Hippocampus abdominalis is known in Australia from Newcastle, New South Wales (NSW) southwards throughout Victoria (Vic), Tasmania (Tas) and westwards as far as the northern Great Australian Bight in South Australia (SA) (Kuiter 2001). It has been found to depths of at least 35 m (Kuiter 2001).
In New Zealand the species is widespread within the 200-mile Economic Exclusion Zone (EEZ), from the Three Kings Islands in the north, to the Snares Islands in the south, and at the Chatham Islands (Scrimgeour 1986, Paulin and Roberts 1992). In New Zealand, depth distribution varies considerably where sightings have been recorded from the intertidal to a maximum depth of 104 m (Amaoka et al. 1990); occurrences from the surface to 40 m are more common (Paulin and Roberts 1992, Francis 1998, Lourie et al. 1999, Stevenson and Beentjes 2001).
Museum Records (Australia)
19 specimens (height 46–250 mm), captured from depths of 0–32 m, ranging in geographical distribution from Newcastle (32°52’S, 151° 75' E) to the northern Great Australian Bight (approx. 32°24’S, 133°30’E) Specimens were collected between 1916 and 1996. There are additional specimens from NSW in various fish collections around Australia, but the identifications of these specimens have not yet been verified [Pogonoski, 2002 #3720].
Follow the link below for Figure 2: known extent of distribution in Australian waters.
The extent of occurrence for H. abdominalis includes the seawaters of south-eastern Australia and New Zealand (Lourie et al. 1999, Lourie et al., 2004). Within New Zealand waters, H. abdominalis are known from the Three Kings Islands in the north, the Snares Islands in the south, and at the Chatham Islands to the east (Scrimgeour 1986, Paulin and Roberts 1992).
Area of occupancy is generally unknown but there is assumed to be suitable habitat throughout the geographic range. Populations of H. abdominalis have been reported from Sydney Harbour, NSW; Lakes Entrance, Port Phillip Bay, Western Port, Vic; Tamar, Derwent and Huon River Estuaries, Tas; Spencer Gulf and Yorke Peninsula, SA (Kuiter 2000 & 2001, Martin-Smith and Vincent 2005, K. Martin-Smith pers. comm., J. Manna pers. comm.), Whangateau Harbour (Kuiter 2000) and Wellington Harbour North Island NZ (Woods 2002).
Habitat and Ecology
Adult 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). 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.): this occurs at all times of the year in at least 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.). 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.).
As with other members of the seahorse and pipefish family, males incubate eggs in an abdominal pouch and eventually release young that look like miniature replicas of adults (Edgar 1997). 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 (in press) 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 number of juveniles (mean ± 1 SE) released per brood in a New Zealand population was 271.2 ± 27 (Woods, in press), 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 about thirty days. Larger males produce more juveniles (Woods, in press). 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, in press). 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). There are no differences in diet between male and female seahorses. Smaller seahorses consume relatively more crustaceans than larger seahorses, where a greater proportion of their gut contents are comprised of amphipods when compared with adults. There is evidence for seasonal differences in diet, with amphipod consumption peaking in spring and summer, and decapod consumption lowest in autumn (Woods 2002).
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.).
Water temperature and chemistry ranges based on 6 samples.
Depth range (m): 1 - 130
Temperature range (°C): 8.720 - 11.538
Nitrate (umol/L): 6.885 - 13.334
Salinity (PPS): 34.388 - 34.692
Oxygen (ml/l): 5.872 - 6.334
Phosphate (umol/l): 0.504 - 0.880
Silicate (umol/l): 2.592 - 3.696
Depth range (m): 1 - 130
Temperature range (°C): 8.720 - 11.538
Nitrate (umol/L): 6.885 - 13.334
Salinity (PPS): 34.388 - 34.692
Oxygen (ml/l): 5.872 - 6.334
Phosphate (umol/l): 0.504 - 0.880
Silicate (umol/l): 2.592 - 3.696
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Recorded at 40 meters.
