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Navy sonar dolphin 'massacre' - the facts

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Analysis For the last twenty-four hours or so the news has been full of beached dolphins, following incidents since Monday near Falmouth in which more than 70 of the marine mammals got into trouble and reportedly up to 30 have died.

Various theories have been advanced for the mass stranding, the largest seen in Britain for a quarter-century. Dolphin beaching incidents are very rare, significantly more so than similar occurrences involving whales.

Increasingly commonly in recent times, cetacean strandings of any sort tend to be blamed on naval sonars. Navies have been "pinging" sound pulses into the water and listening for the echoes en masse since the late 1930s in order to detect submarines, ships and mines, but it is only in the last ten years or so that people have started to link sonar use and cetacean beachings.

Those knowledgeable in the field of sonar theorise that this might be because it is only in recent times that low-frequency active equipment has become common. Until the early 1990s, the prevailing fashion in long-range detection was for the use of "passive" kit, which would not ping sound into the water but merely listen for noises emitted by the enemy ship or sub.

In the last decade or so, however, newer subs and warships have become so quiet that they can seldom be heard by just listening. Nowadays, the trend in long-range scanning is for low-frequency, far-travelling active pings. The Royal Navy's new Sonar 2087, just coming into service, is of this type. Other nations have been using such gear for a while.

When close to an enemy, in the thick of an anti-submarine fight, ships and helicopters will also use mid-frequency active kit to get a more precise fix for targeting. Higher, even shorter-ranging frequencies are used by minehunting ships or survey vessels needing a high-resolution picture of the sea bed.

Mid-frequency and high-frequency kit has been in use since World War II, so if these have anything to do with cetacean strandings people have certainly taken a long time to notice it. In particular, the Royal Navy has been using gear like this off the Cornish coast time out of mind - these are some of the busiest exercise areas in British waters.

With respect to the recent beaching, the navy has confirmed that none of the new low-frequency gear was in use - and no live munitions had been fired since last week. (Though again, live weapons have been fired routinely forever without any link to strandings.)

"Royal Navy vessels have not used low frequency sonar anywhere in the South West areas," a spokesman told the Beeb.

"A survey vessel was conducting trials using a high definition, short range side scan sonar for sea bed mapping trials approximately 12 nautical miles off the coast of Falmouth at the time of the incident."

Sidescan survey gear is and has been widely used worldwide for decades, and not just by navies. The idea that low-frequency active has something to do with strandings in general is at least believable - the idea that sidescan lay behind this incident is ridiculous.

Anyway, if you really like dolphins - and hey, what's not to like?* - there are much more serious things to worry about. Reputable sources indicate that fishing nets kill a thousand marine mammals a day, which rather puts this Cornish business into context. If you want to help cetaceans, pick on fishermen - not navies.

And seriously, UK media people, with all your sonar-kills-dolphins headlines this week. It would be a good idea to pull your head out of the dark for a look round once in a while. ®

*Unless you're a fisherman. Or perhaps a porpoise - apparently dolphins aren't very nice to their smaller relatives.

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