Newsletter - 03/05/2001

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The Loggerhead

The Official newsletter for The African Diving Experience
www.africandiving.com
Volume 6 Date: 04/05/2001

We hope you enjoy the May issue of our monthly newsletter.

Index:

<1) What's happening on the African Diving Experience
<2) Shark of the month - Tiger Shark
<3) Tiger Shark Feeding on Aliwal Shoal, good or bad? We want to hear from you.
<4) Book Review - Secrets of the Ocean Realm by Michelle and Howard Hall
<5) Fish identification tips - Butterflyfish
<6) Equipment tips - Computer Security
<7) Website of the month
<8) Diving emergencies - How to manage Jellyfish and Blue-bottle stings

1. What's happening on the African Diving Experience

As we are growing bit by bit, here are a few of the latest additions to the African Diving Experience:

Tjaart has just finished compiling information on Aliwal Shoal and this has been added to our dive site list. Be sure to have a look at that. This magnificent dive spot will soon be followed by Protea Banks, which will be done with the help of Roland Mauz from African Dive Adventures. Other sites that will soon featured is Wondergat and hopefully a few sites in the Cape for all those who love diving in the cold water.

Be sure to vote in our opinion poll on shark feeding at Aliwal Shoal. For more information on this have a look at section 3 of this newsletter.

We would like to thank you for your continued support in helping us obtain information. If there is anything interresting happening in your area or anything else you would like to make us aware off, we would love to hear from you, so that we can help spread the word.

If you are in need of new scuba diving equipment be sure to start shopping for specials. The winter is just around the corner and this is the time of year when most suppliers give discounts on their products due to the lack of activity in sales. So just hold on for a month or so, till the specials hit the shops.

Interrested in a banner exchange? Do contact us at the following e-mailwillem@dpa-training.com

2. Shark of the month - Tiger Shark
Class: Chondrichthyes (Cartilaginous fish)
Sub class: Elasmobranchii (Sharks and rays)
Order: Carcharhiniformes (Ground sharks)
Family: Carcharhinidae (Requiem sharks)
Genus: Galeocerdo cuvieri (Tiger shark)

The Tiger shark is a relatively common resident along our east coast and has the distinct features of a requiem shark. It has a short, blunt snout, long upper labial furrows, and a big mouth with large, saw-edged, cockscomb-shaped teeth. Spiracles present. The Tiger shark has a dark grey colour with vertical tiger-stripe markings that can fade or be obsolete in adults. It's average size is about 400cm to 650cm with a maximum length of about 800cm. This species lives worldwide in coastal and pelagic waters ranging from the surface to a depth of 140m (up to 350m). It has a wide tolerance for different marine habitats, but seems to prefer turbid waters, occuring on or adjacent to the continental and insular shelves. It is often found in river estuaries, close inshore and in coral atolls and lagoons. Tiger sharks are nocturnal and shows cycles of inshore movement at night and retreat to deeper water during daytime. Tiger sharks are mainly solitary.

Probably the biggest variety of food of all sharks. They feed on fishes, sharks, turtles, birds, invertebrates and even garbage. Such a wide spectrum has often been interpreted as being an unspecialized feeder. However this could reflect a highly specialized adaptation to their biology. Tiger sharks are one of the largest sharks of all and need a lot of food. Their uniquely shaped teeth are highly evolved and therefore allow them to feed on different food items, preventing potential food shortages that could arise with selective feeding. As it has such a large variety of food it might be considered potentially dangerous to humans althoug it is more likelly to feed on humans already dead from other causes.

Reproduction is ovoviviparous with between 10 and 80 pups per litter, during summer. The size of pups at birth is between 50cm and 75cm. The pups are very slender and look different than the adults, different markings are present too.This large omnivorous shark is common world-wide in tropical and warm-temperate coastal waters. It is a relatively fast growing and fecund species, and caught regularly in target and non-target fisheries. There is evidence of declines for several populations where they have been heavily fished. Continued demand, especially for the valuable fins, may result in further declines in the future but this species can withstand a higher level of fishing activity than many other species of shark. Additionally, juvenile survivorship increases where adult tiger shark populations have been depleted by fisheries and predation of young is lessened.

Source: Smiths' Sea Fishes (1986), Sharks and rays of Southern Africa,http:/www.fishbase.org , http://www.shark.ch and http://www.sharkinfo.ch

3. Tiger Shark Feeding on Aliwal Shoal, good or bad? We want to hear from you.

Tiger Shark feeding is being undertaken on Aliwal Shoal, by several dive operators, to attract divers and sharks a like. As far as we understand a bit of chuming is done to attract the sharks. Divers then go down to the ocean floor where bait is placed on the bottom and divers awaits the arrival of these magnificent creatures.

