The Wheeler North Artificial Reef (WNAR) is the largest (and perhaps the best studied) artificial reef in the United States. The reef was put in place to mitigate the loss of the San Onofre kelp bed off the coast of San Onofre, California. Located 2 km offshore of San Clemente, California, it was completed in 2008 and is composed of 125,000 tons of quarry rock covering 178 acres of seafloor.
For my master’s thesis under the advisement of Dr. Chris Lowe at California State University Long Beach, I caught and tagged 45 Kelp Bass Paralabrax clathratus, Barred Sand Bass P. nebulizer, and California Sheephead Semicossyphus pulcher (135 total fish) on WNAR with an acoustic transmitter to see how much of their time they spend on, or very near the reef (site fidelity). The main goal of this study was to provide insight into the “attraction vs. production” debate on artificial reef function. The “production hypothesis” suggests that artificial reef construction increases the amount of habitat on the seafloor and by doing so, the amount of space available for algae, invertebrates, and small fish increases, and eventually the artificial reef becomes a permanent habitat for larger mobile fish where they mate and spawn, thereby increasing the overall "production’ of the area." However, the “attraction hypothesis” suggests that the high abundance of fish found on artificial reefs comes from fish in the surrounding areas being attracted to the artificial reef for the high quality habitat, which simply redistributes the fish in the population rather than actually producing new fish to the area.
To address the attraction/production issue, I tagged the 135 fish on WNAR, and I tagged an additional 20 fish at three different natural reefs that are varying distances away from WNAR. The goal of this portion of the study was to determine if the fish tagged on the natural reefs move to the artificial reef or remained in the area they were tagged. I began tagging in September of 2014 and pulled all of my acoustic receivers out of the water in October 2016, for just over 2 full years of data collection. In general, the overall site fidelity index (number of days detected on WNAR/number of days since tagging) is highly variable between the three species. California Sheephead have high site fidelity to the reef, as 77% of tagged California Sheephead currently remain on the reef and have an overall site fidelity index of (mean ± sd) 0.72 ± 0.24. Kelp Bass show moderate site fidelity to the reef with an overall site fidelity index of 0.48 ± 0.38, while 34% of all tagged Kelp Bass remain on the reef. Barred Sand Bass show the lowest site fidelity to the artificial reef of the three species, with an overall site fidelity index of 0.31 ± 0.26 and only 22% of all tagged Barred Sand Bass remaining on the reef; however, the number of barred sand bass present on a weekly basis was highly variable. I suspect the low residency of the Kelp Bass and Barred Sand Bass, ambush predators, was related to the disappearance of giant kelp from WNAR during the time of the study. Warm water temperatures caused by El Nino conditions restricted giant kelp growth and recruitment, and presumably limited the amount of habitat available for Kelp and Barred Sand bass.
I am in the process of fully analyzing all of the data and intend to graduate in May of this year. By combining my results with other studies currently being done on WNAR (kelp density, invertebrate abundance, fish biomass, etc.), this will add a missing piece (fish movement) to the puzzle of the attraction vs production debate. In doing so, this project could have local and potentially global implications for other artificial reef projects, environmental policy, and proper management of artificial reefs.