Kathy Kuletz talks seabirds shifts in Strait Science talk

In a Strait Science talk hosted by Northwest Campus last Thursday, Dr. Kathy Kuletz presented the latest data on seabirds in the Bering and Chukchi Seas, showing how the unprecedented die offs of recent years appear to be part of a larger trend in the marine ecosystem, which could foreshadow changes in the region for years to come.

Kuletz is a wildlife biologist with the U.S. Fish and Wildlife Service based out of Anchorage. She monitors seabird populations across the state, from the southeast to the Beaufort Sea, but the area in and around the Bering Strait has seen some of the most dramatic shifts in bird populations in recent years. From 2007 through 2019, she organized and participated in observational studies at sea involving more than 90,000 miles of transects. Ships with trained observers sailed along predetermined me cliffside breeding sites for more than a decade. “The Northern Bering and Chukchi Sea ecosystem supports millions of seabirds,” she said, “and it’s also been undergoing some rapid, dramatic changes. And this has affected seabirds at their colonies, and affects their food.”

She added that the region hosts some of the largest seabird colonies in the entire world, providing critical breeding and feeding grounds for around 60 different species, from small, plankton-eating auklets to fish-eating murres. To make sense of this diversity, Kuletz and her colleagues divide birds into six distinct communities, or clusters. Each cluster has a unique distribution of species, often with one species dominant, and is found in a certain region.

The least auklet cluster, for example, is the most populous cluster and is located directly in the Bering Strait. The crested auklet cluster is concentrated to the north, along the Alaskan coast of the Chukchi Sea. Kuletz explained that they also divide the birds into “wanderers” and “homebodies” – non-nesting birds that can follow wherever the food goes, and nesting birds that are tied to a specific colony. Scientists also divide birds based on what they eat, so they can study how they’re affected by shifts in prey.

This division based on diet shows some of the most striking results.

Fish-eating birds, such as murres, puffins and guillemots “have shown quite a dramatic shift towards lower abundance after about 2014 and 2015,” Kuletz said.

Conversely, plankton eaters – mostly auklets – began showing a rise in numbers around the same time, although that trend has been a bit more variable.

The changes were most dramatic in 2017, 2018 and 2019, which also happened to have the warmest ocean temperatures in the region to date. While the exact relationship between bird populations and ocean temperature isn’t totally understood, the correlation is difficult to overlook. But the dynamics are more complex than simple population decline, Kuletz explained. Short-tailed shearwaters, which make up about half of the seabirds in the region during the summer months, decreased in the Bering Sea but increased in the Chukchi over the last few years.

“They’ve not so much increased in overall abundance, but have shifted north,” she said. Short-tailed shearwaters breed in Australia during the Alaskan winter and only come here to feed, so they may be more able to adjust their habits as the region warms.

Nesting species, however, like thick-billed murres, crested auklets and least auklets, all saw significant contraction in their range and poorer reproductive success at their colonies in 2017 through 2019.

Some northern colonies, such as the kittiwake colonies at Cape Lisburne, have actually grown in overall number, but the number of chicks has remained low. “So that suggests immigration from the south – they could not increase just from productivity at the colonies alone,” Kuletz said.

The theory is that as waters warm and food resources shift, birds from southern parts of the region are concentrating in the north where the most food is, causing those colonies to grow. But there still isn’t enough food available to support all those birds plus their chicks, so reproductive success is low.

This is supported by other research on copepods, small plankton that many birds and their chicks rely on. In 2019, there were about half as many copepods in the North Bering Sea as there were just two years prior in 2017.

Larger copepods – the kind that many birds need to feed their young – were almost absent from the North Bering Sea in 2019, helping to explain the lack of reproductive success that year. The same trends appear, if a bit less dramatically, in the Chukchi Sea as well.

These dramatic changes in plankton numbers can cause ripples effects throughout the food chain, which could help explain the alarming numbers of dead, starved seabirds washing up on regional shores in recent years.

“With no ice in the Bering Sea, there was no cold pool for the first time ever in 2018 – no thermal barrier – and this resulted in a lot of very large predatory fish coming up into the North Being Sea and even up into the Chukchi,” Kuletz said. “So this was potential competition for forage fish and zooplankton. We don’t know for sure, but there was definitely some impact.”

The COVID-19 pandemic put a halt on most research during the summer of 2020, but Kuletz said she hoped to get back out and collect more data in 2021. Figuring out how permanent the recent changes are, and if they’ll continue along the same trajectory, is a primary focus of her future research.

She added that increased shipping in the strait could pose an additional threat to birds, since lights from commercial ships, especially in the darker months, could interfere with annual migrations. More ships also means a greater chance of oil spills and vessel strikes.

Research using Automatic Identification System, or AIS, data on ship positions will begin this year, she said, and she hoped future studies could help regulators plan shipping routes to avoid critical areas.

Kuletz also praised the U.S. Coast Guard and Russian Border Guard for recently signing a bilateral agreement on transboundary pollution in the region, and said more cooperation between Russia and the U.S. would be crucial in protecting the ecosystem in the future.