Why do dolphins strand themselves?

It's been a particularly rough patch for dolphins as of late...

In Madagascar, 55 melon-headed whales (a species of dolphin) have died after coming ashore in the northwest part of the country. In Cornwall, 26 dolphins have died in a mass stranding. A pathologist who examined some of the 26 dead mammals said today: "On the face of it, it looks like some sort of mass suicide - but the question is why? The dolphins had swallowed and inhaled big chunks of mud from the estuary. Their lungs and stomachs were full of it. That is very bizarre indeed." An unusual number of dolphin strandings was also noted in Cornwall earlier this year, as well.

The question is indeed 'Why?'.

One hypothesis suggests a natural mechanism, a combination of particular weather conditions and a gently sloping coastline, which can cause the dolphins to not 'see' the approaching shore and result in a stranding. Other, human-induced causes may also be to blame.

Pesticides and other aquatic toxins could play a role. Dolphins stranded in Victoria, Australia over the past two years have shown elevated levels of mercury contamination. "Dolphins may be becoming stranded as a direct consequence of mercury contamination which damages their neurological system. They become potentially confused and disorientated, and strand themselves." Similarly, toxic algal blooms (on the increase in recent years, likely due to agricultural fertilizer runoffs) may lead to epilepsy and behaviourial abnormalities in California sea lions. Even low-levels of chemical contamination can lead to these difficulties in marine mammals. And such persistent chemical pollution is pervasive in the ocean, even affecting the deep-sea cephalopods on which dolphins and whales feed.

Other factor could be sonar and other loud noises produced by ships in coastal waters. Military exercises, including the use of sonar, were noted nearby in the recent Cornwall case. In the Madagascar case, ExxonMobil was carrying out seismic surveying roughly 50 km from the stranding site. The coincidence is certainly interesting, and worthy of further consideration. But determining ultimate cause-and-effect is an extremely difficult process.

I've noted previously, dolphins and other marine mammals have been sighted in unprecedented locales in recent times. Much of this shift in range of these creatures is believed to have been driven by climate change. The melon-headed dolphins in the example fit this pattern, having never before been seen in Madagascar.

Allowing myself to anthropomorphicize for a moment, one chain-of-reasoning that fits these (admittedly selected) facts: As climate changes, the animals-- affected to some degree by persistent chemical pollution -- move to new (and unfamiliar) territories. Not knowing a particular area may mean the creatures are not familiar with the pitfalls (e.g. 'sonar-terminating' coastlines) of a given area. So when startled or panicked, by say sonar or depth charges, the dolphins may make 'poor decisions' (being neurologically damaged) and stumble into a blind alley (a la the natural mechanism noted above).

This is just a homemade hypothesis, unlikely to withstand serious scientific scrutiny. But it illustrative of the problem at hand. Like the Blind Men and the Elephant, we have a collection of facts and perceptions, each of which likely contain some grain of truth. The trick is to discern the true nature of what we face. ExxonMobil and/or the military make easy and tempting targets for blame, but it is difficult to escape the idea that the elephant in the room is really Our Way of Life. The real solution lies in changing our destructive lifestyles so that they better harmonize with the rhythms of Nature.

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Image: ENN