Life History and Behavior
Molecular Biology and Genetics
Barcode data: Hippocampus abdominalis
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Hippocampus abdominalis
Public Records: 2
Specimens with Barcodes: 4
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
No historical data exist for in situ population structure or longevity and little information on growth rates. Only one project has assessed trends in abundance of H. abdominalis where declines of 79–98% were observed in three areas of the Derwent Estuary, Tasmania, Australia between 2001 and 2004 (Martin-Smith and Vincent 2005). Unpublished data from a study of a population of H. abdominalis in Sydney Harbour, NSW, Australia showed no clear trends in abundance between Jan’ 2003 and Jan’ 2005 (K. Martin-Smith pers. comm.). Information from research trawl collections in New Zealand, suggests generally low biomass (e.g., Stevenson and Beentjes 2001), although such trawls are usually conducted away from habitats such as macroalgal stands, where seahorse biomass is likely to be highest. Most available information relates to ex situ breeding, growth, survival and tagging in relation to aquaculture (Woods 2000, 2003a-d & 2005, Woods and Valentino 2003, Woods and Martin-Smith 2004). There is some information available on aspects of reproduction and diet in wild (in-situ and ex-situ) H. abdominalis from Wellington Harbour (North Island, New Zealand) (Woods 2002 [in press], Poortenaar et al. 2004).
The species is thought to face five main threats: 1. bycatch in commercial fisheries (pelagic finfish, benthic shellfish and invertebrate fisheries); 2. unregulated take; 3. risk through intrinsic life history traits; 4. natural predation; and 5. insufficient protection under the CITES 10 cm minimum size limit. Bycatch exploitation appears to be limited in geographical area relative to estimated extent of occurrence and is not suggestive of large-scale exploitation. Unregulated take could become a growing problem if demand in extant traditional medicine markets or in the home aquarium trade increase. In Australia, H. abdominalis would be protected under present legislation. However, the absence of catch limits in New Zealand in terms of numbers or sizes, may present the potential for exploitation to threaten wild populations. This is particularly true in light of the poor protection afforded via CITES. The species has a few life history traits that suggest vulnerability to exploitation (low density), but also other traits thought to confer resilience (rapid growth, short life span, rapid maturation and small size). The synergistic effects of natural predation in combination with exploitation need study.
A relatively conservative measure of the extent of occurrence for H. abdominalis in both Australia and New Zealand can be estimated by using GIS data to calculate the possible area in km2 down to 40 m, which is regarded as the usual depth limit for this species (Paulin and Roberts 1990). For New Zealand, this possible extent of occurrence does not take into account offshore islands (e.g., Chatham Islands, Three Kings Islands etc.) or estuarine areas. This 40 m depth extent of occurrence is calculated at 42,621 km² for New Zealand coastal waters. If the bathymetric constraint is pushed down to 100 m depth (maximum recorded depth for H. abdominalis is 104 m), then the total estimated extent of occurrence becomes 70,117 km² (see Figure 1). Similarly, for Australia, the extent of occurrence is calculated at 176,947 km² for a 0–40 m depth range and 336,696 km² for a 0–100 m distribution. Australian calculations were based on GIS ETOPO2 data with 8 km² grid cell resolution, so numbers should be treated as order of magnitude estimates.
The absence of information on population size, structure and many aspects of the species’ ecology presently precludes the ability to estimate or infer global population trends for H.abdominalis.
Follow the link below for Figure 1: known bathymetric boundaries for the species around coastal mainland New Zealand.
- 1996Vulnerable(Baillie and Groombridge 1996)
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.)
1. Bycatch in commercial demersal fisheries.
2. Unregulated take (recreational, domestic or for export).
3. Intrinsic life history parameters.
4. Natural predation.
5. The appearance of protection under CITES international trade legislation; a 10 cm size limit is likely to provide inadequate protection for this large species of seahorse.
1. Bycatch and Commercial Fisheries
Legislation requires that all interactions of commercial export fisheries with any syngnathid, including H. abdominalis, are recorded. However, there are few documented examples of commercial bycatch of H. abdominalis suggesting either low compliance or few interactions. Given the nature of Australian commercial fisheries operating in the geographic range of H. abdominalis (i.e., gear type, depth range, target species) it is probably unlikely that significant numbers are caught as bycatch. All of these commercial fisheries have been assessed against sustainable fishing guidelines by the Department of Environment & Heritage and certified as not having unacceptable impacts on syngnathids in either the short-term (Wildlife Trade Operation) or long-term (Exempt fishery).
However, despite mandatory reporting of syngnathid exports since 1998, Australian figures differed considerably from import statistics elsewhere. Official Australian government international trade data for the period 1998–2002 showed that declared exports of dried H. abdominalis were minimal (<10 kg) and sourced from aquaculture operations only. However recorded imports of seahorses (potentially including other Australian Hippocampus species) to China, Hong Kong and Taiwan over the same period were over 700 kg. It seems probable that other species of syngnathid (particularly pipehorses, Solegnathus spp.) from Australia were recorded as seahorses when they were imported into Hong Kong and Taiwan through misidentification, translation and data coding errors (Martin-Smith and Vincent in press). Nonetheless, species identities need to be verified in these jurisdictions.
