Mayday Monday – Boat Traffic and Noise Pollution
Primary Threat #3: Boat Traffic and Noise Pollution
Orcas are acoustic beings, and sound is an indispensable aspect of their daily lives. Vocal communication is particularly advanced for orcas and is an essential element of their complex social structure. Each pod has its own dialect, or “accent” on shared calls within clans, which are similar to but distinct from other pods. These dialects are relatively stable over time and are important to maintaining group identity and cohesiveness. Sound is also used for navigation in their environment, and most importantly, for locating food.
Click to listen to a Northern Resident pod, the I15’s, be drowned out by vessel noise: i15s_boat_noise_1.mp3
Southern Residents live in a relatively urban environment, compared their Northern Resident cousins. Because of this, noise pollution is widely regarded as a significant threat to their survival. The same way that urban development on land displaces terrestrial animals, noise pollution in the marine environment is another kind of habitat degradation. There is significant traffic from container ships, ferries, tug boats, recreational boats and fishing vessels in the inland waters where they are found in the summer, and along the coast where they spend their winter. About 20 large vessels (ships over 65 feet in length) travel through the Southern Residents’ current critical habitat every day – that’s almost one every hour.
The ability to communicate while foraging is important to feeding success. They hunt cooperatively, so call exchange is essential, but vessel noise can drown out those calls. Studies have shown that some whales make louder vocalizations to be heard over boat noise, but this increase in volume of calls in a loud environment comes with an energy cost. Scientists liken this to a “cocktail party” effect where whales become louder to be heard in a noisy environment. In US waters, boats are required to stay 200 meters away from orcas, but boat noise from motoring vessels up to 400 meters away can mask echolocation clicks and communication calls. So, even if all boat operators respected this rule, there would still be a significant negative impact. A recent study has shown that vessel speed is the biggest factor influencing noise in the Southern Residents’ habitat – small motorized boats traveling at high speeds can have a larger acoustic impact than larger, slow-moving vessels. New research also indicates that large vessels produce high-frequency noise within the range of Southern Resident vocalizations and echolocations, and can potentially mask these important signals. Also, an unexpected factor in this problem is climate change: changing ocean chemistry (due to increased CO2 emissions) causes sound to travel farther in water, so boats farther away are starting to have a greater impact on their acoustic environment.
Aside from the noise, high boat traffic is disruptive to natural behaviours. There have been documented differences in foraging and travelling patterns near boats compared to when no boats are present. Boats, especially the smaller, faster moving vessels, interrupt the whales’ normal behaviors, and may drive them away from areas necessary to their survival. They modify their surface behavior, with less directional travelling, which means that more energy is used to move. Avoidance takes energy away from feeding, resting, socializing and other necessary activities. Close boat traffic at best disturbs their activities and at worst carries the risk of vessel strikes if boat operators are unaware of whales in the area.
Both the Northern and Southern Residents are protected by Canada’s Species at Risk Act, where the acoustic environment is considered a part of their critical habitat. In the US, for Southern Residents, this is not the case. The Center for Biological Diversity included this in their petition to extend critical habitat, and we are supporting the inclusion of sound in the proposed revision, making it officially a habitat feature essential to their survival.
By supporting this effort, you can help us protect their home and all the elements of it that they need to survive and recover. Please sign our letter to the National Marine Fisheries Service urging quick action to revise and expand critical habitat for the Southern Residents.
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