Published since 1946
Shedding Light on the Continued Decline of Beluga Whales in Cook Inlet, Alaska
In conjunction with the Cook Inlet PhotoID Project and federal agencies, the USGS Washington Cooperative Fish and Wildlife Research Unit is aiming to learn more about the fundamental factors that drive changes in beluga whale population dynamics, specifically what affects the rates at which individuals survive and reproduce. Understanding this piece of the puzzle is critical to future conservation and recovery efforts and will help determine the viability and resilience of this population to the persistent human activities and ongoing climatic changes occurring in the region. However, this iconic whale has not made unraveling this mystery easy.
Beluga whales are arguably one of the most recognizable marine mammal species that inhabits the vast waters of the Arctic. And yet, there are persistent mysteries about this member of the cetacean family, particularly the population in Cook Inlet, Alaska, that continues to decline in numbers. This endangered population has historically been an important cultural and subsistence resource for local Native Alaskan communities, but the small population size can no longer support subsistence hunting. Despite two decades of dedicated research, conservation efforts, and management attention, the population has continued to dwindle at approximately 2% per year, and experts still don’t know exactly why.
Many of the factors that make these belugas unique also make them very challenging to study. The waters of Cook Inlet that these whales call home are dark and turbid, which means the whales are very difficult to see unless they are right at the surface. This habitat feature induces a substantial degree of uncertainty in both ways that researchers aim to track and count whales from year to year: photographic identifications and aerial surveys. In the former, researchers catalogue whales that have been previously identified and whether they are seen with calves. Seeing and counting calves is important for understanding birth rates, but these younger individuals blend right in with the water since they are in fact not white but a darker grey color up until they reach adulthood. In aerial surveys, researchers document and count individuals from the air, which is complicated by the fact that it is virtually impossible to see and count whales that are below the surface.
University of Washington graduate student Amanda Warlick works with Sarah Converse, Washington CRU Unit Leader, in the Quantitative Conservation Lab and is developing statistical models to improve our knowledge of the status of this population in two ways. First, Amanda is producing trends that show for the first time how survival and birth rates have likely changed over time. Second, Amanda is combining both the photo identification catalogue records and the aerial survey data in what is referred to as an integrated population model, which can improve the precision of what researchers know about both the current population status and its future viability. These improvements in precision matter not only for accurately evaluating progress toward recovery goals, but because lifting the moratorium on the subsistence harvest is based on reaching and maintaining certain abundance benchmarks.
One of the main goals of this project is to have a better understanding of which intrinsic factors the population may be most sensitive to. For example, do changes in the population size mirror changes in adult survival? Or are birth rates and calf survival what might be limiting recovery? Once researchers know the answers to those questions, they can take the next important step of identifying external factors that might potentially be negatively impacting the population. Do they have enough of their preferred prey to meet their energetic demands? Are changing temperatures affecting the food web? Is underwater noise from shipping or oil and gas exploration making it harder to communicate or navigate to find prey? Or, most likely, is it a synergistic combination of multiple threats that is affecting the population? Understanding this problem of “cumulative effects” is particularly elusive because it may not be that any one of the threats alone is measurably impactful, but taken together, the combination becomes detrimental.
Unfortunately, one of the ongoing challenges that hampers researchers’ ability to definitively answer these important questions is a lack of information about these potential threats. While researchers have robust information about salmon abundance in one of the most important feeding areas, that is just one of many feeding areas and just one of many prey fish species. Similarly, researchers might have some understanding of noise levels in important habitat areas but lack quantitative data that links those noise levels to behavioral changes that might ultimately affect the rates at which whales survive and give birth. These issues contribute to the ongoing uncertainty that surrounds why this population has failed to show signs of rebounding.
This work will improve our understanding of this endangered whale and will provide an important foundation for future studies exploring the viability of this culturally important and ecologically unique population in the face of ongoing and anticipated climatic changes.
The ONB features articles from U.S. Geological Survey Cooperative Fish and Wildlife Research Units across the country. The Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This story was written by Amanda Warlick, PhD Candidate, Washington Cooperative Fish and Wildlife Research Unit, and edited by Dawn Childs, Information Specialist, USGS Cooperative Fish and Wildlife Research Units.