Detecting North American signal crayfish (Pacifastacus leniusculus) in riffles

Abstract

ABSTRACT1. The spread of the invasive signal crayfish (Pacifastacus leniusculus) outside its natural range is of widespread concern due to the threats posed to native biodiversity. To date, there is no standard protocol for determining signal crayfish presence or absence in a watercourse.2. For the purposes of this investigation, the crayfish detection ability of active sampling methods -handnetting, electrofishing (one, two and three runs), kick sampling and Surber sampling -was tested at 30 sites along the River Clyde, southern central Scotland.3. No single technique was successful in detecting crayfish in 100% of the sites known to contain crayfish and so the application of combinations of techniques was considered. The combination of techniques that resulted in a 100% detection rate was electrofishing (three runs) together with kick sampling. These results suggest that threerun electrofishing and kick sampling are the best candidates for incorporation into a crayfish detection protocol.4. The mean time taken to apply electrofishing (three runs) was significantly greater than the mean time to apply kick sampling. Given the lower effort required for its application, kick sampling is recommended as the preliminary technique: if kick sampling yields a negative result, the application of electrofishing will decrease the chance of recording a false negative presence. If both kick sampling and electrofishing fail to detect crayfish, trapping may further decrease the risk of a false negative result.5. These findings have assisted in the development of a crayfish detection protocol, which will be applied across Scotland to determine the current distribution of signal crayfish.

Dispersal and coexistence of two non-native crayfish species (Pacifastacus leniusculusandProcambarus clarkii) in NE Portugal over a 10-year period

“…Electrofishing is possibly a more effective technique to detect and sample crayfish (e.g. Rabeni, 1997;Price and Welch, 2009;Gladman et al, 2010) butpresents major disadvantages, such as high cheliped loss (JMB pers. obs.…”

“…obs. ; Alonso, 2001;Gladman et al, 2010) or the bias in quantitative studies resulting from inaccurate quantification of the capture effort. Moreover, in conditions of low water depth and cobble-boulder substrate, as in the Maçãs, electrofishing efficiency is severely affected.…”

Effectiveness of stream sampling methods in capturing non-native Rusty Crayfish (<em>Orconectes rusticus</em>) in Ontario

“…in most cases, failure of the removal model was observed as an increase in the number of crayfish captured after the first pass or too few individuals collected. the first sampling pass may disturb or draw out crayfish from areas of cover making them more vulnerable to capture in subsequent passes (Gladman et al 2010). Removal sampling by both electrofishing and hand capture has been suitable for generating population estimates of other streamdwelling crayfish (Rabeni et al 1997;alonzo 2001); however, in those studies, sampling was carried out in much smaller streams and channel width can have a strong influence on efficiency of a method (Zalewski and Cowx 1990).…”

“…However, it was the most labour-intensive method, resulted in the highest rate of mortality, and is less readily adaptable to current stream fish monitoring programs. Gladman et al (2010) and United States National Park Service (2007*) both reported hand capture to be less efficient than electrofishing for sampling stream crayfish.…”

“…However, multiple passes are still preferable to single-pass sampling as this improves native species detection (Gladman et al 2010), and a large percentage of individuals will be vulnerable to capture only after being disturbed by initial sampling efforts. if estimates of population size are required for stream reaches, the likelihood of failure could be reduced by pooling data from randomly distributed sampling sites and applying unbiased removal-type estimators (Heimbuch et al 1997).…”