The first step to understanding the ecological needs of a threatened or endangered species is to identify its geographic range and its temporal distribution within that range. Nearly two decades after the delta smelt was listed as threatened under the federal Endangered Species Act that foundational information had not been synthesized and displayed on maps. In this paper we map the distribution of the fish by life stage, providing coverages that enable resources managers to focus conservation activities, including targeted restoration efforts, where and near where delta smelt are most frequently found. Delta smelt are endemic to and narrowly distributed in the upper San Francisco Estuary wherein a single population adjusts its distribution between years, seasonally, and in response to storm events and other environmental macro-phenomena. Consistently occupied areas, including Suisun Marsh, the Sacramento-San Joaquin rivers confluence, and the north Delta should be high priorities for targeted management actions. The east and south Delta, and the bays and embayments west of the rivers confluence are occupied infrequently by delta smelt and warrant lower priority for management actions, including habitat restoration efforts.
Merz JE, Hamilton SA, Bergman PS, Cavallo B. 2011. Spatial perspective for delta smelt: a summary of contemporary survey data. California Fish and Game 97:164-189.