SCUBA Diving News

Bluefin tuna populations have declined alarmingly over the past few decades due to overfishing fuelled by an increasingly expensive industry.

A new WWF report shows that the international fleets hunting this species to extinction have twice the fishing capacity of current quotas and are netting more than three and a half times the catch levels recommended by scientists to avoid stock collapse.

"WWF's new report uncovers the absurdity of a system long out of control, where hundreds of hi-tech boats are racing to catch a handful of fish," says Dr Sergi Tudela, Head of Fisheries at WWF Mediterranean.

"It is crazy - the numerous new fleets are so modern and costly that fishermen are forced to fish illegally just to survive - and worse still they are fishing themselves out of a job," added Tudela.

To keep fishing capacity within the 2008 legal catch limits imposed by the International Commission for the Conservation of Atlantic Tunas (ICCAT), the Mediterranean fleet would need to shed 229 vessels - almost a third of the current 617-vessel fleet. Reducing fishing effort to scientifically recommended levels would require the decommissioning of 283 vessels.

WWF is calling on concerned countries to dramatically reduce capacity in this fishery as a matter of urgency ahead of the 2008 fishing season that starts at the end of April.

WWF also urges ICCAT, the body tasked with sustainably managing the fishery, to take a lead in proposing radical solutions. Until the fishery is under control and sustainably managed, WWF continues to advocate a fishing ban - and to applaud responsible retailers, restaurants, chefs and consumer groups who are boycotting Mediterranean bluefin in increasing numbers.

"The fishery is unsustainable in every way - economically, socially, and ecologically. When will the situation be brought under control? The time to act is now - while there are still bluefin tuna to save in the Mediterranean," Tudela concluded.

What can you do? If you want to buy a tin of tuna off the supermarket shelf don’t worry – you almost never find bluefin tuna in a tin. Most tinned tuna is yellowfin or skipjack. If you buy fresh tuna ask your fishmonger whether the tuna is Atlantic bluefin, and whether it comes from the Mediterranean. If it does come from the Med, don't buy it. And at the Japanese restaurant check where they source the Atlantic bluefin tuna. If it is from the Mediterranean, avoid it.

Note: the tuna caught in the Med is called "Atlantic Bluefin Tuna" (Thunnus thynnus). Don't think that because it has the word Atlantic in the name that means it was caught there.

Further Reading:
Bluefin tuna in crisis
Race for the last bluefin: Capacity of the purse seine fleet targeting bluefin tuna in the Mediterranean

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Labels: fish, Mediterranean

Is it important that global warming turns fish deaf? Yes. For coral reef fish, sound is vital for them to judge where to settle down and live.

After hatching, reef fish larvae are dispersed by ocean currents for a few weeks. The larval fish must then find their way back to a suitable reef to make their home.

It's thought that the young fish home in on high-frequency noises. Coral reefs are extremely noisy environments, with the crackle of snapping shrimps and the chatter of fish set against a backdrop of wind, rain and surf. Sound carries well underwater, and most fish have great hearing.

Global warming and more acidic oceans, though, can cause fish to be born with deformed earbones. Reasearchers at the Australian Institute of Marine Science in Townsville and the University of Edinburgh, suspected that it might be harder for these fish to pinpoint the origin of a sound, increasing the chance they would get lost in the ocean. And, indeed, their results show that this is so.

Journal References and Further Reading:
Proceedings of the Royal Society, Volume 275, Number 1634 / March 07, 2008
Animal Behaviour, doi:10.1016/j.anbehav.2007.11.004
SOUND: The essential navigation cue for young reef fishes to find their way home


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Labels: coral reef, environment, fish, marine biology, research, sealife

Fishermen are always looking for a tasty catch - but it is the fish that have a natural advantage when it comes to spotting dinner, according to new research from The University of Manchester.

In a paper published this month in the Biophysical Journal, Dr Nicholas Roberts reports how individual light sensitive cells within the retina of goldfish are able to detect polarised light.

It's believed this type of polarisation vision improves visual contrast and can help an animal catch its prey more easily.

Researchers say this latest research is important because it is the first direct experimental evidence of a polarisation detection mechanism in any normal vertebrate eye.

