The rare Murray River crayfish has become an unlikely movie star, thanks to a new underwater video surveying technique that has revealed the species may be more prevalent in clear-water rivers than we thought.
The new method, developed at The Australian National University (ANU), will give researchers more accurate estimates of crayfish populations to ensure future efforts to conserve this icon of the Murray-Darling Basin are as effective as possible.
“If we don’t have accurate estimates of abundance and distribution, we can’t plan how and where we should direct efforts to protect and recover this species. Having a sensitive survey method also means you can quickly detect if your intervention and conservation measures are working,” lead author of the study, Dr Chris Fulton of the Research School of Biology at ANU, said.
“The traditional method for counting crayfish was baited hoop nets which are left to soak and checked once every hour. We thought this might be a bit hit-and-miss, so we tried some different visual techniques.”
The research team travelled to the Goobarragandra and Cotter rivers in southeast Australia to compare three survey techniques: the traditional hoop-netting method; snorkel surveys, in which the researchers snorkelled upriver to spot the crays; and, for the first time, baited underwater video cameras.
“When we used the cameras, we found five times more crayfish than we did using traditional hoop-netting methods along the same stretch of river. In some places where we’d caught no crayfish via hoop-nets, we found some coming to the baited videos,” Dr Fulton said. “This suggests the old netting method has been underestimating how many crayfish are in our rivers, particularly when they are low in numbers.”
The video technique is also much less invasive than capture-based methods, in which the slow-growing crays can lose limbs and claws.
“Crayfish play an important role in river ecosystems,” Dr Fulton explains. “Being detritivores, they tend to feed on the dead and rotting things within a stream. So even when they are rare, these spiny fellows are very important for keeping our rivers and streams healthy.”
The Murray River crayfish is classified as a vulnerable or threatened species across three Australian states. A combination of overfishing, pollution and extreme drought has led to a dramatic decline in crayfish numbers to near extinction in some places. As Murray River crayfish can live for 28 years and take 8-10 years to reach maturity, their populations can take over a decade to recover from a local extinction event.
The research is published in the latest edition of Endangered Species Research.
Vision of the crayfish interacting with the baited camera is available at https://www.youtube.com/watch?v=4dHfIQZnttY.