Prey fields and habitat of deep divers: 3D characterization and modeling of beaked and sperm whale foraging areas
Beaked and sperm whales are of particular concern with regard to their sensitivity to anthropogenic noise. Assessments of the potential risk(s) of noise exposure have historically occurred in the absence of information about the physical and biological environments in which these animals are distributed and make their living diving and feeding.
Understanding the habits and habitats of these whales would therefore increase the effectiveness of these risk assessments. We are investigating the biological and physical characteristics of beaked and sperm whale habitats on the U.S. Navy’s Atlantic Underwater Testing and Evaluation Center (AUTEC), located in the Bahamas in the Tongue of the Ocean (TOTO), and developing methods for long-term monitoring of this and other sensitive areas.
Recent advances in the knowledge of beaked and sperm whale behavior and acoustic activity, coupled with the capabilities of the AUTEC range, allow us to track the distribution and diving and foraging behavior of the whales. Diving and acoustic behavior of individual whales will also be integrated via collaboration with existing tagging programs.
The primary biological property we measure is the distribution and biomass estimates of the prey field. We characterize the prey field using standard echosounder technology, though we will apply novel combinations of sensors and deploy them at depths that will permit more accurate measurements of volume backscatter at depths where these deep diving whales forage. We couple these data with measurements of several physical properties of the areas including the thermohaline structure of the water column, turbulence profiles, and vertical and horizontal current structure. All of the physical and biological data are being combined in a true 3D geospatial model which, while site specific, can be applied to larger regions. This model will be particularly useful for assessing whether a particular area of interest includes biological and physical features preferred by beaked or sperm whales.
Beaked and Sperm Whale Foraging Ecology and Habitat Characterization
This interdisciplinary project is focused on understanding the habitat of deep diving odontocetes, specifically integrating measurements of the biological and physical environment. Using measurements of the prey fields as well as the physical oceanographic regime, we are trying to gain a better understanding of how these deep diving whales use their environment and how that environment is organized, e.g., do physical forces cause the aggregation of certain types of biomass.
So far, we have studied beaked whales in the Tongue of the Ocean, Bahamas. At the U.S. Naval Atlantic Undersea Test and Evaluation Center (AUTEC), the Navy uses their hydrophone test range to record and, in some cases, track vocalizing animals. During an experiment to test for whales’ responses to sonar, we measured the prey fields using a 38 kHz Simrad echosounder, water column turbulence with a deep microstructure profiler, and current speeds and directions with the specialized ADCP system aboard the R/V Revelle. We then combined our measurements with the echolocation click data from the AUTEC array to examine how it varied with the physical and biological structure in the habitat.
Improving Attachments of Non-invasive Electronic Data Loggers to Cetaceans
The uniformly smooth surface of many marine mammals and some other marine organisms make suction cup attachments uncritical of precise placement on the body.
Archival tags for suction cup attachment are generally multi-sensor devices ranging from TDRs (Time-depth recorders), to fine-scale tracking devices and complex sound, image and movement recorders. High sensor sampling rates are often used to ensure that short duration behaviors and movements are sampled. An example high resolution archival tag is the Woods Hole Oceanographic Institution’s digital acoustic recording tag (DTAG). Since 1999, DTAGs have been deployed on over 500 whales from 14 different species and have produced more than n refereed journal publications. In addition to high quality sound recording, this tag incorporates a precision orientation sensor to track the movements of the animal. This versatile sensor suite has enabled a broad range of studies of marine mammal physiology and ethology ranging from studies of locomotion, foraging tactics, echolocation, sound source characteristics to acoustic detectability and response to environmental sound. Because of the high data collection rate of the tag, the recording duration is relatively short (<24 hours) making it appropriate for suction cup attachment. DTAGs are typically attached using 2-4 silicone suction cups. Multiple suction cups are necessary to ensure that the tag follows the movements of the animal accurately.
[W]e should be able to take advantage of existing chemistries either with targeted substrates and enzymes or by altering existing chemistry into a reactive form.
We are investigating the bio-physics of cup/skin interactions to identify the failure modes of current suction cup designs on cetacean skin. Models of cup and skin behavior as well as hydrodynamic drag forces on different sized and shaped packages are being tested to engineer a suction cup with enhanced reliability and longevity over current cup designs. The goal is attachment of multiple days on medium and large whales. The engineered attachments will include sensors to assess retention performance providing a more detailed view of progressive failure modes. Combining these sensor data with behavioral data collected by payload DTAGs will help uncover the factors that most contribute to attachment deterioration. The new devices will be tested in a captive setting and then deployed at sea on wild animals. We are also investigating the biochemistry of the surface of cetacean skin. We know from the literature that the surfaces of cetaceans have cellular architecture and surface chemistries similar to those of human oral cavities and the insides of blood vessels. All these unique surfaces have properties that render them near the bioadhesive minimum and refractive to most kinds of biofouling. However, given a little more detailed information about the chemical properties of these keratinized layers of dead cells, we should be able to take advantage of existing chemistries either with targeted substrates and enzymes or by altering existing chemistry into a reactive form. We are doing surface analysis of skin from stranded animals by using classic staining techniques and with surface mass spectrometry procedures to determine the functional groups of proteins and sugars at the surface of the skin.
Integrating acoustic recorders into the SeaGlider
The Whale ‘Entangler’
Working with the Consortium for Bycatch Reduction and Bellequant Engineering, we have developed an interactive, mechanically explicit ‘video game’ that can be used to ‘reverse engineer’ entanglements of large whales in fishing gear. Large whale entanglements are common along the east coast of the U.S., some are minor but many cause significant injuries or mortality. When whales are discovered with entanglements, significant effort is put toward understanding how and where the lines are wrapped on the animal, and this knowledge is used to strategize about whether the entanglement is life threatening and, if so, how to disentangle the whale.
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