The Smelt Larva Survey, initiated in January 2009, provides near real-time distribution data for longfin smelt larvae in the Delta, Suisun Bay and Suisun Marsh. These data are used by agency managers to assess vulnerability of longfin smelt larvae to entrainment in south Delta export pumps.
Sampling takes place within the first two weeks in January and repeats every other week through the second week in March. Each 4-day survey consists of a single 10-minute oblique tow conducted at each of the 35 survey locations (see map) using an egg and larva net. The 500-micron mesh net is hung on a rigid frame shaped like an inverted-U, which in turn is attached to skis to prevent it from digging into the bottom when deployed. The net mouth area measures 0.37 m2. The conical net tapers back from the frame 3.35 m to a 1-liter cod-end jar, which collects and concentrates the sample. Immediately after each tow, juvenile fishes are removed, identified, measured and returned to the water immediately, and the remaining larvae are preserved in 10% formalin for later identification in the Lab in Stockton.