Tethering Mobile Aquatic Organisms to Measure Predation: A Renewed Call for Caution

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Journal of Experimental Marine Biology and Ecology; Elsevier


Tethering experiments are one of the few approaches available to ecologists to assess predation rates in aquatic environments, and they have provided important insights into the processes driving observed patterns in aquatic communities. The potential for experimental artefacts to arise when tethering mobile prey has been well recognized and was vigorously discussed in the literature around 20 years ago. However, we reviewed 128 published studies that tethered fish and mobile crustaceans and found a growing number since that time that we believe do not adequately consider these potential issues. The majority of studies recognize that tethering mobile prey can only provide a relative rather than absolute estimate of predation rates, yet 16% present and interpret their results as if they reflect absolute natural predation rates. Two thirds of published studies at least acknowledge other potential artefacts, less than half test for them, while one third seemingly give no consideration to potential artefacts or biases of the method. Our review also revealed the potential for a lack of independence between individual replicates. More than two thirds of studies deployed replicate tethered prey a minimum of no>5m apart, with more than one quarter deploying them no>1m apart. Eighty-five percent of studies considered missing prey to represent predation. We deployed 104 tethered fish prey in field trials and monitored them using remote underwater video to determine the causes of prey loss. These trials reinforced the simple but important point that prey missing from tether lines at the end of an experiment can be missing for a variety of reasons other than reflecting predation. They also highlight the potential for underwater video, where it is practical to use, to overcome many of the issues confronting field tethering experiments. Carefully designed tethering studies will continue to be an important tool for ecologists studying patterns of predation in aquatic systems. However, our findings suggest a re-emerging need for researchers to recognize and test for potential biases and artefacts inherent with the technique.

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Marine and Environmental Sciences