Understanding the Behavioral Ecology of Cetaceans

Understanding the Behavioral Ecology of Cetaceans Image

The U.S. Navy’s Energy and Environmental Readiness Division, Office of Naval Research, and SERDP have long been concerned with the potential impacts of naval sounds, such as sonar, on marine mammals, in particular cetaceans (whales, dolphins, and porpoises). A determination that such sounds have adverse consequences on cetaceans could lead to restrictions on the use of sonar for training purposes. However, key information is lacking on the baseline behavior of many cetaceans of concern, how the animal behaves in its environment in the absence of anthropogenic sounds and the factors that may influence its response to both natural and anthropogenic sound. Behavioral response of cetaceans sets the legal and policy threshold for noise exposure of concern. Without baseline information, it is extremely difficult to determine when exposure to anthropogenic sound results in a biologically significant or adverse response.

SERDP and the Navy have coordinated on the development of a science plan focused on the behavioral response of living marine resources, including cetaceans, to naval anthropogenic sound. Understanding baseline behavior was identified as a primary research goal, which SERDP is addressing through four research projects initiated in FY 2011. The response of cetaceans to sound typically depends on the context of exposure and the physiological condition, experience, and behavioral state of exposed individuals. Understanding the behavioral ecology of a species or taxonomic group is important for predicting the contexts when animals may be most sensitive to sound and for predicting when they may be most vulnerable to any potential adverse impacts.

In the first of these research efforts, Ms. Diane Claridge of the Bahamas Marine Mammal Research Organisation is leading a research team to examine deep-diving odontocete (toothed whale) species in the Great Bahama Canyon under the SERDP project Behavioral Ecology of Deep-Diving Odontocetes in the Bahamas (RC-2114). Data gaps associated with the baseline behavioral ecology of six priority species are being addressed. This project will provide a context for interpreting behavioral responses to sonar exposure, specifically at the U.S. Navy's Atlantic Undersea Test and Evaluation Center (AUTEC). Ms. Claridge and her team are developing a unique set of data by integrating information acquired through individual photo-identification, molecular genetics, fatty acids, persistent organic pollutants, and stable isotope profiles. Satellite telemetry and acoustic recordings are being used to characterize the social structure, residency patterns, reproductive biology, diet, foraging ecology, and population structure of these six species. These data will provide much-needed baseline information to assist in modeling the response of cetaceans to sonar and to help establish dose-response thresholds.

Although studies of the physical habitat of deep-diving whales such as sperm (Physeter macrocephalus) and beaked (family Ziphiidae) whales that feed primarily on squid (teuthivores) have kept pace with advances in data logging tags, understanding of the available prey and its distribution and behavior, a key component in the biological habitat of these animals, has not. This lag has been driven by the difficulties in studying squid because of their rapid speed, relatively large size, and foraging depth. Recent advances in acoustic measurements now enable data logging tags to be used to assess squid behavior and distribution in water depths up to 600 m. Teuthivores, however, typically feed at depths of 1000 m. Under the SERDP project Deep Mapping Teuthivorous Whales and Their Prey Fields (RC-2112), Dr. Kelly Benoit-Bird from Oregon State University and her team are developing an effective, easily deployed, adaptable remote sensing tool for measuring both the prey field and occupancy patterns of sperm and beaked whales to depths of at least 1200 m. They will use this tool to understand how the presence of prey affects the behavior of deep-diving whales and their sound exposure risk.

A growing body of evidence suggests that the response of some odontocetes to certain types of anthropogenic sound, including some naval sonar, is consistent with anti‐predator behavior. This has led to speculation that the strong aversive responses resulting in cetacean strandings may reflect an anti-predatory behavior in which animals are responding to sonar signals that they perceive as killer whale sounds. Under the SERDP project Odontocete Cetaceans: Quantifying Behavioral Ecology and Response to Predators Using a Multi-Species Approach (RC-2154), Dr. Andrew Read of the Duke University Marine Laboratory and his team are examining the responses of four species with different social patterns, from solitary species to those that live in permanent family groups, to determine whether social structure influences the response to acoustic stimuli. These observations will be used to create a conceptual model of the anti-predator behavior of these four species that later can be applied to other species. The results will provide a basis for assessing the extent to which behavioral responses to anthropogenic sounds, including naval sonar, may be similar to anti-predatory behavior. These findings will enhance the strategic planning of naval sonar operations to ensure environmental compliance and minimize potential negative impacts.

The long-term consequences of disturbance on cetaceans are particularly difficult to quantify. Noise may reduce foraging rates and thereby body condition. Body condition influences how animals trade off foraging and anti-predator behaviors and modulates responses to human disturbance. Little is known, however, about how body condition might modulate the behavior or reproductive success of free-ranging cetaceans. Under the SERDP project Behavioural Ecology of Cetaceans: The Relationship of Body Condition with Behavior and Reproductive Success (RC-2113), Dr. Patrick Miller of the University of Saint Andrews and his team are quantifying the body condition of individual cetaceans and conducting behavioral ecology studies of how body condition influences their foraging behavior and reproductive status. They are measuring the body density of free-ranging individual Ziphiid Northern bottlenose whales (Hyperoodon ampullatus) and humpback whales (Megaptera novaeangliae) by using analysis of underwater gliding performance measured with high-resolution tags. The findings from this research will advance the ability to predict and measure the potential impact of human disturbance on both individuals and populations of cetaceans.

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