Release of captive-bred and captive-held syngnathids into the wild

Project Seahorse encourages the careful management of captive syngnathids so as to ensure that casual releases into natural habitats do not occur. Syngnathid populations are threatened in some parts of the world and the release of captive-bred or captive-held animals is often viewed as a useful method of bolstering these threatened wild populations. The prospect of captive breeding for release into the wild is also sometimes used as justification for holding animals in captive populations, a means of disposing of unwanted or surplus stock, or a public relations gesture to attract support for an enterprise.

The release of captive animals must, however, be approached carefully as it has the potential to severely damage wild syngnathid population and marine ecosystems. The Re-introduction Specialist Group (RSG) of the World Conservation Union (IUCN) notes that formal releases are lengthy, complex and expensive processes that require preparatory and follow-up activities. They should not be attempted without guaranteed long-term financial political and local support, and the RSG strongly discourages casual releases.

The four main types of releases need to be differentiated as the severity of their impacts varies.

Translocation is the transfer of wild syngnathids from one site to another where conditions may be different. Translocated syngnathids may be held in captivity for variable periods of time before being released into the new site.
Supplementation is the release of captive syngnathids into an area where a wild population still exists.
Re-introduction is the release of captive syngnathids into an area where the local population has been extirpated (gone extinct locally).
Introduction is the release of non-native (exotic) syngnathids into an area where there has never been a population of that species.

Three main conservation issues may arise from planned or accidental releases.

  • Disease transmission: diseases may be transmitted from released syngnathids to wild syngnathids.
  • Genetic threats: released syngnathids may threaten the genetic diversity of wild populations.
  • Community disruptions: released syngnathids may disrupt the structure and function of marine communities.

Disease transmission

The release of captive animals must be managed carefully to diminish the risk of disease transmission to wild populations. While disease undoubtedly occurs in wild populations, it is unlikely to reach the proportions and severity seen in many culturing and holding facilities where animals are often maintained at unnaturally high densities in artificial conditions. All animals in captivity, unlike those in the wild, may survive for long periods of time because of the absence of predators and use of medications. Most worryingly, disease treatments have the potential to hide the effects of a disease-causing organism without necessarily eradicating it. Thorough screening procedures are, therefore, essential in any program that transfers captive syngnathids into the wild.

The risk of disease transmission is increased when non-native syngnathids are introduced into an area. Introduced syngnathids may bring with them new disease organisms against which local species may have little or no natural resistance. The potential for disease transmission from captive to wild populations has been highlighted in the salmon and prawn aquaculture industries in North America, Asia, Europe and elsewhere. Where these impacts have occurred, the effects on wild populations have been severe.

Genetic threats

The genetic diversity of wild populations could be threatened when captive-bred animals are released into the wild. Captive-bred animals are usually obtained from a very limited number of parent animals (founders). Their genetic diversity may, therefore, be quite low in comparison to that found in the wild. If large numbers of these animals are released into an area, there is a very real risk that they could swamp the genetic diversity of the recipient wild population, thus lowering its overall genetic diversity in the long term.

This is problematic as genetic diversity acts as a safeguard against randomly occurring events such as disease epidemics and environmental changes that may otherwise destroy entire local populations. Without this diversity, populations are far more vulnerable to such events. Risks are exacerbated if the released syngnathids are from a captive population that differs genetically from the wild population as this may also lead to fundamental alterations in the genetic structure of the wild population.

The artificial conditions associated with culturing may result in captive-bred fishes having different genetic traits from those in the wild. Thus, the released fishes may be genetically less adapted to conditions in the natural habitat. In the simplest case, the released animals die soon after release, with relatively few conservation consequences. If, however, these animals survive to breed with wild conspecifics, unsuitable genetic traits may be passed on to future generations. This could eventually lead to a reduction in the long-term viability of the wild population, as has occurred, for example, in trout.

Community disruptions

The risk of disruptions to marine communities is perhaps most pronounced when exotic species are introduced into an area. Such introductions may disrupt the structure and function of the local ecosystem, and lead to the extirpation (localised extinction) or extinction of native species. In most cases, the introduced species dies shortly after being released because of incompatibility with the new environment.

In numerous well-known cases, however, the introduced species thrives. The introduction of an exotic syngnathid species into the marine environment, therefore, could potentially lead to the establishment of a viable population that may compete with local species for food and habitat. This could potentially have severe detrimental impacts on the local species and community. Numerous examples of problems associated with the introduction of exotics into aquatic systems exist all over the world. Australia, for example, has a list of noxious introduced fishes, such as the ubiquitous tilapia, goldfish and carp, which are to be destroyed when caught.

The release of captive syngnathids into areas where wild populations of the same species are present carries with it the risk that a sudden influx of new individuals into a small area could result in changes in the social structure of the wild population as a result of increased competition for food, shelter and mates. Such alterations in social and community structure may have negative effects on the viability of the wild population.

Management issues

The re-introduction of captive syngnathids needs to be managed carefully. Many syngnathid populations are declining relatively rapidly and there may well be specific cases in the future where re-introductions may have to be considered. One example might be the Knysna syngnathid (H. capensis), which was recently moved from Vulnerable to Endangered on the IUCN Red List of Threatened Species. The limited and fragmented distribution of this species coupled with the potential for pollution in its estuarine environment renders H. capensis at risk of extirpation. Should this occur, the formal re-introduction of captive-bred syngnathids may become necessary. However, the ill-planned or casual release of syngnathids could have disastrous impacts on the wild population, through the introduction of disease, for example. Thorough preparatory activities must be conducted prior to any release being initiated and a long-term monitoring program put into place. Moreover, the factors leading to the original decline in the wild population would also need to be addressed, and management plans set in place to avoid a similar extirpation of the introduced population.

Conclusion

Releases can potentially severely harm wild populations of syngnathids. The release of captive syngnathids into the wild is an increasingly common activity around the world and is often mistakenly viewed as a valuable contribution to the conservation of wild syngnathids. It would be far better for concerned individuals and organisations to spend their resources on managing wild syngnathid populations in a sustainable manner and to focus on removing the factors that threaten syngnathids in the first place. If conservation is the goal, it will always be preferable to seek to increase the viability of wild populations than to bring animals into captivity for rearing and subsequent release.