A fishy business
The stranding of more than 50 pilot whales on South African beaches this week prompted a mass rescue effort, made news headlines and moved the hearts of people worldwide as beachings always do. Elegant, mysterious, and undeniably intelligent, whales and dolphins cant help but evoke strong emotional responses in us, their primate cousins. Though they are so far removed from us on the evolutionary family tree, most of us cannot help but feel a special affinity for them: though we are so different in physical form and function, we together possess the most complex brains on earth.
Which may explain in part why we find beachings so distressing and confusing: how could animals that are so clever so frequently find themselves helplessly stranded on dry land? Couldnt avoiding the shoreline be simple enough?
We know that whales and dolphins have always beached themselves, and historical accounts of beachings go back hundreds of years beaching may be as natural as drowning. And natural, climatic factors can be involved: a 2005 study in the journal Biology Letters found that beachings in Australia and Tasmania are more common every dozen or so years, when normal variations in climate cause cold, nutrient-rich waters from the Antarctic to drift further north, which whales follow in search of food.
But are whales beaching themselves more than they used to? And could we be to blame? The answer to both questions appears to be a resounding yes.
The most well-known culprit: sonar. The US Navy admitted for the first time in 2002 that their sonar can cause whales to strand, something biologists had suspected for years a mass stranding of dolphins last year in Cornwall was also blamed on naval sonar. Whales and dolphins rely overwhelmingly on sound to communicate and to navigate, so loud noises in their midst will make it as difficult for them to find their way around as thick fogs would to us. Autopsies of beached whales have often shown haemorrhaging near the ears. And a study published last month for the first time showed experimentally that sounds in the same frequency range as military sonar can temporarily cause hearing loss in dolphins. Research from 2002 also indicated that sonar can give whales the bends, possibly because they surface too quickly to escape the sonic assault.
Noise may not be the only problem: a study published last year found that dead whales and dolphins on Cornish beaches have indeed become more frequent over the past century, and the researchers blamed the destructive fishing practice of bottom trawling for playing a major role, saying that more than 60 per cent of the dead animals had been killed as bycatch.
Now a new study in the journal Environmental Pollution suggests that we should be looking at another human activity: analysis of a dozen dead dolphins and a seal from the east coast of the US found levels of persistent pollutants known to be toxic to the nervous system including metabolic byproducts of PCBs, pesticides, and brominated flame retardants in their cerebrospinal fluid and cerebellum grey matter, some at very high levels in the part per million range in the seal, says lead author Dr Eric Montie of the University of South Florida. This is the first survey of such a wide range of toxic chemicals in the brains of dolphins and seals.
The research does not at all prove that these chemicals were responsible for the strandings, cautions Dr Montie. He examined the brains of beached whales because those were the carcasses available to him. Similar analyses on the brains of whales that had not beached would be needed to know if the beached animals had higher than normal levels and that research might be impossible to do.
But it is important to determine whether or not environmental pollutants are having any impact on strandings, he says. Thats definitely one of the reasons we are doing this work. And they are just starting to scratch the surface.