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.[1] Several explanations of the stranding have been proposed.

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Towing a stranded sperm whale off the coast of Aitutaki, Cook Islands, South Pacific.

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Worrying that the sharks may come in any minute for a feed!

Natural

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,[3] 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.[4] In some cases predators (such as killer whales) have been known to panic other whales, herding them towards the shoreline.[4]

Their echolocation system can have difficulty picking up very gently-sloping coastlines.[5] 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.[6] Stirred up sand as well as long-lived microbubbles formed by rain may further exacerbate the effect.

“Follow-me” strandings

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.[7] 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.[8]

 Sonar

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.[9] 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:

 
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Haliphron Atlanticus

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.

Depth range in open-ocean from surface to at least 1,260 m, over depths of up to 6,787 m. Collected in bottom trawls on continental shelves and slopes at depths of 100 to 3,173 m. Possibly not entirely pelagic, but might pass relatively short periods of its life cycle in open waters, soon returning to a life at the bottom especially on continental slopes. Females brood their eggs attached to the oral side of the arm bases near the mouth. Likely an intermittent spawner. The deep umbrella formed by the arms and webs of the female possibly serves as the main organ of locomotion/swimming. When mature, and before autotomized, the hectocotylus of males protrudes from the pouch opening on the inner surface of web between the second and fourth pairs of arms. Feeds on crustaceans and cephalopods (Ref. 96968). Members of the class Cephalopoda are gonochoric. Male and female adults usually die shortly after spawning and brooding, respectively. Mating behavior: Males perform various displays to attract potential females for copulation. During copulation, male grasp the female and inserts the hectocotylus into the female’s mantle cavity where fertilization usually occurs. Life cycle: Embryos hatch into planktonic stage and live for some time before they grow larger and take up a benthic existence as adults (Ref. 833).

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