(DRAFT) - Taxonomy
Species clam, pismo
Species Id M060005
Date 26 AUG 96
TAXONOMY
NAME - clam, pismo
OTHER COMMON NAMES - giant tivela
ELEMENT CODE -
CATEGORY - Aquatic Molluscs
PHYLUM AND SUBPHYLUM - Mollusca,
CLASS AND SUBCLASS - Bivalvia,
ORDER AND SUBORDER - Veneroida,
FAMILY AND SUBFAMILY - Veneridae,
GENUS AND SUBGENUS - Tivela,
SPECIES AND SSP - stultorum,
SCIENTIFIC NAME - Tivela stultorum
AUTHORITY - Mawe
TAXONOMY REFERENCES - 19
Taxonomy - 1 (DRAFT) - Status
Species clam, pismo
Species Id M060005
Date 26 AUG 96
STATUS
Coded Status
Game (Consumptive Recreational)
REFERENCES FOR STATUS - 19
COMMENTS ON STATUS -
The Pismo clam supports an important sport shellfishery. An estimated
150,000 people once sought the clams on Pismo Beach, California, during a
single weekend; however, sea otters have depleted the supply there since
1981, and as of 1986 there is no fishery *19*.
The Pismo clam lives in the sandy beaches along the Central and Southern
California coast -- a habitat that is highly vulnerable to degradation from
dredging and oil pollution (oil spills). Substantial losses of clam
populations resulting from man's manipulation of the coastal zone could be
expected to cause an economic loss to the sport fishery *19*.
In many areas, recruitment of Pismo clams has been very low and the
population has declined almost steadily over years. Exact causes for lack
of recruitment are not fully known. Further losses of parent stocks from
degradation and/or overfishing could be expected to further reduce this
important recreational shellfishery *19*.
Status - 1 (DRAFT) - Distribution
Species clam, pismo
Species Id M060005
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine, intertidal FL2 N
Marine, intertidal FL2 N
REFERENCES FOR NWI - 19
COMMENTS ON HABITAT ASSOCIATIONS -
Pismo clams usually live in the intertidal zone on flat beaches of the open
coast, but are sometimes found in entrance channels to bays, sloughs, and
estuaries. Their normal depth in the sand is 5.2 to 15.6 cm. They live in
an environment of rapid, severe and forceful interaction of water and sand.
They are slow diggers and are found in a characteristic position on the
open coasts related to the waves: the front hinge and excurrent siphon
face the ocean and the mantle edge and incurrent siphon face land. Clams
in bays are oriented at random. They bury themselves by jetting water from
the anterior of the shell while they bury the foot. The weight of the
shell helps to carry the clam downward. The most productive areas for
Pismo clams have extensive upwelling of cool oceanic water that brings with
it inorganic nutrients essential for phytoplankton blooms *19*.
Habitat Associations - 1 (DRAFT) - Food Habits
Species clam, pismo
Species Id M060005
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
DETRITIVORE
FILTERER
REFERENCES FOR TROPHIC LEVEL - 19
LIFESTAGE FOOD FOOD PART
General Phytoplankton
General Zooplankton
General Detritus - Organic
General Bacteria
General See Comments; Food
REFERENCES FOR GENERAL FOOD - 19
COMMENTS ON FOOD -
The Pismo clam is a filter feeder on detritus, although living, one-celled
organisms form a considerable portion of the diet. Water taken in through
the incurrent siphon passes over the gills where food particles are removed.
The types of food utilized include phytoplankton (such as diatoms),
bacteria, zooplankton, eggs and sperm, and detritus from disintegration of
plants and animals. Half of the stomach contents is sand. In feeding a
clam 3 inches long filters as much as 60 l of water per day. Intracellular
digestion is done by phagocytic cells of the digestive diverticulum, aided
by migratory phagocytes in the lumen of the alimentary canal *19*.
Food Habits - 1 (DRAFT) - Environment Associations
Species clam, pismo
Species Id M060005
Date 26 AUG 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
FL Turbidity: Specified in Comments
J Water Temperature: Specified in Comments
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 19
REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 19
REFERENCES FOR FEEDING LARVAE ENVIRONMENTAL ASSOC_ - 19
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Pismo clams usually live in the intertidal zone on flat beaches of the open
coast, but are sometimes found in entrance channels to bays, sloughs and
estuaries. Their normal depth in the sand is 5.2 to 15.6 cm. They live in
an environment of rapid, severe and forceful interaction of water and sand.
