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A novel ‘triple drawdown’ method highlights deficiencies in invasive alien crayfish survey and control techniques

Research output: Contribution to journalArticlepeer-review

Daniel Chadwick, Eleri Pritchard, Paul Bradley, Carl Sayer, Michael Chadwick, Lawrence Eagle, Jan Axmacher

Original languageEnglish
Pages (from-to)316-326
Number of pages11
JournalJOURNAL OF APPLIED ECOLOGY
Volume58
Issue number2
Early online date12 Oct 2020
DOIs
Accepted/In press3 Jul 2020
E-pub ahead of print12 Oct 2020
Published2 Feb 2021

Bibliographical note

Funding Information: We thank all landowners who supported this work by allowing access over their land. We thank the Environment Agency for fieldwork authorisation. We thank volunteers for assistance in the field. We thank Miles Irving who assisted with preparation of figures. We thank NERC for funding this research through the London NERC DTP. Funding Information: We thank all landowners who supported this work by allowing access over their land. We thank the Environment Agency for fieldwork authorisation. We thank volunteers for assistance in the field. We thank Miles Irving who assisted with preparation of figures. We thank NERC for funding this research through the London NERC DTP. Publisher Copyright: © 2020 The Authors. Journal of Applied Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

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Abstract

Freshwater crayfish can be successful invaders that threaten native biota and aquatic ecosystems in numerous countries worldwide. Nonetheless, the inability of conventional crayfish survey techniques like trapping and handsearching to yield quantitative population data has limited the understanding of crayfish invasion biology and associated ecological impacts. Here, we employed a novel ‘triple drawdown’ (TDD) method to sample invasive populations of signal crayfish Pacifastacus leniusculus in a headwater stream in Northern England. The method was compared with conventional techniques of trapping and handsearching. The TDD method proved to be an effective technique with high capture efficiency, reporting signal crayfish densities from 20.5 to 110.4 animals/m 2 at our study sites. These numbers exceed any previous estimates for similar streams. The TDD showed the vast majority of individuals across all sites were juvenile or sub-adult (<26 mm CL), with only 2.3% of the population large enough (≥35 mm CL) to be caught in standard traps. Synthesis and applications. The triple drawdown (TDD) method demonstrates strong inefficiencies and biases in conventional crayfish survey and management techniques. Trapping is not recommended for representative sampling or control of juvenile dominated populations. TDDs, which can be adapted and modified to operate in multiple habitat types and freshwater systems, generate robust quantitative data on invasive crayfish population demographics in situ. This can advance our understanding of the biology of an important invader of freshwater systems around the world. Obtaining this data prior and post-intervention is fundamental to evaluate invasive crayfish management, and we recommend the TDD method to assess the effectiveness of future control measures.

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