U.S. Fish & Wildlife Service

Sacramento Fish & Wildlife OfficeServing the people, conserving the fish, wildlife, and plants of California

A Unit Of The Pacific Southwest Region

Species Information

California Freshwater Shrimp

Syncaris pacifica

Basic Species Information

STATUS

Endangered. This species is in danger of extinction throughout all or a significant portion of its range.

DESCRIPTION

The California freshwater shrimp grows to about 5 cm (2½ inches), about the size of your little finger. If the shrimp was curled up, it would look like the prawns at your supermarket.

This species is a 10-legged crustacean of the family Atyidae. Shrimps from this family can be distinguished from others by the length of their pincer-like claws (chelae) and presence of terminal bristles (setae) at the tips of the first and second chelae. The presence of a short spine above the eye and the angled articulation of the second chelae with the carpus ("wrist") separate the California freshwater shrimp from other shrimp found in California.

Shrimp coloration is quite variable. Males are translucent to nearly transparent. They have small surface and internal color-producing cells (chromatophores) clustered in a pattern to disrupt perception of their body outline and maximize the illusion that they are submerged, decaying vegetation. Undisturbed shrimp move slowly and are virtually invisible on submerged leaf and twig substrates, and among the fine, exposed, live roots of vegetation along undercut stream banks.

The coloration of females ranges from a dark brown to a purple color. In some, a broad tan dorsal band also may be present. Females may change rapidly from this very dark cryptic color to nearly transparent with diffuse chromatophores. Females are generally larger and deeper bodied than males.

FOOD SOURCES

The shrimp are detritus feeders. They eat small decaying particles brought downstream to their pools. They brush up the food with tufts at the ends of their claws and lift it to their mouths. They are one of nature's garbage collectors.

HABITAT

California freshwater shrimp have evolved to survive a broad range of stream and water temperature conditions characteristic of small, perennial coastal streams. They have been found only in low-elevation less than 116 m (less than 380 feet) and low-gradient (generally less than 1 percent) streams.

Excellent habitat conditions include streams of 30 to 91 cm (12 to 36) inches in depth with exposed live roots of trees such as alder and willow along undercut banks greater than 15 cm (6 inches). The banks have overhanging woody debris or stream vegetation and vines such as stinging nettles, grasses, vine maple and mint.

Such areas may provide refuges from swift currents as well as some protection from high sediment concentrations associated with high stream flows. During the winter, the shrimp is found in undercut banks with exposed fine root systems or dense, overhanging vegetation.

MATING

Adults reach sexually maturity by the end of their second summer of growth. Thereafter, they breed once a year in the fall. Females produce about 50 to 120 eggs, which remain attached to their mother throughout the winter.

RANGE

Historically, the shrimp was probably common in low elevation, perennial freshwater streams in Marin, Sonoma, and Napa counties. Today, it is found in 16 stream segments within these counties. The distribution can be separated into four general geographic regions:

  • Tributary streams in the lower Russian River drainage, which flows westward into the Pacific Ocean
  • Coastal streams flowing westward directly into the Pacific Ocean
  • Streams draining into Tomales Bay
  • Streams flowing southward into northern San Pablo Bay.

PREDATORS

Nonnative fish such as bluegill and bass are considered predators.

THREATS

Existing populations of the California freshwater shrimp are threatened by introduced fish, deterioration or loss of habitat resulting from water diversion, impoundments, livestock and dairy activities, agricultural activities and developments, flood control activities, gravel mining, timber harvesting, migration barriers and water pollution.

WHAT YOU CAN DO

Kids have played a major role in saving this species. Since 1992, kids in Marin and Sonoma counties have been helping restore habitat for the species. They have worked on restoring streams, educating adults, raising money and even lobbying Congress.

Read about how 4th graders at the Brookside School programs by kids in Marin and Sonoma counties.

Just about any place you live, you can help restore streams and ponds. Search the Internet for words like volunteer, stream, river, watershed, restoration, clean-up, and the name of your town or area.

Many of the ideas in What You Can Do to Help Wildlife and Plants (201 KB | PDF) can help protect and recover streams. For example, be careful what you pour down sinks. Remember that it will end up in your community's water.

Last updated: December 1, 2017