In New Zealand, seahorses cannot be targeted by commercial fishing (1983 Fisheries Act). As such, they are not part of the New Zealand fisheries Quota Management System (QMS) that regulates the total amount of commercial catch in New Zealand. However, H. abdominalis caught as incidental bycatch during commercial fishing, may be legally sold to Licensed Fish Receivers (LFR) (section 67 of the 1983 Fisheries Act) limited to <10 kg wet weight per 24 hr period (section 67(2)) (Woods 2000). Bycatch has historically been solicited by New Zealand companies with strong Asian connections for domestic medicinal use and for export to countries such as Hong Kong and Taiwan for traditional medicinal (TM) usages (Vincent 1996). Seahorses caught as bycatch, but not sold for TM use, are sometimes kept as aquarium pets or dried as a curio. Seahorses are not known to be used as a food in New Zealand.
Only a short recorded catch history of H. abdominalis in New Zealand is available. Data from the Ministry of Fisheries databases (follow the link below to see Table 1.1) shows the total estimated catch (estimated actual catch by vessel skippers on day of fishing) of H. abdominalis from 1989 through 2005 was 240 kg, whereas the landed catch (recorded at factory/processing plant) for these years was 1,625 kg. It should be noted that because of the difference between the ways in which fishing year is recorded between estimated and landed catch data, estimated catch data appears one fishing year ahead of landed catch data, yet estimated catch and landed catch forms are filled out in the same calendar year. There are obvious disparities between estimated and landed catches, which may indicate either that estimated catch data is underestimated or that landed catch data is incorrect due to reasons such as species miscoding or data entry error. Miscoding of H. abdominalis (SHO) as Silver Dory (SDO – Cyttus novaezelandiae), a fish taken irregularly as bycatch has been known to occur within the fisheries database. The large pipehorse Solegnathus spinosissimus (SDR) is also sometimes misidentified by fishers as seahorses.
Detailed examination of individual Catch Effort Landing Return data (CELR, submitted by quota holders documenting total catch and fishing effort), reveal that the single largest catch of seahorses reported by one fisher was 60 kg in the Nelson/Marlborough dredge fishery. This is the exception in terms of catch size, as the majority of individual CELR’s reported seahorse catches <1 kg. Statistical areas of catch are on the Eastern side of New Zealand and central New Zealand, effectively within Fisheries Management Areas (FMA) 1 (Auckland East), 2 (Central East), 7 (Nelson Marlborough) and 20 (Kapiti Coast). The majority of seahorses were caught in statistical areas 010–011 (south of Auckland, North Island) and the Nelson Marlborough FMA (follow the link below to see Figures 3 & 4). However, the 010–011 data should be queried because of the purported catch method (see below for discussion on purported catch method of bottom long lining). Estimated catch by fishing method is summarised in Table 1.2 (follow the link below).
Seahorses were caught using a variety of methods. However, seahorses were probably not attracted to the fishing equipment through bait action. In the case of set nets, fish traps and cod traps, seahorses probably attach to the fishing equipment to use it as substratum and are then hauled onboard the fishing vessel still attached (Woods, pers. obs). In the case of dredging, seahorses are probably caught by the dredge whilst foraging over shellfish habitat following settlement on suitable near-surface substratum as juveniles (e.g., mussel spat-catching lines).
In the case of the bottom long line (BLL) data, this is probably incorrect and likely to be a species miscoding or data entry error. Bottom long lining for snapper is particularly popular around northern North Island and Bay of Plenty regions (010–011 statistical areas). Seahorses should not get hooked on long lines as the hooks used should be too large (usually size 5–15 hooks) for the seahorse’ small mouth, and seahorses are not attracted to large, non-moving bait. If the BLL data is correct, this leaves the possibility that the seahorses are rapidly colonising and attaching (using their prehensile tails) to set long lines, which in turn implies a very dense mobile surrounding population. This is unlikely given the limited information available on population densities for seahorses. From reviewing the catch data, dredging numbers appear generally feasible given the catch sizes, gear used, and observation of seahorse settlement on substratum above the dredged seafloor.
