A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Gary LaPook
Date: 2007 Mar 21, 13:00 -0700
Gary LaPook wrote: I can add some personal observations. Sunday we were offshore southern California about 5 NM south west of Port Hueneme where we saw two humped back whales. We watched these whales for some time and they appeared to be on about a seven minute schedule. One surfaced so close to the boat that we could hear him blow and then smelled his breath which was very "fishy." Since he had been down only about seven minutes and we were in only thirteen fathoms it would appear George's "fart" theory for the "fishy" smell has been disproved. Last December we visited Sea World in San Diego. We watched an orca (what ever happened to "killer whale") swimming in his large tank through glass underwater windows. At one point the whale scratched his back on a large rock on the bottom. He did this by rolling over and then exhaling a very large bubble which caused him to achieve negative buoyancy so he could then use his weight to press his back against the rock for the scratching process. It would be like a diver releasing air from his buoyancy compensator so that he could sit on the bottom. Whales have obviously figured out this buoyancy thing. Regarding the question of whether the whale exhales before sounding. Even if his lungs were full at the start of the dive so that the whale would have to fight this buoyancy this problem would quickly go away in the first couple hundred feet where at 6 atm pressure the air would be reduced to only 1/6th its surface volume and buoyancy. On Mar 20, 3:48 am, "George Huxtable"
wrote: > Let me start with in apology. This has little (indeed, nothing) to do > with navigation, but about the hydrostatics of sperm whales. If such > question are of no interest to a reader, he should press "delete" now. > > I raise this matter in the hope that others who know more about the > matter than I do can point to where I can find answers. What > information I have comes from "Whales of the World", by Lyall Watson, > a volume I've respected, but which hasn't satisfied my questions. > > My wife and I were recently introduced to two "resident" sperm whales, > who spend their time patrolling an ocean trench which happens to come > close inshore off Kaikoura, New Zealand. > > Sperm whales are the ones with an enormous squareish head, with a > small jaw below it; the head is an immense can of pure spermaceti oil, > containing many tons of the stuff. Their way of life is a strange one, > even by whale standards. They earn their living by swimming down > vertically to the bottom, at depths of a kilometre, sometimes much > more, to graze on squid living near the bottom. These dives commonly > last for 40 minutes or more. Then they return vertically to the > surface to breathe air, for 10 minutes or so. A sequence that's > regular as clockwork. > > It has set me wondering about the physics of the problems that face > such a creature, alternating between regimes at such widely different > pressure, and how it has managed to solve them. Roughly speaking, the > pressure at a kilometre deep is 100 atmospheres, and any gas at that > pressure is compressed to only one hundredth of its volume at the > surface. In general, the volume of liquids and solids, and that of > seawater, changes little with pressure. They are pretty > incompressible. > > There's no way that a whale could exist on a big breath, as a > pearl-diver does, over all that time. Instead, I understand that a > sperm whale is adapted to rely on oxygenated blood that has been > recharged while it was breathing at the surface, and its tissues are > dark red or black because they hold large quantities of that > oxygen-rich blood. > > My first question is this; does such a whale take a last lungful of > air down when it dives, or not? If it does, that air provides buoyancy > as the whale starts to dive from the surface, just when it isn't > needed, as it would have to be overcome by downward drive from the > tail flukes. A whale isn't built like a submarine, with a steel hull > to resist external pressure, but is flexible, allowing outside > pressures to be transmitted throughout its structure. So, at a few > atmospheres of pressure, buoyancy from any inhaled air has been > largely lost, and at a kilometre deep any air aboard is compressed to > only 1% of its original volume, so virtually none of that buoyancy > remains when it's at the bottom. Just where buoyancy might be most > useful, at take-off, to return to the surface, especially in an > emergency. It's hard to imagine that such a creature puts itself in > such danger as to be negatively buoyant at the bottom, and completely > reliant on tail-power to drive upwards out of any fix. > > It seems to me, then, that hydrostatically speaking, any air taken > aboard prior to the dive is disadvantageous. I learn, from Watson's > book, that the rib-cage is designed to collapse completely. Indeed, > that's absolutely essential, to allow any air in the lungs to compress > down to almost nothing. What I ask, is whether that collapse of the > ribs takes place deliberately before the dive, or during it? > > Evidence in the other direction comes from the first spout of a sperm > whale on surfacing, the first outward breath that gives rise to the > old cry of "there she blows"; according to accounts I have read it is > always more conspicuous than later blows. Does this first blow come > from air that's been taken down to depth and brought back again, or > does it actually follow a first, unseen, inward gasp of air? Does > anyone know? > > A related question is the purpose of that immense tank of spermaceti > oil, which takes up most of a sperm whale's enormous head. What's it > really for? Watson points to a possible function as a focussing > element in conjunction with the sperm whale's ultrasonic transducer, > but also mentions the possibility of adjusting buoyancy by regulating > its temperature, in relation the temperature variation with depth of > the sea water. It seems to me unlikely to be possible to change the > temperature of such a great mass of oil in a timescale that would be > useful over a 40-minute dive. However, certain oils and waxes do > change their volume (and therefore buoyancy) quite significantly as > they melt and solidify; indeed, it's likely that the thermostat in the > cooling circuit of your car engine will rely on such an effect. It's > clear that the oil, being lighter that water, could be useful anyway, > in compensating for the creature's weight of bone, to get the average > buoyancy right. Being right at the fore-end of a whale, it must tend > to make it tail-heavy, which may be useful in keeping up the blowhole > on the tip of its nose, out of the water, when it sleeps. > > Another question that arises relates to the whale's digestive system. > No doubt, a whale's digestion continues to act while it's at the > bottom, presumably evolving large quantities of methane and carbon > dioxide. Under such high pressure, that compressed gas may not provide > much volume or buoyancy at the bottom, and it seems likely that carbon > dioxide, under pressure, will dissolve into any watery fluid, just as > it does in a bottle of "pop" (at much lower pressures). But on return, > as the animal approaches the surface, any gases, that it hasn't > expelled while down below, will expand, and may also come out of > solution, as when you take the cap off a pop bottle. Any such increase > in volume will tend to be dramatic, as the surface is neared, doubling > in the final 30 feet! To avoid an explosion, does a whale produce a > gigantic fart, as it nears the surface? Whalers' accounts often refer > to the disgusting fishy smell that comes with a whale's first blow, > but I wonder whether the source of that smell may be not from the > blowhole, but from the other end, bubbling up as it surfaces. > > How, I wonder, has a sperm whale evolved in such a way as to solve > those problems presented by hydrostatics, Archimedes principle and the > Gas Laws? These are no more than musings, from my position of woeful > ignorance about whale physiology. No doubt they have been asked, and > answered, by those with a better understanding. If anyone can provide > those answers, or point me toward them, I will be grateful. > > George. > > contact George Huxtable at geo...---.u-net.com > or at +44 1865 820222 (from UK, 01865 820222) > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To unsubscribe, send email to NavListfirstname.lastname@example.org -~----------~----~----~----~------~----~------~--~---