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Seahorses

Davina Langdale

2nd June, 2003

Bizarrely formed and practising one of nature’s most mysterious parenting methods, the seahorse is the victim of an international trade that kills 20 million of them every year. By Davina Langdale

Sheer weight of traffic

‘Getting up at 4.30am isn’t a whole lot of fun, and pulling on a wetsuit that’s still rather damp and smelly from the day before is even less fun.’ Oxford University research fellow Amanda Vincent has devoted over 10 years of research to the eccentrically beautiful seahorse. Her interest in the evolution of sex differences was piqued by the seahorse – the only species in the world in which the male becomes pregnant.

Seahorses have long been the stuff of myth and legend: a symbol of impudence to the Greek philosopher Plutarch; the miniature offspring of horse-sized parents that pulled Poseidon’s chariot, according to Greek fishermen. Sadly the animal’s unique physiology has also made it a popular feature in traditional Chinese medicine and a prize for aquarium collectors.

‘I began to get frightened about what I perceived to be a really big trade in these animals. I looked around and found there was no data at all, no formal trade records and nobody knew anything about the trade,’ says Vincent. That trade threatens the survival of all 35 of the world’s seahorse species.

THREATS

Traditional Chinese medicine

The number-one threat to seahorses. China imports 20 tonnes or 5-6 million of the animals annually. Seahorses are used to relieve a range of ailments and in virility treatment. The best quality seahorses sell for up to $550 per pound. China’s rapid economic growth has led to a 10-fold increase in the consumption of seahorses over the last 10 years.

The aquarium trade

Seahorses fetch on average between $15 and $70. Hundreds of thousands of animals are captured for aquariums before they have had a chance to breed in the wild. Seahorses are notoriously difficult to keep as they require live brine shrimp for food and are prone to disease in contained environments. Even if they live long enough to breed the young rarely survive. Advertisements for ‘captive-bred’ seahorses usually signify that the pregnant male was caught in the wild and then gave birth in captivity.

The souvenir trade

Each year, several hundred thousand seahorses are captured for souvenirs. Dried seahorses are popular curios in Asia and parts of Europe, and are fashioned into earrings, brooches and keychains.

Infant mortality

Seahorses have a low reproduction rate due to their strict monogamy, and only two of the thousands of young that pairs typically produce ever reach maturity.

Vulnerable home ranges

Seahorse home ranges measure 100 square metres for females and just one square metre for males, which sometimes cling to the same piece of seagrass for weeks. This makes them vulnerable to seine net fishing.

SEAHORSE NUMBERS

US$1,200 cost per kilo of large bleached seahorses in Hong Kong

US$2.80 cost per kilo of small seahorses in Taiwan         

3,000 brine shrimp are consumed by a seahorse per day  

250 seahorses to make up one kilo in the Philippines in 1993

300-450 seahorses to make up one kilo in the Philippines in 1995 US$60-70 price for colourful seahorses for aquariums in Germany

50 per cent decline in seahorse populations in the last decade

39 countries around the world trading in seahorses

35 species of seahorse exist around the world 1 foot length of Pacific seahorse species Hippocampus ingens

100 size in square metres of the home range of a female seahorse

1 size in square metres of the home range of a male seahorse

FISHING METHODS

Unsustainable

Current unsustainable methods of fishing for seahorses use hands, scoop nets or small seine nets that capture everything in their path. Seahorses are also a bycatch of trawl fishing; as many as 80 individuals can be caught in a single trawl.

Sustainable

Amanda Vincent and Project Seahorse have introduced new sustainable methods in the Philippines. Grow-out cages are built by fishermen out of confiscated nets. Caught seahorses are placed in the cages for five months, in which time they grow and reproduce. When the young are released by the male they escape through the nets and repopulate wild regions.

Teaching fishermen to spare the male seahorses, at least until they have given birth, ensures that future generations have a chance of survival. An incentive of two or three pence is paid to the fishermen for each animal deposited.

For more information, visit: www.seahorse.mcgill.ca

SEAHORSE FACTS

Seahorses have been around for 40 million years and yet little is known about them. Their lifespans are unknown, as are their predators and their function in marine ecology. A species that has been part of the marine environment for such a long time must be fulfilling some role in the ecosystem. If seahorses are lost through exploitation by man who is to say there may not be wider repercussions in the marine environment?

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Seahorses range in size from a quarter of an inch to a foot or more.

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The male becomes pregnant when the female deposits her eggs into a pouch in his tail.

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The male protects and nourishes the eggs for a period ranging from 10 days to six weeks before releasing hundreds of miniature seahorses.

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Seahorses have no teeth and swallow their food whole.

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The coronet on each seahorse’s head is nearly as distinctive as a human thumbprint. Seahorses can change colour to match their background.

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Seahorse mating dances can last for nine hours.

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Seahorses can move their eyes independently of one another.

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All 35 species of seahorse are listed as ‘vulnerable’ by the World Conservation Union. A species is listed as ‘vulnerable’ when there is a reduction in its population of 50 per cent over a 10-year period.

This article first appeared in the Ecologist June 2003

 

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