Population estimates, movements, and size structure of the endangered Quitobaquito pupfish, Cyprinodon macularius eremus

Size distributions of Cyprinodon macularius eremus (Quitobaquito pupfish) w ere compared and contrasted from spring, channel, island, and pond habitats of Quitobaquito Springs (Organ Pipe Cactus National Monument, Arizona) dur ing October 1996 through October 1997. The following year, adult pupfish we re marked en masse by application of fluorescent grit via air pressure. An average population estimate of 9,556 pupfish was derived for the entire spr ing complex, and a mean estimate of 591 pupfish was calculated separately f or spring and channel habitats. During spring and early summer, movements b y pupfish from the thermal (26 degreesC) environment of the spring and chan nel into the ambient pond were virtually nonexistent. This suggests the 2 h abitats may be more segregated than originally thought. Potential establish ment of a second population of endangered Quitobaquito pupfish is discussed .