SCUBA Diving News

Trevallys are large silvery fishes with forked tails.
They are fast-swiming predators of the waters above the
reef and in the open sea.

The species we are concentrating on today, the Bluefin
Trevally, is found in the Red Sea and Pacific Ocean. It
is distinctively coloured, being the only trevally with
electric blue fins and blue speckles on a gold or green
background.

This fish can be as large as 1 metre, but you normally
see individuals smaller than this. They range from the
shallows to the depths, usually singly but you may see
a trevally small school.

Bluefin Trevally are currently being trialled for
aquaculture in the Pacific. But if eating this fish
beware of large specimens: they become toxic when over
50 cm.

The fish feeds on other fish and sometimes crustaceans.
It launches high-speed attacks, typical of large
transient predators. However, when feeding on spawning
fish it also ambushes its prey, attacking from a hiding
place. This is unusual in such a fast-swimming fish.
During ambush hunting, it adopts a dark coloration and
defends a section of the reef.

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When the genetic make-up of globally distributed marine species are studied, it is often found that there are significant differences between populations. The differences may be so great that what was thought to be one species is actually two.

A recent study into scalloped hammerhead sharks, Sphyrna lewini, shows that although the fish in the Atlantic and Indo-Pacific populations appear identical, genetically they are different. The scalloped hammerhead in the western north Atlantic is actually a new, cryptic, species.

The study concludes that effective management of large coastal shark species should incorporate this discovery. It indicates that the cryptic scalloped hammerhead is less abundant than S. lewini, making it potentially more susceptible to fishery pressure.

Journal Reference: Marine Biology, Volume 148, Issue 5, Mar 2006


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Orange-face butterflyfish, Chaetondon larvatus, are common in the central Red Sea from Hurghada south. They feed exclusively on table coral (Acropora) where they are seen in pairs from 4 to 12 m.

New research indicates that these butterfly fish grow quickly in their first year, but that growth decreases in their second and third years. When fish get to three years they stop growing and reach their maximum size of 12 cm. There is no difference in the growth of males and females

Journal Reference: Marine Biology, Volume 148, Issue 5, Mar 2006


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To win this great prize, worth $66.55, just subscribe to the free SCUBA News (ISSN 1476-8011) then e-mail SCUBA News with "Beautiful Oceans" as the subject line.



This on-line course provides a good introduction
to coral reefs. However, it also gives much
information to interest experienced reef
watchers. I certainly learned things from it,
and I've been diving for over 20 years, have
a biology degree and regularly consult half a
library of sea-life and marine
biology books. It is also refreshing to
see a project with such a commitment to
preserving the marine environment that they
donate 10% of their profits to marine conservation.

Don't be put off by the term "course". You don't
have to attend any virtual lectures and one of the
main aims is to be fun. You are given access to
the web site where you can see marine videos and
read the course materials. You can work through
at your own pace, and if you need any help, or
want to talk to other students, you use their web
forum. Optionally, you can get the course book
as a pdf file or printed manual.

The manual is well-designed, clear to read with
a photograph or diagram on nearly every page.
Unlike other marine biology texts, it is
specifically aimed at divers but is not just an
identification guide. It instead helps you
understand the layout of a reef and why animals
and plants that live in each reef zone do so.
Organisms are not discussed in isolation but
relative to their environment and behaviour.
A full index would have been helpful though.

Throughout the course there are boxed "quick
quizzes" which reinforce the message given in
the previous pages. Other asides include
"Science Facts" and "Did you know?" which were
some of my favourite bits of information. For
example, "...The plural of fish is 'fishes'
when referring to a group that comprises more
than one species, but 'fish' when referring to
a group that comprises just one species."

The course doesn't try to give a comprehensive
account of a large number of animals. If this
is what you are looking for then you would be
better off buying an identification guide of
the marine life of your diving destination.
What it does do is concentrate on just a few
typical organisms of each coral reef zone:
shore, reef flats, drop-off, etc. It teaches
how to relate the animal's behaviour or
structure to the conditions in which it lives.

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As part of Earth Day 2006, which is taking place on Saturday 22nd April, the Red Sea environmental group HEPCA is is organising Beach and Underwater Clean-ups in El Gouna, Safaga, Marsa Alam, Taba and Hurghada at Magawish Island.

For more information on how you can help with the clean-up contact HEPCA at info@hepca.com

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Whale sharks (Rhincodon typus) aggregate seasonally (March-June) to feed in coastal waters off Ningaloo Reef, Western Australia. According to research published in the journal Marine Biology, the sharks then travel northeast into the Indian Ocean. They use both inshore and offshore habitats and frequently travel vertically up and down, occasionally to a depth of at least 980 m. Vertical migration over a 24-hour period, and twilight descents, were evident in the depth records. The sharks' experienced ambient temperatures ranging between 4.2 and 28.7°C and encountered gradients of up to 20.8°C on dives.

Journal Reference: Marine Biology, Volume 148, Issue 5, Mar 2006

For more on the sharks at Ningaloo Reef see http://scubatravel.co.uk/australia/ningalooshark.html


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An international team of scientists are working at a rapid pace to study environmental conditions behind the fast-acting and widespread coral bleaching currently plaguing Australia's Great Barrier Reef. NASA's satellite data supply scientists with near-real-time sea surface temperature and ocean colour data to give them faster than ever insight into the impact coral bleaching can have on global ecology.

Australia's Great Barrier Reef is a massive marine habitat system made up of 2,900 reefs spanning over 600 continental islands.

Scientists use ocean temperatures and ocean "colour" as indicators of what is happening with coral. Coral is very temperature sensitive. Ocean "colour," or the concentration of chlorophyll in ocean plants, is important because it informs scientists about changes in the ocean's biological productivity. NASA satellites capture both temperature and colour data from their space-based view of the coral reefs.

Bleaching occurs when warmer than tolerable temperatures force corals to cast out the tiny algae that help the coral thrive and give them their color. Without these algae, the corals turn white and eventually die, if the condition persists for too long.

NASA offer a free, Internet-based data distribution system that enables researchers around the globe to customize requests and receive ocean color data and sea surface temperature data.


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The tiny Republic of Kiribati, in the Pacific, has created the world's third-largest marine reserve.

The Phoenix Islands Protected Area bans commercial fishing to protect more than 120 species of coral and 520 species of fish inside its 184,700 sq km (73,800 sq miles). It is the world's first marine park with deep-sea habitat, including underwater mountains.

Kiribati is located in the central Pacific between Hawaii and Fiji. It comprises 33 islands stretching across several hundred miles.

Source: ENN

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