Captive Breeding As A Conservation Tool
Rob Nielsen, Pacific Northwest Herpetological Society, June 1994
One of the most commonly held beliefs of amateur herpetoculturists is that their animals are a valuable source of brood stock for the reintroduction of species that have become extinct in the wild. Certainly there are many recent success stories of captive breeding programs for endangered species. Unfortunately, most animals bred in captivity by or for amateur herpetoculturists would prove to be poor seed stock for restoration of wild populations. Successful captive breeding programs have usually been last-ditch programs managed by State or Federal wildlife agencies in conjunction with zoos and some conservation organizations. Extinct as wild populations, the European bison and Przewalski's horse owe their survival to private herds maintained by zoos and wealthy Europeans. The remaining wild California condors and black-footed ferrets were captured in a desperate and successful attempt to breed captive animals for release into the wild. The Jersey Wildlife Preservation Trust has successfully captive-bred endangered reptiles from Madagascar and Round Island. It will probably be over 20 years before the success of these programs can be accurately assessed.
Zoological societies are strongly supportive of captive breeding programs. These programs fit nicely into their dual objectives of public education and the preservation of species diversity.
Generally, animal rights groups do not support captive breeding programs. This stand is based on the concept that it is immoral to interfere with the lives of all animals. This includes keeping animals captive for any reason (medical research, meat and dairy production, wool, pets, etc.). This moral prohibition can even extend to visual observation, radio-tagging and other research done on wild populations to develop effective management techniques for conservation. This argument seems to be largely theological in nature. Theological arguments of this nature are based on faith in a system of beliefs and not open to rational discussion centered around available information. This essay is intended to present a logical discussion of the pros and cons of captive breeding animals for eventual reintroduction into the wild. Therefore, I will argue the cons of captive breeding programs from the viewpoint of a wildlife biologist.
Most professional wildlife biologists tread a cautious middle-ground. A captive breeding program means that wildlife managers have failed in some fashion to preserve essential habitat critical to the species' long-term survival. Most wild populations become endangered because a portion of their habitat is modified. The change can come about from a change in weather patterns, geological disturbance, the invasion of habitat by new fauna or flora and by human activity. Eventually the change in habitat restricts the completion of the species' life history enough to reduce recruitment and survival below a critical point and extinction occurs.
Prevention of critical habitat loss is the wildlife biologist's preferred management method. There is a tendency for the public to believe that animals can be warehoused in zoological parks until habitat is restored and the wild populations reintroduced. If this were always true, the Connecticut River would teem with Atlantic Salmon.
At one time, Atlantic Salmon were so abundant during the spawning season that farm workers had clauses written into their contracts, prohibiting farmers from feeding their employees exclusive diets of cheap and abundant fish. A combination of dams constructed without fish passage facilities and logging-related damage to spawning areas eliminated salmon from the Connecticut River. During the last half century, millions of dollars have been spent on habitat restoration and fish passage facilities. Massive plants of different hatchery stocks of Atlantic salmon have been released as juveniles into the spawning tributaries of the Connecticut. Few adult fish have returned.
Each tributary stream hosted a separate stock of salmon, genetically programmed to migrate downstream at the correct time, follow the best route to the ocean feeding grounds, and return at the best time to successfully negotiate the trip back to their natal spawning beds. The Connecticut River was host to hundreds of genetically distinct stocks of salmon, each population with a life history maximized for its native tributary stream.
Obviously, it is economically unfeasible to maintain the hundreds of different salmon stocks necessary to successfully reintroduce Atlantic salmon to the Connecticut watershed by a hatchery system. Over a period of time, the few fish that return (either from the initial plant or from strays) will gradually undergo a selection process that produces a stock of fish tailored for each tributary. Unfortunately, this process takes a long time and people tend to be impatient. More hatchery fish will be planted on top of the small developing native populations. The net effect is that any genetic drift or selection occurring which in time would produce truly productive native populations will be swamped by the continued influx of non-adapted hatchery fish (Salmo homogenii?).
Most reptiles bred by herpetoculturists are intentionally domesticated. By domestication, I mean selectively bred to be easily maintained under conditions of captivity. Reptiles are bred to reach early maturity and produce large broods. Non-aggressive behavior and lack of fear for their keepers are desirable traits (reducing stress for both the keeper and the kept). Domesticated strains of reptiles are also bred to display unique color patterns (such as the lack of various pigments, odd patterns of spots or stripes, etc.). Many of these traits are counter to the survival of wild populations.
Captive-bred reptiles are often severely inbred. Although most of the breeders make a genuine effort to prevent inbreeding, most captive populations are based on a small number of ancestors. Inbreeding enables breeders to quickly select traits that are desirable in captive-bred individuals. Recessive traits are quickly expressed in inbred populations (an albino population developed spontaneously in rainbow trout during the study of inbreeding). Usually, the primary concern breeders have over the effects of inbreeding is the possibility of a reduction in fertility and viability (inbreeding depression).
Unfortunately, populations intended for eventual release into the wild require as wide a selection of genetic resources as possible. Inbreeding reduces the heterozygosity of a population, lowering its ability to adapt to novel situations. While inbreeding often produces a homozygous population with poor survival traits in the wild, outbreeding can also cause problems.
When broodstock are too distinctly related, outbreeding depression occurs. An extreme example is the production of hybrid animals from separate species. Although hybridization often produces "hybrid vigor" from an increase in heterozygosity, animals can be too heterozygous,inheriting, inheriting non-compatible genes from distantly related ancestors and experiencing a loss of viability with poor fertility and survivalship rates. It may be obvious to herpetoculturists that hybrid animals aren't suitable for reintroduction into the wild, but who keeps records? Intraspecies and inter-species hybrids are often fertile. How many of these mongrels are transferred to people who breed them without keeping a record of the animal's background? In addition, I've noticed that suppliers often provide little information on the exact location of wild caught specimen's capture or the ancestry of captive-bred animals. Usually, the animal is identified by its physical appearance. I'm sure that any experienced breeder will tell you there is often a big difference between an animal's genotype and its phenotype.
Another problem with the use of captive-bred populations for reintroduction into the wild (or the supplementation of depleted wild populations) is the spread of disease to non-infecteds populations. Attempts to return captive desert tortoises back to their native habitats backfired when released captives spread a respiratory disease to the wild populations. Often, populations of animals resistant to local disease organisms are used to establish captive breeding programs for supplementation of wild populations. When released into area where the disease organism is non-endemic, non-resistant populations are often decimated by the exotic disease.
Based on the arguments put forth in this essay, I do not suggest that captive breeding programs will not continue to be a valuable tool for wildlife conservation. What I do suggest is that populations of reptiles currently bred by herpetoculturists are probably unsuitable as a resource for future introduction into the wild.
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