STATUS OF SPLITTAIL IN THE SACRAMENTO-SAN-JOAQUIN ESTUARY

Analysis of data from four extensive fish surveys in the Sacramento-Sa n Joaquin estuary indicated that splittail Pogonichthys macrolepidotus , endemic to the Central Valley of California, declined by 62% over a 13-year period. Splittails are now found mostly in the estuary, a frac tion of their former range. In a gill-net survey in August 1994, 50% o f the splittails taken in the estuary were from the Suisun Bay area, a nd 50% were just upstream in shallow, well-vegetated areas. Splittails migrate into freshwater to spawn, and river outflow carries juveniles into productive, shallow, low-salinity areas downstream. The high cor relation of abundance of young with river outflow (average r(2), 0.60) and a weak stock-recruitment relationship (r(2) = 0.22) indicate that spawning success depends on favorable environmental conditions create d by high outflows, such as the number of days that lowland areas rema in flooded in the spring. A repeated measures analysis of variance ind icated that splittails prefer shallow, low-salinity habitats. The redu ctions in splittail abundance and range and the movements and habitat preferences of splittail young and adults correspond to trends and hab its of two other species characteristic of the estuary, delta smelt Hy pomesus transpacificus and longfin smelt Spirinchus thaleichthys. The largest threats to these three species are changes in water management and increases in water diversions that reduce spawning and rearing ar eas and other low-salinity habitats in Suisun Bay.