|Listed||February 8, 1999|
|Description||A large minnow with barbels and a deeply forked tail.|
|Habitat||Rivers, sloughs, and fresh and brackish tidal waters.|
|Food||Feed on the bottom on invertebrates and detrital matter.|
|Reproduction||Spawn large numbers of eggs in aquatic vegetation.|
|Threats||Habitat destruction and degradation caused by hydrological changes associated with water diversions, as well as agricultural chemicals and other stressors.|
The Sacramento splittail, Pogonichthys macrolepidotus, is a large cyprinid fish that can exceed 16 in (41 cm) in length. The name splittail refers to the distinctive tail of the fish. Pogon-ichthys means bearded fish, referring to the small barbels (whisker-like sensory organs) on the mouth of the fish, unusual in North American cyprinids. Macro-lepidotus means large-scaled. Adults are characterized by an elongated body, distinct nuchal hump (on the back of the neck), and small, blunt head, usually with barbels at the corners of the slightly subterminal mouth. The enlarged dorsal lobe of the caudal fin distinguishes the splittail from other minnows in the Central Valley of California. Sacramento split-tails are dull, silvery-gold on the sides and olive-gray dorsally.
During spawning season, pectoral, pelvic, and caudal (tail) fins are tinged with an orange-red color. Males develop small white nuptial tubercles on the head. Breeding tubercles (nodules) also appear on the base of the fins.
Splittails are relatively long-lived, frequently reaching five to seven years of age. An analysis of hard parts of the splittail indicate that larger fish may be eight to ten years old. Females are highly fecund, with the largest females producing over 250,000 eggs. Populations fluctuate annually depending on spawning success, which is highly correlated with freshwater outflow and the availability of shallow-water habitat with submerged vegetation. Fish usually reach sexual maturity by the end of their second year. The onset of spawning is associated with rising water levels, increasing water temperatures, and increasing day length. Peak spawning occurs from the months of March through May, although records of spawning exist for late January to early July. In some years, most spawning may take place within a limited period of time. For instance, in 1995, a year of extraordinarily successful spawning, most splittail spawned over a short period in April, even though larval splittail were captured from February through early July. Within each spawning season, older fish reproduce first, followed by younger individuals. Spawning occurs over flooded vegetation in tidal freshwater and euryhaline habitats of estuarine marshes and sloughs and slow-moving reaches of large rivers. Larvae remain in shallow, weedy areas close to spawning sites for 10 to 14 days and move into deeper water as they mature and swimming ability increases.
Splittails are benthic (bottom) foragers. In Suisun Marsh, they feed primarily on opossum shrimp, benthic amphipods, and harpactacoid copepods, although detrital material makes up a large percentage of their stomach contents. In the Delta, clams, crustaceans, insect larvae, and other invertebrates also are found in the diet. Predators include striped bass and other piscivores.
In recent years, they have been found most often in slow-moving sections of rivers and sloughs and dead-end sloughs. Reports from the 1950s, however, mention Sacramento River spawning migrations and catches of splittail during fast tides in Suisun Bay. Because they require flooded vegetation for spawning and rearing, splittail are frequently found in areas subject to flooding. In 1995, after an unusually wet winter, over five million juvenile split-tail were salvaged at the Central Valley Project and State Water Project indicating the magnitude of spawning success in favorable water years. They are year-round residents in Suisun Marsh, concentrating in the dead-end sloughs that typically have small streams feeding into them. They tend to be most abundant where other native fishes are abundant as well. In spring, both adult and young split-tail are frequently found in shallow, flooded areas, such as the Yolo and Sutter bypasses, low riverine parts of delta islands, and river mouths. Historically, the major flood basins distributed throughout the Sacramento and San Joaquin valleys provided spawning and rearing habitat. These flood basins have all been reclaimed or modified for flood control purposes, including Yolo and Sutter bypasses. Although primarily a freshwater species, splittail can tolerate salinities as high as 10 to 18 parts per thousand. California Department of Fish and Game survey data from 1979 through 1994 indicate that the highest abundances occurred in shallow areas of Suisun and Grizzly bays.