They are slow diggers and are found in a characteristic position on the
open coasts related to the waves: the front hinge and excurrent siphon face
the ocean and the mantle edge and incurrent siphon face land. The most
productive areas for Pismo clams have extensive upwelling of cool oceanic
water that brings with it inorganic nutrients essential for phytoplankton
blooms.*19*
COMMENTS ON RESTING JUVENILE ENVIRONMENTAL ASSOC_ -
Post larvae are known to die during heavy runoffs from rivers. Oil and
other pollutants affect mortality. Red tide caused by a dinoflagellate
bloom, as well as extremely cold weather, can kill young clams. Mortality
rates for Pismo clams at Pismo Beach indicate that of 1,000 clams 0.5 year
old, only 5 were still alive at age 7.5.*19*
COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
Little is known about the environmental requirements of the larval stage of
Pismo clams. It has been reported that only a small fraction of 1% of
spawned eggs become mature clams. Causes for the mortality are unknown,
but may include sudden changes in temperature and salinity.*19*
Environment Associations - 1 (DRAFT) - Life History
Species clam, pismo
Species Id M060005
Date 26 AUG 96
LIFE HISTORY
PHYSICAL DESCRIPTION:
The shell of the Pismo clam reaches lengths of 150 mm or more, is strong,
heavy, and generally smooth though sculptured with fine concentric growth
lines; beak nearly central; ligament obvious, elongate, set in deep groove;
periostracum shiny, greenish to brownish; shell pale buff to dark chocolate,
occasionally marked with brown or purple-brown bands *19*.
REPRODUCTION:
The sexes of the Pismo clam are separate although early investigators
believed the clam to be hermaphroditic. Most clams become sexually mature
after their first winter, at shell length as short as 17-20 mm.
Gametogenesis begins in March or April and ripe gametes first appear in
April and May. Gonadal development proceeds rapidly in June and July;
spawning begins in late July or early August and continues to the end of
November. Researchers found that the main spawning of clams at Pismo Beach
and Monterey occurred during September and October with some occurrence from
June to August. Similar findings were found for clams from San Diego.
Discharge of gametes appears to take place when there is a fair rise in
water temperature. As in most bivalves, males usually spawn first and their
release of gametes stimulates the females to spawn. Spawning may occur
several times during the season since only a portion of the gametes ripen at
one time. Hermaphrodites are rare. Out of 289 clams examined, only three
hermaphrodites were found *19*.
Fecundity and Eggs. The eggs of Pismo clams are very small, 0.074-0.081 mm
in diameter. The number of eggs per female increases with shell size,
ranging from 10 to 20 million and averaging 15 million *19*.
Larvae. Little is known about the Pismo clam from the time eggs are spawned
until the clams appear on the beach. The free swimming larval life is
estimated to last for 3 weeks during which the larvae can be swept
alongshore for 40 to 100 miles. Larvae and postlarvae less than 2.3 mm have
never been found drifting in the sea. Recent findings at the California
Fish and Game, Marine Resources Laboratory, Granite Canyon, California,
indicate that the larvae have a high weight/volume ratio and may remain on
or near the bottom most of the time and move very little *19*.
Postlarvae and Recruitment. At metamorphosis the clam develops a foot and
attaches to sand grains with a byssus. This attachment helps the clam to
maintian itself in the constantly moving sand of a wave-beaten coast. The
length of a byssus can range from 45 to 92 mm or as much as five times the
length of the clam. As the clam increases in size the byssus disappears.
The clam's increasing weight and burrowing power then helps to maintain it
on the beach *19*.
LIMITING FACTORS:
The Pismo clam has many predators including gulls, sharks, rays, and some
surf fishes such as the California corbina (Menticirrhus undulatus). Rays
use their wings to create a suction that pulls the clams from the sand.
The rays then mouth the esposed clams and crush and swallow them.
