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The seahorses, with its horse-shape head and upright movement are one of the stranger looking teleosts in the marine environment. Seahorses are grouped into a single genus, Hippocampus spp. and there are currently 33 valid species (Planas et al., 2008). Other Syngnatids genera include the pipefishs, pipehorses and seagdragons (Foster and Vincent, 2004). They are exclusively marine species but several species (H. kuda, H. abdominalis, H. capensis, H. reidi) often tolerate high salinity fluctuations due to their estuarine habitat nature (Foster and Vincent, 2004; Murugan et al., 2009). The size of seahorse species vary from small H. denise (<20 mm height) to big H. abdominalis (>300 mm height) (Foster and Vincent, 2004). Seahorses and pipefish are the only vertebrates which males have brood pouches that accommodate the embryonic stages of its larvae (Dzyuba et al., 2006). The seahorses are important predators of seagrass ecosystems and without such animals there will be some detrimental top-down ecological effects on the food web (Vincent, 1996).
Currently the seahorse faces a multitude of threats from habitat degradation to heavy exploitation by collectors and trawler bycatch (Planas et al., 2008). The seahorse fishery is a highly lucrative international trade that supply the Traditional Chinese Medicine (TCM) and aquarium industries (Vincent, 1996). The exploitations of seahorse resources in many developing countries to supply these markets have decreased the wild populations significantly (Project Seahorse, 2002, 2003). In addition, the decreasing quality of many seahorse habitats due to anthropogenic factors may have decreased the species population further (Alves et al., 2009). However, scarcity of information concerning the seahorse population has hampered the effectiveness of the conservation and management programs (Foster and Vincent, 2004). Therefore, the aim of this report is to highlight the current situation concerning the conservation of seahorses, to identify the threats that the seahorses population face, the research priorities that are needed to facilitate the conservation works and the appropriate management strategies for the conservation of seahorses.
General information on seahorses
Geographic and ecological distribution
The earliest fossil records of seahorse were recently found in the Middle Miocene beds in Slovenia (Zalohar et al., 2009). Two fossil species, H. sarmaticus (which was related to the extant species H. trimaculatus) and H. slovenicus (which was related to the extant species H. bargibanti, H. denise and H. Colemani) were believed to have lived among the seagrass and marcoalgae habitats in the temperate shallow waters of coastal western Central Paraththys Sea (Zalohar et al., 2009). Fossil studies have suggested that the genus Hippocampus originated before the closure of the Tethyan seaway and has been around for about 13-15 million years ago (Zalohar et al., 2009). From these two species, seahorses have spread to all over the globe and now there are currently 33 species under the genus Hippocampus (Planas et al., 2008). The Denise's Pygmy Seahorse (H. denise) is the most current species to be discovered (Zalohar et al., 2009).
Seahorses have a circumglobular distribution, where they can be found in both tropical and temperate regions such as in the Atlantic and Indo-Pacific oceans (50°N-50°S) (Foster and Vincent, 2004; Zalohar et al., 2009). They are often found in the temperate seagrass meadows and in the tropical coral reefs (Foster and Vincent, 2004). Indo-Pacific region has the highest distribution of seahorse species (Foster and Vincent, 2004). However, there is a positive relationship between the latitude and the size of seahorse (Foster and Vincent, 2004). Most species are found in shallow waters (<30 m) but some may inhabit deeper waters up to 100 m (Foster and Vincent, 2004). Seahorses live in a wide variety of benthic habitats, ranging from seagrass meadows to coral reefs, sponges, sea pen, macroalgae, rubble and silt/sandy bottom (Morgan and Panes, 2008). Seahorse species are separated by depth and habitat types, where some species are found in deep waters in gorgonians colonies (e.g. H. trimaculatus, H. spinosissimus, H. kelloggi) while others in shallow seagrass meadows (e.g. H. kuda) (Choo and Liew, 2003). Estuarine seahorses are able to tolerate high salinity fluctuations, where adult seahorses are able to tolerate lower salinities (up to 17 ppt) while juveniles are less tolerant (up to 26 ppt) (Murugan et al., 2009).
