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159th Meeting Lay Language Papers


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Human-made Noises Make Mediterranean Fin Whales Modify Their Behavior

 

Manuel Castellote - manuel.castellote@noaa.gov

National Marine Mammal Laboratory, Alaska Fisheries Science Center/NOAA

Seattle, Washington

 

Christopher W. Clark

Bioacoustics Research Program, Cornell Lab, Cornell University

Ithaca, New York

 

Marc O. Lammers

Hawaii Institute of Marine Biology

Kaneohe, Hawaii

 

Popular version of paper 1aAB8

Presented Monday morning, April 19, 2010

159th ASA Meeting, Baltimore, MD

 

 

Noise from human activities in the ocean can interfere with fin whale communication. This a matter of concern for the scientific community studying the potential negative effect of noise to marine fauna. Fin whales emit sounds in the very low frequency range, where noise from shipping and other human activities is intense.

 

This study shows how fin whales in the Mediterranean Sea modify their acoustic behavior in noisier areas or during noisier times of the day. Their vocalizations tend to decrease in frequency and become shorter in duration and more repetitive (Fig. 1). This change in the acoustic behavior is interpreted as a compensation mechanism to avoid the interference from noise on their communication.

 

 

Figure 1. Regression analysis of ambient noise levels and several acoustic parameters measured in fin whale vocalizations. Results show a highly significant correlation, with a decrease of the acoustic parameters when noise levels increase.

 

Only male fin whales sing, and singing is more vigorous during winter months, when mating is believed to occur. Therefore, the most plausible hypothesis is that fin whale songs are related to mating behavior. If a male modifies his singing behavior as a result of increased ambient noise levels from human activities, this interference has the potential to affect his reproduction success. This is of particular concern for populations of fin whales in areas with intense commercial ship traffic and high noise, such as the Mediterranean Sea.

 

The increase of noise from commercial ship traffic has the potential to negatively affect fin whale survival, first by decreasing the range over which males can be heard by competing males and receptive females, second by forcing males to sing louder and longer and therein expend more energy than normal, and third by decreasing the effectiveness of their songs if they are shifted into different frequency and temporal patterns.

 

Exploration surveys for oil and gas are one of the noisiest human activities made in the marine environment. These surveys produce intense, low-frequency impulses to penetrate the seafloor. Our results show that fin whales changed the features of their songs in the presence of noise from geophysical surveys (Fig. 2) and abandoned the area by moving away from the noise sources and out of our detection area for a time period that extended well beyond the duration of the geophysical survey (Fig. 3). This study provides evidence that fin whales modify their acoustic behavior to compensate for increased ambient noise and that under some conditions will leave an area for an extended period.

 

 

Figure 2. Average values of acoustic parameters measured in fin whale vocalizations in the absence (0) and presence (1) of noise from the geophysical survey.

 

 

Figure 3. Received bearings to fin whale songs in the study area and in which impulses from a distant geophysical exploration survey were detected. Bearings increase at the onset (December 8th) of the geophysical survey indicating that whales moved away from the noise source and out of our detection area. Fin whales did not come back to the study area until January 1st, 17 days after the survey ended, and slowly came back into the original area.

 

Results from this study can be explained by fin whales having two different types of reactions to noise. The first one is observed in the presence of commercial ship noise and is manifested as habituation to a continuous noise source, spatially predictable (ships usually navigate through shipping lanes) and that gradually increased over the last 50 years. The second type of reaction is a sensitization process to the geophysical survey noise, which could become intense enough to generate physiological damage if the whale gets too close to the noise source and that is recurrently present in the Mediterranean Basin.

 

Both the chronic negative impacts of habituation and the acute impacts of sensitization have the potential to negatively affect the survival of fin whales. Neither noise from commercial shipping nor geophysical surveying is currently regulated. Both activities are occurring in a global and increased manner in the oceans.

 

Fin whales are arguably the most sensitive species to shipping and seismic noise in the Mediterranean Sea. The Mediterranean population is at a disadvantage compared to other fin whale populations because of the intensive whaling occurred near the Strait of Gibraltar in the recent past, because of the high isolation situation for the Mediterranean population and because the intense human pressure over their ecosystem. Results from the present challenge to reduce, control and regulate noise in the Mediterranean Sea will be for sure an example to follow or to avoid in other oceanic basins where human pressure is less compressed and ecological consequences of this contaminant will take a bit longer to be evident.