The moon snail, Polinices sp., eats clams up to 2 years old. It drills a
Life History - 1 (DRAFT) - Life History
Species clam, pismo
Species Id M060005
Date 26 AUG 96
hole in the shell with its rasping tongue and then inserts the tongue
through the hole and eats the soft body of the clam. Cancer crabs, Cancer,
have been observed to crack the shell of clams up to 2.5 cm long with their
front pincers. At Sunset Beach, Santa Cruz County, researchers watched
gulls pick up sublegal size clams discarded by diggers, climb to an altitude
of 9 to 12 m, and then dop the clams on the hard packed sand. The fall
broke the shells and enabled the gulls to eat the clam. In areas where sea
otters (Enhydra lutris) forage, clam populations decreased significantly. A
sea otter has been observed to eat 24 Pismo clams in 2.5 h. Researchers
reported that a sea otter can consume 80 clams per day. Clams decreased
from 6.5 to 0.5/m(squared) at Moss Landing and from 0.55-0.80
clams/m(squared) to 0.15 clams/m(squared) at Zmudowski Beach from 1972 to
1974. Researchers estimated that otters ate 520,000 to 700,000 Pismo clams
in one year at Monterey Bay. Sea otters are directly responsible for the
loss of the clam sport fishery in the Pismo Beach area. The sport catch
declined from 343,000 clams in 1978 to 0 in 1983.
Larval cestodes have been found in Pismo clams. They occur as
yellowish-white cysts, 3.2-3.8 mm in diameter. The cestodes have been
identified as the larval stage of tapeworms in stringrays and skates. The
parasites can stop clam's sexual development but are not harmful to man if
eaten. Commensal pea crabs, occasionally found in the mantle cavity, feed
on food particles collected by the clam's gills *19*.
POPULATION ATTRIBUTES:
Maturity and Life Span. Pismo clams mature during the first full summer of
life at La Jolla, California, and during the second summer of life in the
northern edge of their range. They are 17 mm to 31 mm long at first
maturity. Researchers found that females spawn for the first time in the
second or third summer after hatching.
The age of the Pismo clam can be determined by rings on the shell. The
rings used in age determination are usually formed in fall or winter, or
when the clam is subjected to the most prolonged period of disturbances.
The longest clam on record at Pismo Beach was seven and three-eighths inches
long and was about 26 years old, but the ages of a number of clams from Baja
California have exceeded 35 years *19*.
Growth Characteristics. The Pismo clam grows continuously throughout its
life. Increase in shell growth is greatest in spring, summer, and early
fall. The average yearly increase in length during the first 4 years of
life is slightly more than 20 mm. At age 10 the annual increase is usually
not more than 5 mm. Minimum legal length on most beaches (4.5 inches) is
first reached in 5 years but may not be reached until 8 or 9 years. At
Pismo Beach, clams reach legal minimum length between ages 7 and 8.
Growth rates apparently vary among beaches. Researchers who constructed
growth curves for clams from four beaches between Morro and Monterey Bays,
reported that clams from Turtle Bay grew fastest and those from Morro Bay
slowest *19*.
REFERENCES FOR LIFE HISTORY- 19
Life History - 2 (DRAFT) - Management Practices
Species clam, pismo
Species Id M060005
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Existing Regulating harvest - setting bag/creel limits
Existing Regulating harvest - setting size limits
Beneficial Controlling pollution [thermal, chemical, physical]
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 19
REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 19
COMMENTS ON MANAGEMENT PRACTICES -
The daily bag limit of clams has been reduced over the years from 200 in
1911 to 10 in 1985. As of 1986, they must be 4.5 inches or greater in
length in San Luis Obispo County and south, and 5.0 inches or greater in
Monterey County and north. All undersize clams must be returned to a hole
(dug while looking for clams) *19*.
Causes for the mortality are unknown, but may include sudden changes in
temperature and salinity. Post larvae are known to die during heavy runoffs
from rivers. Oil and other pollutants affect mortality. Red tide caused by
a dinoflagellate bloom, as well as extremely cold weather, can kill young
clams. Mortality rates for Pismo clams at Pismo Beach, indicate that of
1,000 clams 0.5 year old, only 5 were still alive at age 7.5 *19*.
Management Practices - 1 (DRAFT) - References
Species clam, pismo
Species Id M060005
Date 26 AUG 96
References
19* Shaw, W., T. Hassler. 1989. Species Profiles: Life Histories and
Environmental Requirements of Coastal Fishes and Invertebrates
(Pacific Southwest)--Pismo Clam. U.S. Fish and Wildlife Service
Biol. Rep. 82(11.95) pp 12.
References - 1