UAF scientists determine the future of Arctic walrus

Josh Hartman - Walruses and Climate Change.jpg

Nicole and Casey remove bones from a calf killed the previous year during a trampling event. Photo by Kelsey Gobroski/UAM.

 

Researchers at UAF in the Water and Environmental Research Center (WERC) are using thousand-year-old walrus bones to learn if walruses today will adapt to climate change. Nicole Misarti, a Research Assistant Professor with WERC, is the principal investigator. Patrick Charapata, presented the research, which is the first of its kind. He was co-advised by Associate Professor Lara Horstmann, with the College of Fisheries and Ocean Sciences, and Misarti.

“Walruses are considered a sentinel species in the Arctic; they are a species that warns humans of upcoming danger,” reads WERC’s project WALRUS webpage. “Climate change is nothing new, walruses have weathered change before, but the problem is that there are not enough long term data for us to understand how the walrus population adjusts to a changing Arctic climate.”

Prior to this project, no research had been conducted on hormone concentrations in any marine mammal bone. Even though these assays had been performed on rats and humans, there was no way of knowing if hormone accumulation occurred in these tissues and in this species.

One of the major elements the team is examining is if stress hormone and reproductive hormone concentration in marine mammal bone can predict population size and stressors. If this is possible, they can use walrus bones from thousands of years ago to understand how the walrus population functioned prior to the anthropogenic acceleration of climate change. This lends insight to what the reproductive activity was like and, potentially, how stressed the population was.

With walrus research efforts under way in the past several decades, researchers can model walrus populations from thousands of years ago through today. This model could then help researchers determine if the current population spurts and declines (common in most any wild population) can be differentiated from climate-associated declines.

The WERC team sourced subsistence-hunted walrus from St. Lawrence Island, ground the bone down, extracted the hormones and ran what is called light chromatography tandem mass spectrometry. The process tells researchers what concentration of each hormone is in each bone sample. They discovered, bone not only accumulates stress and reproductive hormones, it also produces some of its own.

After establishing their methodology was appropriate, the team went through marine mammal graveyards near subsistence villages. Some of the bones recovered were 3,600 years old. They also sampled and tested walrus specimens available at the University of Alaska Museum. After running through these samples, they were able to find that the hormone levels have been relatively consistent throughout their study period.

Modern walruses are experiencing a lower overall production of reproductive hormones. It is possible this lower concentration is due to an early 20th century population boom that occurred after commercial harvest subsided. Walrus population has had a decline, but their population is still estimated as relatively high in comparison to prior known periods.

This does not mean the species has adapted to climate change. There are still major issues they face due to sea ice loss. These include, but are not limited to, longer migrations for females and offspring, stampedes resulting from mass overhauls (walrus mass beaching rather than lounging on sea ice) and potential detrimental effects on their benthic, or bottom-dwelling, prey.

Walrus are a candidate species to be listed under the Endangered Species Act. By the end of 2017, more research similar to WERC’s may develop a sound decision.

This article was corrected on Oct. 6, 2016. The article originally implied that Misarti was Charapata’s only advisor. He was co-advised by both Misarti and Horstmann.

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