Seahorses: Unique Creatures Threatened by Habitat Loss and Overfishing

Written By: | Date Posted: 01/01/2004 | 3 Comments |
PacificSeahorseBaltimore1

Giant Pacific seahorse (Hippocampus ingens) - this species of seahorse lives in tropical and subtropical waters along the Pacific Ocean. Displayed at the National Aquarium in Baltimore.

Seahorses are small fish that inhabit shallow temperate and tropical waters along coastal ecosystems throughout the world’s oceans. They are unique in many ways. Their appearance is so different from that of other fish that people long ago believed they were insects. Instead of what we normally think of as fish, these creatures look like an amalgam of parts from different species of animals. Their head resembles that of a miniature horse. Their small, delicate fins remind us of fish. They also have long, prehensile tails that seem out of place in a fish. Despite such odd combinations, seahorses are among nature’s most beautiful creations. They look like ornaments in their coral reef, seagrass and mangrove habitats. They are also unique because in seahorses it is the male rather than the female who becomes pregnant. Seahorses are also totally monogamous. This essay describes these wonderful creatures and current threats to their habitats and long-term survival.

General Characteristics

There are about 35 different species of seahorses. Until recently, the smallest was believed to be a tiny Australian seahorse called Hippocampus minotaur, which measures between 10-20 millimeters. However, the pigmy seahorse which measures about 16 mm is now believed to be the smallest species (CNN 2003). At the other end of the scale, the Pacific Seahorse (Hippocampus ingens) measures up to about 300 mm. Their defining physical characteristics are a horse-like head that is bent at an angle and ends in a long snout, independently swiveling eyes, and a prehensile tail. Unlike most fish, they do not have scales. Seahorses have one dorsal fin that helps them move forwards and backward, two small pectoral fins that are used for stabilization and steering and to move up and down, and an anal fin that is usually very small. Seahorses have a relatively short lifespan, ranging between one and four years, depending on the species. The appearance of some present day seahorses is very similar to fossils, which suggests they have changed little over time (Kuiter 2000).

Seahorses are found in tropical and subtropical waters around the world. Some are found in sub temperate waters in Australia, New Zealand, Japan, South Africa and Europe (Kuiter 2000). Two species, the long-snouted Hippocampus guttulatus and the short-snouted Hippocampus hippocampus, are sometimes found in the temperate waters of the United Kingdom (McCarthy 2003). There are about 11 species of seahorses living in Australian waters. In the American continent, only four species have been described. Three live in the Atlantic Ocean and one of them, Hippocampus erectus, lives as far north as Canada and its southern range may extend as far south as Uruguay. Hippocampus reidi makes its home along coral reefs from Florida through the Caribbean and down to South America. Another species, Hippocampus zosterae lives in the Gulf of Mexico and the Caribbean. There is one species that lives in the Pacific Ocean in the Americas: Hippocampus ingens. It lives in waters from Baja California down to Ecuador (Vincent 1996).

Barbour's seahorse (Hippocampus barbouri) displayed at the National Aquarium in Baltimore.

Barbour's seahorse (Hippocampus barbouri) displayed at the National Aquarium in Baltimore.

Seahorses are diurnal and carnivorous, feeding on small crustaceans and fish. They usually ambush their prey and inhale rapidly to catch their food. Seahorses rely on camouflage in order to hunt and to avoid predators. Like octopuses and chameleons, they have developed ways to change their appearance in order to blend into their habitat. Seahorses are able to grow skin filaments and tendrils to match the texture of their background and to change colors (Vincent 1994). Their camouflage makes them blend with their coral and seagrass habitats. Their natural predators include large fishes such as flatheads, tuna, skates, rays, cods, trumpeters, snappers and perches. Crabs, penguins and other water birds are also known to eat seahorses occasionally. Seahorses are most vulnerable to these predators when they are young. In addition to these predators, seahorses are killed by heavy storms which sometimes wash them ashore.

Although they inhabit temperate and tropical waters throughout the world, seahorses live in seagrasses, coral reefs and mangroves, which means their habitats are mostly confined to waters along the world’s coastlines. Most seahorses live in depths of 1 to 15 meters, though some are found at depths of up to 60 meters. Within their habitats, seahorses seem to have relatively small ranges. A study of an Australian species called Hippocampus whitei showed that males use a range of only about one square meter while females have a home range of about 100 m2 (Vincent 1996). Males and females sometimes differ in color, shape and spine arrangement. Males are generally slimmer and less spiny. Their color may also change during and after mating (Kuiter 2000).

