Diving community & world diving guide.

Pelagic Thresher Sharks

The Pelagic Thresher shark (Alopias pelagicus) is the smallest of three species of Thresher sharks, the Common Thresher and the Big Eye Thresher being the other two, all are listed as vulnerable on the INUC Red List. While the number of Thresher sharks are on the decline they still are a common species of shark to be caught by commercial fisherman and in many places are still sought after as a game fish. They are seldom seen by divers however. The three species are all technically pelagic, in that they generally live in deep water. The Common and the Big Eye are known to visit shallow areas to feed and will at times stay for a while before dipping back into the deep waters. Threshers will also breach, a trait common with dolphins and whales but not common with sharks.  Generally they have no pattern to when they visit shallow waters, also Threshers are loners. They seldom travel with another of their species and are shy around divers. These are some of the reasons that Threshers are not as common a sight to divers.

The Pelagic Thresher lives in warm tropical waters and are migratory. They can be found in the tropical and semi-tropical waters of the Pacific and Indian Oceans including the Red Sea. Not as much is known about them as the other two species. The Pelagic Thresher seems to be the one that values its privacy the most. Individual sharks separate themselves from others with both horizontal and vertical distances. They seem to keep themselves at depths between 60 and 250 meters. While they are believed to be highly migratory, there has been no studies to conclude the range of individual sharks. Unlike other marine animals threshers migrate individually not in pods.

I was on the internet the other day searching for some information on dive watches and came up with a number of interesting comments on the web. Some of them made me wonder if I was really out of touch with diving, or do I just have a different viewpoint of “most” divers. My first shock was learning that I never owned a “serious” dive watch. A leading dive magazine had an article which included this quote, “a serious dive watch must be able to withstand 20 atm of pressure”. My first dive watch was a Citizen Hyper Aqualand that include a depth gauge and allowed the dive profile to be exported to my PC, but it was only rated for 100 meters or only 10 atm. I was very happy with the watch and never had any problems with it not being a “serious” dive watch.  For myself, I am happy diving at less than 4atm, so the 20 atm of pressure threshold is not that important to me.  Later in the article under a title of “For The Deep Diver”, they discussed a watch rated at 1,000 meters. To their credit they did mention that the diver would be crushed before the watch.

Another website told me what is the most popular watch for scuba divers and going to that company's website learned that the watch is “At home in the oceans, where it remains an indispensable instrument for every diver”  the watch being described is the $8,000 Rolex Oyster Perpetual Submariner. While a model of the submariner was available when I purchased my Aqualand, I never gave it any consideration. Another website had an article for the “5 Best Diving Watches”, the lowest price one was more expensive that the last new car I purchased and the most expensive was in the range of my house.

What could be better than to walk into the sea early in the morning with your dive gear and a picturesque view of Mount Fuji?  At Osezaki on the northwest tip of the Izu Peninsula south of Tokyo, this is exactly what you'll get if the weather is good.  Small and protected, this little bay is where divers from Tokyo go to get certified, get further training, or simply dive for fun.  It faces out into Suruga Bay, one of the deepest bays in Japan at around 2,500m with around 1,000 kinds of fish.  The view of Mount Fuji makes Osezaki Bay quite possibly the most scenic dive location in Japan. 

Crowded with divers in the summer, the bay is wide with several dive shops, restaurants and inns lining the big sandy beach.  It's also very sheltered and the sea is calm, which makes it ideal for training and a chance to put various skills into practice.  After signing in and arranging their dives with one of the many dive shops, divers pick a spot on the beach, lay out some picnic sheets and set up their equipment before walking into the water.  Once in, the underwater scenery begins with a stone grey pebbly and rocky bottom at the shoreline.  When visibility is good, this part is not to be dismissed because even at 2-3m of water you can see up close the seaweed sticking to the rocks and an array of fish darting about below.  The next feature is a pile of big rocks and concrete boulders, followed by a slight drop into sand, mud and muck to around 8m. From then on the bottom becomes sandy, muddy and mucky, spreading out towards the deeper depths.  With no more drop offs, divers are free to swim out into the unknown.  There's usually very little current, so diving conditions are normally not the least bit challenging but when it's crowded with divers stirring up the bottom or gathering around to photograph the next nudibranch, visibility can get pretty poor.

Like The Superhero's Sidekick- The Value Of A Wetsuit Is Often Overlooked

The wetsuit is often the first piece of dive equipment many divers purchases after they have their own  mask and fins. It is also very likely the least researched and understood purchase a new diver will make. While he will spend hours and hours researching on the internet and asking other divers about their BCD's and Regulators, when it comes the wetsuit it is likely just asking the instructor how thick should I get. The wetsuit helps your diving with three important functions: Thermal protection, Buoyancy and protection from scrape and cuts. In my view, the wetsuit is the most individualized item in your kit. Double that for the ladies as in many cases the style element is more important to them. While any wet suit that is a proper fit and appropriate for the water temperatures will do, a little research and clear thinking will get you a suit that is the best wetsuit for your diving. I have broken out a few points to consider.

