What causes whales to beach?

tumblr_nryfrf29Ug1tww4pgo1_1280

“Toward dawn we shared with you
your hour of desolation,
the huge lingering passion
of your unearthly outcry.”

– from ‘The Wellfleet Whale’ by Stanley Kunitz

 

As you may well be aware, a member of the UK’s only resident pod of Orca was washed up dead on The Isle of Tiree last week. The female Orca named Lulu was identified by her unique scars, saddle path and eye patch. The Hebrides Whale and Dolphin Trust (HWDS) who have been monitoring the population, hadn’t seen Lulu since July 2014. There are now just 3 females left in this fragile pod, which according to Orca expert Dr Andy Foote, is too late to be saved from extinction.

The pod has not produced offspring in several generations, and there are now believed to be only 8 individual remaining. Dr Andy Foote believes the main culprit for the diminishing Orca population off the coast of Scotland is human based condiments. A study into the cause of death of Lulu confirmed the death was due to entanglement.

“There were deep, granulating wounds … consistent with a rope wrapping around the tail and trailing behind the animal, probably still attached to something at the other end. This would have made normal swimming very difficult, and we suspect the animal had been entangled for several days. She hadn’t fed recently but had swallowed a large amount of seawater, most likely as she eventually succumbed to the entanglement and drowned.”

With news of a further case of whale entanglement, this time a Humpback Whale, in Loch Eribol, Durness, it is ever more obvious how at risk whale populations can be.

So what causes whales to become stranded? Are humans to blame for all of the whales washed up on to beaches?

 

What causes beaching?

As are constantly reminded in nature documentaries, cetaceans are extremely intelligent animals with highly advanced senses of direction and navigation skills. Something pretty serious surely needs to have gone wrong to lead a whale or dolphin or even an entire pod, to become stranded.

Unlike in the case, the type of standings which usually causes the greatest media attention and human sympathy is mass stranding’s. Fortunately, this is a much less common situation, when multiple dead animals turn up in a single location. Mass stranding’s often occurs when an individual whale gets into trouble and lets out a distress call, prompting the rest of the pod to follow and become beached alongside. That said, there is no definitive reason for mass stranding, and can be difficult to understand the cause.

 

Death by natural causes

Throughout history whales that have been found beached, have been attributed to natural and environmental factors.  Natural causes can include factors such as poor or extreme weather conditions, animals being pushed into shore by heavy wave action. The degradation of physical conditions due to old age or illness, or problems arising whilst trying to give birth*. Dolphins especially can suffer when trying to hunt too closely to shore and accidently beach themselves.  Even navigational errors can prove fatal if the animals get lost, finding themselves on the wrong end of a quickly receding tide.

Situations can also occur when individuals fail to correctly pick up very gently-sloping coastlines, and find themselves in much shallower water than they expect to be in.  In several mass stranding ‘hot-spots’ such as Ocean Beach in Tasmania and Geography Bay in Western Australia, this hypothesis has been suggested. In both these places the slope is very slight and research has been conducted showing that the gentle slope may affect the echolocation used by the whales, enough to make it inaudible. This would therefore cause the animals to become confused and disorientated, often resulting in them becoming beached.

Another theory, however somewhat controversial, is one researched by former U.S. Geological Survey geologist Jim Berkland which states that radical changes in the Earths magnetic field, which occur just prior to earthquakes, are to blame for increases in beached whales. Berkland states that this interference affects the ability of sea mammals and migratory birds to navigate, explaining the increase in mass stranding.

Another possible explanation  may be ‘follow me stranding’ were larger cetaceans follow smaller dolphins or porpoises into shallower waters. Large whales often use smaller ones to locate prey, following the pods. If a combination of strong tidal flow and strange seabed topography is encountered, the larger animals can be at a much higher risk of finding themselves become trapped, and getting beached.

Orca, who predate on both Dolphins and Porpoises, will also follow them into shallower waters. However, Orca stranding are actually very rare. Even when compared with the frequency of stranding in dolphins.  It seems that Orca have some sort of strategy for avoiding beaching.  Orca, being more intelligent and powerful, have simply learned to operate more affectively in shallow water. It is also a possibility that Dolphins are chased in shore by Orca. The Dolphins either beach as a result of attempting to escape or are chased towards shore by orca, in an attempt to trap them. This alternative theory is perhaps strengthened when you consider the predatory tactics of the Orca of the Peninsula Valdes in Argentina. They are known to arrive at a specific time every year’s, just as young Elephant seals are first taking to the water, not realizing the deadly threat’s lurking. Orca thrust themselves completely out of the sea in pursuit, becoming very skilled at beaching themselves, and retreating back into sea on the next wave.

 

Man-made Causes

Man made causes although not as common as Natural causes, are by far the more worrying reasons for whales becoming beached. The individual is often washed ashore dead, or near death. Reasons for this can be as a result of illness brought about by contamination and/or pollution. Oceanic pollution is distressingly high. It can affect whales by either directly harming them, or by harming their food sources. Diminished food supply causing starvation. Both of these factors can impede reproduction.

Other human factors can be caused by animals becoming entangled in fishing nets and ropes, either discarded or still being used. Whales often become trapped, leading them to drown, or entangled, inhibiting the ability of individual to swim or feed properly. Many countries have legislation to inhibit discarding of fishing nets/ropes, however other don’t. With many species being extremely wide ranging and the potential for nets and ropes to travel great distances in oceanic currents, the stability of the legislation is limited.

A slightly less obvious way in which human activity is thought to lead to their beaching behaviours, is through naval activities. There is evidence that the very loud noises produced by anti-submarine sonar cause injuries to cetaceans, which may lead to beaching. Necropsies have also found internal injuries in large numbers of beached animals, and it has been suggested that the use of sonar may be responsible for these whale deaths. it was been proposed that the sonar can causes serious hemorrhaging by creating extremely loud and rapid pressure changes in the water. This has been backed up on several occasions when beaching of cetaceans has occurred briefly following Navy sonar exercises. In March 2000, the US Navy accepted the responsibility for the deaths of 17 whales in the Bahamas, which seemed to have died as a result of acoustically-induced hemorrhages around the ears. These injuries probably lead to the whales becoming disorientated and resulted in them becoming stranded.

Sonar can also lead to injury in whales by causing a form of decompression sickness. Exactly how the sonar is able to create the bubble formation which causes the bends, is not properly understood.

 

Conclusion

Although death by natural causes is more common and wide ranging, as far as the case of Lulu, it is more tragic as she died as a result of human interference. As previously mentioned, Orca standings are very unusual. Her death was rare and caused by a factor which in an ideal world, could never have been caused.

 

*Mothers sometimes seek the relative security and protection of shallower waters, but can easily find themselves in trouble.

2,278 total views, 2 views today

The following two tabs change content below.
Ben Wright

Ben Wright

I am a consultant ecologist with a special interest in protected species and birds. I have some past experience in science writing. I formally wrote a science column for a local paper, and composed a book based on the column (Science Matters) which has just been published.

You may also like...

Leave a Reply

Your email address will not be published. Required fields are marked *

Blue Captcha Image
Refresh

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Powered by Calculate Your BMI