Dr Roberts says: "Vision is the primary sense of many animals and the way they see their world is of fundamental importance to understanding aspects of their behaviour.

"Numerous animals have amazing visual abilities, which allow them to see the world in very different ways. One such ability is polarisation vision.

"Just as fishermen wear Polaroid sunglasses to help improve contrast, many different animals - including fish - have evolved to do the very same thing without the need of sunglasses. It is a surprisingly common ability throughout the animal kingdom."

Journal Reference: Biophys J. 2007 Nov 1;93(9):3241-8.

Photo Credit:US National Oceanic and Atmospheric Administration

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Labels: fish, research, sealife

Blue Tangs are often found roaming the reef, in search of their favourite food - algae. They are surgeonfish which may appear either singly or in large schools, which can contain hundreds of individuals.

The name surgeonfish comes from the defensive spines located on the caudal peduncle (the part of the fish between the tail and the rest of the body) which are as sharp as a surgeon's scalpel. They are herbivorous, eating plants and algae, so their spines are used only for defense.

Blue Tangs are sometimes found schooling with other members of the surgeonfish family. These schools form around dusk when nocturnal predators, such as moray eels, begin to hunt. These schools provoke an aggressive reaction from the smaller damselfishes defending patches of algae.

The true Blue Tang is Acanthurus coeruleus, which found in the Caribbean Sea. Other fish are also sometimes referred to as Blue Tang. In the Red Sea, for example, there is Zebrasoma xanthurum, more properly known as Yellowtail Tang. Also in the Indo-Pacific masquerading as Blue Tang is the Palette Surgeon, Paracanthurus hepatus; familiar if you've watched the "Finding Nemo" film.

As you might expect, blue tangs are largely blue. The Caribbean Blue Tang, Acanthurus coeruleus, has a bright yellow or white spine. It lives between 3 and 28 m on rocky or coral reefs. As it is unafraid of divers you can usually get quite close to it.

The Blue Tang, and other surgeonfish, are important on a shallow coral reef because they help keep the algae in check. Without them the algae would grow so fast that coral larvae settling and trying to make a start on the reef would soon be overgrown.

Further reading:

Beautiful Oceans Coral Reef Architecture & Organisms,
The Blue Planet

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Labels: fish, marine biology, sealife

Fish use the threat of punishment to keep would-be jumpers in the mating queue firmly in line and the social order stable, a new study led has found.

Studying small goby fish at Lizard Island on Australia's Great Barrier Reef, Dr Marian Wong and colleagues have shown the threat of expulsion from the group acts as a powerful deterrent to keep subordinate fish from challenging those more dominant than themselves.

In fact the subordinate fish deliberately diet - or starve themselves - in order to remain smaller than their superiors and so present no threat that might lead to their being cast out, and perishing as a result.

"Many animals have social queues in which the smaller members wait their turn before they can mate. We wanted to find out how they maintain stability in a situation where you'd expect there would be a lot of competition," says Dr Wong.

In the case of the gobies, only the top male and top female mate, and all the other females have to wait their turn in a queue based on their size - the fishy equivalent of the barnyard pecking order.

Dr Wong found that each fish has a size difference of about 5 per cent from the one above and the one below it in the queue. If the difference in size decreases below this threshold, a challenge is on as the junior fish tries to jump the mating queue - and the superior one responds by trying to drive it out of the group.

Her fascinating discovery is that, in order to avoid constant fights and keep the social order stable, the fish seem to accept the threat of punishment - and adjust their own size in order to avoid presenting a challenge to the one above them.

"Social hierarchies are very stable in these fish and in practice challenges and expulsions are extremely rare - probably because expulsion from the group and the coral reef it occupies means almost certain death to the loser.

"It is clear the fish accept the threat of punishment and co-operate as a way of maintaining their social order - and that's not so very different to how humans and other animals behave."

Dr Wong said that experimentally it has always proved extremely difficult to demonstrate how higher animals, such as apes, use punishment to control subordinates and discourage anti-social activity because of the difficulty in observing and interpreting their behaviour.

In the case of the gobies the effect is much more apparent because they seek to maintain a particular size ratio relative to the fish above them in the queue, in order not to provoke a conflict.

