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    Re: Noisy Sea Surface
    From: Trevor Kenchington
    Date: 2003 Nov 15, 17:23 -0400

    George,
    
    My apologies. I understood you to have meant that you could hear these
    "clickers" when venturing on deck at night. Scrub the idea of the source
    of the sound being animals venturing out of the water at night.
    
    My own experience on the water has largely been either in boats too
    small to offer shelter from above-water sounds or else in vessels large
    enough that the noise from generators and fans never stops. I had not
    realized that intermediate-sized yachts provided such good acoustic
    coupling with in-water sound. Since yours, at least, evidently does so,
    I withdraw my suggestion that the "clickers" are necessarily on the hull
    itself.
    
    If they are further off, your suggestion of crustaceans signalling to
    potential mates is certainly a possibility. As you probably know, some
    crabs are renowned for doing that, though I am not sure that such
    behaviour has ever been formally reported for any English species.
    However, if these animals are around (rather than on) your boat, the
    possibility of finfish as a source has to be considered. Many (most?)
    fish make a variety of sounds and some could be audible as clicks. If
    you do discover what species are in the area, I may be able to check
    their known sounds. (There are fairly extensive published records for
    North Atlantic species.)
    
    I assume that we can rule out marine mammals. Whales certainly make a
    variety of sounds (don't think that seals do when in the water) but I
    expect you would be aware of their presence if one swam into your anchorage.
    
    
    Trevor Kenchington
    
    
    
    You wrote:
    
    > My observations of noises from "clickers" off the South coast of England
    > are similar to those of Keith Williams in New Zealand.
    >
    > That is: they are certainly individual clicks and not at all drawn-out
    > "scrapes". They are heard from below decks, the sound being transmitted
    > through the water and the hull, and not (or at least, very attenuated) from
    > on deck. I have heard many clicks per second, but these seem to be from
    > multiple sources, from all around the hull, not just from one or two
    > clickers, clicking madly from one place.
    >
    > Often, sounds are heard from below, in the cabin, transmitted through the
    > water, that would never be audible from the cockpit. For example, when the
    > Navy is exercising nearby, what I presume to be anti-submarine sonar, with
    > all sort of whistles and warbles. Or the rumble of the chains from a
    > chain-ferry a mile or so away. I presume that if the sound has an
    > undervater origin then it gets transmitted best underwater.
    >
    > I shouldn't give the impression that such clickings are predictable or
    > frequent in our waters. I hear them only rarely, but most often from
    > certain anchorages. They don't occur often enough to make for an easy
    > research project.
    >
    > In Worbarrow Bay (a few miles East of Portland Bill), where I've noticed
    > these clickings most often, there's an additional hazard when anchoring for
    > the night. The shingle beach is a popular spot for night-anglers, who set
    > up with an umbrella and a beach-casting rod. My anchoring spot is usually
    > just about casting distance from the beach, but we have an anchor-light and
    > they usually avoid us when casting. I mention this, because the presence of
    > anglers usually (but not always...) denotes the presence of fish. I've
    > never asked what they were after, though. Next summer, I will.
    >
    > My guess has been that the clicks came from lovelorn crustacea who are
    > exploiting the sound-carrying properties of water to attract the opposite
    > sex. But I have no real evidence to back up that hunch.
    >
    > I know that boat-hulls are attractive to certain fish, and my home berth
    > (fishing not allowed) has a plentiful resident population of grey mullet,
    > some really large ones. These graze, most efficiently, on the weed and
    > fouling on the hulls, leaving a pair of parallel clean lines where their
    > lips have tracked across. I doubt whether grey mullet make good eating at
    > the best of times, but these must take in a good helping of antifoul with
    > their diet, so I wouldn't fancy them.
    >
    > George.
    
    
    --
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
    
                         Science Serving the Fisheries
                          http://home.istar.ca/~gadus
    
    
    

       
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