2. Unregulated take (Recreational, Domestic or for Export)
As H. abdominalis is protected by legislation throughout its geographic range, unregulated take should not pose a threat to populations. In State waters (<2 nautical miles from the coast) relevant laws in NSW, SA, Vic and Tas require that all recreational and domestic fishers hold a permit, which should ensure that the take is sustainable. Illegal take has been reported sporadically (D. Harasti, pers. comm.). However, there is little evidence of systematic IUU (illegal unregulated and unreported) fishing of H. abdominalis. Similarly, in Australian Commonwealth (federal) waters (2 nm to the edge of the EEZ), all syngnathids are protected as listed marine species by the Environment Protection and Biodiversity Conservation Act (EPBC), where under this legislation it is an offence to take, trade, injure or kill listed species except under permits issued by the Minister of the Environment. Under the former Australian Wildlife Protection Act (Regulation of Exports and Imports (WPA) (1 and the present EPBC (effective for syngnathids 2001), syngnathids have had the same level of protection since 1998.
As a non-QMS species, the recording of accurate export data for H. abdominalis has historically not taken place. Dried seahorses were either included in the export category 0305.59.00 (Other fish, whether or not salted but not smoked), or 0301.10.00 (Ornamental fish). Therefore, reconciliation of exports with estimated and landed catches is not historically possible. There are no catch limits for the amateur-take of seahorses in New Zealand in terms of numbers or sizes.
3. Intrinsic Life History Traits
By virtue of their life history characteristics, seahorses are generally regarded as being particularly vulnerable to direct over-exploitation, indirect fishing pressure through non-selective fishing gear or other disruptions such as habitat loss/degradation and environmental pollution around their coastal habitats (Lourie et al. 1999, Bell et al. 2003, Foster and Vincent 2004, Martin-Smith and Vincent 2005). Some of these traits apply to H. abdominalis, while other aspects of their life history may confer resilience.
Records from Australia and benthic trawls in New Zealand suggest that like other seahorses, populations are generally sparse (therefore individuals might have difficulty finding a mate in affected areas). However, mark-recapture studies in Tasmania and NSW have shown no evidence of mate fidelity as has been observed in other seahorse species (K. Martin-Smith, pers. comm.). It should be noted that trawled soft bottom may represent marginal habitat for the species, and populations may be more abundant in areas with greater rugosity or diverse benthic structure.
In fishes, a particular suite of life history traits is correlated with high recovery rate (Hutchings and Reynolds 2004); this includes rapid growth, short life span, small body size and low age at maturity (Reynolds et al. 2001). It appears that at least some of these traits may be relevant to H. abdominalis.
The age and growth rates of wild H. abdominalis are not well documented. The only in-situ data on growth for H. abdominalis (northern New Zealand) reports rates of 2.8 mm per month increases in standard length (SL) for small seahorses, and rates of up to 14.9 mm per month for 16 cm SL seahorses (Van Dijken 2001). Based on operculum ageing and length/weight relationships in wild animals, Lovett (1969) estimated that for H. abdominalis in Tasmania, seahorses from 9.1 to 11 cm in length were one year old; those 9.1–16.1 cm were 1–2 years old; those 14.4–19 cm were 2–3 years old; those 18–22 cm were 3–4 years old; and finally, those over 22 cm in length were 4+ years old. It is difficult to contextualize in situ growth rates or lifespan of H. abdominalis relative to other seahorse species because these data are generally not yet available. However, longevity is short when compared with families such as, for example, scorpaenids, serranids and lutjanids that live >25–40 years (Coleman et al. 2000).
If Lovett’s age/growth estimates are broadly applicable across the species’ range, then H. abdominalis reaches first sexual maturity at around one year of age (wild H. abdominalis 10 cm in length from Wellington Harbour were capable of brooding embryos, Woods, in press). Reproductive output of male H. abdominalis increases in terms of brood number, with size (Woods, in press). Seahorses show a relationship between maximum size and the appearance of reproductive characteristics (inferred to represent size at first reproduction) typical of other bony fishes (Foster and Vincent 2004), suggesting that they be not more vulnerable to exploitation than other teleosts.