"The gobies have shed new light on our understanding of how social stability is maintained in animals," she says.

The paper entitled "The threat of punishment enforces peaceful cooperation and stabilizes queues in a coral-reef fish" was co-authored with Dr Philip Munday and Professor Geoff Jones of CoECRS and Dr Peter Buston of the Biological Station of Doñana, Spain. It appears in Proceedings of the Royal Society B, 274.

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Labels: environment, fish, marine biology, research, sealife

Egypt have cancelled a decree which allowed companies to collect reef fish and export them to Europe and other markets .

According to the Hurghada Environmental Protection and Conservation Association (HEPCA), the previous decision had a devastating effect on nature and on the coral reef condition in the whole area. HEPCA launched a huge campaign against this decision and lobbied with other agencies, enthusiastic individuals, and major media representatives.

As a result of the decision HEPCA have ceased legal actions against the Minister's old decree.

Further Reading: http://www.hepca.com/

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Labels: environment, fish, Red Sea, sealife

Seahorses are delightful to spot, curling onto sponges, coral or sea grass. They range in size from the tiny Hippocampus denise which is just 16 mm, to the 35 cm (1 foot) Pacific seahorse.

Seahorses are not easily seen as they blend in with their surroundings. They can change skin colour to match their environment and even grow skin filaments to imitate seaweed or sea grass growths.

The seahorse is remarkable as the male becomes pregnant. The female seahorse deposits her eggs into the male's pouch where they are fertilised. The eggs remain in the male's pouch until they hatch, when the male gives birth to tiny seahorses. The time to hatching takes between 10 days and four weeks, depending on the species and water temperature. Male seahorses are often pregnant for as many as 7 months in the year. The natural lifespan of seahorses is not known, but believed to be from one year for small species to five years for a larger species.

Seahorses are opportunistic predators, sitting and waiting until prey come close enough and then sucking them rapidly from the water with their long snouts. Their eyes move independently of each other, maximizing their search area. They will eat anything small enough to fit into their mouths

The name hippocampus comes from the ancient Greek, loosely hippos meaning horse and campus meaning sea monster. Hippocampi refer to the mythical creatures on which the sea gods rode. Early zoologists initially classified seahorses as insects not fish.

All seahorses for which data is available are listed on the IUCN Red List of Threatened Species as either Vulnerable or Endangered. This means they are facing a high risk of extinction in the wild. There are many reasons for their vulnerability. Seahorses are exploited for traditional medicines and the aquarium trade. Male brooding means that young depend on parental survival for far longer than in most fish. Many species are monogamous so widowed animals don't reproduce until they have found a new partner. Their low population density and low mobility means that this can take some time. Habitat degradation is also a real threat to populations as they mainly inhabit shallow, coastal areas, which are highly influenced by human activities.

Further Reading

IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 20 April 2007.

Project Seahorse - http://seahorse.fisheries.ubc.ca/

Seahorse photo taken in Dominica, copyright Harald Jahn.

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Labels: Caribbean, Dominica, fish, seahorse, sealife

The Geometric moray has a long body with one continuous fin along its back. Like other morays it has elongated nostrils. You can easily recognise it by the dashed lines patterning its face, as shown in our photo.

Morays live in holes and generally hunt by night, locating
their prey by their excellent sense of smell. Moving with
snake-like motions, they are extremely quick. When at rest
you may see them rhythmically opening and closing their
mouths. They do this to maintain a respiratory current
past the gills.

The Geometric moray is the most common eel in the Red Sea.
It is also found throughout the Western Indian Ocean:
Madagascar, Mauritius, Oman, Mozambique, Seychelles,
South Africa, etc.

Quite small for a moray, the Geometric moray reaches
65 cm long. It lives at depths down to 40 m on coral and
rocky reefs. You may see groups of up to 10 young eels
sheltering in rock crevices.

The black dashes on the face and body of this moray mark
its pores. These are part of its lateral line system which
detects changes in pressure and so can be used to detect
movement and vibration in the surrounding water.

The Geometric moray, Siderea grisea is also known as the Grey Moray and Gymnothorax griseus.


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Labels: fish, marine biology, sealife