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Diving with Seahorses

A Diver's best Friend

The seahorse is one of 4 families in the syngnathiform family order which also includes pipefish, flag tail pipefish and seadragons.

Barbigants pygmy seahorse - Dive the World

Seahorses like sheltered areas and are well camouflaged. They camouflage themselves by changing colour quickly to blend in with their surroundings. They also allow encrusting organisms to settle on them and they can grow long skin appendages to match their surroundings even better. During mating their skin will lighten and darken. Generally the easiest part of the seahorse to spot is the tail.

They swim in an upright position with their tails down and their heads up. Their dorsal fin moves them forward and the pectoral fin controls steering and turning.

The pygmy seahorse is a recently discovered relative of the common sea horse and one of the divers most sought after finds. A lot of deco time and a magnifying glass will help in the search for these cryptic critters. They are roughly 15mm in length although some are smaller, and as their tail is always curled around a seafan, they appear even smaller.

Very little is known about the life cycle of seahorses. They are thought to eat the same zooplankton as the seafans that they inhabit and they seem to prefer seafans to other family members, as there are normally few other inhabitants on a pygmy's seafan.

Seahorse Fact Sheet

Family name: Hippocampinae
Order name: Syngnathidae
Common name: Seahorse
Scientific name: Hippocampus

Distinguishing Features

They are characterised by an elongated body encased in bony rings. Instead of scales that are found on most fish, seahorses have a thin layer of skin stretched over a series of bony plates. These plates show themselves as the bony rings along their body's trunk. They have no pelvic fins but most have small pectoral fins and a single dorsal fin. They have a prehensile tail (able to grasp) and a tube-like mouth with no teeth, and small gill openings.

Unlike (most) humans but similar to chameleons, seahorses can move their eyes independently of each other. They range in size from 10 mm to 35 cm, the largest species being the Pacific seahorse. They also have a coronet on top of their head which is distinctive in all Hippocampus members, in the same way that a thumb print is in humans.

Feeding habits

Seahorses eat small crustaceans which they catch by staying still and lying in wait. When prey comes near they snap them up. Their tube like mouth creates a vacuum that sucks prey in and they swallow their food whole. They can eat up to 3,000 brine shrimp per day.

Reproduction

Sea horses are unusual in a couple of ways. One is that they are monogamous and have long courtship periods when mating. Monogamy is unusual in all animals but especially in fish. There is some evidence to suggest that the longer a couple of seahorses stick together, the better they are at producing babies. Indeed, a male seahorse that is involved in an intimate relationship can be pregnant for as many as 7 months of the year. Once the male has given birth, he often becomes pregnant again right away.

Seahorse in Bali, Indonesia

Another unusual aspect of the sea horse is that it's the male of the species that becomes pregnant and carries the eggs in a pouch on his belly, after the eggs have been deposited there by the female. The eggs are fertilised in the pouch and incubated until they hatch. Incubation lasts between 10 days and 4 weeks, depending on the species and water temperature.

At hatching, the male gives birth to fully developed but tiny versions of its species. The natural lifespan of seahorses is not known, but believed to be from 1 year for small species to 5 years for a larger species.

It is common in the fish world for the males to take care of the eggs by guarding them or fanning them to keep them clean and provide enough oxygen. But seahorses take parental care to an extreme unknown elsewhere in the animal kingdom. A capillary system provides nutrients to the young.

Distribution

Seahorses are found all over the world and inhabit coral reefs and sea grass beds.

The Barbigants pygmy seahorse (hippocampus barbiganti) can be found all over Indonesia in various colours and at all depths. They can be found in the muricella sea fans in Papua New Guinea, Philippines and Malaysia. These sea fans have bulbous red polyps as do the pygmy seahorses. This, along with their small size, is what makes them so difficult to spot.

Denise Hackett recently discovered a new pygmy seahorse species in Indonesia. It's named after her, Hippocampus Denise, but it's often called the 'plucked chicken pygmy seahorse' due to its unusual appearance with a lack of the typical bumps (tubercles). Hippocampus Denise is normally found in light yellow gorgonians which, like the pygmy, are less bulbous with smaller polyps.

The weedy pygmy seahorse is an even newer discovery. First recorded in the Banda Sea in 2000, they are now regularly seen at Wakatobi and the Lembeh Strait. The Raja Ampat area is another good place to find them. This species is the smallest and most cryptic. They seem to move around more than other species making them even harder to pin point.

Ecological Considerations

Pygmy and common seahorses such as the tigertail, are sensitive to stress and too much harassment from divers is certainly not good for them. They particularly dislike bright lights and will turn their heads away if a diver shines a dive light at them. Placing a red filter (or red plastic bag with an elastic band over it) on to a dive light will give a softer diffused light that they will be less sensitive to and should enable photographers to get better pictures.

Threats

Tiger-tail sea horse, diving at Kapalai, Malaysia. Photo courtesy of Ketrick Chin

Seahorse numbers around the world are diminishing. They are used as a traditional medicine in China, Japan, Korea, Indonesia and the Philippines. Dried seahorses are viewed as a cure for a range of conditions such as asthma and skin disease, but they are most commonly used as a treatment of sexual dysfunction. Asian nations consume around 45 tons of dried sea horse annually. That's equates to about 16 million of them!

One problem is that many of the harvested seahorses are juveniles and have not had a chance to breed and reproduce. A large seahorse can sell for up to US$ 550 per pound in Hong Kong so it is clearly big business. There is no clinical proof that they have any medicinal benefits but the Chinese have been using them as a fundamental part of their traditional medicine for centuries and there is a strong conviction that there is a benefit.

They are also being over-collected for the aquarium trade in Europe, North America and Japan. Furthermore, seahorse habitat is under threat. Sea grass areas, mangroves and coral reefs are declining world wide.

Protective Measures

Seahorses are not yet considered endangered but they are red flagged as 'threatened' on several conservation lists which act as warnings without specifically enforcing any restrictions on their trade. However, some more progressive nations do have unilateral protective measures in place. For example, catching sea horses in South Africa has been outlawed, partly as a result of the collapse in the numbers of the endemic Knysna Seahorse.

Dive Sites

More detailed information on seahorse diving destinations:

The Americas

  • Galapagos, Ecuador • Sea of Cortez in Mexico

Australia

  • Osprey Reef • Ribbon Reefs

Burma - Myanmar

  • Mergui Archipelago

Indonesia

  • Ambon • Bali
  • Bunaken • Cenderawasih Bay
  • Flores • Komodo
  • Lembeh Strait • Raja Ampat
  • Triton Bay • Wakatobi

Malaysia

  • Kapalai • Mabul Island

Thailand

  • Phi Phi Islands • Phuket

Dive The World Recommendations: Indonesia and Malaysia.


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