Low fecundity is also cited as a life history trait that may confer risk to a species, although other authors point out that there is no relationship between fecundity and a population’s potential for recovery (Hutchings and Reynolds 2004). Seahorses have small brood sizes relative to other fishes with parental care (Foster and Vincent 2004). However, seahorses also mate iteratively which increases their overall reproductive output. H. abdominalis in particular appears to be reproductive year around, with the greatest proportion of juveniles occurring in the Austral summer (M. Hickford, unpublished data). Seahorses are also released from the male brood pouch fully metamorphosed, such that although numerically small relative to many other teleosts, broods of H. abdominalis may experience greater survivorship than other young.
4. Natural Predation
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.). No research has yet addressed the effects of predation in any species of seahorse. Presumably H. abdominalis should have evolved to sustain natural predation rates, but the effects of predation in combination with exploitation remain unknown.
5. The Appearance of Protection Under CITES Appendix II legislation
All seahorse species are listed on CITES Appendix II, which, although still permitting trade, requires that such trade is determined to be non-detrimental to exploited populations. To issue a Non-Detriment Finding (NDF) the relevant CITES regulatory body must have a reasonable knowledge of the biology and ecology of the seahorse species concerned. In lieu of NDFs, a minimum seahorse height, such as the 10 cm minimum height (mHT) recommended by CITES may be used. The 10 cm mHT size restriction is an across-species compromise that provides one value for all species in the genus. For the majority of seahorse species that are similarly sized, such a minimum size restriction may well be applicable. However, the 10 cm mHT might not be applicable to seahorse species that are markedly different from an average seahorse size. For brooding male H. abdominalis from Wellington Harbour, when the CITES 10 cm mHT size restriction is translated to length (11.56 cm SL) and plotted against recorded brood sizes, it appears that this size restriction is not an adequate protective measure for H. abdominalis at this location (Woods, in press) as the data suggest that males appear to begin brooding just before the proposed minimum 10 cm mHT size and produce relatively low numbers of juveniles, leaving the most productive males (number of juveniles produced) open to exploitation. A larger minimum size restriction to allow sustainable exploitation of this species would appear to be required. Reproductive output should be modeled in light of in situ survivorship data in order to understand the implications of the 10 cm size limit for population persistence. Australia’s legislation should enable NDFs through appropriate management of permits at the State level and assessment of commercial export fishing operations under the EPBC.
CITES Appendix II-listing for entire genus (Lourie et al. 2004). Australia and New Zealand are CITES parties.
1. Listed as Data Deficient by Environment Australia.
2. 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).
3. All syngnathids and solenostomids were gazetted as marine species under s248 of the Environment Protection and Biodiversity Conservation Act (EPBC) Act 1999 (Pogonoski et al. 2002), with implementation effective in 2001 (Lourie et al. 2001, Martin-Smith, pers. comm.).
4. Protection under the relevant fisheries laws in NSW, SA, Tas and Vic.
5. No ASFB Listing (Pogonoski et al. 2002).
6. Present in the following Australian Marine Protected Areas: Jervis Bay Marine Park, southern NSW. Suspected to be in most NSW Aquatic Reserves within its range (Pogononski et al. 2002).
1. Seahorses cannot be targeted by commercial fisheries, but can be sold to Licensed Fish Receivers as regulated quantities of bycatch (see Threats section).
2. Big bellied seahorses are present in the following New Zealand marine reserves, where legislation protects all wildlife from extraction or harm: Kapiti Island reserve (2,167 ha area), Kokomohua reserve, Te Angiangi reserve, Te Wharawhara (1,075 ha area) (Woods pers.obs). They may also be present in other existing marine reserves but their presence has not been documented. There are many more marine reserve areas currently under review around New Zealand, which may include seahorses in their fauna.
Relevance to Humans and Ecosystems
|This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (July 2012)|
The big-belly seahorse or pot-bellied seahorse, Hippocampus abdominalis, is one of the largest seahorse species in the world with a length of up to 35 cm, and is the largest in Australia. Seahorses are members of the Syngnathidae family, and are teleost fishes. They are found in southeast Australia and New Zealand, and are listed on Appendix II of CITES.
The big-belly seahorse is found among algae, seagrasses, and rocky reefs in shallow water, and attached to sponges and colonial hydroids in deeper areas. They also attach to jetty piles and other man-made objects, and can be found in estuaries. They usually inhabit waters less than 50 m deep, but have been found as deep as 104 m. Juveniles are pelagic or attached to drifting seaweed.
