of the resilience polar bears have exhibited in response to sea ice loss so far in this region.
Q: What makes the information you have collected important?
Ryan: The U.S. Fish and Wildlife Service manages the Chukchi Sea polar bear subpopulation, but those management efforts require up-to-date information on how bears are responding to sea ice loss. Specifically, ensuring that Alaska Natives have access to polar bears for subsistence and cultural traditions requires that we know how the subpopulation is doing to ensure removals won’t diminish the long-term persistence of bears. This research helps us to ensure the bears are doing well between periods when we can physically handle them and can support their continued use as a subsistence resource by Alaska Native people.
Q: So is this the future of polar bear monitoring? And could this approach be extended to other hard to study animals in the Arctic or elsewhere?
Karyn: We absolutely need to directly collect data on polar bears for long-term monitoring. But what this study offers is a way to fill gaps so that data may not need to be continuously collect. It also offers a way to perhaps identify when data needs to be collected by determining when specific environmental conditions important to polar bear body condition and reproduction have changed and might meaningfully impact the status of the population.
Ryan: I totally agree with Karyn. There have been years with decent sea ice since 2017 that we could have worked on but it’s not possible to know until very shortly before a field season if the ice will be sufficient for us to safely work on. Given the time required for us to plan these massive field efforts, that level of uncertainty is hard to deal with. This research really helps us keep our finger on the pulse of the subpopulation, even in years we can’t physically observe the bears.
I believe the approach we developed in this study could be applied to other study systems where researchers have difficulty interacting with a population at regular intervals. But it would likely require a period of extensive field work to establish links between demographic and environmental variables that can be used in years without sampling.
Justin: Changes in the Arctic ecosystem will likely affect how we study polar bears and other animals. Field seasons and the collection of data will need to be flexible to account for sudden snow-melt events or substantial changes in sea ice. Researchers will also need to consider innovative methods to assess study animals. For example, assessments of population abundance may need to consider new and multiple sources to non-invasively collect samples for identifying individuals.
Declines in sea ice extent in the Arctic are impacting multiple facets of northern ecosystems. Loss of sea ice has significantly changed the way wildlife and people can access those ecosystems. Here, we talk with federal and state biologists about how declines in sea ice in the Chukchi Sea region are changing the way they must study the health and status of polar bear populations.
Return to USGS Alaska Q&A Series
USGS Alaska Science Center Karyn Rode has been studying polar bears in the Chukchi Sea for over a decade. This region lies off the coast of northwestern Alaska and is usually locked up with vast amounts of sea ice through the fall, winter, and spring. Karyn’s research typically involved working from a helicopter to collect information on the status of individual polar bears, their health and reproductive rates, and from these data, quantify the overall condition of the bears in the Chukchi Sea region.
However, since 2017, Karyn and her colleagues from the U.S. Fish and Wildlife Service and the Alaska Department of Fish and Game have been unable to continue research in their standard way due to substantial declines in spring sea ice cover in the Chukchi Sea. The sea ice that did occur has become thinner, more broken, and less safe to work on. So, they came up with some new ways to determine polar bear population status in the vast Chukchi Sea region.
Karyn and her colleagues recently completed a study that uses environmental data and indices of seal health (ecological data) to estimate the body condition and recruitment of polar bears in the Chukchi Sea during the period of poor spring sea ice conditions after 2017, when direct assessments of condition were not feasible. They found that some environmental and ecological data were available that accurately described past changes in polar bear population status (when field data had been collected) that could be used to predict population status in the years when direct data collection was not possible (2018 to 2022).
In this Q&A we talk with Karyn and her colleagues about how they devised and carried out this plan to still track the overall condition of Chukchi Sea polar bears using data on sea ice, atmospheric conditions, and indices of seal health instead of direct data collected from polar bears on the sea ice.
A capture-based polar bear research program that started in 2008 was forced to end in 2017 due to lack of sufficient spring sea ice needed to safely capture and sample bears, and although spring sea ice cover has partially recovered in recent years large areas of open water still make access to polar bear habitat hazardous.
Q: Hi Everyone. So, it sounds like poor ice conditions ended your field research efforts in 2017. Did you think that was the end of polar bear monitoring at that time?
