Female California, jveshmder shrimp with eggs, cmrt&y oj-Larry Serpa,
The California freshwater shrimp
is an endangered species.
Endangered species are
plants and animals that are
in immediate danger of
becoming extinct.
Threatened species are plants,
and animals whose population
numbers are so low that they
may become endangered in the
The U.S. Environmental
Protection Agency's (EPA)
Endangered Species Protection
Program (ESPP) will help
ensure that pesticide use does
not jeopardize the survival of
listed species.
California Freshwater Shrimp fynujurkpudfiox.
Description and Ecology
Status Endangered, listed October 31, 1988.
Critical Habitat Not designated.
Appearance The California freshwater shrimp is a 10-
legged crustacean belonging to the atyid family. Of the three
other atyid members in North America, two are also listed
as endangered (Kentucky cave shrimp (Palaemonias ganteri)
and Alabama cave shrimp (Palaemonias atabamae)) and one
which once inhabited coastal streams in California is believed
to be extinct (Pasadena shrimp (Syncaris pasadenae)).
These species were believed to have been isolated from a
marine environment during the Jurassic period. They are
anatomically distinguished from other shrimp by the length of
their pincer-like claws (chelae) and the bristles (setae) at the
tips of the first two chelae. These bristles are especially useful
for sweeping food particles off surfaces and in toward their
mouths. California freshwater shrimp are further distinguished
by a short spine on the body above the eye and a particular
angled articulation of the second chelae with the "wrist"
California freshwater shrimp are small. Females are usually
deeper bodied and range from 1.3 to 1.8 inches from the
eye orbit to the tip of the tail, while males range from 1.2 to
1.5 inches. Coloration varies and works to camouflage these
shrimp against their habitat. Male shrimp are transparent or
nearly so, with surface and interior chromatophores (pigment
holding cells) that cluster into patterns that disguise the
outline of the body. As such, they appear to be just more
underwater detritus. Females have similar coloration but may
be darker brown or almost purple, and might have a broad
tan dorsal band. Both males and females have the ability
to darken simultaneously or gradually, but the female has a
greater range from dark to light and vice versa. The created
effect shades their forms into the shadows of roots, branches
and the undercut bank. Even the visible internal organs
become part of the disguise.
Range California freshwater shrimp may once have been
common in the low-elevation perennial freshwater streams
of Marin, Sonoma and Napa counties. They are still found
in all three counties but in much fewer numbers and fewer
streams. The distribution of the shrimp has been separated
into four drainage units: 1) tributary streams of the lower
Russian River drainage, that flow westward to the Pacific
Ocean, 2) coastal streams flowing westward directly into
the Pacific Ocean, 3) streams draining into Tomales Bay,
and 4) streams flowing southward into San Pablo Bay. While
California freshwater shrimp in laboratories can tolerate
brackish waters, they are unable to tolerate ocean salinities.
It is thought that the isolated streams that harbor these
shrimp were once connected, but later separated by geologic
uplift and rising sea level.
Habitat Within the low elevation-low gradient streams
inhabited by the California freshwater shrimp, the most
suitable reaches are characterized by submerged undercut
banks, overhanging plants such as blackberry, woody debris,
and the exposed live root systems of willow or alder. The
shrimp uses microhabitat variations depending on the season.
In the winter, rainy season, when stream flow is high and fast
and laden with suspended sediment, California freshwater
shrimp find protection beneath the undercut banks amidst
Courtesy oj- Lorry Serpa,
Syncark pacified,
Office of Pesticide Programs (7507P)
February 2010

Calihriua Fretfamuter Shrimp
exposed roots or dense, overhanging vegetation. In the
summer when flow is low they retreat to isolated pools
with minimal cover but more opaque water. Largely absent
now, at one time debris dams may have been important
feeding and resting places. These dams would have
gathered the detritus (shrimp food) and leaf litter that
would become more detritus, and would have sheltered
the shrimp during high flows. The optimal stream depth for
California freshwater shrimp is 1—3 feet.
Biology and Behavior While not everything is
known about the reproduction of California freshwater
shrimp, insight from the ecology of other freshwater
and marine shrimp, and observations suggest that
they breed once a year in late summer, immediately
following the last molt of the female. Egg-bearing female
California freshwater shrimp have been noted in autumn
(September-November). Fifty to 120 eggs adhere to the
swimming legs on the abdomen (pleopods), and are cared
for and protected there through the winter, high-water
season. The young are released in May or early June, the
most favorable time of the hydrological cycle.
Newly hatched young are only about 0.2 inches long, but
grow rapidly to 0.8 inches by early autumn. Growth slows
through autumn, winter, and spring, but resumes during
their second summer. At this time the size difference be-
tween males and females is apparent, and both are sexu-
ally mature. They may live more than three years.
California freshwater shrimp are described as collectors.
They feed on fine organic material, fecai matter, under-
water plants, free-floating algae and algae attached to
underwater surfaces, zooplankton, and similar materials.
They also scavenge on dead animals and shrimp.
Although these freshwater shrimp are able to remain
nearly motionless for large periods of time, a likely survival
strategy, they can swim forward and backward and "skip"
over the water surface when disturbed. They likely are
prey for a number of native fish, and introduced fish such
as the mosquitofish, and green sunfish.
Recovery Plan The U.S. Fish and Wildlife Service
(FWS) developed a recovery plan for the California
freshwater shrimp in 1998. Recovery plans outline
reasonable actions that FWS believes are required to
recover or protect listed species. FWS prepares recovery
plans, sometimes with the assistance of recovery teams,
contractors, state agencies, and others. Recovery plans
do not necessarily represent the views nor the official
positions or approvals of any individuals or agencies, other
than FWS, involved in the plan formulation. Approved
recovery plans are subject to modification as dictated
by new findings, changes in species' status, and the
completion of recovery tasks.
California Freshwater Shrimp
Information Sources
Primary Reference Beacham, Walton, Castronova,
Frank F., and Sessine, Suzanne (eds.) 2001. Beacham's
Guide to the Endangered Species of North America, Gale
Group, New York. Vol. 3, pp. 1413-1418.
Listing Notice US. Fish and Wildlife Service 1988.
Federal Register 53, No. 210, pp. 43884-43889. October
31, 1988. http://ecos.fws.gov/docs/federal_register/
Recovery Plan U.S. Fish and Wildlife Service,
Portland, Oregon. 1998. California Freshwater Shrimp
(Syncaris pacifica Holmes) Recovery Plan, 94 pp. http://
Species Account U.S. Fish and Wildlife Service,
Sacramento Fish and Wildlife Office, 2007 http://www.
Courtesy of Larry Serpa,
Courtesy of Larry Serpa,
Habitat:-for Catifortua, frevkwrzter skrimpj La/jusUtas Creek/Larry Se-rpa.