Why whales beach themselves
Whale and dolphin strandings aren?t new. Here is a school of blackfish - a type of cetacean commonly called whales, but actually in the dolphin family - stranded on the shore of Cape Cod, Massachusetts in 1902.
The technical name for it is whale stranding. We spoke to Darlene Ketten at Woods Hole Oceanographic Institution. For 20 years, she’s studied whales and dolphins stranded on the coast of Massachusetts.
Darlene Ketten: People sometimes think that, oh, well they’ve come on shore because they want help. Actually it usually is that they’ve come on shore by mistake, sometimes in a panic perhaps or sometimes just from weakness.
The animals can be weakened by disease or by toxins produced by the algae that cause red tides. Scientists have also suggested that whales might use Earth’s magnetic field to navigate and that if the magnetic field is distorted – maybe through solar activity or magnetic anomolies on the sea floor – a whale might become disoriented. But Ketten said not everyone agrees that whales use magnetic fields to navigate.
And sometimes humans cause whale strandings. In 2002, 14 beaked whales washed ashore in the Canary Islands. Navy ships in the area were using active sonar, a system that emits loud sounds to “see” underwater. Some scientists think that the whales fled from the sound, and as they did, they rose too fast and got what divers call “the bends.”
Ketten hopes her study of stranded sea animals will yield better ideas for how to rescue them.
Our thanks to the National Fish and Wildlfie Foundation.
Read the full text of Earth & Sky’s interview with Darlene Ketten.
A 2003 study in the journal Nature found that beaked whales had been affected by military sonar and subsequently died from “the bends” and washed ashore in the Canary Islands. Read more …
The world’s longest–running dolphin research program, the Sarasota Dolphin Research Program.
Darlene Ketten says it’s clear that high intensity, active sonar sometimes leads to whale beachings. But the mechanism isn’t completely clear.
Ketten told Earth & Sky:
“Some of the 7 animals that died in the Canary incident had fatty bubbles not air bubbles. Fatty bubbles can occur from almost any type of injury and in fact they are common in broken bone cases. They even happen after death if a body is rolled around or dragged over rocks. Air bubbles are the classic symptom of bends or DCS (decompression syndrome). Air bubbles were reported in a paper in Nature but those were in animals that stranded in Britain over several years; but those were tissues that had been collected in many different ways, some from animals that were in advanced decay. They also reported the fatty bubbles in the Canaries animals in the same paper so people often confuse which animals had the air vs. fats.
“There have also been some conference papers since then that report air bubbles in many strandings but a lot of these have the problem of probably being artifacts from the way the necropsy was done. When you cut into the animal, you can cut through major vessels, especially in the abdomen or brain and when you do, air leaks in through the cut vessel. It is difficult to avoid and many people assisting with necropsies are unaware of the problem. Consequently, it is still controversial how significant the findings of air bubbles are.
“There is a paper suggesting that surfacing too fast could cause bends in whales but so far, the cases reporting air bubbles don’t really match a classic bends picture. Just to further confuse the issue there are diseases that can also produce some bubble like structures in some of the affected organs reported in the Nature article, so you have to consider that possibility as well. Sorry that this is so complex, but I suppose the bottom line is that you could say that some of the injuries in the Canaries animals raised the spectre that something like the bends may have occured but there are also other equally possible causes that need to be investigated and the answers are not clear yet.”
Sometimes an animal dies at sea and merely washes up on shore. But even a live, yet weakened animal on the shore has a low chance of surviving.
Ketten said, “They’re really designed to be in the water to be buoyed up by the water itself. They are not designed to lie with their whole body weight crushing them down against the sand or rocks of the beach. And also they’re designed to be very well insulated so they don’t lose body heat in the water. Especially in tropical areas, a whale or dolphin that ends up on the beach is going to be cooking in it’s own body heat pretty fast.”
Ketten said that, about half the time, it’s not possible to tell the exact cause of death in a whale or dolphin stranding. She added, “Sometimes it’s really obvious, something like a ship strike . . . And sometimes the answers are equivocal: we know this animal was hit by a ship, but we can’t tell because of its decay condition if the strike was before or after death. And sometimes we can just see that the animal was basically weak and it had a number of problems wrong with it, a number of pathologies or diseases, but we don’t know which thing really killed it.”
Bill Rossiter, President of Cetacean Society International, wrote to Earth & Sky: “Cape Cod is one of the world’s major mass stranding hotspots, and also gets a wide variety of species in single strandings. It is also one of the few places in the U.S. where there is a well established effort for rescue, rehabilitation and release, and a long–running volunteer program.” Learn more at the Cape Cod Stranding Network and at the Provincetown Center for Coastal Studies.
Our thanks to:
Darlene Ketten
Woods Hole Oceanographic Institution
Woods Hole, MA