Biological characteristic of seahorse
Seahorses are cryptic species, as they rely on their camouflage ability to mimic the surrounding and enable them to hunt for food and hide from danger (Zalohar et al., 2009). They feed on live prey but the types of diets depend on their life stages (Foster and Vincent, 2004). Other natural defence mechanisms in seahorses include bony plates and spines that make them unpalatable to predator fishes (Foster and Vincent, 2004). Otherwise, they are a group of very vulnerable animals due to their small size, poor swimming ability, strong site fidelity, low fecundity and sparse distribution (Murugan et al., 2009; Zalohar et al., 2009). Generally, seahorse population densities ranges from low (<1 individual/m2) to high (10 individual/m2) (Foster and Vincent, 2004). Seahorses prefer habitats that can provide a suitable hiding place for them, have many holdfast structures for attachments, in addition to having an abundance of planktonic prey (Zalohar et al., 2009). Holdfast structures can be from many resources such as seagrass blades, macroalgae, tunicates, bryozoans, worm tubings, sea urchin or artificial structures (Zalohar et al., 2009). Seahorses use their tail to attach themselves to the holdfast and to stabilize the body against strong current (Zalohar et al., 2009).
The lifespan of seahorses ranges from 1-5 years (Foster and Vincent, 2004; Martin-Smith and Vincent, 2005; Curtis and Vincent, 2006). The number of male to female seahorses are usually near equal ratio (≈ 1 male : 1.2 female) (Hora and Joyeus, 2009; Murugan et al., 2009). Most seahorse are monogamous, where mating occurs exclusively between the same partner in a single breeding session, but they may change partners in other cycles (Foster and Vincent, 2004; Planas et al., 2008). Seahorses also have lengthy parental care (Foster and Vincent, 2004). Breeding season in the wild depend on the local environmental factors (light, temperature, food availability) and have peak periods (Foster and Vincent, 2004). There is a direct transfer of clutches from female to the brood pouch of male (Foster and Vincent, 2004). Eggs are generally bigger than other teleost brooders, and juveniles are more developed when released (Foster and Vincent, 2004). Depending on the species, seahorses have brood size ranging from 85-683 juveniles .
After a period of brooding (depending on species and sizes), seahorse can release anywhere from 5-2000 juveniles (Foster and Vincent, 2004). The size of juveniles ranges from 2-20 mm (height) and not related to the adult size (Foster and Vincent, 2004). Larvae pelagic durations range from 2 to 8 weeks depending on the species (Foster and Vincent, 2004). Seahorse populations generally have poor recruitment and have small home ranges (Curtis and Vincent, 2006). However, there are reports that seahorses can disperse great distances by hitchhiking on floating holdfast (e.g. seagrass blades) and swept away by the current to new sites (Zalohar et al., 2009).
Threats to seahorse
Seahorse populations are decreasing due to the combined factors of commercial trade, bycatch in shrimp fisheries, habitat loss and degradation (Fig. 1) (Morgan and Panes, 2008; Planas et al., 2008). One of the main threats to seahorse populations is the loss of natural habitat due to anthropogenic factors, landscape alteration and environmental degradation (Alves et al., 2009). Seagrass meadows are declining and under constant threats from coastal area development that contributes high suspended particles loads (Freeman et al., 2008). Studies have shown that there is a positive relationship between the quality of benthic habitat and seahorse density (Marcus et al., 2007). They also face major threats from incidental catches by the shrimp trawlers and to a lesser extent from targeted collection by skin diving (Murugan et al., 2009). Recent trends also have shown increased demand of seahorses by the aquarium and aquaculture industry (Martin-Smith and Vincent, 2005). Seahorses are also collected to be sold as curios (as key chains and jewelleries) and ornamental decorations (Baum and Vincent, 2005; Murugan et al., 2009). Other threats to seahorse populations are from invasive species (such as starfish and green crab) and reproduction limitation due to its low density and mobility (Allee effect) (Martin-Smith and Vincent, 2005).
