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Gregory R. Mann, Ph.D. {ret.}

Abalone

“Haliotis asinina”

In the animal kingdom, Abalone belong to the phylum Mollusca, a group which includes clams, scallops, sea slugs, sea snails, octopuses and squid. Abalone are members of the family Haliotidae and the genus haliotis, which means “sea ear” referring to the flattened shape of the shell. The name Abalone is probably derived from the Spanish-American word aulon or aulone. The most conspicuous part of any Abalone is the shell, with its row of respiratory pores. Shells are prized because of their inner, iridescent layer and the meat is considered a delicacy in Asian culture. The muscular foot has a strong suction power permitting the Abalone to clamp tightly to rocky surfaces. A column of shell muscle attaches the body to its shell. The mantle circles the foot as does the epipodium, a sensory structure & extension of the foot which bears tentacles. The epipodium projects beyond the shell edge in the living animal. The epipodium surface may be smooth or pebbly in appearance and its edge may be frilly or scalloped. It is the most reliable structure for identifying Abalone species. The internal organs are arranged around the foot and under the shell. The most conspicuous organ the crescent-shaped gonad, is gray or green in females and cream colored in males. It extends around the side opposite the pores and to the rear of the Abalone. The Abalone has a pair of eyes, a mouth and an enlarged pair of tentacles. Inside the mouth is a long, file-like tongue called the radula, which scrapes algal matter to a size that can be ingested. The gill chamber is next to the mouth and under the respiratory pores. Water is drawn in under the edge of the shell and then flows over the gills and out the pores. Waste & reproductive products are carried out in the flow of water. Since it has no obvious brain structure, the Abalone is considered to be a primitive animal. However, it does have a heart on its left side and blood flows through the arteries, sinuses and veins assisted by the surrounding tissues and muscles. The sexes are separate and can be distinguished in individuals as small as one inch when the gonads begin to develop. The eggs or sperm are released through the pores with the respiratory current. This is known as broadcast spawning.

A 1.5 inch Abalone may spawn 10,000 eggs or more at a time, while an 8 inch Abalone may spawn 11 million or more. Spawning may be controlled by the water temperature or length of the day. The presence of eggs and sperm in the water may stimulate other Abalone to spawn, thus increasing the chances of fertilization egg hatches as a microscopic, free living larvae. It drifts with the currents for about a week, then the Abalone larvae settles to the bottom, sheds its swimming hairs (cilia) and begins to develop the adult shell form. If suitable habitat is located, it may grow to adulthood. The chance that an individual larva will survive to adulthood is very low however. Fortunately Abalone and most mollusks are prolific spawners but the mortality still probably exceeds 99%. Hybrid Abalone are not uncommon in areas where several species occur together. All species can hybridize, but the most common hybrids are red & white with pink. Abalone eat marine algae in the wild and on some farms. The adults feed on loose pieces drifting with the surge or current. Large brown algae is preferred. Many Abalone farms now use high quality manufactured food, which is healthy, efficient and produces very high quality meat. The color banding on many Abalone shells is due to changes in the types of algae eaten. Juvenile Abalone graze on rock encrusting coral-line algae and on diatoms & bacterial films. As they grow, they increasingly rely on drift algae. Abalone farming to date, has been limited and hampered by the quality & quantity of the macro-algae sources worldwide. Although some Abalone farms have successfully fed manufactured food for nearly 25 years, a high quality low cost manufactured food has been a recent development.

The movement in growth rate & health of the animals and ease of production are truly astounding. Throughout its life, an Abalone contends with a variety of predators. The eggs & larvae are eaten by filter-feeding animals. Though juvenile Abalone hide, they are active at night (nocturnal) and crabs, lobsters, octopuses, sea stars, fish and predatory snails prey on them. Abalone in shallow water may be crushed by storm tossed rocks. Large Abalone are not threatened by the predators of their earlier life but larger and often more efficient predators now become important. Fishes can dislodge some Abalone and swallow them whole. Even very large Abalone are no match for the crushing jaws of a Bat Ray. The Pacific Sea Otter is the most effective predator, capable of removing all exposed Abalone within reach. Only those in deep crevices or under large rocks will survive. Abalone are one of the first food items taken by otters as they move into new habitat. In the last 20+ years, the commercial catch of Abalone worldwide has declined from 18,000 metric ton to a little over 10,000 metric ton.

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