There are about 35 different species of seahorses. Until recently, the smallest was believed to be a tiny Australian seahorse called Hippocampus minotaur, which measures between 10-20 millimeters. However, the pigmy seahorse which measures about 16 mm is now believed to be the smallest species (CNN 2003). At the other end of the scale, the Pacific Seahorse (Hippocampus ingens) measures up to about 300 mm. Their defining physical characteristics are a horse-like head that is bent at an angle and ends in a long snout, independently swiveling eyes, and a prehensile tail. Unlike most fish, they do not have scales. Seahorses have one dorsal fin that helps them move forwards and backward, two small pectoral fins that are used for stabilization and steering and to move up and down, and an anal fin that is usually very small. Seahorses have a relatively short lifespan, ranging between one and four years, depending on the species. The appearance of some present day seahorses is very similar to fossils, which suggests they have changed little over time (Kuiter 2000).

Seahorses are found in tropical and subtropical waters around the world. Some are found in sub temperate waters in Australia, New Zealand, Japan, South Africa and Europe (Kuiter 2000). Two species, the long-snouted Hippocampus guttulatus and the short-snouted Hippocampus hippocampus, are sometimes found in the temperate waters of the United Kingdom (McCarthy 2003). There are about 11 species of seahorses living in Australian waters. In the American continent, only four species have been described. Three live in the Atlantic Ocean and one of them, Hippocampus erectus, lives as far north as Canada and its southern range may extend as far south as Uruguay. Hippocampus reidi makes its home along coral reefs from Florida through the Caribbean and down to South America. Another species, Hippocampus zosterae lives in the Gulf of Mexico and the Caribbean. There is one species that lives in the Pacific Ocean in the Americas: Hippocampus ingens. It lives in waters from Baja California down to Ecuador (Vincent 1996).

Seahorses are diurnal and carnivorous, feeding on small crustaceans and fish. They usually ambush their prey and inhale rapidly to catch their food. Seahorses rely on camouflage in order to hunt and to avoid predators. Like octopuses and chameleons, they have developed ways to change their appearance in order to blend into their habitat. Seahorses are able to grow skin filaments and tendrils to match the texture of their background and to change colors (Vincent 1994). Their camouflage makes them blend with their coral and seagrass habitats. Their natural predators include large fishes such as flatheads, tuna, skates, rays, cods, trumpeters, snappers and perches. Crabs, penguins and other water birds are also known to eat seahorses occasionally. Seahorses are most vulnerable to these predators when they are young. In addition to these predators, seahorses are killed by heavy storms which sometimes wash them ashore.

Although they inhabit temperate and tropical waters throughout the world, seahorses live in seagrasses, coral reefs and mangroves, which means their habitats are mostly confined to waters along the world’s coastlines. Most seahorses live in depths of 1 to 15 meters, though some are found at depths of up to 60 meters. Within their habitats, seahorses seem to have relatively small ranges. A study of an Australian species called Hippocampus whitei showed that males use a range of only about one square meter while females have a home range of about 100 m2 (Vincent 1996). Males and females sometimes differ in color, shape and spine arrangement. Males are generally slimmer and less spiny. Their color may also change during and after mating (Kuiter 2000).

Longsnouted seahorse (Hippocampus reidi) - displayed at the New York Aquarium.

Longsnouted seahorse (Hippocampus reidi) - displayed at the New York Aquarium.

Perhaps the most curious characteristic of seahorses is the fact that males rather females become pregnant. In many species of fish the male cares for the young by fanning the eggs once they are laid by the female in order to provide them with oxygen. Males are also know to guard the eggs once females have laid them (Vincent 1994). But seahorses go one step further. The female deposits her eggs in a pouch found in the male. The eggs are then fertilized by the male and tissue envelops them. A capillary network provides the fertilized eggs with oxygen. Pregnancy in the male seahorse lasts between 10 days and six weeks depending on the species. The durations of pregnancies also depends on water temperature. The male seahorse usually goes into labor at night. Baby seahorses look like miniature adults and are totally independent the moment the step out of their father’s pouch (Vincent 1996).

The size of seahorse broods is much smaller than that of most fishes. About 100-200 seahorses are born at a time. However, the size of broods vary from one species to another. While some of the smaller species may have broods as small as five seahorses other species may have as many as 1,500 offspring per pregnancy. Seahorse pairs reproduce several times per year. For example, Hippocampus whitei pairs living in Australian waters produce about seven consecutive pregnancies in a year, which result in about 1,000 seahorses (Vincent 1996).

