Seahorse Tales and Pregnant Males¦Dr Glenn Moore

Northern Suburbs Branch 17 March 2021

Dr Glenn Moore is Curator of Fishes at the Western Australian Museum and has been studying the biology of the Western Australian Seahorse for more than 20 years. His primary interest is in the evolution, reproduction, behaviour, mate choice and movements of the species. His presentation took us on a journey into the everyday life of this highly recognisable, but little known about creature.

Seahorses belong to the family of fish Syngnathidae (fused jaw) along with sea dragons and pipefish. Like fish, they have gills, fins and swim bladder. Unlike other fish, they have a bent neck, which is sometimes movable, bony plates instead of scales, prehensile tail with no tail fin and no teeth. They swim vertically with a dorsal fin and are found in mostly tropical shallow waters. Size can be from 1cm for pygmy seahorses to 30cm for the largest.

Picture credit: Dr Glenn Moore

One of the greatest threats to seahorses is as traditional medicines in S E Asia, areas in Africa and the central Pacific. Originally, larger seahorses were preferred but now all sizes are under threat as the dried seahorse can be ground up and sold as capsules. Some dried specimens are sold as curios, even gold dipped. Dredging, trawling and infill are also responsible for large loss of numbers. Local species can be purchased for aquaria and collected with a license. All seahorses belong to the genus Hippocampus. The IUCN red list has 42 species listed, one as endangered, 12 as vulnerable and 17 as data deficient. They are listed with over 38,700 species as protected by CITES against over-exploitation through international trade and also the Federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999).

Picture credit: Dr Glenn Moore

Glenn informed us that the Western Australian species Hippocampus subelongatus occurs from Cape Leeuwin to Shark Bay to a depth of 1-20m in muddy, silty water typically around pylons and jetties. It is roughly 20cm in length, can be brown, white, yellow or red and breeds over the summer months (October – March).

Female White's Seahorse, depositing eggs in the male's pouch

Courtship can last 3-4 days after which the female uses an ovipositor to put her eggs in the male’s pouch where they are immediately fertilized by his sperm. The female then leaves. Gestation is about 12 days after which the male “gives birth”. Most species appear to be monogamous as the pair do not move far and hence expend less energy finding a mate. Pairs may breed 3-4 times in a season with the female having eggs ready for the male as soon as each brood is released.

Photo credit: David and Leanne Atkinson

Glenn finished his talk with a discussion on some research on sexual selection by the Western Australian seahorse, which indicates that large males prefer to mate with large females and small males mate with small females.

Willy Dadour

Don Poynton, our chairperson opened this St Patrick’s Day meeting with a short presentation about shamrock and clover. Many of the subterranean clover cultivars have been developed in Western Australia where this important nitrogen fixing legume is used in pastures and in rotation with crops. Thanks Don.