Threats to the viability of natural seahorse population. The threats are the combined factors of population loss due to direct harvesting and fisheries bycatch, and from habitat degradation due to various anthopogenic causes. The seahorse from direct and accidental catches are sold to the TCM, aquarium, curios and even aquaculture industries where there are constant high demand (Morgan and Panes, 2008; Planas et al., 2008; Alves et al., 2009).
At the global scale, as much as 20-25 million seahorses were traded annually in about 45 countries (Hora and Joyeus, 2009; Murugan et al., 2009). From these figures, more than 50 tonnes of dried seahorses were traded annually (Murugan et al., 2009). One kilogram of dried weight represents some 260 to 1000 individual seahorses depending on harvest size and species (Vincent, 1996). Countries like India, Brazil, Mexico, Thailand, Vietnam and the Philippines are the major exporters of seahorse (Vincent, 1996; Hora and Joyeus, 2009; Murugan et al., 2009). Seahorse trade expanded from China in the mid 1980's but there were earlier known trade recorded in South America since the 1970's (Baum and Vincent, 2005). Currently, several thousands of live seahorses are exported annually from South American countries such as Costa Rica, Mexico, Panama and Brazil (Baum and Vincent, 2005). However, the main markets for seahorse products are the Far East region, particularly China and Hong Kong especially for their traditional medicine industries (Baum and Vincent, 2005).
The earliest records of the use of seahorse were by the Greeks in 342 BC for the treatment of urinal problems, baldness, rabies and infertility (Vincent, 1996). Since then, seahorses are highly sought after by the Traditional Chinese Medicine (TCM) industry (Hora and Joyeus, 2009; Murugan et al., 2009). Historical records showed that the seahorse has been used in the traditional chinese medicine since 720 AD (Vincent, 1996). The TCM industry uses seahorse for myriad of treatments, such as asthma, arteriosclerosis, impotence, backpain, skin disease, for healing of open wounds and broken bones, ease of childbirth, reduce throat phlegm and as a general tonic (Vincent, 1995). However, most healing properties of these traditional medicines are still untested in science and their effectiveness are highly subjective (Vincent, 1995). The wide arrays of healing properties from one source of medicine (seahorse) may have influenced more by folk lores than traditional medicinal knowledge (Vincent, 1995).
With the advancement of technology, the TCM industry has began producing proprietary medicine tablets which contain seahorse ingredient (Vincent, 1995). The mass production of seahorse related proprietary medicine (e.g. tablets and powder forms) has encourage higher consumption of seahorse of all grades and qualities, even those formerly rejected when sold in its dried form (Vincent, 1996). Beside China, there are also reports of uses of seahorse as traditional remedies in other countries. In Indonesia and the Philippines, seahorses are used as aphrodisiac in their traditional medicine (Vincent, 1995). In Brazil, seahorses are use in traditional medicine (zootherapeutics) to treat asthma for human and pets (Alves et al., 2009). Often in poor areas without access to proper industrialized drugs and medical facilities, sometime the only option for people is to rely on traditional medicine (Alves et al., 2009).
Management issues of seahorse
Seahorse conservation status
Based on the IUCN reports, all the known seahorse species are currently classified into three categories; seven species are classified as 'Vulnerable', H. capensis is classified as 'Endangered' while the other 25 species are classified as 'Data Deficient' (Table 2). The whole genus Hippocampus spp., however has been classified as 'Vulnerable' (Marcus et al., 2007). H. capensis is classified as 'Endangered' based on the reasons that its extent of occurrence is very limited, as it is only found in several estuaries in South Africa and is facing threats from continued habitat decline and high population fluctuations (Lockyear, 2000). Seven species are classified as 'Vulnerable' based on the reasons that there are continued decline in population size due to high level of exploitation and habitat degradation and the cause of reduction have not ceased (Project Seahorse, 2002, 2003; IUCN, 2009). H. comes is classified with the A2 category due to its continued population decline of 30-50% in the past 3 generations mainly from studies done in the Philippines (Project Seahorse, 2002). Other species were classified as 'Vulnerable' due to estimate and/or projected population size reduction of more than 30% in the past and future due to the aforementioned reasons (Project Seahorse, 2002, 2003). The other 25 species did not have sufficient data to be classified accordingly and more studies are needed.
