[MARMAM] new publication on walruses and vessels using statistical matching techniques

Taylor, Rebecca L rebeccataylor at usgs.gov
Wed Mar 15 13:23:29 PDT 2023


My coauthors and I are pleased to announce the following open access publication, which is available at the link below: "Exploring effects of vessels on walrus behaviors using telemetry, automatic identification system data and matching."

https://doi.org/10.1002/ecs2.4433

Abstract
Arctic marine mammals have had little exposure to vessel traffic and potential associated disturbance, but sea ice loss has increased accessibility of Arctic waters to vessels. Vessel disturbance could influence marine mammal population dynamics by altering behavioral activity budgets that affect energy balance, which in turn can affect birth and death rates. As an initial step in
studying these linkages, we conducted the first comprehensive analysis to evaluate the effects of vessel exposure on Pacific walrus (Odobenus rosmarus divergens) behaviors. We obtained >120,000 h of location and behavior (foraging, in-water not foraging, and hauled out) data from 218 satellite-tagged walruses and linked them to vessel locations from the marine automatic
identification system (AIS). This yielded 206 vessel-exposed walrus telemetry hours for comparison to unexposed hours, which we used to assess if vessel exposure altered walrus behavior. We developed a filter to account for misclassification of vessel exposure of telemetered walruses. Then we tested for an effect of vessel exposure on walrus behaviors using a combination of
exact and propensity score-based matching to account for confounding covariates, and we conducted statistical power analyses. We did not detect an effect of vessel exposure on walrus behaviors even when statistical power was high (i.e., for foraging walruses), which may have been due to the sample size-driven need to define vessel presence within a larger than desired distance (15-km measured radius) around a walrus. Although this study did not determine at what distance vessel exposure affects walrus behaviors, it provided an upper bound on the distance at which the vessels encountered may disturb foraging
walruses. When more situation-specific information is lacking, this distance could be used as a conservative buffer to maintain between vessels and areas of high use by foraging walruses. Studies on behavioral consequences of closer proximities between walruses and vessels are needed, and our assessments of misclassification rates and statistical power can be used for future studies. We demonstrated that analytical approaches such as matching, which are rarely used in wildlife studies, are particularly useful for testing hypotheses with observational data.

Citation: Taylor, Rebecca L., Chadwick V. Jay, William S. Beatty, Anthony S. Fischbach, Lori T. Quakenbush, and Justin A. Crawford. 2023. “Exploring Effects of Vessels on Walrus Behaviors Using Telemetry, Automatic Identification System Data and Matching.”
Ecosphere 14(3): e4433. https://doi.org/10.1002/ecs2.4433


Rebecca Taylor
Research Statistician
Alaska Science Center
U. S. Geological Survey
(907) 786-7004

Pronouns: She/her
Please note I sometimes send and answer email outside normal work hours.
This helps me with my schedule but is not intended to pressure others to do the same.
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