The SDRP is a leader in the study of marine mammal foraging ecology. Over the years, SDRP researchers have documented a variety of foraging behaviors used by bottlenose dolphins and have unveiled patterns of their habitat use and prey preference. This type of information is critical for the protection of these species and the environment in which they live. Prior to joining the SDRP team, I examined the foraging ecology of a much larger marine mammal, the humpback whale, in a much colder area, the Western Antarctic Peninsula, WAP, with several long-time SDRP affiliates (Doug Nowacek, Ari Friedlaender, etc.) to similarly learn about these animals so that they could be better protected. Humpback whales and other top predators in the WAP are facing decreases in quantities of their primary prey, Antarctic Krill, whose life is intimately tied to the sea ice. Whether humpback whales can adapt to such changes in their prey source is unknown and requires a basic understanding of their foraging ecology in this region. Therefore, as part of my dissertation research at Duke University, I used digital acoustic recording tags (DTAGs) to examine the fine-scale diving and foraging behaviors of these large, marine predators.
Frequent readers of Nicks n Notches may recognize the term ‘DTAG’ in reference to a tool currently being used by colleagues at SDRP to examine coordination and communication of bottlenose dolphins in Sarasota Bay, Florida. DTAGs are a versatile research tool as they record the depth, pitch, roll, and heading of an animal 50 times a second as well as all the sounds an animal makes and hears. The rich dataset obtained from these tags can be used to uncover a wide-range of behaviors executed by tagged animals, such as signature whistles made by bottlenose dolphins and lunge feeding events executed by humpback whales. As part of a multi-disciplinary effort, 13 humpback whales were fitted with DTAGs in 2009 and 2010 in the near-shore waters of the WAP in an attempt to better understand their fine-scale behaviors. Using the data collected by these tags and a customized software program called TrackPlot, I was able to visualize the three-dimensional movements of these whales and to pinpoint their discrete feeding attempts. This information, combined with concurrent measurements of the density and distribution of the Antarctic Krill they were pursuing, have allowed me and my colleagues to uncover some of the basic (and impressive) life-history traits of this recovering Antarctic predator.
Some of the highlights of our research include our finding that the WAP is an important and persistent foraging region for humpback whales: high densities of humpbacks can be found in this region in the austral summer and fall feeding on super-aggregations of Antarctic Krill (these aggregations can be up to 10s of kilometers wide and 100s of meters thick with estimated biomasses of up to 2.0 million tons). Humpback whales appear to temporally and spatially track the movements of these aggregations and exhibit a feeding pattern that aligns with the movements of their prey. Humpbacks rest at the surface during the day when Antarctic Krill are at depth hiding from their predators, and feed primarily at night when krill come to the surface to feed. Our research has also revealed that humpbacks can make up to 900(!) lunges a night and often dive longer than is to be expected based on the amount of their presumed oxygen stores. Behaviors such as these suggest to us that humpback whales are taking advantage of the dense prey aggregations that occur in these waters, and they highlight the importance of this region and its resources in the recovery of this large Antarctic predator. While Sarasota Bay lacks humpback whales and Antarctic Krill, I hope to use the skills I gained doing this research to continue advancing our understanding of bottlenose dolphin foraging behavior and the areas of importance to their survival.
This research really was a team effort; therefore, there are many people whom I wish to thank. Specifically Doug Nowacek, Ari Friedlaender, Andy Read, Dave Johnston, Pat Halpin, Daniel Rubenstein, James Hench, Alison Stimpert, Colin Ware, Corrie Curtice, Elliot Hazen, Amanda Katlenberg, and the crews of United States Antarctic Program’s RVIB Nathaniel B Palmer and ARSV Laurence M Gould greatly contributed to the success of this research. This research was conducted under NMFS MMPA Permit 808-1735, Antarctic Conservation Act Permit 2009-014, and was supported by NSF grant number ANT-07-39483.
This article appeared on pages 11-12 in the December 2015 issue of Nicks n Notches.