Status of scientific knowledge and research priorities
Seahorse is a data deficient group of animals in fisheries (Curtis and Vincent, 2008). Currently, there have been many studies on the reproduction and mating of seahorses but less information is available on other aspects such as growth rate and natural population sizes (Foster and Vincent, 2004). Thus, more studies are needed on the specific species ecology and life history, in-situ abundance and comparison with internationally traded volumes (Morgan and Panes, 2008). Specifically, more scientific focus should be given to the relationship between seahorse population density and fisheries impact, age/stage based mortality due to natural condition and fishing pressure, natural growth rate of seahorses and the age at first maturity (Foster and Vincent,2004; Martin-Smith, 2006). Population models studies commonly applied in other commercial teleost species are still lacking for seahorse, thus more predictive response models studies applying methods such as yield per recruit (YPR), population viability analysis (PVA) and minimum viable population size (MVP) methods are needed to give better estimates of the actual population sizes (Martin-Smith, 2006). Only when these information are available do fishery managers and conservationists able to understand the impact of the global trade and consumption on the wild seahorse population and hopefully it will aids in the planning of seahorse conservation and management programs (Vincent, 1996).
International actions, legislations, local legislations, conservation actions
The entire genus of Hippocampus spp. was also listed in the Appendix II of Convention on International Trade in Endangered Species (CITES) since 2002 even if the implementation only began in 2004 (Project Seahorse, 2003). The international trade of seahorse are limited by the CITES convention, and the whole genus is classified as Vulnerable under IUCN Red List (Marcus et al., 2007). However, many countries where seahorses are found have specific laws and local legislations that deal with conservation of coastal marine habitats, but with varying degrees of enforcement and effectiveness (Vincent, 1996; Project Seahorse, 2002, 2003). Conservation programs focusing on coastal marine habitats and seahorse are carried out by international organizations such as Project Seahorse (Project Seahorse, 2009). In addition, many of coastal marine habitats associated with seahorses are listed in the Ramsar List of Wetland of International Importance (RAMSAR, 2009). However, being listed do not necessary mean automatic protection status for the sites since the convention only promote the 'wise use' of wetlands in each of the member's territories and in many instances wetlands are still facing considerable threats from human developments (Seto and Fragkias, 2007).
Management strategies appropriate for conservation
Some of the recommendations by CITES to its signatory countries in a workshop on seahorse conservation in 2004 were to implement the minimum size for seahorse trade, for export countries to make available basic information on their local seahorse populations and trends, identify the extent of seahorse related habitats and new areas suitable for conservation purposes, active enforcement of available laws on fisheries that may threaten seahorse populations, and more systematic record of seahorse export especially in relation to taxonomic and export volume data (Bruckner et al., 2005). One of the biggest hurdles in seahorse conservation is the increasing global market demand for seahorse from the TCM and aquarium industries (Baum and Vincent, 2005). One way to decrease the demand of seahorse in TCM industry is through cooperation with the industry itself to find alternative sources of cure that can replace the usage of seahorse in their prescriptions, while the aquarium industry and their clients should be made to realize that seahorse life expectancy in captivity is very short and it is a difficult species to look after, thus it does not make a good aquarium species (Vincent, 1996).