Karyn: At the time I don’t recall thinking that we wouldn’t be coming back for 5 years. I thought we just had a combination of poor conditions that required us to end our field season early in 2017. The changes in the ice were obviously consistent with Arctic warming but at that point the primary focus was on declines in summer sea ice, not ice in March and April. I didn’t anticipate that we would see substantially reduced spring sea ice, the lowest recorded, in the years that followed.
Ryan: I wasn’t sure at the time if it would end our field research efforts, but I knew it was the beginning of a shift towards new sea ice conditions we had been anticipating that would make those efforts more challenging. Two more failed years of trying to get onto the sea ice in 2018 and 2019, however, solidified for me that we need to find new ways to monitor this subpopulation of polar bears.
Q: How did you start to explore other sources of data that could be used to predict aspects of population health for Chukchi Sea polar bears?
Karyn: From the start of our collaborative studies in 2008, we had an objective of identifying what factors (e.g., prey health, sea ice conditions, etc.) affected the abundance of polar bears in the Chukchi Sea. We knew that identifying these factors can help predict how a population will respond to environmental change. We had hoped to collect at least 10 years of data, but when we could no longer collect data in 2018 and 2019, we started to look at the 8 years of data we had in hand to see if we could identify whether various measures of prey and sea ice availability – as well as other variables – were related to the condition and reproduction of polar bears in the region. In 2022, we published a paper describing these relationships which led us to consider whether ice and prey information could help us estimate polar bear body condition and reproduction.
Lori: The Alaska Department of Fish and Game has worked with Alaska Native hunters of the region to sample the seal harvest for decades to monitor the status and health of ringed, bearded, and spotted seals (ringed and bearded seals are the primary prey of polar bears). Through the harvest surveys, we can monitor seal body condition, productivity, age at maturity, and proportion of pups in the harvest, annually. These metrics provide an index of the status of seal population health. If seals are doing well, it is more likely bears will also be doing well and vice versa.
Justin: Seal status and health was predicted to decline with changes in the Arctic ecosystem. However, while sea ice has decreased during the last two decades, indices of health suggest ringed and bearded seals in Alaska are healthy and producing pups that are successfully weaned.
Karyn: The data collected by Alaska Department of Fish and Game was critical to being able to predict how polar bears may be responding to sea ice loss. The resilience of ringed and bearded seals to sea ice loss in the Chukchi Sea seems to be an important aspect of the resilience polar bears have exhibited in response to sea ice loss so far in this region.
Q: What makes the information you have collected important?
Ryan: The U.S. Fish and Wildlife Service manages the Chukchi Sea polar bear subpopulation, but those management efforts require up-to-date information on how bears are responding to sea ice loss. Specifically, ensuring that Alaska Natives have access to polar bears for subsistence and cultural traditions requires that we know how the subpopulation is doing to ensure removals won’t diminish the long-term persistence of bears. This research helps us to ensure the bears are doing well between periods when we can physically handle them and can support their continued use as a subsistence resource by Alaska Native people.
Q: So is this the future of polar bear monitoring? And could this approach be extended to other hard to study animals in the Arctic or elsewhere?
Karyn: We absolutely need to directly collect data on polar bears for long-term monitoring. But what this study offers is a way to fill gaps so that data may not need to be continuously collect. It also offers a way to perhaps identify when data needs to be collected by determining when specific environmental conditions important to polar bear body condition and reproduction have changed and might meaningfully impact the status of the population.
Ryan: I totally agree with Karyn. There have been years with decent sea ice since 2017 that we could have worked on but it’s not possible to know until very shortly before a field season if the ice will be sufficient for us to safely work on. Given the time required for us to plan these massive field efforts, that level of uncertainty is hard to deal with. This research really helps us keep our finger on the pulse of the subpopulation, even in years we can’t physically observe the bears.
I believe the approach we developed in this study could be applied to other study systems where researchers have difficulty interacting with a population at regular intervals. But it would likely require a period of extensive field work to establish links between demographic and environmental variables that can be used in years without sampling.
Justin: Changes in the Arctic ecosystem will likely affect how we study polar bears and other animals. Field seasons and the collection of data will need to be flexible to account for sudden snow-melt events or substantial changes in sea ice. Researchers will also need to consider innovative methods to assess study animals. For example, assessments of population abundance may need to consider new and multiple sources to non-invasively collect samples for identifying individuals.