When native and alien species meet. Impact assessment and management of invasive crayfish and fish in riverine ecosystems

Thursday 30 May 2024, 12:30 pm
PhD student
P. Lemmers drs. ing.
prof. dr. R.S.E.W. Leuven
dr. G. van der Velde

Organisms are increasingly being introduced outside their natural range due to the growing globalisation of human activities. The establishment of invasive alien species can have far-reaching negative ecological and socio-economic consequences associated with high social costs. But not every introduced species (or exotic species) is invasive. This research study includes five sub-studies analysing the risks posed by recently released crayfish and fish in Dutch freshwater ecosystems. The first three were impact studies that showed that 1) native species can recover in the absence of exotic species, 2) not only the exotic species themselves but also the parasites they carry can have an important role in the impact chain on native species, and 3) exotic species need not always behave in an invasive manner. They are sometimes able to adapt, allowing them to co-occur with native species. The fourth study shows that such impact studies are valuable for the risk assessment of exotic species, which can be used to determine a priority-setting into high, moderate or low risk species. Based on this, appropriate mitigation measures for high-risk invasive exotic species can be applied in a cost-effective manner, as shown in study five.

Pim Lemmers (1989) obtained his Master's degree in Forest and Nature Conservation from Wageningen University in 2016. Shortly afterwards, he joined ecological consultancy Natuurbalans – Limes Divergens BV, where he works as an ecologist on a project basis on applied ecological studies and issues around various native and non-native animal species. In 2017, he started his PhD research as an external PhD candidate under the supervision of Rob Leuven and Gerard van der Velde. For almost seven years, he worked in his spare time on assessing the impact of invasive crayfish and fish found in Dutch nature and finding appropriate management measures for high-risk species. After completing his PhD research, he will remain with his current employer.