A global review of research around the impacts of dams has found they are significantly harmful to diadromous species - fish, eels, crustaceans and snails that rely on connected rivers and oceans to complete their life cycles.
University of Tasmania freshwater animal ecologist and Lecturer, Dr Jia Huan Liew , together with colleagues, including lead author Jeffrey Chan from the University of Hong Kong, found these disruptions to migratory species were far-reaching: reducing the abundance of species, species diversity and genetic diversity among populations.
Published in Biological Reviews, the study is the first comprehensive global synthesis of the impacts of dam-induced fragmentation on diadromous species.
Dr Liew said the study, which looked at more than 100 prior research outcomes, confirmed that dams represented a major threat to freshwater biodiversity.
It found obstructions like dams blocked breeding migratory routes and feeding grounds between coastal waters and rivers, and that fish passes - structures that help fish navigate obstacles in a river so they can move more freely between habitats,and also known as fish ladders - produced consistently poor outcomes.
"Despite their widespread use, fish passes often underperform, particularly when designed without understanding the specific behaviours and traits of local species," Dr Liew said.
"We found the impacts of dams were the harshest on species that cannot survive in isolated, landlocked environments, and fish with limited climbing abilities, unlike better climbers such as eels," he said.
"Dam removal, while costly and sometimes constrained by societal needs, remains the most consistently effective strategy for restoring connectivity."
This study offers crucial insights for managing freshwater biodiversity amid rising global dam construction and climate-induced ecological changes, but the researchers said there was more to be investigated.
"Much of our current knowledge in this area is based on temperate fish like salmon and there is a huge gap in our understanding of the effects of dams on tropical species and other non-fish species like migratory snails and crabs."
"There are many ways to measure the impacts of dams before they're built and to optimise their design and location, depending on their context, so what we really need to do is be as thorough as possible during planning stages to understand and mitigate harm to our wildlife before it happens."
Read the full journal article here: https://doi.org/10.1111/brv.70032
