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Thread: Thresher sharks and the new ISC 4th cell

  1. #1
    Nicholas Smith Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo's Avatar
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    Thresher sharks and the new ISC 4th cell

    I completed my Mod 3 on Sunday at Ohshima, just outside Tokyo Bay, in a dive that I'll remember for a long time.


    The bright summer sun, which had pounded us for a month, was just starting to abate. Still, sweat was pouring down my face and streaming off my nose in a steady trickle as I struggled to attach my sidemounts to recalcitrant D-rings. My buddy was already in the water and waiting at the bottom, enjoying the cool relief from the summer. I finally heard the reassuring snap of metal on metal and jumped. The surface may have registered a perfect 26 degrees, but it felt like an icy slap in the face for my overheated body.

    The clash of the tropical ‘Kuroshio’ current from the South and the bracingly cold, mineral-rich ‘Oyashio’ from the North made for a thick pea-green broth for the first 20 metres, which cut visibility right back to 3 metres. As we passed 25 metres, we hit a sharp thermocline, which took the temperature down to 16 degrees. I had elected to wear a couple of layers of 5mm wetsuit instead of diving dry, and though my buddies in dry suits moaned like a Women’s Institute meeting that had run out of wool, the cool was keeping me sharp and focussed. From then on, the kelp forest gave way to coral: tall thick trunks of white soft coral and large black fans of hard coral.

    Where we’d started with a sharp slope on our right side, that was soon mirrored by another to our left. Soon we were on a wide runway, which lazily slipped away to 85m, then more quickly fell away to 200. The path was unmistakable, bounded on both sides by a riot of colour from the hanging gardens of coral on either side. A tight mat of fish fussed over the coral like a swarm of nectar-hungry bees. By the time we passed the 40m mark, visibility was good enough to see divers ahead drop through the 100m mark. Everything was tropical bar the temperature: the visibility, the coral, the fish life and the colour.

    I had used the ISC fourth cell for my VR3 for the first time the previous day. It had measured the PO2 worryingly high for most of the descent, compared to the handsets, and I’d instructed the computer to ignore it. This time I was intent on getting it to work with a different way of calibrating: thus far the effort was paying off, but I was watching it like a hawk and comparing the result with my handsets.

    As we hit 85m, my tongue started to sizzle like in my days as a Judo player when a strangle was really starting to bite on my carotids. Then it was a sign I was seconds away from losing consciousness. I slid a hand under my tight hood, which I’d cast back off my head, but it gave little relief. Whether I was seeing flashes of light or dreamt them, I eased back the PO2 to 1.2 for peace of mind. This I wasn’t going to miss.

    How like a Japanese to have such an encyclopaedic knowledge of rare fish: my buddy, Tanaka-san, pointed out a rainbow-coloured tosanoides flavofasciatus, which is never seen above 50m.
    http://www.izuzuki.com/Zukan/Fish/hata/kishimaHD.html

    The entertainment on this dive, however, was reserved for the ascent. As we passed 50m, my buddy pointed out a guitar fish half buried in the sand – like a stingray, but with a row of fins on its back. As he stroked its back and made to grab for it, it exploded off the seafloor, then lazily settled a few metres away. Instinctively it knew we weren’t stopping. Shark number one.

    As we stopped for a bubble stop at 30m, I started doing a 360 to pass the time. Barely had I turned when I spotted it: the massive rippling muscle and distinctive whip tail of a thresher shark. It was swimming determinedly along a contour line around 33m, perpendicular to our path, just below us. It was well off to my left when I spotted it, giving us plenty of time to watch it at leisure. Entranced, there was no way I was taking my eye off if, but my buddy evidently heard my whoop as he added his yee-hah to my cheers. It saw us and judged no threat from two such fragile divers, though doubtless it had sensed us well before it saw us, and was intrigued. All threshers are listed as vulnerable to extinction, and are especially exciting for divers, as they generally steer well away from coastal areas, preferring the deep open ocean. This was a thintail thresher, or Nitari as the Japanese call it: it’s the smallest of the threshers, at around 3m. The tail is used as a fearsome whip to stun prey, though their prey is juvenile tuna and mackerel, certainly not man. Shark number two. We just hung there whooping and punching the air as it disappeared into the gloom.

