Multi-scale drivers of efficiency in rorqual whale engulfment filtration feeding
Keywords: Biology.

Rorqual whales, the largest predators on earth, employ a unique, energetically expensive foraging style that enables bulk feeding on small prey. Intermittent-engulfment ram-filtration feeding, known as lunge feeding, involves sequentially accelerating the whole body to between 2.5 and 5 m/s, engulfing a volume of water that can exceed body mass, and then filtering that water. Although this process is energetically costly and limits dive times in these animals, it is highly efficient because it mixes the benefits of processing tens to hundreds of kg of tiny prey in a single gulp with the benefits of raptorial feeding that allow capture of maneuverable prey and active selection of high quality parcels. However, most of these interactions between predators and prey occur in deep water environments that are inaccessible to human observers; until recently observations of this phenomenon were limited to surface observations and a few fortunate diver videos, implying that aspects of this largest biomechanical event on earth were still poorly understood. The development of miniaturized bio-logging devices in the last decade has enabled the first detailed observations of this phenomenon, and this thesis presents some of the first observations of lunge feeding utilizing new technology that integrates video with 3D accelerometry. Chapter 1 describes a newly developed analysis technique to determine speed from these devices as part of an overall effort to streamline the transfer of data from the tags into biologically meaningful metrics. Chapter 2 describes the first observations of skull and jaw kinematics during lunge feeding made in concert with body kinematic data and determines that krill-feeding whales demonstrate a high degree of stereotypy while feeding, but that fish-feeding whales display higher flexibility in engulfment timing in relation to speed. Chapter 3 further explores this diversity by examining the specific predator/prey dynamics of lunge-feeding humpback whales foraging on schools of anchovies and describes for the first time how it is that these giant predators can lunge at high speed at fish schools without dispersing them. Finally, Chapter 4 discusses how the unique spatial scales of feeding employed by rorqual whales suggest that hydroacoustic prey data be analyzed at a corresponding spatial scale. Utilizing tag data in combination with hydroacoustic prey data, this final chapter describes how the spatial distribution of krill within some large krill swarms facilitates shorter inter-lunge intervals and enables higher foraging rates overall. In concert with the higher prey density in these patches, the overall effect is to double prey input in these types of patches. The high-quality of these patches draws extraordinarily large aggregations of rorqual whales into geographically constrained regions, yet these super groups do not appear to be competitive in nature. By presenting new techniques in both bio-logging and prey analysis, this thesis sets the stage for future work to better determine the role of these dynamic consumers in their ecosystems. The effect of the large-scale anthropogenic removal of these animals from the ocean is still poorly understood, and fundamental questions about their biology and physiology remain unknown. The scales of investigation described herein begin to address major components of these questions as well as directly set the stage for future investigations via new analytical techniques.