If you have not heard, on February 10th, 2017, over 400 long-finned pilot whales stranded in New Zealand. Long-finned pilot whales are apparently the kings of mass stranding and seem to take this title extremely seriously, especially in New Zealand. (In 1918, an estimated 1000 pilot whales stranded on New Zealand shores!) Since the Feb. 10th strandings, marine biologists and volunteers have been trying to refloat some of the animals back into deeper waters. Apparently, the refloating efforts have been met with mixed success as some of the whales restranded. However, as of Feb. 12, it seems that all of the whales that were deemed releasable have been guided out to deeper waters with the tide. Because of the strong social bonds among pilot whales, rescuers try to refloat them in larger groups, instead of individually, thereby decreasing a pilot whale’s compulsion to restrand trying to rejoin its pod.
Some scientists think that this strong social cohesion is a contributing factor as to why the whales mass strand in the first place. For instance, if one whale was sick and stranded and subsequently sent out a distress signal, then the rest of the pod would beach themselves in an effort to assist the ailing whale. From the array of articles that I read to compile this post, this social-cohesion theory appears to be one of over a dozen potential reasons as to why pilot whales mass strand, including suicide, predator avoidance, and geomagnetic anomalies. The cause most adamantly supported by researchers appears to be beach topography. Researchers propose that the gently sloping beaches in certain areas of New Zealand make them “hotspots” for mass strandings because a mild beach gradient disrupts the whales’ echolocation and results in the whales never receiving an echo. Hence, the whales continue swimming, believing that there are no physical obstructions ahead. While offshore cetaceans appear to be the most common species to mass strand, inshore cetaceans tend to strand less frequently or only individually, which some researchers attribute to their “street smarts,” so to say, about the shoreline. One of the articles that I read even talked about interspecies altruism regarding strandings, and it was one of my favorite discoveries from the articles: “In 2008, it was widely reported that a mother and calf pygmy sperm whale [offshore cetacean], which had stranded and been refloated. . ., but seemed unable to find their way to deeper water, were rescued by a resident bottlenose dolphin [inshore cetacean]. The dolphin, which locals had named Moko, appeared to lead the two disoriented whales past a sandbar and into a channel that took them safely out to sea.” (New Zealand Geographic article)
In what appeared to be unintended perfect timing, a scientific publication about noise-induced hearing loss in mass stranded cetaceans was released on Feb. 6th by Morell et al. As I mentioned earlier, the current, predominant theory as to why cetaceans mass strand is beach topography. However, an important point of concern for scientists is the impact that human-generated (anthropogenic) noise and military sonar are having on the animals’ hearing. Morell et al. state in Implementation of a method to visualize noise-induced hearing loss in mass stranded cetaceans that “evidence of inner ear damage, compatible with noise-induced hearing loss, has not yet been described in a cetacean mass strand event.” The lack of support for ear damage contributing to mass stranding events does not mean that it could not be a potential factor. The absence of a correlation may stem from the apparent lack of adequate samples. Evidently, ear tissue degrades relatively quickly after death, making it difficult for scientists to obtain useful samples. Morell et al. outline some methods for improving sample preservation and include some fantastic scanning electron microscope images of the inside of the organ of Corti. I wanted to include this publication in the post because my M.S. thesis focused on a histological approach to sensory biology as well. It was nice to expand my histological knowledge past whiskers! 🙂 Morell et al. were not able to give any concrete connections between cetacean hearing loss and mass stranding events because not much is known about the normal cetacean ear design in general. However, Morell et al. did state that, in one case, there was an absence of specialized hair cells within the ear that would be consistent with the pilot whale losing low-frequency hearing. Hearing loss in this region of the ear appears to correspond well with human activities, such as pile driving, seismic surveys, and geophysical experiments. The article was relatively jargonless, and the images of the outer hair cells were really remarkable to see. I would strongly suggest at least looking through the pictures. If you need a refresher in auditory terminology, try watching this short video before reading the article.
After all of that being said, I leave you with some of my marine mammal stranding training advice: Do not try to refloat stranded marine animals on your own! Although pilot whales may not typically strand for overt health reasons, many other marine animals do. If you send them back into the water, they will most likely drown. Contact a stranding network near you and wait until trained responders arrive. Just try to keep the animal’s skin wet and shaded. If it is a cetacean, you can also dig holes in the sand underneath their fins and fill the holes with water to help the animal regulate its body temperature and alleviate stress on its flipper joints. Finally, be careful! They are still wild animals, not cuddly selfie opportunities… Have a great week!
The Puzzle of Pilot Whales (New Zealand Geographic), Mass Stranding: Hundreds of Pilot Whales Returned to the Water (Live Science), Hundreds of Pilot Whales Die After Beaching in New Zealand (The New York Times), ‘It was really haunting’: 416 beached whales propel New Zealanders into frenzied rescue mission (The Washington Post), Implementation of a method to visualize noise-induced hearing loss in mass stranded cetaceans (Morell et al. 2017)