PI Dr. Leigh Torres, Florence Sullivan (2015-2017) Lisa Hildebrand (2018-2021), Allison Dawn (2021-2023), Celest Sorrentino (2024-present)

Linking predator-prey interactions is a favorite topic among ecologists, but can be expensive and challenging to accomplish at fine scales, particularly in shallow waters that limit traditional prey mapping methods. The Pacific Coast Feeding Group (PCFG) of gray whales forages in the Oregon near-shore environment, making them accessible for study with creative, low budget technology. This project aims to link gray whale foraging behavior with fine-scale prey distributions, using inexpensive field methods (e.g., theodolite, GoPro cameras and shallow net tows deployed off a research kayak) that have broad applications.

For 11 consecutive summers we have non-invasively tracked gray whale movements with shore-based theodolites in Port Orford, Oregon, USA while offering internship opportunities for high school and undergraduate students (JASPER). When conditions allow, a research kayak is concurrently navigated to sampling stations in two comparative study areas, Mill Rocks and Tichenor Cove. GoPro cameras are used to record zooplankton relative density in the water column and zooplankton net tows are used to assess community structure. We also identify and count each zooplankton we catch in the nets to describe how community changes with environmental conditions. Whale behaviors are categorized into search, forage, and transit behaviors using the Residence in Space and Time method. Despite being only one kilometer apart, we have found significant spatio-temporal differences in the community assemblages of zooplankton between the two study areas, and whales demonstrate fine-scale habitat selection relative to this prey availability.

The influence of prey

Prey quality had been assessed through bomb calorimetry, a method used to determine the caloric content of organic matter. This analysis (conducted in collaboration with COZI) allowed us to determine whether zooplankton species vary in their caloric content along the Oregon coast, and therefore have different energetic benefits for gray whales. Our results indicate that prey quality, does vary by prey species and reproductive stage, however not by time or space. We have also documented the trade-offs foraging whales make between target prey patches with more quality or more quantity.

The influence of the environment

Changes in the environment can have a rippling affecting both gray whales and the prey communities’ gray whales depend on. We have documented an indirect trophic cascade, which an increase in purple sea urchin has lead to a decline in bull kelp density, reducing zooplankton prey habitat. Gray whales respond to these shifting environmental conditions through their behavior, using a variety of foraging tactics that change depending on habitat, prey type, and even their own body size. Additionally, we have found intermittent upwelling, the cyclical, alternating pattern of strong wind events that push cold, nutrient-rich deep water to the surface, is a primary driver of zooplankton abundance and gray whale foraging effort.

The GEMM Lab's fine-scale gray whale foraging ecology project in Port Orford, Oregon

Publications: 

Dawn, A., Hildebrand, L., Sullivan, F. A., Barlow, D., & Torres, L. G. (2025). Intermittent upwelling impacts zooplankton and their gray whale predators at multiple scales. Marine Ecology Progress Series, 752, 1-19. https://doi.org/10.3354/meps14721 

Hildebrand, L., F.A. Sullivan, R.A. Orben, S. Derville, and L.G. Torres, Trade-offs in prey quantity and quality in gray whale foraging. Marine Ecology Progress Series, 2022. 695: p. 189-201. https://doi.org/10.3354/meps14115

Hildebrand, L., K.S. Bernard, and L.G. Torres, Do Gray Whales Count Calories? Comparing Energetic Values of Gray Whale Prey Across Two Different Feeding Grounds in the Eastern North Pacific. Frontiers in Marine Science, 2021. 8: p. 683634. https://doi.org/10.3389/fmars.2021.683634

Hildebrand, L., S. Derville, I. Hildebrand, and L.G. Torres, Exploring indirect effects of a classic trophic cascade between urchins and kelp on zooplankton and whales. Scientific Reports, 2024. 14(1): p. 9815. https://doi.org/10.1038/s41598-024-59964-x

 

Blogs: 

 

Collaborators:

Dr. Aaron Galloway, Oregon Institute of Marine Biology, University of Oregon

Tom Calvanese, OSU Port Orford Field Station

Dave Lacey, South Coast Tours

Kevin Buch and Taylor Eaton, OSU Research Office

 

Funding:

 

Linking predator-prey interactions is a favorite topic among ecologists, but can be expensive and challenging to accomplish at fine scales, particularly in shallow waters that limit traditional prey mapping methods. The Pacific Coast Feeding Group of gray whales forages in the Oregon near-shore environment, making them accessible for study with creative, low budget technology.