Deep Mapping of Teuthivorous Whales and Their Prey Fields
SERDP 2016 Project-of-the-Year Award for Resource Conservation and Resiliency
Recent research and development efforts have helped to greatly expand the understanding of both the behavior and biology of deep diving marine mammals. There have been several studies of the physical habitat of these deep-diving predators but our understanding of the available prey, a key component in the biological habitat of these animals, is not as well developed. The main prey of these marine mammals are squid and they have proven to be difficult to study due to their rapid speed, relatively large size, and depth range. A SERDP-funded project led by Dr. Kelly J. Benoit-Bird from Oregon State University and the Monterey Bay Aquarium Research Institute (MBARI) and her team aimed to address this gap in research through the development of a new platform to carry the acoustic instruments needed to assess squid and then utilize the tool to understand the foraging ecology of deep-diving teuthivores (squid eaters).
Study efforts targeted habitat used differentially by deep-diving, air-breathing predators (beaked whales and Risso’s dolphins were chosen as the study subjects) to empirically sample their prey’s distributions on and off a United States Navy testing range. Dual-frequency (38 and 120 kHz) split-beam echosounders were integrated into a REMUS 600 autonomous underwater vehicle (AUV), effectively doubling the range of quantitative, multifrequency acoustic data into the mesopelagic zone (600 to 1200 meters).
Results of this project showed significant spatial variability in the size, composition, total biomass, and spatial organization of biota over all spatial scales examined and was consistent with the general distribution patterns of foraging Cuvier’s beaked whales observed in separate studies. Remarkable differences were found in prey characteristics between regions at depth, changes that were unobserved in surface layers. The revelation that animals deep in the water column are so spatially heterogeneous at scales from 10 meters to 50 km critically affects the understanding of the processes driving predator-prey interactions, energy transfer, biogeochemical cycling, and other ecological processes in the deep sea and the connections between the productive surface mixed layer and the deep water column.
The research team also explored the behavior of Risso’s dolphins foraging in somewhat shallower scattering layers off Santa Catalina, California using a similar approach. Active acoustic measurements demonstrated that Risso’s dolphins dove to discrete prey layers throughout the day and night with only slightly higher detection rates at night. Dolphins were detected in all three layers during the day with over half of detections in the middle layer, 20% of detections in the deepest layer, and 10% falling outside the main layers. Dolphins were found less frequently in areas where the shallow, intermittent layer was absent, suggesting that this layer, though containing the smallest prey and the lowest densities of squid, was an important component of their foraging strategy. The technology and approaches used in this project are already being transitioned to additional applications within the marine mammal community.
For this significant work, Dr. Benoit-Bird and her project team received the 2016 SERDP Project-of-the-Year Award for Resource Conservation and Resiliency for their project titled Deep Mapping of Teuthivorous Whales and Their Prey Fields.
- Kelly J. Benoit-Bird, Oregon State University and MBARI
- Mark A. Moline, University of Delaware
- Brandon L. Southall, Southall Environmental Associates