The coloration is dark brown, dark green, dark blue or almost black.[4] The silvery interior of the shell shows a pale pinkish and greenish iridescence. The exterior of the shell is smoother than most abalones, or may have low obsolete coarse spiral lirae and lines of growth. The shell is oval, evenly convex, the two sides equally curved. The back of the shell is regularly convex, with little algal growth.[4] The shell is not carinated at the row of holes. The spire is near the margin. The cavity of the spire is minute, concealed or nearly so. The muscle scar is generally not distinct. There are usually five to seven small, open respiratory holes, or pores, along the left side of the shell[4] and the rims of the holes are flush with the rest of the shell. These holes collectively make up what is known as the selenizone which form as the shell grows. The columellar plate is not truncate below, sloping inward, its face concave. The rear of the shell is spiralled, and the mantle, foot and tentacles are black.[5] The interior of the shell is pearly with pink and green iridescence.[4]
The black abalone's shell length can reach a maximum of 20 cm (7.9 in), being typically 10–14 cm (3.9–5.5 in) long.[6]
Anatomy of Haliotis cracherodii
In the living animal, the tentacles on the epipodium, the mantle, and the foot are black.[6]
Prehistoric distribution has been confirmed along much of this range from archaeological recovery at a variety of PacificcoastalNative American sites. For example, Chumash peoples in central California were known to have been harvesting black abalone approximately a millennium earlier in the Morro Bay area.[8]
Two black abalone shells in a tide pool at low tide
Black abalones cling to rocky surfaces in the low intertidal zone, up to 6 m deep. They can typically be found wedged into crevices, cracks, and holes during low tide. They generally occur in areas of moderate to high surf.[6] Juveniles tend to reside in crevices to reduce their risk of predation, but the larger adults will move out onto rock surfaces.[9]
Life cycle
Life cycle of Haliotis cracherodii
Black abalone reach sexual maturity at 3 years and can live 30 years or more.[6][10] Spawning occurs in spring and early summer; occasionally, a second spawn occurs in the fall.[10] Black abalone are broadcast spawners, and successful spawning requires that individuals be grouped closely together. Larvae are free-swimming for between 5 and 14 days before they settle onto hard substrate, usually near larger individuals,[10] where they then metamorphose into their adult form, develop a shell and settle onto a rock.[9] Juveniles do not tend to disperse great distances, and current populations of black abalone are generally composed of individuals that were spawned locally. Juveniles settle in crevices and remain hidden until they reach approximately 4 inches in length. At that point, adults congregate in more exposed areas such as rocks and in tide pools.[10] They are thought to be able to live for between 25 and 75 years, and will begin to reproduce between three and seven years.[9]
Feeding habits
Black abalones are herbivorous gastropods, and feed mostly on drift algae and kelp. Their primary food species depend on the habitat. In southern California habitats, black abalones are thought to feed on the giant kelp (Macrocystis pyrifera) and feather boa kelp (Egregia menziesii), while in central and northern California habitats they feed on the bull kelp (Nereocystis leutkeana).[6]
Humans have harvested black abalones along the California Coast for at least 10,000 years. On San Miguel Island, archaeological evidence shows that the Island Chumash people and their ancestors ate black abalone for millennia and also used the shells to make fishhooks, beads, and ornaments. After the Chumash and other California Indians were devastated by European diseases, and sea otters were nearly eradicated from California waters by the historic fur trade, black abalone populations rebounded and attracted an intensive intertidal fishery conducted primarily by Chinese immigrants from the 1850s to about 1900.[10]
Conservation status
Black abalone are listed on the International Union for Conservation of Nature's Red List as Critically Endangered (CR A4e).[9] On June 23, 1999, the U.S. National Marine Fisheries Service (NMFS) designated the black abalone as a candidate for protection under the Endangered Species Act (64 FR 33466).[12] On December 21, 2006, the Center for Biological Diversity submitted a petition to NMFS to list the black abalone.[13] On January 11, 2008, NMFS completed their status review of the species and proposed that it be listed as endangered.[14][15] Black abalone were listed as endangered on January 14, 2009.[16] The NMFS designated critical habitat for the endangered black abalone on October 27, 2011.[17] The state of California has introduced an Abalone Recovery Management Plan to guide conservation efforts.[18]
Black abalone have dramatically declined in numbers throughout their historical range, and are locally extirpated in certain areas. This decline was initiated by overfishing. Following World War II, the California abalone fishery was not managed for individual species. Therefore, it resulted in a systematic depletion of various abalone species as the fishery over-harvested one species and then moved on to the next in an attempt to meet demand.[10] Black abalone were the last to be targeted, with the peak harvest occurring in the 1970s. Additionally, improved harvesting technologies that expanded the harvesting areas and supported larger harvests per unit effort were not initiated.[10] Now, all abalone fisheries in California are managed by the California Department of Fish and Game, which restricts the size of abalones caught, and the season in which harvesting can take place.[9] In Mexico, there is a total allowable catch limit for black abalones.[9] Even though harvesting black abalone is regulated in California, poaching still occurs. Other threats include coastal development for residential areas, harbours and waste discharges, compounded by commercial and recreational fishing of the black abalone.[9]
The depleted stocks of black abalone were further reduced by withering syndrome, first discovered in 1985, when commercial fishermen reported large numbers of empty shells and dying abalones on the shores of several of the Californian Channel Islands (including the islands of Santa Cruz, Anacapa, Santa Rosa, Santa Barbara, San Miguel, and San Clemente).[10][11] This disease impairs the production of digestive enzymes, effectively starving the abalone to death. Following onset of symptoms, the animal usually quickly dies. In many locations, percentages greater than 90% of individuals have been lost, and in some places, a total loss of the black abalone population occurred.[9] The disease spread from the Channel Islands to the mainland coast in 1992, where it devastated most populations in warmer waters south of Point Conception or in locally warmer waters further north.[6][19][20]
^"73 FR 1986"(PDF). Federal Register. 73 (8): 1986. January 11, 2008.
^"74 FR 1937"(PDF). Federal Register. 74 (9): 1937. January 14, 2009. Archived from the original(PDF) on February 15, 2013.
^NMFS. Endangered and Threatened Wildlife and Plants: Final Rulemaking To Designate Critical Habitat for Black Abalone.Federal Register;; v76, (October 27, 2011), 66805-66844.
