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A new Methods paper comparing SCUBA diving to bubble-free diving suggests that fish are deterred by the sound of SCUBA bubbles, particularly in heavily fished areas, which can result in potentially biased fish counts and research conclusions.

Steven Lindfield and colleagues from the University of Western Australia studied coral reef fish populations in Guam using two diving systems: the commonly used SCUBA equipment that produces bubbles, and a silent closed-circuit rebreather (CCR) that doesn’t produce bubbles.

To carry out the studies all divers used an underwater stereo-video system, and the footage was later used to figure out the number of fish present in the area, fish length and weight, and the minimum distance fish would allow a diver to approach before fleeing.

The findings show that within protected areas of water where no fishing occurs, fish surveys carried out by SCUBA divers and bubble-free divers produced similar results. However, in areas of water where fishing occurs, the bubble-free divers recorded 48% more species and up to 260% greater fish abundance, suggesting that they were able to sneak up on fish that usually shy away from SCUBA divers.

In their paper the authors state: “These results highlight the general importance of identifying all major sources of error associated with sampling populations in such variable environments. More specifically, it indicates how such errors can result in erroneous conclusions being drawn on the impacts of fishing and the effectiveness of marine protected areas (MPAs)”.

The paper can be found here: Lindfield, S. J., Harvey, E. S., McIlwain, J. L., Halford, A. R. (2014), Silent fish surveys: bubble-free diving highlights inaccuracies associated with SCUBA-based surveys in heavily fished areas. Methods in Ecology and Evolution. doi: 10.1111/2041-210X.12262