Seashorse

Of the 34 known species of seahorse, New Zealand has but one, ’Hippocampus abdominalis’. Details of which are described here.

This peculiar fish is so highly adapted for its special lifestyle that it has lost most of its fish-like features but, like other bony fish, it still has fins, gills and an internal swim bladder for buoyancy.

Its distinctive body shape is described by it scientific name, Hippocampus, which translates as ‘hippos’ meaning horse and ‘campus’ meaning sea-monster.

This "horse" seldom travels far and is usually tethered to seaweed or other objects by its long prehensile tail. It cannot swim like other fish because it does not have a streamlined shape. It still has a dorsal fin and reduced pectoral fins but has lost the caudal (tail) and pelvic fins.

H. abdominalis can swim horizontally and often does when escaping from danger, but swims upright when moving more slowly. Direction and stability are controlled by its small pectoral fins just behind its head.

Seahorses usually live in shallow coastal waters less than 20 meters deep but are found in a variety of habitats wherever there are suitable supports to cling to. Often this is among the swaying bladder wracks of subtidal seaweed gardens or in kelp forests but they are also found hanging on to finger sponges, mangroves and the mooring lines of boats and mussel farm buoys.

They are widespread around the country having been recorded from the Three Kings Islands in the far north down to Stewart Island and also far from the mainland around the Snares and Chatham Islands.

Camouflaged with body colours like the seaweeds that they often live amongst, they are usually hard to spot. When accidentally discovered or fished (bycatch) they are all too often collected to be dried as curios or sold to make traditional medicines. Consequently these wonderful native fish along with pressure from bycatch and habitat loss have the potential for wild stocks to decline.

The seahorse’s long, narrow snout forms an extended tube for sucking up tiny creatures like fish larvae and small crustaceans and good binocular vision allows it too snap up any fast moving prey that comes too close. An adult seahorse, held in captivity, has been known to eat up to 3000 tiny brine shrimps in a single day.

Overseas, seahorses are renowned for their pair bonding. Males and females form pairs for the breeding season and reinforce their relationships with regular ritual greetings that include mutual entwining of tails and such intimate behaviour is very rare in fish. However, there is no evidence of pair bonding in our native seahorse H. abdominalis either in the wild or captivity.

When females are about to lay eggs, males pursue them and remarkably the chosen male takes the eggs directly from the female into a large abdominal pouch. There they are fertilised with his sperm and he broods the developing young. Depending on the water temperature, brooding may last from 30 to 50 days till the young are large enough to swim away.

Large New Zealand seahorses may "give birth" to more than 700 juveniles. Each one is a miniature model of an adult though the large head is out of proportion with the under-developed body.

New-born seahorses (fry) are about 2 cm long but with voracious appetites. In warmer northern waters they can grow to 10 cm in only 4 months and are then ready to begin breeding. The life span of the New Zealand seahorse in the wild is not known but it may live for up to 4 years, grow to about 30 cm in length and then weigh between 40 and 60 grams.

By plucking movable skull bones against each other, seahorses can make small clicking noises that are clearly audible by divers. Some reports of intense clicking "conversations" during courtship suggest that this is an important means

of communication between individuals.

They are also able to alter their body colour and the intensity of skin patterns. Breeding pairs have been observed to brighten within seconds of meeting each other, apparently signaling interest or recognition.

Seahorses are most vulnerable in the early stages of life when they are free swimming and looking for new habitat. Some have been found in the stomachs of penguins. Their behavioral camouflage of clinging motionless to seaweeds and changing their body colours to match their surroundings, usually provides good protection. However some are taken by sea birds, crabs and large pelagic fish like snapper, and angler fish.

All over the world seahorses are threatened by over exploitation. Millions are ground up to make traditional medicines and many are captured for live display in aquariums or to be dried as novelty ornaments.

It was estimated that over 20 million dried seahorses and several hundred thousand live specimens were traded in 1995. Recent evidence suggests that the trade is much larger than this. Such excessive capture has seriously endangered wild populations in many countries.

To relieve pressure on wild populations there have been recent attempts to farm the fish. Some small scale ventures have been quite successful but larger farms have had management and marketing problems. Concern is that these ventures create new markets and thus put more pressure on the wild stock. The threats to wild stocks therefore remain serious.

Survey Seahorse 2000

This infomation was made possible with community funding from the following organisations: The ASB Trust, The Portage Licensing Trust, The Pacific Development and Conservation Trust. Illustrations: copyright John Walsby