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California Abalone

The recent demise of abalone in southern California evokes memories of the fate of bison in the United States in the nineteenth century. Once so abundant their disappearance was unimaginable, the abalone that supported huge commercial and sport fisheries 30 years ago are now on the brink of extinction.

   

Abalone are marine snails, with some 70 modern species occurring globally. Fossil abalone first appear in Cretaceous rocks dating from about 70 million years ago, in what is now California (Lindberg 1992). Humans have exploited abalone for food, tools, and jewelry for millennia (Shepherd et al. 1992). Five of the eight eastern Pacific abalones were abundant enough to support multimillion-dollar fisheries through most of the twentieth century. However, abalone populations in southern California recently collapsed under a flawed management approach (Davis et al. 1992; Richards and Davis 1993; State of California 1995). This situation has caused worldwide concern because abalone management practices in Australia, New Zealand, South Africa, and elsewhere were based on the same assumptions and strategies as in California (Shepherd et al. 1992). In the mid-1990's, California fisheries for four abalone species were closed to prevent harvest-induced extinctions, but even that drastic action may have been too late to save the white abalone (Davis et al. 1996). The story of these populations, the fisheries they supported, and efforts to restore them is a harbinger for coastal marine fisheries. The lessons learned in efforts to restore and sustain California abalone can be applied profitably to coastal resources worldwide.

   

Biology

 

Abalone cling to rocks, from wave-swept intertidal ledges down into the twilight zone of deep reefs at 65 meters, wherever they can catch drifting fronds of kelp and other algae. In California, species separate themselves roughly by depth and latitude (Haaker et al. 1986). Black abalone live in tidal pools from Oregon to the southern tip of Baja California. Green abalone, pink abalone, and white abalone prefer southern climes, with each species occupying increasingly deeper waters, respectively, from Point Conception into Baja California. Red abalone, the largest species, occupies the broadest range, from tidal pools in Oregon to deep reefs as far south as Bahia Tortugas, Baja California. Flat abalone, pinto abalone, and threaded abalone are relatively rare and are only incidentally involved in California fisheries.

   

Abalone have separate sexes. To reproduce, they broadcast sperm and eggs into the sea, relying on high gamete densities for successful fertilization, a reproductive strategy requiring densely aggregated adults for success. The larvae are free-swimming for only a few days before settling to the bottom as juveniles. California abalones mature between 3 and 7 years of age and may live for 35 to 54 years, commonly reaching sizes of 15-25 centimeters in length and 1-2 kilograms. Fecundity increases exponentially with size. Newly mature females produce only a few hundred thousand eggs each year, whereas older individuals produce 10-15 million eggs (Hahn 1989).

   

Management Strategies

 

California's management strategy to sustain exploited abalone populations was based on a surplus yield model. It was implemented through minimum harvest sizes, based on growth rates and size at maturity. Under this scheme, abalone were permitted to reproduce for the first few years of maturity and then were harvested. Since no relationship between spawning stock and recruitment had been defined, fishery managers assumed cohorts of young abalone could sustain harvests with no other constraints (Tegner et al. 1989). Closed seasons protected spawning aggregations. Other regulations, such as bag limits on sport fishers and limited entry to the commercial fishery, attempted to allocate limited resources equitably.

   

In northern California, an additional management measure protects more brood stock of red abalone, thus assuring a sustained fishery. Only sport breath-hold diving or shore-picking in the intertidal zone is allowed. Zoning use in this way separates commercial and sport fishing and protects a large spawning stock of big abalone. The inherent depth limit imposed by breath-hold diving creates a refuge at greater depths, thereby protecting sufficient brood stock to replenish the harvest in adjacent shallow waters. This refugia-based red abalone fishery is the only sustained abalone fishery in California today.

   

Serial Depletion

 

Truly sustainable fisheries are based on sustained populations of target species. The frontier approach to fishery management practiced in many areas today produces a pseudo-sustained fishery. This approach unrealistically assumes the availability of an endless supply of new, unexploited populations, but it has the virtue of economic expediency.

   

Following a fishing hiatus during World War II, southern California abalone fisheries grew rapidly. Soon, readily available and well-known abalone populations along mainland shorelines were exhausted. Then lightweight, mobile, inexpensive diving gear, fast boats, modern navigational aids, and improved knowledge of abalone and the coastal environment made available virtually all of the pristine abalone habitat on offshore reefs. After 25 years of apparently sustained fisheries, abalone landings began declining in the 1970's. A careful examination of this harvest shows it was not truly sustained but rather the result of serial depletion (Dugan and Davis 1993; State of California 1995). Fishery landings and fleet income were sustained at the expense of a series of abalone populations in different areas. Only after landings of pink abalone and red abalone declined in the 1970's did the fishery shift to green and white abalone in shallow and deep water, respectively. When white and green abalone populations collapsed, harvest shifted to intertidal black abalone. Then, as the remnants of the black abalone population succumbed to disease, the diving fishery shifted to red sea urchins. Income to the diving fleet during this period remained relatively stable. The fishery had been sustained, but the productivity of the exploited populations was destroyed in the process.

   

The success of serial depletion in sustaining fishery income obscured the need to restore severely depleted stocks and to protect more reproductive capacity of abalone populations. Denial that abalone populations were imperiled obstructed efforts to improve management. The virtual absence of fishery-independent information made it difficult to assess population status and gave fishery landings data more credibility than they warranted. These gaps in accessible information delayed remedial actions, making restoration more costly and perhaps impossible for some species.

   

Current Population Status

 

Few fishery-independent data exist for abalone in California. Since 1982 the National Park Service and the California Department of Fish and Game have jointly monitored population dynamics of nearly 100 marine taxa, including the five common abalones, in Channel Islands National Park (Davis et al. 1994). Other population trends must be inferred from fishery landings, with considerable uncertainty and ambiguity.

   

Black abalone populations in California survived with harvests of 2,000 metric tons per year for the last third of the nineteenth century. Large populations accumulated after harvest ceased in 1900, with densities often exceeding 125 abalone per square meter on the Channel Islands (Richards and Davis 1993; Figure). When harvest resumed in 1968, annual landings quickly rose to 870 metric tons. By the mid-1980's black abalone were found primarily on offshore islands and inaccessible sections of the coast north of Santa Barbara. A withering foot disease caused massive deaths in these remnant populations, beginning in 1985 on the Channel Islands and spreading to the mainland (Haaker et al. 1992). Relict populations of apparently disease-resistant individuals survive on the islands at less than 1% of their former abundance.



Figure. Intertidal black abalone on Santa Rosa Island, California, before the catastrophic population collapse in the late 1980's. Courtesy G. E. Davis, USGS

White abalone occurred at average densities of 10,000 per hectare in the early 1970's (Tutschulte 1976). Ten years later, densities at the historical center of their abundance were 10 per hectare. By the early 1990's densities were only 1 per hectare, and the species was in danger of extinction (Davis et al. 1996).

   

In Channel Islands National Park, exploited pink abalone population densities fell from 250 per hectare to less than 14 per hectare in the 1980's, while a population protected in an ecological reserve remained relatively stable at about 400 per hectare (Davis et al. 1992). Red abalone population densities in the park dropped from more than 1,000 per hectare to less than 10 per hectare in the 1980's. Fishery landings reflected these population trends. Pink abalone landings fell from 48 metric tons to 7 metric tons, and red abalone landings dropped from 235 metric tons in 1980 to 120 metric tons in 1986. There are no recent fishery-independent data for green abalone populations.

   

Fishery Status

 

California abalone fisheries landed more than 4,000 metric tons per year during the 1950's and 1960's, split roughly equally among sport and commercial interests (State of California 1995). After harvest started in 1968, black abalone landings peaked quickly at 870 metric tons in 1973 and stabilized at 225 metric tons in the early 1980's. Then, reflecting the rapid population collapse, landings dropped to less than one metric ton in 1993, when the fishery was closed to protect disease-resistant stock for use in restoration efforts. Landings of black, white, pink and green abalones fell in the 1990's to less than 4% of the early 1970's landings, from 882 metric tons to 32 metric tons. The California Fish and Game Commission closed the pink, green, and white abalone fisheries in 1996 to prevent extinction of reproductive stocks (State of California 1995).

   

For more than 20 years, sport and commercial abalone fisheries generated $15-$20 million per year for the state's economy. The abalone population trends of the 1980's, caused largely by a flawed harvest scheme, must be reversed if the productivity of these fisheries is to be restored.

   

Only red abalone still support fisheries in California. The sport-only red abalone fishery in northern California annually produces about 1,000 metric tons (Tegner et al. 1992). Although generally stable, continued productivity of that fishery is now threatened by poaching, induced by the extremely high value of individual abalone ($32 per pink abalone to $100 per white abalone). Abalone fisheries in southern California are now concentrated on a small population of red abalone around San Miguel Island, in western Channel Islands National Park and National Marine Sanctuary. This population is located at the edge of the southern-flowing California current, and recruitment to this population may be provided from unharvested populations to the north. Annual commercial red abalone landings have apparently stabilized at about 170 metric tons, less than 15% of the 1,200 ton landings of 30 years ago.

   

Restoration Plans

 

Restoring populations of slow-growing, long-lived abalones to levels that can sustain productive fisheries will take decades and will require active intervention. Closing the Orange County shoreline to abalone harvest in 1977 and waiting 15 years for populations to recover spontaneously was ineffective (Tegner 1992). Abalone are not unusual in this respect. Recent analysis of 128 marine fish stocks revealed that only 3 species might be able to recover spontaneously from severe harvest-induced reductions (Meyers et al. 1995). Active brood-stock husbandry now seems to offer the only promising abalone restoration approach (Tegner 1992, 1993).

   

Formal comprehensive plans have not yet been made to restore the productivity of California abalone populations. Limited research on recruitment dynamics, larval and juvenile stocking feasibility, and brood-stock husbandry are under way. White abalone stocks are so low that extremely expensive, large-scale surveys of deep reefs are needed just to find enough individuals for captive breeding and rearing programs and to test new strategies, such as aggregating adults in refugia (Davis and Haaker 1995).

   
  Author
Gary E. Davis
National Park Service
Channel Islands National Park
1901 Spinnaker Drive
Ventura, California 93001-4354

References


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