I posted a short video on the Bloggerheadseaturtle Facebook page the other day about ocean noise pollution and realized that I have never done a post about the topic yet. So here is my short post about noise pollution! Some of my post comes from information found in this neat PDF file by IFAW (International Fund for Animal Welfare).
Marine mammals often vocalize to communicate, but long-distance vocalizations are especially important for porpoises, whales, and dolphins. However, noise pollution in the ocean from boating/shipping, seismic surveys, construction, and sonar are making it increasingly difficult for these marine mammals to communicate or echolocate. Since 1942, a blue whale’s vocalization distance has decreased from 1,600km to 160km (in 2012). Furthermore, “Both right and blue whales have been found to increase their vocalizations in the presence of sound sources within their vocal range, presumably to make themselves heard…” If you would rather watch a video than read, OceanCare: Silent Oceans put together a short, educational video that summarizes the information in the IFAW booklet well. I also found this article that shows the distribution of vocalizations of right whales in Boston harbor and just how overshadowing the noise from one commercial ship can be. I think that the images in this article help with visualizing the issue. I knew noise pollution was a major concern for marine mammals, but I did not realize how far the calls can actually propagate. Using numbers does not help me as much as landmarks. So, in the article, it said that blue whales singing in Canada can be heard in Puerto Rico! That resonates more with me. That is some important long distance calling that could definitely affect mating and migration behaviors!
Another interesting fact that I found was that baby humpback whales seem to “whisper” to their mothers. Baby humpback whale calls are higher and quieter than adult noises. Researchers suggest that this helps the infant stay protected against potential predators because the baby is less likely to be detected acoustically. Increased noise pollution could affect relationships between mothers and their calves. I learned in graduate school that whales seem to be changing their songs to different frequencies in response to ocean noise pollution. However, I found it difficult to actually find an article stating this definitively (feel free to share one by commenting!). Most articles were rather vague other than the fact that whales seem to be increasing their vocalizations (as mentioned above). However, I also discovered an article on birds showing that they alter their songs in response to traffic noise. North American Flycatchers will sing shorter, deeper notes in the presence of traffic noise. Although audible, these altered songs might be considered “less sexy” by females, thereby affecting mating success. Maybe something similar is happening with cetaceans. Hopefully, new research that outlines the specific threats of ocean noise becomes available soon, or it is unlikely that any legislation will change.
I have never conducted acoustical studies on cetaceans, but the seals and sea lions that we house at my job are in an open water enclosure. Within a few months of me starting my position, some boats were in the harbor running sonar tests. All of the animals began acting strangely and none of them worked properly for the weeks that sonar testing was being carried out. So, in honor of the silent ocean theme, I leave you with a picture of Luca during his headphone fitting for my experiments. Have a great week!