Silent Rebreather Diving Doesn’t Make You Invisible

Does a closed-circuit rebreather give you Harry Potter's Cloak of Invisibility? We hear so often that selling point for Closed-Circuit Rebreather courses -- that CCR diving doesn't scare away the fish. However, you are still a big, obtrusive animal in the underwater world, whether emitting bubbles or not. Fish are not blind.

The conventional way to survey fish populations, by noisy open-circuit scuba, might mean that fish get frightened away from the survey zone. Scientists have studied the effect by comparing results from both traditional scuba surveys and those using closed-circuit silent diving techniques.

For this study, orchestrated by the Australian National University, researchers conducted 66 paired scuba and rebreather fish surveys at locations in the Hawaiian Islands with relatively high, moderate, and light fishing pressure. They found no significant differences in biomass estimates between scuba and rebreather surveys when data were pooled.

However, there were differences at the most heavily fished location, Oahu, where biomass estimates from scuba divers were significantly lower for several targeted fish groups, including surgeon fish, wrasses, and snappers, as well as for all targeted fishes combined. In fact, they amounted to only 32% and 68% of the mean rebreather biomass count.

The conclusion seems to be in pristine waters, scuba divers see just as many fish as rebreather divers.