Morphological features and vulnerability
Seahorses are unique creatures, immediately standing out for their morphological features. The upright posture, head bent down at an angle and the small mouth at the end of their snouts are just some of the characteristics that make them such iconic creatures. Hence, many people find it surprising to learn that taxonomically they are within the fish group. They are, in fact, members of the pipefish family. They are scientifically called Syngnathidae, which means ‘jaw-fused’. A total of 56 genera and more than 320 species belong to this family. Below the classification (Kuiter, 2003).
SUBFAMILY: HIPPOCAMPINAE-SEAHORSES AND PIGMY PIPEHORSES
There are at least 80 species of seahorses distributed across the oceans. Most species inhabit the tropical and subtropical zones, but many can also be found in temperate areas. However, none of the species have a wide geographical range. Mostly they live within 5 to 30 meters depth, depending on the species. Different species have different habitat associations, as some could be associated with seagrass, some with soft corals and others with less accessible deeper waters. This further illustrates how seahorses are such diverse and special creatures which need to be given special consideration (Kuiter, 2003).
The vulnerability of seahorses (Hippocampus spp.).
Although seahorses are iconic creatures, they are also very vulnerable due to their small size and life history characteristics. The group of seahorses (Hippocampus spp.) of the family Syngnathidae on the IUCN Red List of Threatened Species shows 2 species as “Endangered”, 12 as “Vulnerable”, 1 as “Near Threatened”, 17 as “Data Deficient”, 12 as “Least Concern”. The entire genus Hippocampus was listed as threatened by the Convention on International Trade in Endangered Species (CITES 2004). This is due to some of their life history traits which make them very vulnerable to overexploitation and habitat degradation (Jennings et al. 1999; Sadovy, 2001).
They are identified by some special biological characteristics and life history traits, such as sparse distribution, low mobility, long parental care and low fecundity, which makes them very vulnerable to different kinds of disturbances. In addition, anthropogenic exploitation is very common among these creatures. The largest issue faced by these species is the lack of knowledge about their life history characteristics, which leads to difficulties in structuring new conservation strategies to protect them.
The species Hippocampus guttulatus, which inhabits European waters, is a great example, as barriers exist within its geographic distribution. This greatly restricts/compromises the gene flow and shows high vulnerability, mainly due to weak swimming mode, the evolution of brooded young, which limit their dispersal potential. Due to variability in the coastal environment, seahorses often experience non-ideal conditions, which lead to their decline as well.
Concerns over the overexploitation of seahorses and species-specific management strategies for conservation
There are many concerns over the exploitation and unsustainable trade of seahorses. In fact, the Hippocampus genus was listed in the Appendix II of the Convention on International Trade in 2002 (Vincent et. al. 2011), but still its trade was allowed, once no decline was caused to the seahorse population when exporting them. Despite this, a lack of data is present and most of the seahorse populations are declining, due to the massive exportation happening to many different species within the genus.
Due to their appearance and mating system, they are used by aquarists, who simulate their life cycle in captivity, causing problems in their breeding cycle. Generally, attempts to keep and culture seahorses end in biological and economic failure, due to poor treatment in terms of nutrition and disease. Thus, completion of the life cycle in captivity and reproduction of the next generation is not usually reported. Therefore, many wild seahorses are overexploited and at risk (Wilson and Vincent 2000).
In addition, attempts to culture seahorses on a larger scale are also not successful. This occurs mainly in Asian countries as well as Australia, New Zealand, South Africa and the US. However, there is an important amount of literature published in China which states that seahorse culturing is well understood, but also problems have been reported. Their vulnerability to diseases and high mortality rates led to the closure of many seahorse farms in China. Recently, seeing seahorses as a conservation cause, led to the establishment of successful cultures of captive seahorses. However, they are still overexploited (Vincent, 1990). The main problems which lead to the overexploitation of seahorses are: sparse distribution, low mobility, small home ranges, low fecundity, lengthy parental care, mate fidelity (Vincent, 1990).
In many areas seahorses are under threat due to overexploitation and habitat loss, thus marine protected areas (MPAs) could help their protection by removing fishing pressure and protecting essential habitats. The protection of seahorses could be implemented by specific management options which could lead to the application of a maximum size limit (Foster & Vincent 2004), implementation of closures at certain periods of time throughout the year (Vincent, et. al. 2007) and the implementation of no-take MPAs (Morgan & Vincent, 2013).
