As humans, it is a natural tendency for us to try to save endangered animals and to breed animals in controlled environments because we think this is what is best for them. In many cases, we believe that captive breeding is a way of rescuing or saving these animals from being further threatened or endangered. However, a recent study shows that captive breeding is handicapping the reproductive capabilities of endangered species.
Hitoshi Araki and his colleagues from Oregon State University’s Department of Zoology conducted a research on the steelhead trouts (Oncorhynchus spp). Multiple generations of steelhead trouts were reared in captivity and bred in the wild. Observing their reproductive success rates, the researchers found that captive breeding had a negative effect on their genes and that the reproductive success rates of the steelhead trouts were reduced by approximately 40% per generation. This means that the negative effects on reproduction accumulated after each generation, which is exactly what was observed in the three-generation of the trouts’ pedigree.
For the Pacific salmon and steelhead trout, both endangered species, hatchery programs are very common. So what is the goal of these hatchery programs? Well, the goal of many hatchery programs for marine organisms is to increase their population size as fish are high in demand for human-consumption. Every year, more than five billion juvenile hatchery fish are released in the North Pacific. While hatchery fish are meant to increase the number of fish population, they are actually decreasing the natural population because hatchery fish tend to have poor genes in comparison to fish that are were raised in natural environments. This low fitness is a huge threat to the endangered species’ population as it decreases their reproductive capabilities.
So how exactly did the researchers measure the trouts’ reproductive success? First, the researchers constructed a three-generation pedigree of steelhead trouts. They compared adult-to-adult reproductive success of two different types of captive-reared fish: captive-reared fish from two wild-born parents, and captive-reared fish from a wild-born parent and a first-generation captive-reared parent. Both fish generations originated from the same local population in order to exclude any factors regarding their origin.
The study showed that the reproductive success of captive-reared fish from a wild-born parent and a first-generation captive-reared parent was only 55% of that of captive-reared fish from two wild-born parents. Comparing the reproductive capabilities of captive-reared fish to that of wild-born fish, researchers found that the wild-born fish were 59.5% more likely to be successful. Researchers found that there was no difference whether the mother was a captive-rear or wild-born parent.
Captive breeding has been most commonly used for critically endangered species. Theoretically, captive breeding gives species of declining natural populations a chance to thrive, and, ultimately, their population size would recover. However, in reality, the deleterious alleles of captive-reared trouts accumulate and weaken the gene pool of the next generation of trouts. This formerly unforeseen problem now sheds light on the question whether human interventions efforts, specifically captive breeding, can and may have deleterious effects on the species that we are trying to rescue.
One of the most startling findings of this study is that reproductive success declined sharply even after the trout were held in captivity for just a short time. However, the mystery as to why is still unresolved. What is the cause of this immediate fitness decline? All that we know for now is that the repeat use of captive-reared organisms for reproduction significantly reduces the fitness of the endangered species. Reducing the fitness of an already endangered species? Now that’s food for thought!
Sources: Araki, H. et al. Genetic effects of captive breeding cause a rapid, cumulative fitness decline in the wild. Science. 16 Oct. 2012. Web. 5 Oct. 2007.