Material

Wetsuits are made out of neoprene and the thickness determines the thermal properties. Neoprene is a rubber material injected with nitrogen during the manufacturing process. Back when I bought my first wetsuit 17 years ago, not only was that a true statement it was the entire statement. While still true it is a little more complicated. Wetsuit today are made from neoprene that in many cases have had other materials included in the manufacturing process. Spandex or similar material is often added to the neoprene to allow it to stretch and concur to your body better. These suits are generally easier to get on and off. While being worn they hug the body closer eliminating air pockets. The major manufacturers are all using this material. I would be cautious of getting a suit using standard neoprene as the new materials  are better suited for diving. Similarly related, get a suit that is designed for scuba diving. The grade of neoprene used in wetsuits for are sports are not able to withstand the pressure encounter while diving.

In early June, hoards of divers and non-divers arrive for an annual clean-up project aimed at removing debris and litter from the lake bottom and surrounding areas.  The lake is around 900 meters in altitude and goes down to a depth of around 138m.  Following a Mount Fuji eruption in the 9th century, a large prehistoric lake separated into three smaller ones that are still connected with each other by underground waterways.  LakeMotosuko is one of the three.

Before the clean up, divers can pick up a map from the organizers, which marks out areas with the most litter.  Once separated into pairs, they are then free to choose where they want to go and head right in.  The lake is caked in thick sediment (ash and silt) so stable buoyancy is crucial.  Kicking hard will stir up the sediment and worsen visibility, making things difficult not just for yourself but also for your buddy and in the worst case you can lose each other altogether.  Each buddy pair also has a mesh bag to put the litter into so the diver with the bag must remain suitably buoyant as his or her load becomes heavier.  

Upon descent, the underwater scenery begins with a slope of sediment and volcanic rocks, strewn with items like fish hooks, fishing lines, beer cans, plastic containers, hair ties and small boxes that once contained takeaway meals.  Usually the clean up is conducted at a maximum depth of around 9-10 metres.   A lot of debris is simply dumped into Lake Motosuko due to the camp sites, excursion boats and windsurfing facilities that are close by, while pollution from various water activities has made the lake cloudy so despite swimming carefully, visibility is not altogether great.  However, there is some life to be spotted such as weed-like plants and some large grey fish that are probably a type of trout, as rainbow and brown trout are known to inhabit the lake in addition to shrimp and other smaller fish.  At 16 degrees the water is cold.  Wearing a dry suit is the best option by far but it’s possible to cope in a 5-7mm wetsuit and a 3mm hood and vest underneath.  A hood and gloves are also essential.  Due to the altitude and low temperature, 30 minutes is the recommended time to stay underwater.

If you were to make a list of what you paid for the different items in your diving kit by price, the wetsuit would be far down on the list. Still it is a fairly decent amount, and most divers find that it is the first thing that they have to replace. Wetsuits generally need to be replaced because of three reasons: The suit loses it thermal and buoyancy properties, it sustains physical damage due to snags or rips,or the wetsuit shrinks around the stomach area due to too many after dive beers.

The second and third reason there is not much advice we can give, but there are a number of items we can do to prolong the life of a wet suit to keep it from losing its thermal and buoyancy properties.  Neoprene is the material most wetsuits are made of. It is a foam like synthetic rubber material that has had nitrogen injected into it during the manufacturing process. It often has a cloth backing for support. The trapped gas bubbles provides the buoyancy and thermal properties that the wetsuit is noted for. Over time these gas bubbles will “pop” escaping from the foam, as they do so the buoyancy and thermal abilities lessen. Certain actions increases the process while others will minimize the effects.

Tips For A Long Life Wetsuit

  ▪  When purchasing your first wetsuit insure you get one made for diving, looks can be deceiving. A wetsuit made for surfers may look very similar, however, it will have considerable more gas in the neoprene. This will help the surfer stay warmer per each mm of material and have greater buoyancy. The more gas in the suit will make it more fragile and under pressure will very quickly breakdown. A suit designed for swimmers has even more gas and may not even last through your open water training.

  ▪  Shower after each use. Salt from the water as well as salt from your skin and body oils will speed up the natural process of the neoprene breaking down. The easiest way to help eliminate the salt is wear your suit in the shower. Your wetsuit doe not like hot water.  While an after dive hot shower may feel great your first shower should at best be warm for circulation reasons. So wear your suit when you start your shower and get some of the salt off it as you get the salt out of your hair. The shampoo is okay for your suit. If you are finish diving for the day, then remove the suit, turn it inside out, rinse and place in a tub of clean water. Let it soak for thirty minutes, plenty of time for you to finish your shower and dry off.