Credit: Radboud University
Certain invasive exotic species, such as the red swamp crayfish, are harmful to our environment because they nibble on aquatic plants, dig burrows in banks, and transmit crayfish plague to native species. “But there are also non-native fish and crayfish that are not harmful and do not need to be controlled,” ecologist Pim Lemmers argues in his Ph.D. thesis, which he will defend at Radboud University on 30 May.
The red swamp crayfish has a bad reputation, and not without good reason. “It really is the worst,” says Lemmers. “It walks on land, destroys aquatic plants, and digs into banks, to the detriment of water quality. It is a real problem.”
The spinycheek crayfish, on the other hand, is currently causing far fewer problems in the Netherlands. It does not burrow in banks, although it did in the past transmit crayfish plague, thus contributing to the drastic decline of European crayfish in the Netherlands.
For his Ph.D. research, Lemmers studied various exotic species—animal species that do not naturally occur in the Netherlands—and their ecological and socio-economic impact. To do so, he carried out a lot of lab and field work. Armed with a special fishing net and waders, he went into the Meuse, the Rhine, and several of their tributaries.
“We used electro-fishing: an electrified fishing net that allows you to pull fish towards you. As soon as you switch off the current, the fish immediately swim away,” says Lemmers. He counted, measured and determined the fish he caught in the rivers, and took some specimens to the lab to examine the ratio of stable isotopes of nitrogen and carbon in their muscle tissue.
“This data allowed me to deduce exactly what the fish were eating. If an exotic species eats totally different food from a native species, it is probably not causing harm,” he adds. This method allowed him to carry out a risk analysis and determine which exotic species were dangerous and which not.
2024-05-27 13:00:02
Post from phys.org