|Scientific Name:||Hippocampus abdominalis Lesson, 1827|
Hippocampus agnesae Fowler, 1907
Hippocampus bleekeri Fowler, 1907
Hippocampus graciliformis McCulloch, 1911
|Taxonomic Source(s):||Armstrong, P. 2001. Genetic and morphological variation in pot-bellied seahorses (Hippocampus abdominalis): is there evidence for two species? B.Sc. (Hons.) Thesis, School of Aquaculture, University of Tasmania.|
|Taxonomic Notes:||Hippocampus abdominalis was first described from New Zealand and there is a question as to whether specimens from Australia represent the same species. Studies that have addressed this question do not support the existence of multiple species based on morphological, meristic, and genetic data (357 bp, cyt b) and show more variation within populations than among populations (Armstrong 2001, Lourie et al. 2016). There is some genetic divergence between Australian and New Zealand populations (814bp cytb, 624bp CO1, 404bp CR, plus four microsatellite loci), however, the level of divergence is low (1.4–1.7%, Nickel and Cursons 2012). Divergence within New Zealand is 0.7–2.2% without any clear geographical structure (Nickel 2009; Nickel and Cursons 2012). The name H. abdominalis takes precedence with H. agnesae and H. bleekeri being treated as synonyms. Hippocampus graciliformis is a juvenile specimen of H. abdominalis and therefore is also synonymized.|
|Red List Category & Criteria:||Least Concern ver 3.1|
Hippocampus abdominalis is a coastal seahorse that inhabits intertidal pools, macroalgae, rocky outcrops, and artificial structures. The species may be threatened locally by coastal development. They are caught as bycatch at low levels. The species is a habitat generalist, is protected by various state and federal measures throughout its range, is subject to CITES Appendix II, and occurs in several protected areas. Therefore H. abdominalis is listed as Least Concern.
|Previously published Red List assessments:|
|Range Description:||Hippocampus abdominalis occurs in the marine waters of south-eastern Australia and all around New Zealand (Kuiter 2001, Nickel and Cursons 2012). In Australia the species occurs from the Great Australian Bight to Newcastle and throughout Tasmanian waters (Lourie et al. 2016).|
Native:Australia (New South Wales, South Australia, Tasmania, Victoria); New Zealand
|FAO Marine Fishing Areas:|
Indian Ocean – eastern; Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||To date there have been few dedicated surveys or population estimates for Hippocampus abdominalis. At most reported locations in Australia, H. abdominalis appears to be rare or scarce. Mean peak densities in the Derwent Estuary, Tasmania were 0.12–1.11 individuals per 100 m² in 2000–2002, but subsequently declined significantly. In Tasmanian macroalgal (Ecklonia) habitats, densities of fewer than one individual per 500 m² are generally recorded (K. Martin-Smith, pers. comm. 2006). Numbers from trawls in New Zealand suggest that on soft bottoms, the species may be widespread if scarce, but further documentation is needed. |
Exceptions to sparse populations are aggregations on some artificial structures and one documented report of large numbers aggregated on rafting seagrass (J. Manna pers. comm. 2006).
Further research is needed in order to determine population size and trends in abundance for this species.
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Hippocampus abdominalis have been recorded from harbours, protected coastal bays and deep waters with sponges (Kuiter 1993, Kuiter 2001). Depth range varies considerably from the surface down to 104 m (Amaoka et al. 1990, Paulin and Roberts 1992, Francis 1998, Lourie et al. 1999, Stevenson and Beentjes 2001). Habitat varies from intertidal rock pools to, more commonly, amongst shallow macroalgal stands (e.g., Ecklonia, [Kuiter 2000]), submerged rocky outcrops, exposed open sea floor and artificial structures (Francis 1998, Woods 2003). In Tasmania, H. abdominalis are reported as common near the entrances of large estuaries on muddy bottoms, or near reef edges, feeding on small crustaceans (Last et al. 1983). They occur in water temperatures of 8-24°C, and have been shown to perish in captivity beyond 26°C (Martinez-Cardenas and Purser 2011). It is not definitively known whether they occupy home ranges or are free-ranging, although some evidence suggests certain populations may exhibit site fidelity (Van Dijken 2001). Unlike most seahorse species, H. abdominalis is a relatively strong swimmer and has been known to swim over hundreds of meters in the course of a day (Vincent 1990). Adults are also known to occur in open water and to raft on macroalgal rafts (Kingsford and Choat 1985) and seagrass (J. Manna pers. comm. 2006): this occurs at all times of the year in New Zealand (Kingsford and Choat 1985, Kingsford 1986). Artificial structures appear to be important habitats for H. abdominalis: in particular, jetties, nets and salmon cages. For example, hundreds of individuals have been observed on anti-predator nets surrounding salmon aquaculture pens in the Huon Estuary, Tasmania (Marshall 2004, K. Martin-Smith, pers. comm. 2006). Similarly, H. abdominalis have been observed in reasonably large numbers on the net of a swimming enclosure in Sydney Harbour since 2003 (K. Martin-Smith, pers. comm. 2006). |
As with other members of the seahorse and pipefish family, this species is ovoviviparous and males incubate eggs in an abdominal pouch and eventually release live young (Foster and Vincent 2004). The pouch is developed at about six months of age, but first breeding occurs closer to 12 months (R. Kuiter, pers comm. in Pogonoski et al. 2002). Spawning occurs mainly from (the Austral) spring to summer, where Woods (2005) found brooding males present throughout the year, but with an apparently lower incidence of brooding in winter. Similarly, Poortenaar et al. (2004) examined the reproductive biology of female H. abdominalis, looking at ovarian morphology, reproductive condition and sex steroid levels. Using these indices, they found that females were capable of reproductive activity throughout the year, presenting the potential for a protracted spawning season (Poortenaar et al. 2004). The species is socially polygamous but genetically monogamous in that they display promiscuous courtship activities but become pregnant by one female only (Wilson and Martin-Smith 2007). They also exhibit mutual mate choice (Bahr et al. 2012).
