He’s male, he’s pregnant and she still wants more

I WROTE last week about the battle of the sexes among phalaropes, little wading birds which used to breed in Ireland.

RTÉ screened documentaries recently on Kealan Doyle’s work with seahorses, creatures whose domestic arrangements are even more bizarre.

The phalarope daddy does all the child-rearing but the mammy still shoulders the burden of pregnancy and delivers the eggs. In seahorses, however, even the pregnancy is taken over by the male.

There are about 40 species of seahorse worldwide. Their close relatives the pipe-fish, skinny eel-like creatures with long thin snouts, are common in Irish waters. Although dead seahorses turned up along our shores in the past, it was thought until fairly recently that we had none here. Their camouflage is so effective that even scuba-diving naturalists failed to notice the two local species.

Seahorses may resemble shrimps and prawns but they are fish, not crustaceans. Their anatomy, despite appearances, is fundamentally the same as that of salmon or mackerel. Skin stretched over bony rings gives them an elongated tubular appearance. They have no tail-fins or scales.

Propelled by the dorsal fin on their backs and steering with little pectoral fins located just behind the eyes, seahorses are not strong swimmers. They don’t need to be; theirs is a very sedentary lifestyle. Instead of swimming around like normal fish, they prefer to remain at one location throughout their lives.

With bodies held vertically in the midst of corals or sea-grass clumps, they grip the vegetation with their tails to avoid being swept away by currents. The eyes, unlike those of most fish, can move about in their sockets. Each eye does so independently so that seahorses can see both in front and behind them at the same time.

Stealth hunters, they wait for tiny fish and invertebrates to approach. Then the long snout goes into action, sucking the hapless creatures down the throat like a child sipping lemonade through a straw.

A male’s territory may be only 1m² in extent. When a female joins him, an elaborate courtship ritual commences. It can last for days.

He has a pouch like a kangaroo’s, into which she deposits eggs for him to fertilise. There may be up to 1,000 in a batch. Supplied with food and oxygen in the pouch, the young spend two to four weeks there. Then the male goes into labour, experiencing contractions like human mothers. Delivery takes up to 12 hours. Once released, the fully-developed little seahorses drift away on the current. No more nurturing is provided by the parents.

But there is little rest for the happy father. The female returns immediately and the courtship ritual begins again. Soon he is burdened with another batch of eggs. The unseemly haste is crucial to the success of this strange breeding strategy. By having him take over the pregnancy, she can devote her resources to producing more eggs. With the increased production of young, the pair stand a better chance of rearing a few offspring to breeding age.

Seahorse babies, like those of most fishes, have very low survival rates; it’s thought that only one in a thousand reaches adulthood.

But seahorses are in trouble. The Seahorse Trust estimates that more then 20 million are killed each year for the Chinese medicine trade. The fidelity and devotion of seahorses to their mates, and the intensity of their mating displays, led to the notion that eating them would increase sexual appetite and prowess. Science can find no basis for the claim but even well-educated Chinese people continue to believe this nonsense.

But quack medicine is not the only offender. Every year, a million seahorses are turned into souvenir brick-a-brack, while the aquarium pet trade takes another million. With such pressures, the future for seahorses is dim. It was thought that they couldn’t be bred in captivity but research by Kealan Doyle and his colleagues at Seahorse Aquariums in Connemara have shown that they can.

Seahorse farming on a wide scale is not yet possible but, if it can be developed, there may be just a ray of hope for the survival of these extraordinary little creatures.