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Sonar Of Baleen Whales

To the best of my (D.M.) knowledge, no sonar has yet (in 2013) been discovered in the non-toothed, the "baleen," whales.
But, isn't it obvious that large whales must have sonar, or something like it, else they would often injure themselves by crashing into reefs or into the seafloor? Also, how would they find the large schools of small critters that they feed upon?

It is possible to build echoscopic sonar of a sort that would work for baleens. It seems likely that Nature has already done this. What remains to be found are sounds made by baleens that are sufficiently feature-constant. Probably the features are of much longer duration than the "fangs" of the duration 1/100,000 second, in the clicks of dolphins. Probably, in compatibility with the long click-features, the sensors are widely spaced (feet apart rather than fractions of an inch) on the head.