STRANDINGS AND RESCUES
Cetacean stranding is a phenomenon in which cetaceans strand themselves on land, usually on a beach. Beached whales often die due to dehydration, collapsing under their own weight, or drowning when high tide covers the blowhole. Several explanations of the stranding have been proposed.
Towing a stranded sperm whale off the coast of Aitutaki, Cook Islands, South Pacific.
Worrying that the sharks may come in any minute for a feed!
Whales have beached throughout human history, so many strandings can be attributed to natural and environmental factors, such as rough weather, weakness due to old age or infection, difficulty giving birth, hunting too close to shore, or navigation errors.
In 2004, scientists at the University of Tasmanialinked whale strandings and weather, hypothesizing that when cool Antarctic waters rich in squid and fish flow north, whales follow their prey closer towards land. In some cases predators (such as killer whales) have been known to panic other whales, herding them towards the shoreline.
Their echolocation system can have difficulty picking up very gently-sloping coastlines. This theory accounts for mass beaching hot spots such as Ocean Beach, Tasmania and Geographe Bay, Western Australia where the slope is about half a degree (approximately 8 m (26 ft) deep 1 km (0.62 mi) out to sea). The University of Western Australia Bioacoustics group proposes that repeated reflections between the surface and ocean bottom in gently-sloping shallow water may attenuate sound so much that the echo is inaudible to the whales. Stirred up sand as well as long-lived microbubbles formed by rain may further exacerbate the effect.
Some strandings may be caused by larger cetaceans following dolphins and porpoisesinto shallow coastal waters. The larger animals may habituate to following faster-moving dolphins. If they encounter an adverse combination of tidal flow and seabed topography, the larger species may become trapped.
Sometimes following a dolphin can help a whale escape danger. In 2008, a local dolphin was followed out to open water by two Pygmy sperm whales that had become lost behind a sandbar at Mahia Beach, New Zealand. It may be possible to train dolphins to lead trapped whales out to sea.
Pods of killer whales, predators of dolphins and porpoises, very rarely strand. It may be that heading for shallow waters protects the smaller animals from predators and that killer whales have learned to stay away. Alternatively, killer whales have learned how to operate in shallow waters, particularly in their pursuit of seals. The latter is certainly the case in Península Valdés, Argentina, and the Crozet Islands of the Indian Ocean, where killer whales pursue seals up shelving gravel beaches to the edge of the littoral zone. The pursuing dolphins are occasionally partially thrust out of the sea by a combination of their own impetus and retreating water and have to wait for the next wave to carry them back to sea.
There is evidence that active sonar leads to beaching. On some occasions cetaceans have stranded shortly after military sonar was active in the area, suggesting a link. Theories describing how sonar may cause whale deaths have also been advanced after necropsiesfound internal injuries in stranded cetaceans. In contrast, some who strand themselves due to seemingly natural causes are usually healthy prior to beaching:
The seven-arm octopus (Haliphron atlanticus) is one of the two largest known species of octopus; based on scientific records, it has a maximum estimated total length of 3.5 m (11 ft) and mass of 75 kg (165 lb). The only other similarly large extant species is the giant Pacific octopus, Enteroctopus dofleini.
For future references, we keep collected samples frozen. Our freezers contain hundreds of samples of organs, skin biopsies, bodily fluids, etc. This octopus is probably the largest in our collection. It’s the hands-on slimiest job to being a scientist.