Dive Dry with Dr. Bill

012: Abalone

When I began diving Catalina waters in the late 60's, my students introduced me to abalone... not in an ecological sense, but as a tasty culinary experience. Coming from the Midwest and East, I had never eaten this shellfish. In those days I could literally watch an abalone grow for a year or two before I harvested it, and black abalone were thick on the rocks at low tide (but who ate them?). Trips into Avalon during the summer usually included an abalone burger at Rosie's.

In just a few decades abalone have become a rarity in southern California waters and are now illegal to take here. I did observe seven individuals of two species in the Casino Dive Park in 2001, but only saw one adult and one small juvenile this summer. The presence of the juvenile indicates some reproduction is occuring locally, but in the 60's and 70's I would routinely find juveniles under rocks in the intertidal. In 2000 the California Dept. of Fish and Game began developing an Abalone Recovery and Management Plan to address this important marine conservation issue. How did this come about?

When the former Toyon school did archaeological digs on the island, abalone shells were a major midden component indicating a rich harvest by our early residents. With the elimination of the sea otter in our area by the late 1820's and removal of Catalina's Native Americans by 1832, abalone populations probably increased. In the 1850's Chinese Americans harvested intertidal species until this practice was prohibited in 1900. Japanese Americans then began free diving for abalone. Commercial harvesting of abalone in southern California was banned from 1913 until 1943 when wartime food needs led to reopening the fishery. The commercial fishery peaked in 1957 when nearly 5.5 million pounds were landed.

About this time SCUBA diving and recreational or sport harvest entered the equation. Back when taking abalone was legal, we were often cautioned to use "ab irons" carefully to avoid injuring the animal if it were under-sized. Abalone have no mechanism to clot blood if injured, and could easily die from wounds received by careless divers. These commercial and recreational harvests certainly reduced abalone populations significantly.

There are eight species found along the California coast: the red, pink, black, green, white, pinto, threaded and flat abalone. We'll skip the scientific names! Different abalone species take 5-10 years or more to grow to legal size, depending on food supply and other environmental conditions. Young abalone feed on diatom and bacterial slimes on the rocks, while adults use the rich kelp resources, capturing mostly drifting kelp blades to feed on. This feeding pattern puts them in competition with several species of sea urchins, and high concentrations of urchins (such as barrens) will limit the number of abalone in an area. El Nino events decrease kelp beds and thereby also impact abalone populations. The elevated temperatures can even affect reproduction, sometimes preventing it altogether.

Abalone are synchronous broadcast spawners. That simply means males and females release their reproductive products into the water at the same time. Successful reproduction therefore requires high density to ensure fertilization. It is estimated abalone must be closer than four feet from one another for success. Fertilized eggs sink to the bottom and hatch, releasing abalone larvae which drift in the plankton for a few days before settling to the bottom where they often live protected under rocks. In addition to humans, abalone are eaten by crabs, lobsters, snails, octopus, starfish, fish (like sheephead) and sea otters.

Disease and parasites also have reduced abalone populations in the Channel Islands region. Withering foot syndrome (WFS), a bacterial disease that affects several species of abalone, was first noted in the 1980's following the 1982-83 El Nino. The WFS bacteria block the production of certain digestive enzymes, causing the abalone to use its own muscle (foot) tissue as an alternate food source. It primarily affects shallow water species like blacks and greens, especially during periods of higher water temperature such as El Nino events. Abalone in cooler, northern California waters are not affected much. Although this disease may be a natural event, its effects were disasterous due to the already greatly reduced population sizes of abalone. In the early 1990's another potential threat, a parasitic worm introduced on aquacultured abalone from South Africa, was stopped before it seriously affected wild populations of California abalone.

The abalone's slow growth, limited reproduction, high death rate in young abalone and susceptibility to injury make them vulnerable to human and other impacts, and slow to recover from these impacts. The new Marine Protected Areas (MPA's) required under California's Marine Life Protection Act (MLPA) will undoubtedly be one important management tool in the recovery of the abalone. However, the limited dispersal of most abalone species means this will only repopulate local areas. The current total closure in southern California is necessary to give regional recovery of these species a chance. I hope the recovery occurs within my lifetime so I can taste another ab burger at Rosie's!

© 2003 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Image caption: Two green abalone in Casino Dive Park;
abalone feeding on algae in aquarium; small abalone in palm of diver's glove

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia