Skip to main content
Monterey Bay National Marine Sanctuary National Marine Sanctuaries Home Page National Oceanic and Atmospheric Administration Home Page

Research Technical Report

A PDF version of this report is available at:

Status Review Report for Black Abalone (Haliotis cracherodii Leach, 1814)



VanBlaricom, G., M. Neuman, J. Butler, A. DeVogelaere, R. Gustafson, C. Mobley, D. Richards, S. Rumsey, and B. Taylor (January 2009)

Unpublished document produced for the Black Abalone Status Review Team, Office of Protected Resources, Southwest Region, National Marine Fisheries Service, Long Beach, CA, USA. January 2009. 135 pp.


The black abalone (Haliotis cracherodii Leach, 1814) is a relatively large prosobranch gastropod mollusk ranging from approximately Pt. Arena in northern California, USA, to Bahia Tortugas and Isla Guadalupe, Mexico. Populations of black abalone on offshore Islands, especially those of southern California, were particularly large prior to the middle 1980s. Black abalone occur in rocky intertidal and shallow subtidal habitats on exposed outer coasts, where they occur primarily in crevice microhabitats and feed preferentially on large drifting fragments of marine algae such as kelps. Black abalone reach a maximum size of about 200 mm (maximum diameter of the elliptical shell) but more typically reach sizes in the range of 100-140 mm. Maximum longevity is thought to be 20-30 years. Black abalone have separate sexes and are broadcast spawners. Lecithotrophic larvae are thought to be planktonic for 4-10 days before settlement and metamorphosis. Dispersal capability of larvae is limited, and genetic data indicate population structure on a spatial scale consistent with known dispersal characteristics. Black abalone shells are abundant in midden deposits left by Native American cultures in a number of locations, but especially in the Channel Islands of southern California, suggesting that black abalone served as a significant source of human nutrition among indigenous peoples along the coasts of California and Baja California in times past. Black abalone were popular targets for recreational harvest through much of the twentieth century, and have been harvested commercially since the 1950s. During a brief period in the early 1970s black abalone were the predominant commercially harvested abalone species in California as measured by tonnage landed. Black abalone have been harvested intermittently by commercial fishing cooperatives along the coast of the Baja California Peninsula, primarily in the region between the U.S.-Mexico border and the border between the States of Baja California and Baja California Sur. Since 1990, commercial harvests of black abalone in Mexico have declined by more than 98%.

A lethal disease, withering syndrome, was first detected in black abalone at Santa Cruz Island, California, in 1985. The disease is caused by a Rickettsiales-like prokaryotic pathogen of unknown origin that invades digestive epithelial cells and disrupts absorption of digested materials from the gut lumen into the tissues. Progressive signs of disease include pedal atrophy, diminished responsiveness to tactile stimuli, discoloration of the epipodium, and a loss of ability to maintain adhesion to rocky substratum. The etiological agent of withering syndrome has been formally described and is presently known as 'Candidatus Xenohaliotis californiensis'. Withering syndrome spread progressively through the California Islands from 1986 to the middle 1990s, and spread to mainland populations in both California and Mexico beginning in 1988 at a site near Diablo Canyon, California. Withering syndrome has caused mass mortalities of 95% or greater in black abalone at virtually every location that has been investigated. At present (January 2008), all known black abalone populations south of Monterey County, California, have experienced major losses, thought largely to be due to withering syndrome. Available evidence indicates that mass mortalities associated with the disease continue to expand northward along the California coast. Information from Mexico indicates widespread occurrence of withering syndrome and mass mortalities of black abalone over the past two decades. Rate of black abalone mortality associated with withering syndrome is known to be enhanced by periods of ocean warming, such as those associated with recent El Niño - Southern Oscillation oceanographic events in the Pacific Ocean. This pattern suggests that progression of ocean warming, associated with large-scale climate change, may facilitate further and more prolonged vulnerability of black abalone to effects of withering syndrome.

Other factors may have contributed to losses in black abalone populations in recent decades. Consumption by natural predators may be important to survival rate for all ages and sizes of black abalone. Excessive harvests, especially in California by commercial interests and recreational fishers, probably contributed to losses as well. Close proximity and ready access of mainland populations of black abalone to human activity and population centers probably have facilitated high rates of illegal harvest for many decades in California and Mexico. Black abalone are probably vulnerable to certain types of pollution such as major oil spills in coastal marine waters, but few such occurrences have been documented to date.

