Improving The Outcomes Of Native Freshwater Fish Reintroductions
Biodiversity loss is a major concern for ecologists worldwide, particularly within freshwater ecosystems. Freshwater ecosystems represent only 0.01% of the global water supply and 0.8% of the Earth’s surface. And yet, they support over 40% of known fish species. The fact that they support such a disproportionate high number of species and tend to be more vulnerable to biodiversity loss means that freshwater ecosystems are a high priority for conservation efforts globally.
Conservation biologists from Minnesota, U.S., recently carried out a comprehensive literature review to provide an overview of trends in native fish reintroductions. They wanted to identify potential predictors of the reintroduction outcomes. This would help managers attempting to reintroduce native fish to have the best chance of success. Also, being able to predict reintroduction outcomes might very well increase the willingness of stakeholders and decision makers to invest in reintroduction projects.
After going through 260 individual cases of fish reintroduction, and recording 149 successful and 109 unsuccessful attempts, the researchers arrived at several interesting findings. Inadequately addressing the initial cause of population decline was the best predictor of reintroduction failure. This means that it is vital to correctly identify and fix any issues that lead to the decline in the first place. Variables associated with habitats, such as water quality and prey availability, were also good predictors of reintroduction outcomes. Specifically, confirming the presence of a suitable habitat at a reintroduction site seems to be the most important action to avoid spawning failure.
Interestingly, the presence of non-native fish at reintroduction sites was an important predictor of author-defined failure, but not of biological outcomes. This means that the reintroduction could have been delayed or otherwise hindered but the fish still survived and reproduced. Finally, variables associated with stocking (i.e., the practice of raising fish in a hatchery before releasing them to supplement existing or create new populations), such as genetic diversity and duration of stocking, were less good predictors. But, the use of locally adapted fish and stocking over a long period of time were important factors in preventing mortality in the reintroduced population. All in all, the results suggest that the habitat we choose for reintroduction is more important to success than the species being reintroduced.
Despite the high number of studied cases, the authors note that their work represents just a sample of reintroduction efforts. In the field of conservational biology, successful projects tend to be published more often than failed projects or those with uncertain outcomes. Among their recommendations, the researchers stress the importance of long-term monitoring.