Longfin Smelt have declined as other pelagic fish species have over the past two decades. The species was listed in 2009 under the California Endangered Species Act. In a previous blog1 I described trends in their abundance and distribution in the upper Bay and Delta. Below is a chart depicting the long-term trend in another standard CDFW survey, the San Francisco Bay Midwater Trawl Survey. The index is the average catch for the April and May monthly surveys at a basic array of 28-44 standard stations from San Francisco Bay upstream into the central Delta. Yearling smelt are dominant in the April surveys, while young predominate in the May surveys.
As in other surveys, the index pattern clearly shows a sharp reduction in average catch since 2007. The average catch is particularly low in the last three years. There was no May survey in 2008. Similar patterns were evident in the Fall Midwater Trawl Survey, Summer Townet Survey, Winter Kodiak Trawl Survey, 20-mm Smelt Survey, and the Larval Fish Survey.