Differential Fish Count: Rebreather vs. Open Circuit

Overview

Objectives/Goals The objective was to determine whether a diver would see more Paralabrax clathratus (an overhunted species of sea bass living off the coast of California) with a rebreather or with open circuit scuba. The hypothesis was that one would see more fish using a close circuit rebreather than open circuit scuba. Methods/Materials Before diving, it was necessary to build a closed circuit scuba system to accommodate smaller sized individuals. Two weeks was spent building and modifying the rebreather. Open circuit testing was done using standard scuba equipment. Three weeks was spent training to use the rebreather and understanding mixed gas physiology. A team of four divers went to Shaw's Cove in Laguna Beach to do testing. A 50 meter semi-permanent transect line was placed at 6 meters of depth. 34 transects on open circuit scuba and 25 on closed circuit rebreather were conducted in 17 man dives (15 hours). Fish counts were recorded on underwater slates. The data was statistically analyzed looking at mean, median, standard deviation, confidence interval, and student T test. Results Data showed that a median of 2 fish was seen on open circuit scuba and 5 fish were seen on closed circuit rebreathers. A standard deviation of one was obtained giving a confidence interval of 95%. Using student T test analysis, a P value less than 0.05 was calculated, showing the means of the two groups were statistically different. Conclusions/Discussion More accurate fish counts can be obtained using closed circuit rebreathers instead of open circuit scuba. Differences in fish counts can be explained by disturbance from bubbles generated by open circuit scuba. Closed circuit rebreather technology would be useful for observing elusive fish species, getting accurate counts and ultimately helping to formulate fishing quotas.

Awards (1)

• Third Place

Competition history

• CSEF 2010 Environmental Science (Junior Division Only) · Entry J1201

Resources

• CSEF project summary ↗

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