Lined seahorse  (Hippocampus erectus)

The lined seahorse is classified as Vulnerable (VU) on the IUCN Red List (1), and listed on Appendix II of CITES (3).

A large seahorse with a deep chest, the lined seahorse (Hippocampus erectus) has the upright posture, prehensile tail and horse-like head set at right angles to the body which make seahorses some of the most unusual-looking of all fish (4). Instead of having scales, as most other fish do, seahorses have a layer of skin stretched over a bony armour that is arranged into a series of rings (5) (6). Swimming is powered by the rapidly oscillating dorsal fin, and they steer using the fins on either side of the body (the pectoral fins) (5). The colouration of the lined seahorse varies from ash-grey, orange, brown, yellow and red to black, and brown individuals are usually paler on the front (5) (6). The body is often marked with a characteristic pattern of pearly white lines, which follow the contour of the neck and for which this species is named, as well as tiny white dots on the tail and a darker or paler ‘saddle’ across the back (5) (6).

The lined seahorse occurs in the Western Atlantic, from the southern tip of Nova Scotia in Canada, along the east coast of the USA, and south to the Gulf of Mexico, the Caribbean and Venezuela (1) (2). Additionally, a southern form that appears to be genetically distinct from the north Atlantic specimens, and which may prove to be a separate species, is known from Rio de Janeiro, Brazil, and possibly Suriname (1) (2).

Adult lined seahorses are known from the surface and bottom waters of both shallow and deep areas of channels, bays, salt marshes and near-shore coastal waters, up to depths of 73 metres (1) (6). The lined seahorse is associated with, and often found clinging to, aquatic vegetation such as mangroves, seagrasses, sponges, soft corals and floating Sargassum, and has been found over oyster beds and weed-covered banks (1) (6). Newborn juveniles tend to swim near the water’s surface (6).

Seahorses are fairly unusual amongst fish for being monogamous, mating exclusively with the same partner throughout their life, or until their partner dies. ‘Greeting dances’ are performed each morning by the pair to confirm and strengthen their bond (4). Unusually, it is the male, and not the female, that becomes pregnant in seahorses (7). Males have an incubation or ‘brood’ pocket on the lower side of the tail, into which female lined seahorses lay between 250 and 650 eggs during courtship, depending on the size of the individual. Egg development within the brood pocket lasts around 20 to 21 days. After hatching, the embryos continue to be carried in the pouch until they are capable of fairly active swimming (4). The young look like miniature adult seahorses, are independent from birth, and receive no further parental care (7). The lined seahorse reaches adult size in eight to ten months (4).

Seahorses are carnivorous species that are unable to move rapidly enough to chase their prey. Thus, they use their elongated snout to suck in small crustaceans, such as baby brine shrimp, and may feed for up to ten hours each day (4).

Lined seahorses are threatened by targeted catch and incidental capture by fisheries, as well as by habitat degradation (1). There is a huge demand for this species, which is sold live to the aquarium trade, and dried as curios and for traditional Chinese medicine (4). As such, the lined seahorse is among the most commonly caught seahorses (1) (4). The lined seahorse is a particularly popular aquarium fish in North America, with thousands collected each year in Florida alone, destined for the aquarium trade. This species is Brazil's 6th most important marine ornamental export,and is also sold dried as curios in Mexico along the Caribbean coast(1). Dried specimens are also traded as traditional Chinese medicine (1), being considered by some as a powerful aphrodisiac, and are used to treat an array of ailments from impotence and infertility to asthma, throat infections and lethargy (4).

Shrimp and other trawl fisheries are responsible for much of the indirect harvesting of this seahorse through incidental capture as bycatch. Additionally, the lined seahorse has been affected by habitat degradation caused by coastal development, pollution and increased sedimentation. In northeast Brazil, for example, the development of shrimp farms has destroyed much of the coastal mangrove habitats where seahorses live (1).

All seahorses are listed on Appendix II of CITES, which permits only individuals over 10 centimetres to be landed, in order to allow continued reproduction (1) (6). Trade is also fully monitored in the USA, although this relies on the honesty of traders’ declarations. Targeted fisheries for the aquarium trade are monitored and regulated in Florida, with limitations on the number of commercial harvesters. However, non-selective exploitation through incidental capture is not monitored in any state (1).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the lined seahorse and other seahorses see:

• Project Seahorse:
  http://seahorse.fisheries.ubc.ca/
• The Seahorse Trust:
  http://theseahorsetrust.co.uk/