Seahorses are totally monogamous. No seahorse has ever been observed to abandon its mate. If a seahorse loses its mate to a predator the female will stay in her home range but a male will venture out and look for a single female (Vincent 1994). However, because seahorses have low mobility and low population densities finding a new partner may take some time (Vincent 1996).

The Syngnathidae Family

Leafy seadragon (Phycodurus eques) displayed at the New York Aquarium.Leafy seadragons live in Southern Australian waters.

Leafy seadragon (Phycodurus eques) displayed at the New York Aquarium.Leafy seadragons live in Southern Australian waters.

Seahorses are grouped in the genus Hippocampus and they belong to the family Syngnathidae, which includes over 320 species. The word Syngnathidae means ‘jaw-fused’ (Kuiter 2000). This family of fishes also includes seadragons, pipefishes and pipehorses. Whereas pipefishes have long, straight bodies and tail fins that make them look like familiar fishes, pipehorses have heads that are bent at an angle of about 30 degrees to their straight bodies. Pipehorses also have tails that are able to grasp objects. Seadragons resemble seahorses but have dazzling arrays of ornamentation as protective camouflage. The weedy seadragon (Phyllopteryx taeniolatus) is a solitary species that is widespread in southern Australian waters. Those that live in deeper water tend to be brighter colored and less ‘leafy’. The leafy seadragon (Phycodurus eques) also lives in southern Australian waters along reefs, feeding mainly on crustaceans. Australia seems to have the largest diversity of syngnathids in its waters, with approximately half of all known species – including eleven species of seahorses – making their home there (Kuiter 2000).

Threats To Seahorses

Northern seahorse (Hippocampus hudsonius) - displayed at the New York Aquarium. These seahorses live along the Western Atlantic Ocean.

Northern seahorse (Hippocampus hudsonius) - displayed at the New York Aquarium. These seahorses live along the Western Atlantic Ocean.

Seahorses are threatened throughout their range as a result of habitat loss and over-fishing. They are exploited for traditional Asian medicine markets, the pet trade, and for food. In Europe seahorses were also used historically for medicinal purposes. Seahorses there were used to treat fevers, baldness, infertility, rabies, and other maladies. Today, however, seahorses are more likely to be used for traditional medicine in China, Japan and Korea. Their consumption is believed to aid in treatments for fatigue, throat infections, asthma, sexual dysfunction, injuries and fractures, heart disease, kidney and liver disease, incontinence, difficult or delayed childbirth, skin diseases, mental disorders and many other ailments. In some places, such as the Philippines, they are also used as good luck charms or for superstitious purposes, such as warding off evil spirits. Their widespread use in traditional medicine markets has led some scientists to study their genetic sequence in order to understand how their immune systems work and what aspects of their molecular profiles may explain their pharmacological use (Genomics and Genetics Weekly 2003).

Trade in seahorses is very common. Amanda Vincent, in her study for Traffic International titled The International Trade in Seahorses, estimated that annual consumption of seahorses in Asia alone is about 16 million individuals, which represents about 45 tons of dried seahorses. According to the author, this figure probably underestimates the real size of trade in seahorses in Asia significantly, since countries such as Japan, Korea, Malaysia, and Singapore, which are believed to consume a large quantity of seahorses, were not included in the calculation due to lack of data. The largest importers of seahorses are China (about 20 tons), Taiwan (about 11.2 tons) and Hong Kong (about 10 tons). In the case of China, demand for seahorses is larger than supply and trade in these fish is expected to grow in the future (Vincent 1996). Seahorses can be very expensive. In the early 1990s a pound of seahorses in a Hong Kong pharmacy sold for US$125-400 (Vincent 1994).

The largest exporters of seahorses are believed to be India, Philippines, Thailand and Vietnam. According to Vincent’s estimates, Thailand alone may export 15 tons of dried seahorses per year, while Vietnam may export about 5 tons. Little is known about the trade in seahorses in Latin America. Mexico, some Central American countries, Ecuador and other South American countries may also export seahorses in large amounts (Vincent 1996).

These numbers are cause for concern. Anecdotal evidence, collected by Vincent and colleagues from fishermen in five Asian countries, suggests that seahorse populations are declining rapidly. According to the fishermen interviewed, populations declined by half during the five year period prior to the interviews. The impact of trade on seahorse populations is difficult to ascertain because data on seahorse trade and on seahorse populations and distributions are not readily available.