The big-belly seahorse has a forward-tilted, a long-snouted head, a distended but narrow pot belly, and a long, coiled tail. It swims using its dorsal fin with a vertical stance; when not swimming, it coils its prehensile tail around any suitable growth, such as seaweed, waiting for planktonic animals to drift by, when they are sucked up by the small mouth set at the tip of the snout much like a vacuum cleaner. Seahorses are voracious feeders, eating mainly crustaceans, such as shrimp, and other small animals living among the seaweed, such as copepods and amphipods. They do not chew, so they can eat to excess because of their small gut tract. Each eye moves separately, making it easier for them to see food and predators.
Distinguishing males from females is easy: The male has a smooth, soft, pouch-like area at the base of its abdomen where the stomach meets the tail on the front side. Males also have a fin there, but it is less obvious. The female has more of a pointed stomach with a very obvious fin at the base of it.
In the wild, breeding can commence when the seahorses are about one year old, and this can be reduced to about eight months when in captivity. Breeding in big-belly seahorses year-round, with peaks in the warmer months.
Courtship initiation involves a series of colour changes and postural displays. Dilating the opening of the brood pouch slightly, the male inflates the pouch to balloon-like proportions with water by swimming forwards, or by pushing his body forwards in a pumping action, then closing the pouch opening. At the same time, he lightens his pouch in colour to white or light yellow. The male also brightens his overall body colouration, typically intensifying the yellow. A male repeatedly approaches his selected female with his head tucked down, and dorsal and pectoral fins rapidly fluttering.
If the female is not receptive, she ignores the male, which then looks for another potential mate. If no females are receptive, the male stops displaying and deflates the pouch by dilating the pouch opening and bending forwards, expelling the water inside. If a female is receptive to a courting male, she reciprocates with her own color changes and head tucking, typically intensifying the lighter colours such as yellow and white, highlighting the contrast between these colours and her overall darker blotching and banding patterning. A series of short bursts of swimming together in tandem then ensues, sometimes with tails entwined, or with the female tightly rolling her tail up. This has often been described as ‘dancing’. After coming to rest, the male attempts to get the female to swim towards the water surface with him by repeatedly pointing his snout upwards.
If the female responds by also pointing her snout upwards, then the final stage of courtship follows. This involves both the male and female swimming directly upwards towards the water surface with both their heads pointing upwards and tails pointing straight down. If they reach the water surface, one or both seahorses can often be seen and heard to snap their heads. To transfer her eggs to the male, the female faces the male, slightly above him. Pressing the base of her abdomen against the male's pouch, she then squirts her eggs through the opening in the front of his dilated pouch.
The male seahorse brood 300-700 young at a time, and can have up to four broods in summer. Their colouring is a variable shade of brown, mottled with yellow-brown and with darker splotches. The tail is often circled with yellow bands. In deeper water where the tail is anchored to other colourful forms of life, such as sponges and hydroids, they often take on these colours.
The big-belly seahorse is a popular aquarium species and dried specimens are sold as traditional medicine in Asia. Stocks come from the wild or are aquarium-reared. They are easy to keep in aquariums and feed on small shrimp and crustaceans.
- A. B. Wilson and K. M. Martin-Smith (2007) Genetic monogamy despite social promiscuity in the pot-bellied seahorse (Hippocampus abdominalis), Molecular Ecology, 16, 2345–2352.
- Froese, Rainer and Pauly, Daniel, eds. (2006). "Hippocampus abdominalis" in FishBase. May 2006 version.
- Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8
- Chris M. C. Woods, National Institute of Water and Atmospheric Research, Received 16 July 2002; received in revised form 16 October 2002; accepted 14 November 2002 pp. 538. Effects of varying Artemia enrichment on growth and survival of juvenile seahorses, Hippocampus abdominalis. (Aquaculture 220 (2003)).
- Chris M. C. WOODS, New Zealand Journal of Marine and Freshwater Research, 2000, Vol. 34 pp. 475–485. Preliminary observations on breeding and rearing the seahorse Hippocampus abdominalis (Teleostei: Syngnathidae) in captivity. (The Royal Society of New Zealand 2000).
- Chris M. C. Woods, New Zealand Journal of Marine and Freshwater Research, 2002, Vol. 36: 655–660. Natural diet of the seahorse Hippocampus abdominalis. The Royal Society of New Zealand 2002
- Chris M. C. Woods, New Zealand Journal of Marine and Freshwater Research, 2005, Vol. 39: 881–888 Reproductive output of male seahorses, Hippocampus abdominalis, from Wellington Harbour, New Zealand: implications for conservation. (The Royal Society of New Zealand 2005).
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