Noise Pollution and Whale Behavior
In the oceans, where distances can be long and visibility can be short, many animal species rely on sound to communicate, navigate, and monitor their surroundings. The haunting cries and clicks of whales are both beautiful and vital to their survival. Using "songs" cetaceans can communicate with one another across several hundred kilometers of ocean. Whale sonar allows the animals to find food, safely travel along irregular coastlines, and migrate to and from breeding and feeding grounds. Some whales uses bursts of loud noise to drive and confuse their prey.
These activities are becoming more and more difficult as manmade noise in the sea has increased dramatically. Ship traffic, oil and gas exploration, scientific research activities, and the use of military sonar and communications equipment have caused an increase in ambient marine noise of two orders of magnitude in the last 60 years.
Recent studies suggest that noise pollution can harm whales directly by damaging their hearing, and in extreme cases, causing internal bleeding and death. More commonly, it appears that excessive or prolonged noise can cause behavioral changes that interfere with the health and survival of the animals.
In this activity, you will consider one type of whale behavior that has been linked to manmade noise, stranding. When whales strand, or beach themselves, they often die. Death may be due to the factors that drove them ashore initially, or to exposure and dehydration and organ damage caused by the unsupported weight of their own bodies.
Instructions: A group of whales—mothers and their calves—is migrating along a coastline. Using sonar and song, they are keeping in touch with one another and away from shallow water. Their journey is uneventful, until human and natural activity causes underwater noise levels to rise.
Click the image repeatedly to add noise to the marine environment, and observe how whale behavior is affected. Once you have seen the combined results of noise pollution on this group of whales, answer the questions that follow.
- Describe how whale behavior changed in the simulation as noise levels increased. Speculate on why noise had these effects.
The whales first veered away from the sounds, then began to move erratically, and finally ran aground. They may have been trying to avoid noises that they found painful or frightening at first. When the noise became very loud and came from many different directions, the animals seem to have gotten disoriented or injured, so that they stranded themselves by accident or design.
- Not all whale strandings are driven by noise pollution. What natural causes might lead to strandings? How can scientists determine whether noise was the deciding factor?
Whales might run aground as they flee from predators or chase prey. Their ability to navigate or to sense dangerously shallow water might also be lost to illness or injury. The cause of a stranding might be revealed through examining the animals for signs of hearing damage or disease. Attempts could be made to correlate the stranding with nearby human activity that generates intense noise, such as military exercises or offshore drilling.
- The number of whale strandings worldwide seems to be increasing in recent years. Which of the sources of noise in the simulation do you think may be most responsible? Explain.
Human activity at sea has increased at the same time as the strandings have become more frequent. Of the manmade noises, sonar seems the most likely culprit. It involves very loud noises, often emitted in intense bursts, and intended to travel long distances underwater. Ship and propeller noise occurs mainly on the surface. Since whales themselves use sonar, it also seems possible that human sonar might overlap the frequencies heard and used by whales to navigate, which could interfere with their ability to orient themselves. Thus, sonar seems to have the ability to cause both confusion and physical damage to whales.
- Some noises can cause migrating whales to strand themselves. How else might noise pollution affect whale behavior during migration?
Whales might veer off course to avoid noise pollution, lengthening an already arduous journey. The added stress on very old and very young animals could prove harmful, even fatal. Since whales use sound to communicate with and identify with one another, noise pollution could cause pod members to lose track of one another, and mother/calf pairs to become separated. Feeding and mating might be disrupted, which could affect the health and sustainability of whale populations.
- How could man-made noise pollution be reduced or redistributed to minimize its effect on whales?
Many whale species have precise patterns of migration. Boat traffic and military activity could be restricted along the route and in feeding and birthing areas when whales are present. Sonar training exercises could be concentrated in areas where whales do not congregate, and attempts could be made to determine and avoid the frequencies that cause the most harm.
Critical ThinkingClimate researchers are using a technique called acoustic thermometry to track changes in ocean conditions due to global warming. Since the speed of sound in water varies with temperature, by transmitting and measuring low frequency sounds across ocean basins, scientists can monitor water temperature. But while this research may ultimately help protect ocean ecosystems, it may harm sound-sensitive animals like whales in the process. How should scientists balance the potential hazard to whales against the possible benefit to the marine environment?
Scientists seek to understand and explain how the natural world works. Many of the questions raised in this endeavor have no absolute answers.
The scientists should conduct experiments to determine how whales might be affected before the system is widely deployed. Perhaps there are frequencies or sound intensities that would minimize harm and yet still be effective in monitoring temperature.
If the only way to track ocean climate change does threaten whales, then it is a very difficult decision. Whales are among the most endangered and most beloved marine animals. It would be very hard to get popular or political support for research that risks their already uncertain future. But global warming could disrupt the entire ocean ecosystem. Are whales more important than all the other species? And it seems likely that if research is halted and environmental changes aren't tracked and possibly avoided, the whales will suffer anyway.