Abalone

What is abalone?

The word ABALONE comes from the American Spanish (a California coastal Indian language) word Abulòn meaning ear shell. Within the SeaWorld, abalone belongs to marine gastropod mollusks in the family Haliotidae and the genus Haliotis. Abalone are sea snails. They vary in size from different species. The group Mollusca includes: clams, scallops, sea slugs, octopuses and squid. Mollusks are world wide and predominantly marine. Common names for abalone also include: Ear-shells, Sea-ears and Venus'-ears, as well as Perlemoen in South Africa, Muttonfish or Muttonshells in Australia, Ormer in Jersey and Guernsey, and Paua in New Zealand.

What do they look like?

In adult form they have a soft body surrounded by a mantle, an anterior head and a large muscular foot. Mollusks are known for their beautifully formed and colored shell. The spiral structure, which is common in snail shells, is flat in the abalone.

Where do they live?

The abalone naturally interacts with their habitat using their foot. They crawl from place to place like a typical snail. The abalone cannot crawl over loose surfaces like sand where they can be easily overturned and are then open to predators. They are in this way limited to where it can live. Abalone is generally found in hard areas like rock or coral. Abalone also avoid the light as rule. In daytime they are generally found hiding in crevices on rocky reefs or under rocky overhangs.

Anatomy

The most striking part of any abalone is the shell, with its row of respiratory pores. Shells are valued because of their inner layer. The muscular foot has a strong suction power permitting the abalone to hold tightly to rocky surfaces. A line of shell muscle attaches the body to its shell. The mantle circles the foot as does the epipodium, a sensory structure and expansion of the foot which bears tentacles. The epipodium projects beyond the shell edge in the living animal. The epipodium surface may be smooth or rough in appearance and its edge may be frilly or scalloped.

Internal organs

The internal organs are arranged around the foot and under the shell. The most noticeable organ, the curved-shaped gonad, is gray or green in females and cream coloured 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 a bloated 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.

Breathing

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 and 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.

Species

There is only the one genus in the family Haliotidae, and about four to seven subgenera. The number of species recognized worldwide is about 100. Within the South-African seawaters only one species is predominately found – Haliotis midae. This is also the species farmed in South-Africa. This specific species is found all around Dyer Island.

Life cycle

Food

Abalone have different food needs for the different stages of development. Generally abalone eat marine algae in the wild. The adults feed on loose pieces drifting with the flow or current. Large algae are preferred. For cultured abalone, many farms now use high quality manufactured food, which is healthy, efficient and produces very high quality meat. Wild abalone tend to stay in one location waiting for food to drift by. However, they will move daily, seasonally or when food becomes limited for a long period. The colour banding on many abalone shells is due to changes in the types of algae eaten. Juvenile abalone nibbles on rock encrusting coralline algae and on diatoms and bacterial films. As they grow they more and more rely on drifting algae.

Manufactured food

Abalone farming, to date, has been limited and hampered by the quality and 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 improvement in growth rate and health of the animals and ease of production are truly astounding.

Reproduction

The sexes are separate and can be distinguished in individuals as small as 2cm when the gonads begin to develop. The eggs or sperm are released through the pores with the respiratory current. Fertility is high and increases with size from 10 000 to 11 million eggs at a time. Spawning may be controlled by the water temperature or day length. The eggs hatch as microscopic, free living larvae. It drifts with the currents for about a week, then the abalone larvae settle to the bottom, shed their 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.

What are the main threats that abalone face?

In the wild:

Right through its life, an abalone contends with a range of predators. The eggs and larvae are eaten by filter-feeding animals. Though juvenile abalone hide, they are active at night and crabs, lobsters, octopuses, starfish, fish and predatory snails prey on them. Abalone in shallow water may be crushed by storm tossed rocks.Large abalone is not threatened by the predators of their earlier life, but larger, and often more efficient predators now become important. Some fish can dislodge some abalone and swallow them whole. The sea otter is the most effective predator, capable of removing all exposed abalone within reach. Only those under large rocks will survive. Abalone is one of the first food items taken by otters as they move into new habitat.

Declining population:

In the last 20+ years, the business-related catching of abalone worldwide has declined. The reasons for this can be a combination of the following:

Predation.
Mortality of small abalone for many reasons.
Over harvesting.
Competition. Sea urchins and other species, utilizing abalone food and living space.
Illegal harvesting. Some people ignore the regulations enacted to protect abalone because abalone brings high prices.
Loss of habitat. Coastal "development" and pollution have ruined large numbers.

Number 5 (Illegal harvesting-poaching) is the largest and most important reason for the decline. Poached abalone generally finds its way to the markets overseas and brings good money for the poacher. This fact makes it all the more worthwhile for the poacher, but it is illegal and more attention must be given to it in any way possible.

What has the South-African government done to protect abalone?

In short. The government is acting to bring the poaching numbers down. In 2007, because of widespread poaching of abalone, the South African government listed perlemoen as an endangered species according to the CITES section III appendix, which requests member governments to monitor the trade in this species. Severe restrictions have been set in place.