Three distinct sets of bubbles moved around on the surface of the water, with Richard keeping a watchful eye. Renae and I knelt on the back deck of the boat, labeling bottles and sample vials.
We both looked up from our perch to see three divers now at the surface of the water where the bubbles had been. As Brandon, Brett and Chuck made their way over, bags were handed up to us, water samples were poured into bottles, the GoPros were turned off, and the bottom samples heaved over the side of the boat. After carefully sifting the sediment through sieves, we saw what we’d come for– clams!
About a year ago, our lab group was brainstorming new research questions. Renae had previously worked on a project that studied walrus in Bristol Bay, Alaska and had begun to wonder about the patterns their team had observed. During the summer, adult and sub-adult males use terrestrial haul-outs in Bristol Bay as resting sites between foraging trips to find clams and mussels—their primary food source. Four historic haul-outs were simultaneously monitored to record the first and last date of walrus attendance at a haulout, and the maximum number of animals using each location on any given day.
When haul-out abundance numbers were compared between haul-outs across a summer season, occasionally it appeared when walrus attendance declined at one haulout numbers would rise at another a few days later. Were walrus moving between haul-outs? If they use multiple sites, what triggers movement between locations?
It has been suggested these observations could be due to increased commercial fisheries activities, disturbance from aircraft and boat traffic, or changes in prey availability. Understanding if changes in prey availability is a driver of walrus movement quickly caught our interest due to the emerging trend of adult female walrus and their depended calves hauling out in massive herds on beaches in the Arctic. While there have been rare events of walrus herds on Arctic beaches recorded previously (1930-32; 1978), this occurrence has happened almost every year since 2010, likely as a result of climate change reducing the quantity and quality of the arctic sea ice.
Does walrus foraging behavior change when forced to densely cluster on a terrestrial haulout rather than dispersed on several ice floes? Do walrus forage near the terrestrial site, grazing the seafloor for their prey and moving on when resources run out? Or do they travel farther in arctic waters to return to traditional foraging grounds? How might these patterns change if prey availability shifts due to climate change and ocean acidification? Studying movement ecology of male walrus in Bristol Bay may be a good proxy to answer these questions.
The only problem…current methods for monitoring changes in the benthic, or seafloor, community of clams, bivalves and other mollusks (e.g. bottom grabs) are costly and are typically only done at a coarse spatial and temporal scale that might not help us understand localized changes within a season. However, newer molecular techniques are becoming more and more useful for ecological monitoring as they can reduce the costs, and increase the resolution of the data.
One technique that is still in the early stages of development is environmental DNA, or eDNA. eDNA is the DNA that is shed from of all living things as they move throughout their environment. Skin cells, sneeze particles, exhalation, urine and feces—all of these sources of DNA enter the environment and remain there for some period of time before degrading. Therefore, if you know the genetic markers for a specific species of interest, you can take something as simple as a cup of water from a stream* and detect if a frog had been there! (*okay it’s not quite that simple but you get the idea).
So in partnership with Point Defiance Zoo, and with funding from the Dr. Holly Reed Conservation Fund, we set out to validate if eDNA could be a useful tool for monitoring the prey for Pacific Walrus. Throughout the winter we’ll post more about how our fieldwork went, how the samples we collected are analyzed in the lab at the ASLC, what our findings are, and more about the importance of this work for walrus conservation!
Written by: Amy Bishop & Renae Sattler
Permits for Photo: State of Alaska Land Use Permit #LAS28018 & State of Alaska Department of Fish and Game Special Area Permit #FH 11-II-0083-SA
Sampling Activities Conducted under Aquatic Resource Permit CF-18-096