CITES technical committee has been considering the blanket minimum trade size of 100 mm for all seahorse species to allow the adults to reproduce before being legally caught as many of the traded species reached reproductive age before growing to this size (with the exception of smaller species such as H. kelloggi) (Foster and Vincent, 2005). If accepted, this standard size would need to be adopted by all 167 CITES signatory countries (Foster and Vincent, 2005). The 100 mm minimum size limit proposal is just an interim measure before some other permanent solutions can be found (Curtis and Vincent, 2008). Model analyses have shown that the implementation of this minimum size limit can actually decrease the decline and extinction of seahorse population by as much as 50%, at a minimal cost of 5.6% reduction in output (Curtis and Vincent, 2008). The use of a single standard minimum size for the seahorse trade facilitate the monitoring of seahorse exports as custom officers do not need detailed taxonomic description of each seahorse species and their specific minimum sizes (Foster and Vincent, 2005). An outright ban on the trade of seahorse may be unrealistic to enforce and counterproductive as too many poor communities are involved in this industry and it would be harder to track the activities if they go underground (Vincent, 1995). The minimum size standard however does not solve the problem of incidental landing of small seahorses in fisheries bycatch (Foster and Vincent, 2005).
To conserve seahorses in their natural environment, they can be considered as a flagship species for estuarine conservation (Martin-Smith and Vincent, 2005; Shokri et al., 2009). Seahorses and their allies are charismatic fishes that able to garner high public sympathy and support (Shokri et al., 2009). In addition, studies have found that using syngnathids densities and assemblages for the conservation of seagrass habitats have benefited other fish as well (Shokri et al., 2009). As Marine Protected Areas (MPAs) are relatively free from fishing pressure, it is suggested as a management strategy for the conservation of seahorses (Marcus et al., 2007). Studies have indicated that the seahorse populations benefited from demarcation of such protective areas (Marcus et al., 2007). Concurrently, implementing policies where degraded coastal marine habitat areas are compensated with the creation of new habitats by transplantation of similar size and species may help maintain the viability of seahorses' habitats (Duarte, 2002). Specific management objectives need be defined on the national and regional scales and all available options identified to facilitate in the implementation of conservation programs of coastal marine organisms including seahorse (Martin-Smith, 2006). There is no single management strategy for all seahorse species as biological and ecological requirements for each species sometime varied greatly and even contradictory thus localized strategies that look into the needs of each species are recommended (Curtis et al., 2007).
Aquaculture options pro and cons
The culture of seahorse is a recent phenomenon, and has been conducted for few species only (Planas et al., 2008). For examples, H. trimaculatus is one of the important commercial species of seahorse (Murugan et al., 2009). The H. reidi is another seahorse species suitable for aquaculture due to its fast growth (0.77±0.01 mm day-1), low mortality and early maturity (Hora and Joyeus, 2009). The culture of H. trimaculatus takes about 6.5 months to reach maximum size (125 mm), but have lower survival rate (≈65%) compared to H. kuda (Murugan et al., 2009). The culture of H. reidi takes about 4 months to reach the size of 80-85 mm (Hora and Joyeus, 2009). There is less public opposition to the cultivation of seahorses since aquaculture enterprises do not utilize the marine environment (as most cultivation are done on land) thus the perceived lack of direct environmental impact (Tlusty, 2002). Culture aspects such as light intensity, stocking density, salinity and feeding frequency directly influence the growth rate of juveniles and affect the development of broodpouch of males (Lin et al., 2009).
The knowledge about seahorse and its culture is scarce but has been increasing gradually due to its conservation concerns and high market demand (Planas et al., 2008). There is still considerable lack of information (optimum temperature, salinity, photoperiod) to enable a successful aquaculture venture of seahorse (Hora and Joyeus, 2009). Broodstock supply is often a prevalent problem in seahorse aquaculture and culturists often rely on the wild population to meet its demand (Murugan et al., 2009). Attempts to use second generation broodstocks have met with the problem of lower fecundity and egg quality often decreases as length of broodstock captivity increases (Planas et al., 2008; Murugan et al., 2009). Culture of seahorse are also prone to problems of matching the size of feed to the stage of culture, and mortality during the pelagic phase due to ingestion of air bubble are common (Hora and Joyeus, 2009; Murugan et al., 2009). Livefeeds commonly used in seahorse aquaculture include wild zooplankton, artemia and mysid shrimps (Hora and Joyeus, 2009). Finding suitable diet for days-old larvae is difficult as the commonly used artemia livefeed is too big for the larvae at this stage (Hora and Joyeus, 2009). Without proper feeding, juvenile seahorses can suffer deformities that ultimately lower their survival chances (Hora and Joyeus, 2009; Murugan et al., 2009). Seahorses also often suffer from tailrot deseases in culture conditions (Planas et al., 2008).