To allow better assessment, it is essential to monitor multiple sites for a long period of time. Some biological aspects of the species such as the slow movement and strong site fidelity, small home range, early reproduction and lack of dispersive larval phase could suggest a positive response to the establishment of an MPA. However, some negative responses could be represented by the specific preferences of certain habitats not being met by an MPA and the increase of predators inside an MPA, which could lead to a decline in the species abundance (Harasti et al. 2014). Additionally, pollution and anthropogenic stressors could lead to a decline of the Syngnathids. However, there haven’t been many studies conducted on the effects of MPA’s on the Syngnathids.
Conservation strategies and future research
The main goals of the species conservation is the preservation of stable populations in their natural habitats. Implementation on the study of their ecology and life history traits is needed to conduct proper conservation management actions. Hence, genetic monitoring is advised for threatened species, such as within the Hippocampus genus, due to their vulnerability and the vulnerability of their preferred habitats.
As a conservation strategy, captive breeding programs could be useful for improving the survival of threatened species. One of the main aims of captive breeding is to be able to maintain the maximum possible genetic integrity of the species. However, one of the main threats is represented by the direct exploitation, for the uses in traditional medicine and aquaria. To avoid this, more documentation and monitoring strategies should be developed by producer regulators, such as reducing maximum allowable sizes (Foster & Vincent 2004). By doing this, seahorses could reproduce, increasing the population and reaching larger sizes. It is, however, very hard to protect seahorses from fishing by trawling. It is not just related to the seahorse conservation, but in this case, it is the whole general overfishing epidemic, which is very difficult to mitigate against. There are already many conservation actions which are trying to lead to more sustainable and environmentally-friendly ways of fishing, but this is still a large challenge to face.
Overall, seahorses are very vulnerable to anthropogenic stressors and environmental disturbances. Their life history traits and biological characteristics render them more vulnerable than other, larger species across the world. Thus, they deserve special attention and new conservation strategies to preserve them for future generations.
CITES (2004) Convention on International Trade in Endangered Species of Wild Fauna and Flora. Thirteenth meeting of the Conference of the Parties, Bangkok (Thailand), 2–14 October 2004.
Foster, S.J. and Vincent, A.C.J. 2004. Life history and ecology of seahorses: implications for conservation and management. Journal of Fish Biology 65: 1-61.
Harasti, D., Martin-Smith, K., & Gladstone, W. (2014). Does a no-take marine protected area benefit seahorses? PloS one, 9(8), e105462.
IUCN (2013) 2013 IUCN Red List of Threatened Species.
Available at: http://www.iucnredlist.org/
Jennings, S., Reynolds, J. D. & Polunin, N. V. C. (1999). Prediction the vulnerability of tropical reef fishes to exploitation with phylogenies and life histories. Conservation Biology 13, 1466–1475
Kuiter, R. H. (2003). Seahorses, pipefishes and their relatives: A comprehensive guide to syngnathiformes (Revis ed.). Chorleywood, UK: TMC Publishing.
Morgan S, Vincent ACJ (2013) Life-history reference points for management of an exploited tropical seahorse. Marine and Freshwater Research 64: 185–200.
Sadovy, Y., 2001. The threat of fishing to highly fecund fishes. Journal of Fish Biology, 59, 90–108
Vincent, A. C. J. (1990). Reproductive Ecology of Seahorses. PhD Thesis, Cambridge University, U.K
Vincent, A.C.J., Meeuwig, J.J., Pajaro, M.G. & Parante, N.C. (2007) Characterizing a small-scale, data-poor, artisanal fishery: seahorses in the central Philippines. Fisheries Research. 86:207-215.
Vincent ACJ, Foster SJ, Koldewey HJ (2011) Conservation and management of seahorses and other Syngnathidae. Journal of Fish Biology 78: 1681–1724
Wilson, M. J., & Vincent, A. C. (2000). Preliminary success in closing the life cycle of exploited seahorse species, Hippocampus spp., in captivity. Aquarium Sciences and Conservation, 2(4), 179-196.