Recent research indicates that splittail will use the Yolo and Sutter bypasses during the winter and spring months for foraging and spawning. However, the Yolo Bypass may only be used by splittail during wet winters, when water from the Sacramento River over-tops the Fremont Weir and spills over the Sacramento Weir into the Bypass. In 1998, the Yolo and Sutter bypasses provided good habitat for fish, particularly splittail, when they were flooded for several weeks in March and April. In order to provide spawning habitat for splittail, water must remain on the bypasses until fish have completed spawning, and larvae are able to swim out on their own, during the draining process.
The Sacramento splittail is native to the Central Valley of California, where it was once widely distributed. Historically, it was found as far north as Redding on the Sacramento River, as far south as the present-day site of the Friant Dam on the San Joaquin River, and up tributaries of the Sacramento River as far as the current Oroville Dam on the Feather River and the Folsom Dam on the American River.
The Sacramento splittail was once part of the diet of Native Americans living in the Central Valley. Recreational anglers reported catches of 50 or more per day prior to the damming of its riverine habitats. They were captured in the past in southern San Francisco Bay and at the mouth of Coyote Creek in Santa Clara County, but the species is no longer present there.
The splittail is primarily threatened by the altered hydraulics and reduced Delta outflow caused by the export of freshwater from the Sacramento and San Joaquin rivers through operation of the State and Federal water projects. These operations include not only the export of water from the Delta but also diversion of water to storage during periods of high run-off, which reduce instream flows and available submerged aquatic habitat for spawning and rearing. These hydrological effects, coupled with severe drought years, introduced aquatic species, the loss of shallow-water habitat to reclamation activities, and other human-caused actions, have reduced the species' capacity to recover from natural seasonal fluctuations in hydrology for which it was adapted. Additional threats to this species include
- direct and indirect mortality at power plants and in-Delta water diversion sites;
- reduced river flows and changes in the seasonal patterns of flows in the Sacramento and San Joaquin rivers and their tributaries;
- the loss of spawning and nursery habitat as a consequence of draining and diking for agriculture;
- the loss of shallow-water habitat due to levee slope protection, marina construction, and other bank-oriented construction activities;
- the reduction in the availability of highly productive brackish-water habitat;
- the presence of toxic substances, especially agricultural and industrial chemicals and heavy metals in their aquatic habitat;
- human and natural disturbance of the food web through altered hydrology and introduction of exotic species;
- flood control operations that strand eggs, larvae, juveniles, and adults;
- the increase in severity of these effects by several years of drought; and
- entrainment (pulling) of fish through un-screened or inadequately screened municipal and agricultural diversions. The Sacramento splittail is now restricted to a small portion of its former range. However, during wet years, the species migrates up the Sacramento River as far as the Red Bluff diversion dam in Tehama County, and into the lowermost reaches of the Feather and American rivers. Overall, its abundance has declined by about 60% from 1984 through 1993. The greatest declines (over 80%) occurred in the shallow Suisun Bay area, the center of the range of the species. Splittail populations are now 35%-60% of what they were in the 1940s.
Conservation and Recovery
Protective measures currently being implemented to benefit the delta smelt may benefit the splittail, such as restrictions on pumping under certain conditions. However, the ecological requirements of these species differ, especially with respect to timing of important development stages and habitat uses. Unlike delta smelt, splittail require flooded lowland habitat for spawning and are particularly vulnerable to disturbance or destruction of marshy habitat.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
U. S. Fish and Wildlife Service
Sacramento Fish and Wildlife Office
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
U. S. Fish and Wildlife Service. 8 February 1999. "Determination of Threatened Status for the Sacramento Splittail." Federal Register 64(25): 5963-5981.