The Anacapa Giant Sea Bass Study

Monitoring Giant Sea Bass Around
Anacapa Island

From 1981 - 1996, I was logging an average of 150 dives each year in the waters off the Southern and Central California coast. During those years on over 2000 dives, I had seen adult giant sea bass on only three occasions, all of them at Anacapa Island. My first sighting ever, was of a group of three individuals in a thick kelp forest on the south side of Anacapa in back in1982. The other sightings were each of single fish on the north side of the island, one in 1995, and the other in 1996. Then to my surprise, on a routine dive in May of 1997, I found myself in the midst of 12 sub-adult and giant sea bass.

This eventful dive marked the start of the monitoring project that my husband and I have been conducting since that time, observing the giant sea bass at Anacapa Island.

During 1997 my husband, Captain Jim Oleson and I were operating a charter dive boat taking recreational divers to Anacapa Island several times each week. This provided an ideal opportunity to begin monitoring the giant sea bass. At the start of the project, very little was known of giant sea bass behavior. We started monitoring the site where the aggregation was first discovered, as well as sampling 28 additional areas around Anacapa Island. Anacapa is a small island with approximately 10 miles of shoreline, and is located just 12 miles off the Coast of Ventura County. With its small size and proximity to several harbors, Anacapa is an ideal place to try to learn more about these large and interesting fish. Following 1997, Jim and I no longer operated the charter vessel, yet with the help of others in the boating, science, and diving communities we kept the surveys active. By late 1999 we were able to put a small private boat into operations for the project, and now have logged nearly 800 dives searching for giant sea bass and have recorded over 200 sightings. Though both my husband & I still work full or part time in the waters around the California Channel Islands, this project is not yet funded in any way. We are dedicated to the project because we hope to learn important information that will lead to continued protection for these fish as they struggle to make a comeback from a population severely depressed from overfishing, and possibly other complex changes in their environment.

Through conducting survey dives year round, we have discovered a pattern or season associated with the giant sea bass sightings. At Anacapa, giant sea bass are generally found each year between the months of May and September. This period roughly corresponds with the spawning season of the giant sea bass. During this season, the sub-adult and adult giant sea bass appear to aggregate at three preferred areas around the island where we are 15% to 55% more likely record sightings. Abruptly, in the fall sightings drop to near zero, even at the aggregation sites. We have identified cleaning stations, and recorded cleaning behavior in fish species not previously known to serve as cleaners. We discovered that giant sea bass can dramatically change the pattern of color they exhibit and we are starting to see trends in behaviors that accompany these changes. Through notes and photos, we are identifying individual fish by unique markings, and have learned that some fish have site fidelity over the years. Behaviors that may be associated to spawning have also been observed, yet we have not yet witnessed spawning in the wild. This is one goal we would still like to achieve. Additional goals include attempting to estimate the population of giant sea bass that utilize the habitat around Anacapa Island, and expanding our surveys to other Channel Islands.
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