SACRAMENTO SPLITTAIL } Pogonichthys macrolepidotus
DESCRIPTION: The splittail is a relatively large member of the minnow family that grows to more than 12 inches. Splittail have an elongate body, a blunt head, and an upper tail fin lobe distinctively larger than the lower lobe. Splittail are silver on the sides and olive gray on their backs. Adults develop a hump on their nape. During breeding season, splittail take on a red-orange hue on their tail, pectoral, and pelvic fins.
HABITAT: Splittail are primarily freshwater fish but can tolerate moderate salty water. They are found mostly in slow-moving marshy sections of rivers and dead-end sloughs. Floodplains may be important for spawning.
RANGE: The splittail formerly occurred in lakes and rivers throughout the Central Valley as far north as Redding on the Sacramento River and as far south as the Friant Dam on the San Joaquin River, as well as in the Sacramento-San Joaquin River Delta, but today it is largely restricted to the Delta, Suisun Bay, Suisun Marsh, and Napa Marsh.
MIGRATION: The splittail is rare among North American minnows in that it makes dramatic annual spawning migrations from the brackish estuary to upstream freshwater tributaries and floodplains. Juvenile splittail move downstream to brackish areas and deeper offshore habitat as they mature.
BREEDING: Splittail adults migrate upstream from brackish areas in the late winter and spring to spawn in freshwater . Splittail likely spawn in floodplains on submerged vegetation in temporarily flooded upland and riparian habitat. Spawning also occurs in the lower reaches of rivers, bypasses used for flood management, dead-end sloughs, and larger sloughs. Spawning is most successful in extremely wet years when large areas of floodplains and river margins are inundated for extended periods of time.
LIFE CYCLE: Larvae and juvenile splittail remain upstream in shallow, vegetated areas inshore near spawning sites until floodplains begin to dry, when they emigrate downstream to tidal freshwater and brackish portions of the estuary. Splittail generally mature by the end of their second year.
FEEDING: Splittail are bottom foragers that feed extensively on opossum shrimp and will also eat earthworms, clams, insect larvae, and other invertebrates.
THREATS: These fish are threatened by reduced water outflow and changed estuarine hydraulics due to dams and water diversions, modification of spawning habitat by wetland draining and filling, climatic change, toxic substances, introduced species, and fishing.
POPULATION TREND: Formerly common in the Sacramento, San Joaquin, Feather, and American rivers, the splittail is extinct in all but a fraction of its former range. Populations in the minnow’s constricted range in the Delta are estimated to be only 35 to 60 percent as abundant as they were in 1940; the percentage decline over the species’ historic range is much greater. Splittail numbers in the Delta have declined steadily since 1980, and in 1992 numbers declined to the lowest on record. Population levels appear to fluctuate widely from year to year.