The number of captive-bred salmon released into the wild each year are astonishing. In the United States, hatchery-reared Pacific salmon were released in excess of two billion times in 2016.
What if releasing hatchery fish into the wild—a regular practice—was actually doing more damage than good?
Recent research from UNC Greensboro experts revealed that the traditional fishery management strategy offers no benefit, actually harms the target species, and has an adverse overall effect on ecosystems.
Dr. Akira Terui, a freshwater ecologist at UNC Greensboro and the study’s principal author, stated in the press release that many resource managers think it is always a good idea to return native animals that have been raised in captivity into the wild. Yet, the availability of resources in ecosystems is delicately balanced, and introducing a lot of new people can upset that. Imagine cramming 100 people into a studio apartment; that arrangement is unworkable.
Deliberate release of native species threatens ecological stability is the title of a study that was written up in the Proceedings of the National Academy of Sciences.
Programs for release are seen to be economically and ecologically advantageous because release logically benefits populations. This firm conviction made it difficult to evaluate hatchery releases’ effects on ecosystems objectively. Ecosystems can only support a certain number of species, though. The environment might suffer if we release people in excess of this limit, Terui warned EcoWatch in an email.
The scientists employed mathematical modeling to forecast how large-scale releases of fish from captivity may affect wild species. To test and validate their estimates, they analyzed data collected from 97 Japanese rivers over the course of more than 20 years of stream monitoring.
According to Terui in the press release, the ecosystem’s delicate equilibrium that permits diverse fish species with comparable needs to coexist is precarious. The populations of the other species drop as a result of increased competition for resources when a species is released in large numbers into an ecosystem that is not able to support them.
The research team discovered that the discharge of the captive-bred fish significantly damaged the native species. The fish being released into the environment are genetically distinct from the wild species and disseminate genes that lower their ability to thrive in their native habitat, according to studies conducted over the previous 20 years, according to Terui.
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We discovered that a species’ naturally bred populations decline as a result of competition from a large number of captive-raised individuals. According to Terui in the press release, replacing naturally existing members of a species with captive-bred ones has the potential to impair genetic diversity and reproductive fitness.
According to Terui, fish grown in captivity exhibit different behaviors than salmon raised in the wild, which may have an impact on the salmon’s survival.
Hatchery people have a lot of distinctive characteristics. For instance, hatchery salmon are renowned for their bravery. According to Terui, these variations are thought to develop as a result of adaptation to the imprisoned habitat. Although there is ample evidence that nursery fish perform poorly in the wild, as far as I can tell, the precise mechanisms underlying this tendency are still unknown.
Having said that, hatchery fish have a variety of traits (such as behavior) that may make them less likely to survive in the wild. For instance, brash young individuals might compete better for food, but they might be more susceptible to predators. This is merely an illustration; there may be further options.
Too many members of a given species can disturb the delicate balance that plants and animals must maintain with their surroundings in order for ecosystems to function properly.
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If we release hatchery fish into the environment in excess of what the ecosystem can handle, there may be too much competition among the released species and with other species for resources (such as food and habitat). Terui told EcoWatch that this has a negative effect on ecosystems.
Terui continued by saying that before releasing young animals into the wild, hatcheries should determine if specific habitats can maintain them.
The condition of the receiving ecosystem should be carefully taken into account in hatchery initiatives. If the environment is damaged, it is unlikely that it would be able to support the liberated persons; instead, it will make the competition for the meager resources, which are already impaired, worse.
Hatchery projects, in my opinion, are only useful in a few specific circumstances. Instead, Terui argues that we should place a higher priority on environmental preservation and restoration so that ecosystems can sustain healthy and long-lasting populations.
The research team discovered that over time, the native fish saw larger population density swings and fewer species overall once hatchery salmon were released into the wild. This population instability makes it more likely that some populations may vanish entirely.
Currently, the U.S. Fish and Wildlife Service invests hundreds of millions of dollars in fish hatcheries each year. Terui stated in the news release that natural resource managers need to take into account other objectives including habitat conservation.
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By removing dams that isolate wild fish from their natural habitats, it is possible to boost wild fish populations without releasing large quantities of hatchery fish.
Fish populations may rise as a result of dam removal. Because of the significant river fragmentation, there is little access to viable habitats within a watershed. Terui told EcoWatch that expanding access to prospective habitats might be a significant strategy for improving the sustainability of fisheries and biodiversity preservation.