    From 30 to 10m we generally annoyed the local wildlife. Tanaka-san amused himself catching porcupinefish, which blew themselves up into big, spiked footballs – albeit with those ridiculous bulging eyes and fat-boy panting mouths breaking the illusion of a heavily armed poison fish. Actually, its skin and intestines are infused with the lethal tetrodotoxin nerve poison, so it's not much of a meal.

    I amused myself with poking my head under every boulder and into every nook and cranny on the ascent. The Meg doesn’t seem to like extended periods in the head-straight-down position, and was croaking asthmatically. As I poked my head beneath one boulder a small, scared Japanese bullhead shark stared back at me.
    http://ja.wikipedia.org/wiki/%E3%83%8D%E3%82%B3%E3%82%B6%E3%83%A1
    These primative heterodonts have been around since the early Jurassic period. This one has a leopard skin pattern, a distinctive toothless-looking mouth and a sharp knitting needle defence forward of its first dorsal fin. It was the size of a small child. They’re not especially rare, but it is a pleasure to have 10 minutes watching one at leisure. I doubt it was enjoying the experience as much as we did, as it backed up into the fissure – though without showing particular unease. Shark number three.

    The fourth cell had proved itself well. Much of the time it was precisely in line with the Meg’s handsets. I’d taken care to calibrate the two handsets and the fourth cell simultaneously, to ensure the conditions were the same. The main adjustment I’d made was to switch the oxygen manual add to the diluent side, to prevent the fourth cell spiking. The strategy worked well and was easier to manage than I’d feared.

    I took the hydrofoil back to Tokyo afterwards, taking a little over an hour into the heart of the city. Past the bustle of leviathan containerships and tankers supplying the massive megalopolis, past the petrochemical and steel plants and the giant statue of Kwannon, goddess of mercy, who looks down benevolently on Tokyo Bay through half-closed eyes. Past a forest of vast loading cranes, under the Rainbow Bridge and into the quiet hum of an ordered city of accountants and computer salesman where nothing dramatic ever really seems to happen. I’d sent my mound of equipment ahead for just $10, so all that remained was to take a 10-minute taxi ride home. Who would know that such an adventure playground exists under 90 minutes from central Tokyo?
    Last edited by Abbo; 28th August 2007 at 07:22.

  2. #2
    RBW Member tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining's Avatar
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    Re: Thresher sharks and the new ISC 4th cell

    Hi Nick

    Thanks for the Pm, It sounds like you had good fun during your course and that you like the 4th cell, after all that trouble getting it I'm glad you got it to work, mines on its way back from the factory so should get to use it on a mixed gas course next week.

    By all means come and join me in the new year for some of our deeper wreck dives, you may also wish to come and lend a hand as support diver on some deep dives I am doing in January here in Thailand.

    Take care and dive safe.

  3. #3
    Nicholas Smith Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo's Avatar
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    Megalodon

    Re: Thresher sharks and the new ISC 4th cell

    Quote Originally Posted by tecdivertraining  View Original Post
    Hi Nick

    Thanks for the Pm, It sounds like you had good fun during your course and that you like the 4th cell, after all that trouble getting it I'm glad you got it to work, mines on its way back from the factory so should get to use it on a mixed gas course next week.

    By all means come and join me in the new year for some of our deeper wreck dives, you may also wish to come and lend a hand as support diver on some deep dives I am doing in January here in Thailand.

    Take care and dive safe.
    Cheers, I would really enjoy that. I'll spin you a note about dates when I have my plans better worked out.

    For years I had been going overseas to do trimix dives, believing that there was nobody doing that kind of thing in Japan because of the very restrictive laws on handling of high pressure gases. There appears to be a small, tight knit group of people mixing their own gases and regularly doing 100m dives. A couple of the divers are members of this forum, but almost never log on and never post. Tanaka-san is an amazing find as he is immensely knowlegeable and a true gent. The whole diving situation is complicated by the protection racket run by the fishermen, who have been allowed to believe they own the sea, and everyone else needs to pay to use it. The building of Tokyo's new airport has been set back a couple of years because of the need to negotiate with them. The effort is worth it, though, as the diving can be simply stunning, and can be got to within 90 minutes from central Tokyo.

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