There are a few arguments doing the rounds on this issue. One that we have picked up says that doing a dive such as this gives one a new image of these amazing creatures and will discard all myths of the fiercesome predator of the ocean as seen in the Jaws movies. The other side to the argument is that if the feeding continues unregulated and uncontrolled on a regular basis the sharks will start to associate divers with food. If this starts to happen we will loose one of the incredible diving spots around our coast line and who would want that to happen.

We want to hear your opinion on this issue. For this we have created a voting form at the following url: http://www.delportdupreez.co.za/diving/form.htm or you can find a link to it on our home page at http://www.africandiving.com
We will update the page as we recieve responses. You can also vote by sending an e-mail to
willem@dpa-training.com stating whether you agree with the feeding or not and any comments you would like to add. We will also keep you updated on the results as well as interresting arguments on this issue, in the following issues of this newsletter.

Let us know what you think about this issue.

4. Book Review - Secrets of the Ocean Realm by Michelle and Howard Hall

This coffee table book is about the exploration done by Michelle and Howard Hall. This married couple has dived in almost every destination in the world and even has their own TV show (it was on SABC 3 in Dec/Jan of 1999/2000). This book features some wonderful photographs on the kelp forests of California, sharks of the seas and a few particularly stunning photographs of the authors diving with Grey whales. This is one of those books which makes you want to quit your day job, become a beach bum and dive for the rest of your life.

New Holland publishes this book.

5. Fish identification tips - Butterflyfish

1. With very few exceptions ALL Butterflyfish have a black line through their eye. Possible reason for this is that is disguises the position of the eye, preventing damage to the eye from some fishes which could attack the eye. ie. Piano Blennies, Sabretooth Blennies, Triggers etc. This can also be confusing to a potential predator in that the Butterfly's direction of
escape is less predictable.

2. They all are laterally compressed i.e. a narrow but deep fish. This also allows escape from predators by day, and enables the fish to sleep in small cracks and recesses at night.

3. To a greater or lesser extent they all have an elongated snout enabling them to feed within the narrow recesses on the reef.

4. Their diet varies according to the species, and ranges from plankton with the Bristletooth Butterfly, exclusively coral polyps with the Maypole Butterfly, and algae and inverterbrates with most other species.

Supplied by Reefteach in Sodwana Bay (http://www.reefteach.co.za)

6. Equipment tips - Computer Security

Losing a wrist-mounted computer under water is expensive and could be downright dangerous on a decompression dive. So how can you secure it to your wrist in case of strap failure? Punch a small hole in the centre of a wide portion of the "buckle" half of the computer strap - usually it's the part with the line of holes in that breaks. Thread a wrist-lanyard from the dive shop or from your spares box through the hole. These come in a range of colours and have a spring-loaded plastic cord lock to tighten them up in use. Once your wet- or drysuit is on, put the lanyard over your wrist before strapping the computer on properly. Should the strap break, the lanyard will stop several thousand randís worth of technology disappearing into the depths

Source: http://www.scubadiving.com

7. Website of the month
The following sites are our choice for websites of the month:

http://www.shark.ch or http://www.sharkinfo.ch

If you need information about sharks, this is the place to go. They have a wide variety of sharks in their shark database and can even adopt a shark to assist in funding their research. The site is availible in English and German. The site is packed full of information and a must to find everything you need to know about these magnificent creatures.

8. Diving emergencies - How to manage Jellyfish and Blue-bottle stings

  • Get the victim out of the water as soon as possible
  • If the stinger is a sea-wasp, apply a tourniquet, rope, string or any ligature above the sting if it is on the arm or leg.
  • Do not use a tourniquet for other blue-bottles or jellyfish. If available, aliminium sulphate solution spray (e.g. stingos) is helpfull in alleviating pain.
  • Pour vinigar over the stings and pieces of tentacle. If unavailable, alcohol or any spirits will help.
  • This inactivates the venom and must be done before any attempt is made to remove the tentacles, still loaded with active nematocysts, which will worsen the condition of the diver and even poisen the rescuer.
  • Scrape of the inactivated tenticles with a knife.
  • Drying them with powder makes this easier.
  • Apply more vinegar as a poultice.
  • Summon medical aid if the stinger was a sea-wasp pr if there is now rapid improvement after vinegar treatment.
  • Be alert for the development of respitory failure. Rescue breathing or CPR must be given if needed.
  • Transfer to hospital if shock is stabilised.
  • Do not forget to release the tourniquet (maximum 2 hours)

Source: How to manage diving problems by Allan Kayle

Divers do it deeper.
Willem du Preez and Tjaart de Beer
Web masters for the African Diving Experience

This newsletter was sponsored by:
+ Dpa Training - Computer training at your fingertips.
Special Thanks to the following people and company's for helping us obtain information for our website.
 +
Mseni Lodge and Amoray diving - Sodwana Bay
 +
Reefteach - Sodwana Bay
 +
Ocean Divers Pretoria
 +
Andy Cobb Eco Diving
 +
The East Coast Fish-Watch Project
 +
African Dive Adventures - Protea Banks

Updated on: 06/03/2003