EPA's Vessel General Permit and Small Vessel General

Black abalone have also experienced severe declines due to a temperature-related disease called
withering syndrome. This bacteria-based disease prevents assimilation of nutrients in the
digestive system and results in abalone that “wither” as individuals consume body tissues. The
disease was first identified west of Santa Cruz and Anacapa islands in 1985 and 1986 before
spreading to Santa Rosa Island and Santa Barbara Island by 1988. The disease made its
appearance along the mainland in 1988 in San Luis Obispo county, where 85% of the resident
black abalone died in Diablo Cove. This die-off was attributed to the presence of warm-water
effluent from a nuclear power facility. From 1988 to the early 1990’s, withering syndrome
continued to spread throughout the Channel islands to 2000, when it was estimated that only 1%
of the original population remained (Richards 2000).
Natural threats
Along with depletion from commercial harvests, withering syndrome has also been significant in
black abalone decline. Withering syndrome is a chronic, degenerative disease responsible for
mass mortalities (Moore et al. 2000). Warm temperature, although not associated with the
initiation of withering syndrome, is associated with increased mortality rates (Lafferty and Kuris
1993, Harvell et al. 2009). This has been observed from power plant effluent and incursions of
warm water into traditionally temperate regions. In red abalone, higher rates of infection and
more prominent signs of infection are associated with El Niño events (Moore et al. 2009).
Interspecific competition has not been studied in black abalone, but blacklip abalone face
significant competition for algal resources by sea urchins (Strain and Johnson 2009).
Compounding these factors are reproductive factors that further hamper species recovery. At
low densities, individuals aggregate for spawning are not close enough for fertilization to occur.
As a result, annual recruitment of juvenile black abalone has declined steeply since adult
populations dropped below half of initial densities (Richards and Davis 1993).
Black abalone at various life stages experience predation from several species. Juvenile abalone
hiding amongst rocks are food for crabs, lobsters, octopi, starfish, fish, and predatory snails
(Haaker et al. 1986). Abalone of intermediate sizes are vulnerable to octopus and fish predation,
particularly sheepshead and cabezon. As adults, black abalone are primarily preyed upon by sea
otters, which can be major regulators of black abalone populations, but are not know to extirpate
communities as other threats are known to (Braje et al. 2009, Johnson et al. 2009). Interactions
with other species can hinder species recovery in other ways, namely competition for space and
food resources. Purple and red sea urchins tend to feed on the same kelp and brown algae food
as black abalone and, when in high abundance and food is plentiful, have the potential to outcompete
abalone for food (Leighton 1968, Paine 1974, Tegner and Levin 1982, Tegner 1989,
Miller and Lawrenz-Miller 1993). However, abalone tend to inhabit different habitats than these
urchin species (CDFG 1993). Space competition may also occur between black abalone and
sand castle worms. This species cements itself to the underside of rocks, the same habitat that
black abalone seek for refuge (Connell et al. 1988). This could limit the habitat available for
black abalone to recruit into during recovery. Other factors that can threaten black abalone
include storms (crushing abalone between rocks and sedimentation in rocky habitat), fresh water
input, sedimentation on gills leading to asphyxiation, and temperature impacts on reproduction
and growth (Cox 1960, 1962).
198