I am a Research Scientist with the Institute of Marine Sciences at the University of California, Santa Cruz. I study the behavior and ecology of marine mammals and how they relate to oceanographic processes. Some of my recent work includes: characterizing a major marine heatwave in the North Pacific and its effects on the reproduction and foraging ecology of the northern elephant seal; niche partitioning and foraging behavior of Weddell seals and penguins in the Ross Sea; and the movement and behavior of California sea lions in response to predators and human disturbance.

Live Animal Tracking

These maps will update with new locations daily! You can click on individual animals in the right-hand menu to zoom in on individual tracks.

Weddell seals instrumented at Cape Crozier, November 2024. Our team completed these deployments as part of a collaboration with Michelle LaRue’s Lab examining niche partitioning between Weddell seals, emperor penguins, and Adélie penguins.

California sea lions instrumented at Año Nuevo Island, October 2024 as part of the Monterey Bay White Sharks project led by Barb Block (Stanford) and Dan Costa (UCSC). Our goal is to examine how the presence of a predator (white sharks) modifies prey behavior (sea lions).

Media Coverage

Preview PBS’s Dynamic Planet: Ice, an episode featuring work from Greenland to the Himalayas to the Antarctic. (Sorry, the full episode is behind a paywall!) This episode features a vignette following my field team as we completed biologging deployments on Weddell seals in Erebus Bay in November 2019.

To see some of what our animal-borne video cameras discovered, check out these papers published by the newly minted Dr. Rose Foster-Dyer: Prey targeted by lactating Weddell seals in Erebus Bay, Antarctica and First observations of Weddell seals foraging in sponges

Recent Publication

Two decades of three-dimensional movement data from adult female northern elephant seals.
Costa DP, RR Holser, TR Keates, et al. (2024).
Scientific Data. DOI:10.1038/s41597-024-04084-4

Figure showing map of northern elephant seal tracks and histograms of maximum dive depth

Figure showing example diving data to illustrate dive analysis

All of the tracks (map) and dive depths (histograms) in the elephant seal data set. Black data are the post-breeding trip and white data are the post-molt trip.

We provide a curated northern elephant seal movement data set spanning 2004-2020, including a detailed description of data processing.
The data set represents 3,844,927 dives and 596,815 locations collected from 475 individual seals with 178 repeat samplings over 17 years.
Raw and processed data are publicly available with metadata: https://doi.org/10.7291/D10D61 and https://doi.org/10.7291/D18D7W
Data processing was completed in MATLAB and R
All processing code is also available: https://github.com/rholser/NES_TrackDive_DataProcessing

An example of elephant seal dive data before and after correction. Shaded regions indicate different dive phases.

Flow chart illustrating elephant seal movement data processing steps — Flow chart showing the steps of data processing for both diving and tracking data.