Pacific Rocky Intertidal Monitoring: Trends and Synthesis

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Haliotis rufescens (Red Abalone)

Haliotis rufescens (Swainson 1822)

Phylum Mollusca, class Gastropoda, order Archaeogastropoda

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Description

Shell exterior is brick red to pink and commonly overgrown with epiphytes reaching a maximum of 30 cm. There are usually 3-4 oval, open respiratory pores which are externally raised above the shell’s surface. The shell interior is iridescent with a large, oval muscle scar. (Morris et al. 1980). The mantle and tentacles are black and the underside of the foot is yellowish. 

Habitat and Geographic Range

Red abalone inhabit rocky areas with kelp. They are uncommon in the low intertidal zone and more abundant subtidally to around 40 m depth (up to 180 m). Their current range is from Oregon to Baja (California Fish and Game Commission 2005).

Synonyms

Similar species

Haliotis cracherodii, (black abalone), is the primary species encountered in the intertidal,  and has a smooth dark shell with 5-9 round, flat shell holes. Pink (H. corrugata) and green (H. fulgens) abalone occasionally occur in the intertidal. Pinks are dull green to reddish brown, highly corrugated, with 2-4 large, elevated holes, and the edge of the shell is usually quite scalloped. Greens are olive green to reddish brown, with numerous, broad, flat-topped ribs, and 5-7 small, circular, slightly elevated holes.

Natural History

The red abalone is the largest species of abalone in the world and the most common abalone found in Northern California. Red abalone sometimes occur intertidally, but are more common subtidally. Most California abalones mature at between 3 and 7 years of age and may live for 35 to 54 years (Haaker et al., 1986). They are slow-growing herbivores, feeding mostly on drift kelp. Sea otters and humans are the main predators of adults. Where sea otters are present red abalone occur mostly in deep cracks and crevices, but they may be seen out in the open in regions lacking sea otters (Hines and Pearse 1982).

Abalone broadcast spawn, releasing their eggs and sperm into the ocean. Fecundity (number of gametes produced) is directly related to adult size, with older, larger individuals producing significantly higher numbers of gametes than newly mature, smaller animals. Because gametes are broadcast into the nearshore environment, successful fertilization relies on large  adult populations living in close proximity (Prince et al. 1987). Warm water was shown to have deleterious affects on sperm production of red abalone suggesting the importance of considering ocean warming trends in recovery and management plans (Rogers-Bennett et. al. 2010). Larval development rate and length of the swimming larval period are also influenced by temperature. At their optimum temperature (14-16 o C), red abalone larvae hatch about one day after fertilization, develop into a morphologically mature veliger larvae after three days and are capable of metamorphosis after about seven days (Morse et al. 1979). Red abalone settlement and metamorphosis are strongly associated with the presence of crustose coralline algae (Morse et al. 1984, Boxshall 2000).

Red abalone populations have declined mainly due to overharvesting, predation by sea otters and disease. A chronic wasting disease called withering syndrome (WS) has affected red abalone populations, although, the disease is not well studied for this species. See the black abalone species description for more information on WS. The presence of WS in red abalone has been most notable in red abalone commercial farms, especially during oceanic warming events such as the 1997-98 El Niño (Moore et al. 2000). The recovery of sea otters (Enhydra lutris) along the California coast, during the 1900s, has created contention within the commercial and recreational fisheries for red abalone. Sea otters have been shown to affect abalone densities, sizes and behavior. The challenge of protecting both sea otters and abalone populations requires special consideration. Fanshawe et al. suggest that where sea otters limit the sustainability of red abalone it may be necessary to create two spatially separated categories of marine protected areas (2003).  

Human uses of red abalone dates to prehistoric times with shells found in Channel Island archaeological sites dated to between 11,500 and 12,000 years before present (Braje et. Al. 2009). Red abalone shells are abundant in Chumash middens (refuse deposits) of the Northern Channel Islands dated between about 7500 and 3300 years ago. The modern Californian fishery for abalone peaked in the 1950s and '60s with a subsequent decline in populations. Due to drastic population declines, the commercial fishery of red abalone was closed in 1997. Currently, red abalone are legally harvested on a restricted, recreational basis only in Northern California (north of San Francisco). An Abalone Recovery and Management Plan (ARMP) was adopted in 2005 by the Fish and Game Commission to manage the recreational fishery in Northern California and aid in the recovery of the depleted abalone in the rest of California (California Fish and Game Commission 2005).  

Since most of the wild populations of abalone have been decimated, abalone farming has become an increasingly successful mariculture. Attempts to culture abalone began in California in the 1960s and developed into a successful business by the 1980s (Leighton 1989). Red and green abalone are the only species farmed on a large scale in California with red abalone farming concentrated north of Point Conception.

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