Overall, seahorse aquaculture is only viable if the intention is for conservation purpose, or if there is some environmental benefit to be derived from the venture, but should not be for any economic or cultural benefits, or to replace the harvest of wild animals (Tlusty, 2002). However, in the present situation, this is often not the case since most aquaculture ventures are profit driven and most will try to tap into the high demands from the TCM and aquarium industries. Removal of broodstock from the wild is strongly discouraged (Tlusty, 2002). Ultimately, some conservationists feel that aquaculture is not the answer to seahorse conservation (Vincent, 1995; Tlusty, 2002).
Prognosis for the future of seahorse
With increasing global population and decreasing available land space, development in coastal areas will likely to increase further, bringing with it the associated problems of terrestrial based pollution, increased coastal erosion and sea reclamation projects that may threaten the coastal marine habitats which are homes to the seahorses. In addition, the current pattern of climate change and projected sea level rise of 0.5cm yr-1 may see many of the present shallow coastal areas becoming unsuitable for seahorse habitats (mangrove, seagrass, macroalgae) (Duarte, 2002). The present trend of coastal marine habitats loss is projected to further decline in the future thus many of the associated animals such as seahorses and dugong may face a very bleak future of being critically endangered or even face extinction if no stronger proactive actions are implemented from now (Duarte, 2002).
As for the situation with the global market for seahorse products, the increasing economic development in China and its surrounding nations will likely to increase further the demand for seahorse products (Vincent, 1996). With more people having higher disposable income than before, whom many are already well accustomed consumers of seahorse products, the seahorse demand and consumption in the region will likely (or has already?) increase to an unsustainable level unless the people are informed of the conservation value of highly vulnerable species such as the seahorse (Vincent, 1996).
The future of the many of the seahorse species are closely linked to the viability of their surrounding habitats and the fishing pressure that they face. The most vulnerable species to face extinction are the shallow water species living in coastal area near human populations, since exploitation rates and habitat degradations in these locations are the most worrying. For people in these areas, socio-economic and development issues will take priorities over conservation concerns unless there is a significant shift of public perception on the value of conserving animals such as seahorses. Seahorse, like any other teleost fishes, can be a renewable fisheries resource if they are properly managed with the backing of local community support and sound scientific data.
- Implementation of the 100 mm minimum size for seahorse trade (Bruckner et al., 2005)
- Gathering of basic information of local seahorse populations and trends in exporting countries (Bruckner et al., 2005)
- dentification of the extent of seahorse related habitats and new areas suitable for conservation purposes (Bruckner et al., 2005)
- Active enforcement of available laws on threats to seahorse populations and habitat (Bruckner et al., 2005)
- Adopting a more systematic system of recording seahorse export data and verifying the taxonomy of exported species (Bruckner et al., 2005)
- Cooperation with the TCM industry to find alternative sources of cure to replace the usage of seahorse in their prescriptions (Vincent, 1996)
- Discourage the rearing of seahorse in the aquarium industry due to complicated maintenance and short lifespan (Vincent, 1996).
- Promotion of seahorse as a flagship species for estuarine conservation (Martin-Smith and Vincent, 2005)
- Using MPAs as a management strategy for the conservation of seahorses (Marcus et al., 2007).
- Implementing policies where degraded coastal marine habitat areas are compensated with the creation of new habitats of similar features (Duarte, 2002).