One of the primary research objectives of the Bioacoustics Research Program is to understand the potential impact of man-made underwater sound on whales and the functions of the whale's low-frequency sounds.

In collaboration with Don Croll, Bernie Tershy, and Jason Gedamke (UC Santa Cruz), Alejandro Acevedo (California Academy of Sciences), Sergio Flores and Jorge Urban, (Universidad Autonoma de Baja California Sur), BRP's director, Christopher Clark, went to the Sea of Cortez off Loreto, Mexico to pursue this overall objective, but more specifically, to examine whether acoustic monitoring equipment could be used to detect whales and reliably estimate the number of individuals in an area. As part of this research, BRP designed, built and implemented oceanographic instrumentation for both remote and real-time monitoring, detecting, locating and tracking of free-ranging whales.

Scientists have suggested that the long, stereotyped sequences of low-frequency sounds produced by fin whales could function in navigation, breeding, or food location. To test these hypotheses, we used an integrated approach, involving an international team of scientists with expertise in whale acoustics, foraging and tagging, visual survey, biopsy sampling, and photo-ID. This combination allowed us to place the various vocal behaviors, often from known individuals, within the proper ecological framework. By this procedure, interpretations of vocal functions were related to the sex of the individual and the proper context within which the behavior occurred.

Field research was conducted in the late winter through early spring in 1999 and 2000. The field study site was in the Sea of Cortez off Loreto, Mexico. Research was conducted from a modified fishing vessel, with a 23' rigid hull inflatable boat and a 25' dory. We deployed six seafloor recording units (referred to as pop-ups) throughout the study area. These autonomous units recorded continuously (at 2000 Hz sampling rate) for the duration of the study.

BRP director Christopher Clark and engineer Tom Calupca prepare a pop-up for deployment in the Sea of Cortez.

During daily fieldwork, we integrated information on prey fields (using a dual-frequency Simrad echo sounder), water temperature, marine mammal sighting density (conducting visual surveys), individual diving/movement patterns (deploying time-depth-recording tags), individual's sex and ID (utilizing biopsy sampling), and acoustic activity (deploying a 16-element towed hydrophone array). Systematic visual survey, biopsy sampling and photo-ID efforts were conducted throughout the study period on a regular basis.

The towed array was linked to beamforming software which allowed us to determine directions to individual animals producing long sequences of 20-Hz sounds (songs) of fin whales. In 2000, acoustic positions of fin whale singers were computed in real-time and coordinated with visual sightings. This allowed us to direct the biopsy team to vocal animals. Genetic analysis of the biopsy samples revealed an overall sex ratio of 1:1, 21 males and 22 females. However, all of the nine singing fin whales biopsied were males, strongly suggesting that only males sing. This is the first time that genetic and acoustic techniques have been integrated to determine the sex of vocalizing whales.

Pop-ups were recovered at the end of the field research. Once we returned to Cornell, the six channels of pop-up data were merged so that we could detect, locate and track the movements of all vocal animals throughout the study area over the three week study periods. This allowed us to compare acoustic activities of specific individuals with food aggregations, the visual survey distributions and the activities of non-singers. By merging visual survey, photo-ID and pop-up data we were able to compare estimates of the total number of animals utilizing the study area by three independent methods.

This results of this research suggest that the long, low-frequency songs of male fin whales function to attract females to dense patches of food, where mating then occurs.

The findings of this study help to focus growing concern over the potential effects of human-produced underwater noise on large whales. If whales rely on long-distance acoustic signals to find each other for mating, the recovery rate of fin whale populations from past exploitation could be impeded by low-frequency sounds generated by human activities such as commercial shipping, military sonar, and seismic surveys.

This research was supported by the US Office of Naval Research.

Listen to vocalizations of finback whales
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