In addition to traditional Asian medicine markets, live seahorses are also traded and sold as pets. Estimates of the size of this trade are uncertain, but Vincent (1996) estimates it to be in the hundreds of thousands per year. Most seahorses traded in the pet market go to the United States, Canada, Europe, Japan or Taiwan. Unfortunately, seahorses are very difficult to keep as pets and mortality rates are very high. Seahorses suffer high rates of physiological damage during transport from the wild to aquarium retailers. They are susceptible to many fungal, parasitic and bacterial diseases if the water in their aquariums is not sufficiently clean or if the water temperature is not right, and they have specific diets that are hard to meet if owners lack good information about their husbandry.

Dwarf seahorses (Hippocampus zosterae) - displayed at the National Aquarium in Baltimore.

Dwarf seahorses (Hippocampus zosterae) - displayed at the National Aquarium in Baltimore.

Seahorses retain their shape and texture when they die and as a result they are often sold as ‘curios’ or souvenirs. They are commonly turned to keychains by punching a hole through their eyes or used to make jewelry such as earrings and brooches. These curios are often sold to tourists at beach resorts.

As mentioned earlier, seahorses live in coastal habitats, often close to large human populations. These habitats are being damaged and degraded in many parts of the world as a result of pollution, siltation, dredging, dumping of wastes and other human activities. Seahorse populations are also affected in some parts by destructive fishing practices such as trawling by commercial fishers, and cyanide and dynamite fishing by artisanal fishers. In 2003 the World Conservation Monitoring Centre (WCMC) and the United Nations Environment Programme (UNEP) published a World Atlas of Seagrasses, noting that in the 1990s about 15% of seagrasses, a major habitat for seahorses, were destroyed by human activities around the world’s oceans (McCarthy 2003).

Seahorses are vulnerable to all these human pressures for a number of reasons. They have lengthy parental care and relatively small brood size and survival rate. They are sparsely distributed which means their partners are not easily replaced. They also have low mobility and small home ranges, which makes recolonization a lengthy process (Vincent, 1996).

The Future of Seahorses

Pot-bellied seahorses (Hippocampus abdominalis) - displayed at the National Aquarium in Baltimore.

Pot-bellied seahorses (Hippocampus abdominalis) - displayed at the National Aquarium in Baltimore.

Seahorses are miniature wonders of nature. Unfortunately, international trade in seahorses as well as habitat loss may jeopardize their continued survival. More research and data gathering is needed in order to understand how trade in seahorses for traditional medicine in Asian markets and for the pet markets is affecting seahorse populations. Researchers such as Vincent suggest that trade in these species is already very large in terms of volume and that given economic conditions it is likely to grow in the near future. In order to ascertain the survival of these creatures Vincent (1996) suggests conducting additional research in the areas of seahorse population densities, size distributions, mobility, migration, longevity, mortality, fecundity and young dispersal. The protection of key seahorse habitats such as seagrasses, coral reefs and mangroves will also be critical to their survival. Seagrasses, in particular, seem to lack protection and are currently disappearing or being damaged rapidly.

References

CNN. May 12 2003. “World’s smallest seahorse discovered.” Available online at: http://www.cnn.com/2003/TECH/science/05/11/tiny.seahorse.reut/index.html – access date: May 12, 2003.

Genomics & Genetics Weekly. 2003. “Complementary and Alternative Medicine: Chinese medicine uses the seahorse; molecular profiling reveals many lectins.” Genomics & Genetics Weekly. November 7. Page 29.

Kuiter, Rudie. 2000. Seahorses, Pipefishes and their relatives: A comprehensive guide to Syngnathiformes. TMC Publishing: Chorleywood, UK.

McCarthy, Michael. 2003. “At Risk: A Vital Terrain that Feeds the Ocean’s Most Fragile Creatures.” The Independent (London). October 15. Page 9.

Vincent, Amanda C. J. 1994. “The Improbable Seahorse.” National Geographic. October issue. Pages 126-140.

Vincent, Amanda C.J. 1996. The International Trade in Seahorses. Traffic International.

3 Responses to “Seahorses: Unique Creatures Threatened by Habitat Loss and Overfishing”

  1. kyrie Says:

    It was totally disappointing that seahorse are being neglected without knowing how beautiful they are. I find seahorse beautiful to match up different type of fish (safe one). I will have mine someday.

  2. Sharron Smith Says:

    Leave it to man to mess up Jehovah God’s creation!!!!!

  3. Tina Says:

    Yooooooooo dawg dese seahorses be da sickest stuff I ever did seen

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