All forms of legal harvest of black abalone were suspended by the State of California in 1993, in response to documentation of population damage caused by withering syndrome. In 1997 the State of California placed all abalone harvests south of the Golden Gate under indefinite moratorium. At present the only surviving fishery for abalone in California is the recreational harvest of red abalone (Haliotis rufescens Swainson, 1822) in northern California. On 23 June 1999 the black abalone was added to the list of Candidate Species by the National Marine Fisheries Service (NMFS; 64 FR 33466), in the context of consideration for federal protected status pursuant to the Endangered Species Act of 1973 (ESA; 16 U.S.C. 1531 et seq.) as amended. The black abalone was transferred to the NMFS List of Species of Concern on 15 April 2004 (69 FR 19975). The species was added to the Red List of Threatened Species by the World Conservation Union (IUCN) in 2003, and was classified as "critically endangered". NMFS initiated an informal status review for black abalone on 15 July 2003, and conducted biological scoping workshops on 29-30 January 2004 and 31 July-1 August 2006. A formal status review was announced by NMFS on 17 October 2006 (71 FR 61021). On 27 December 2006 NMFS received a petition from the Center for Biological Diversity (CBD) requesting that black abalone be added to the List of Threatened and Endangered Species as defined by the ESA, and that critical habitat for the species be designated concurrent with a decision on listing. As required by section 4(b)(3)(A) of the ESA, NMFS published a finding on 13 April 2007 (72 FR 18616) indicating that the CBD petition presented substantial scientific information, and that the petitioned action might be warranted.

In June 2007 NMFS convened the Black Abalone Status Review Team (SRT) with the charge to develop a Black Abalone Status Review Report (Status Review) as mandated by the ESA. The purposes of the Status Review are to evaluate available information and data on the following topics as they relate to ESA listing: (1) long-term trends in abundance throughout the species range; (2) potential factors for the species' decline throughout its range (e.g., over-harvesting, natural predation, disease, habitat loss, etc.); (3) historic and current range, distribution and habitat use of the species; (4) status of populations in Baja California, Mexico; (5) historic and current estimates of population size and available habitat; (6) knowledge of various life history parameters (size/age at maturity, fecundity, length of larval stage, larval dispersal dynamics, etc.); and (7) projections of population growth or decline and risk of extinction.

The work of the SRT has been facilitated by the large number of longitudinal fisheryindependent studies that have been made in black abalone populations. Many are of substantial duration, with four exceeding two decades. A strikingly consistent pattern in the extensive data, detected across a number of locations, is the reduction of black abalone densities to low numbers in apparent response to the effects of withering syndrome. Recent analyses of interactions of population trends and local size frequency distributions indicate that, in virtually all such cases, densities have been reduced to a point where successful fertilization may not be possible. This pattern is a consequence of the breeding system in black abalone, requiring that animals of different gender spawn in temporal synchrony while in close proximity in order to achieve successful fertilization and larval production. Because of the extreme turbulence typical of rocky intertidal habitats on exposed outer coast locations, isolated individual black abalone have no chance of successful fertilization, even if in optimal health and reproductive status, because gametes are immediately dispersed before encounter with gametes of the opposite sex is possible.

The SRT has concluded that reduction in local densities below thresholds necessary for successful fertilization during spawning has been a widespread and pervasive consequence of population reductions by withering syndrome and other factors. Based on available information and the collective experience and expertise of the SRT, it is concluded that the likelihood that black abalone can spontaneously develop attributes that would reverse effects of reduced densities is extremely low. The SRT also has concluded that a reduction or cessation of the northward spread of withering syndrome effects, to those populations of black abalone not yet affected by the disease, is highly unlikely. Although illegal harvest, natural predation, and possibly other factors may be contributing to the present status of black abalone, it is the view of the SRT that risks associated with withering syndrome are the primary cause for concern about the survival of black abalone as a species.

The SRT agrees unanimously that without identification, development, and implementation of effective measures to counter the population-level effects of withering syndrome, black abalone are likely to become effectively extinct within 30 years. The actual loss of all black abalone may linger for a longer period of undetermined duration because long-lived individuals may persist after local populations are no longer able to reproduce because of reduced local densities. However, persistence of a few individuals at very low density will not forestall extinction of the species. The Team therefore believes that black abalone is in danger of extinction throughout all of its range. Continued maximum levels of protection from other sources of anthropogenic mortality will be essential to mainain any hope of recovery of black abalone while population-scale disease counter-measures are considered, developed, and implemented.

Reviewed: April 11, 2024
Web Site Owner: National Ocean Service

Take Our Survey | Privacy Statement | Site Disclaimer
National Marine Sanctuaries | National Ocean Service | National Oceanic and Atmospheric Administration |