Catch per unit effort of Murray River crayfish by snorkel surveys, baited remote underwater videocameras, subsampling video footage and finally, hoop netting.
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Estimating crayfish abundance
Obtaining robust estimates of species distributions and abundance are crucial to effective management of biodiversity. The freshwater crayfish of Australia (Genus Euastacus) are a highly diverse, charismatic yet highly vulnerable clade. Traditional sampling techniques include baited hoop nets, yet their efficacy has not been evaluated. In this study, we examined whether snorkel surveys, baited remote underwater cameras, or hoop nets were the best technique for surveying Murray River crayfish in montane rivers. The results were clear-cut. Snorkel-based surveys were far more effective for detecting crays, while baited remote underwater cameras were solid performers. Sadly, hoop nets were not as effective in these environments. Visual surveys and deploying baited cameras may be more effective methods for surveying crayfish in montane streams with low turbidity.
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Power of video
Frames from video of a crayfish entering, feeding on a bait and then leaving.
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In addition to being a fantastic survey tool, underwater video can reveal a great wealth of behavioural information that cannot be gleaned using other methods. In this study, we found that cameras were a powerful survey tool, but the gems were in the additional observations that came with using video. For example, we observed that in numerous occasions, crayfish would approach the bait, but never actually feed upon it. Furthermore, crayfish visitation times were usually short. As such, in an hour long deployment, it was possible for numerous crayfish to visit the bait and for individuals to return repeatedly to the bait. Intraspecific interactions were common, with multiple crayfish feeding on the bait concurrently.
Murray River crayfish are an iconic species. Sadly, they are in decline.
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Fulton, C.J., Starrs, D., Ruibal, M.P., and B.C. Ebner (2012) Counting crayfish: active searching and baited cameras trump conventional hoop netting in detecting Euastacus armatus Endangered Species Research 19: 39-45 LINK