The number of juveniles (mean ± 1 SE) released per brood in a New Zealand population was 271.2 ± 27 (Woods 2005), whereas the maximum reported brood size for the species in aquaculture is 1,116 (R. Hawkins pers comm. in Lourie et al., 2004). Juveniles 16–19 mm in standard length, are released from the pouch after 24 days (Whittington et al. 2015). Larger males produce more juveniles (Woods 2005). Juvenile length and weight are not correlated with the number of juveniles per brood, parent male size or parent male pouch volume. The percentage of pouch contents that are non-viable (i.e., premature or non-viable eggs) upon juvenile release tends to be low (1.1 ± 0.2%; mean ± 1 SE of the total pouch contents) (Woods 2005). Following release from the parent male, juveniles are believed to be pelagic, at least for several weeks, Juveniles up to 8 cm in length have been collected in surface waters of the open ocean over the Chatham Rise in New Zealand (Woods, pers. obs.) and adult H. abdominalis have been captured near-shore associated with floating seaweed and debris (Kingsford and Choat 1985). The propensity for rafting presents a possible large-scale dispersal mechanism for this species.
The diet of wild adult H. abdominalis consists largely of crustaceans, in particular amphipods, caridean shrimp, and peracarids (Woods 2002).
Natural predators of H. abdominalis include fishes such as skates (Dipturus spp.), red cod (Pseudophycis bachus), trumpeter (Latris lineata), blue cod (Parapercis colias), ling (Genypterus blacodes), sea perch (Helicolenus percoides) (Graham 1974), and banded wrasse (Notolabrus fucicola) (Denny and Schiel 2001) in NZ. In Australia, H. abdominalis is taken by flathead (Platycephalus spp.), Australian salmon (Arripsis truttacea), striped anglerfish (Antennarius striatus) and birds such as cormorants (Phalacrocorax spp.) and fairy penguins (Eudyptula minor) (Kuiter 2000, K. Martin-Smith pers. comm. 2006).
This species is reported to be more active at dusk and at night than during the day in New Zealand (Paulin and Roberts 1992). In Australia, H. abdominalis has been observed aggregating in groups at night (K. Martin-Smith, pers. comm. 2006).
|Continuing decline in area, extent and/or quality of habitat:||No|
|Use and Trade:||This species is recorded in trade in low numbers (Martin-Smith and Vincent 2006, CITES 2016). They are used as curios, in traditional medicines, and the aquarium trade (Vincent et al. 2011).|
Hippocampus abdominalis is threatened by localized habitat loss and degradation due to coastal development and by being caught as bycatch in demersal trawl fisheries. Bycatch levels are thought to be low.
Globally, all seahorses are listed on Appendix II of CITES.
In Australia all syngnathids have been subject to the export controls of the Commonwealth Wildlife Protection (Regulation of Exports and Imports) Act 1982 since 1 January 1998 (Lourie et al. 2004). All syngnathids and solenostomids were gazetted as marine species under s248 of the Environment Protection and Biodiversity Conservation Act (EPBC) Act 1999.
In New Zealand seahorses cannot be targeted by commercial fisheries, but can be sold to Licensed Fish Receivers as regulated quantities of bycatch.
This species occurs in several marine protected areas, including Jervis Bay Marine Park.
|Citation:||Pollom, R. 2017. Hippocampus abdominalis. The IUCN Red List of Threatened Species 2017: e.T10057A54903879.Downloaded on 22 May 2018.|
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