ESWR page - Endangered Species & Wetlands Report

EXECUTIVE SUMMARY
The Center for Biological Diversity, the Bay Institute and the Natural Resources Defense
Council formally request that the U.S. Fish and Wildlife Service (USFWS) change the
listing of the delta smelt (Hypomesus transpacificus) from threatened to endangered
under the federal Endangered Species Act (ESA), on an emergency basis. In the past few
years, the delta smelt population has plummeted to the lowest levels ever recorded and,
based on population viability analysis, the species is in imminent danger of extinction,
the criterion for endangered status. Recent surveys indicate that environmental
conditions in the delta smelt’s critical habitat, the upper San Francisco Bay/Sacramento-
San Joaquin Delta Estuary, have also declined, threatening the planktonic food web upon
which the species depends. The magnitude and frequency of occurrence of threats to the
species identified by USFWS are also increasing. The petitioners are conservation
organizations with an interest in protecting the delta smelt and its Delta habitat.
Delta smelt are endemic to the upper reaches of the Bay-Delta Estuary. The species
requires specific environmental conditions (freshwater flow, water temperature, salinity)
and habitat types (shallow open waters) within the estuary for migration, spawning, egg
incubation, rearing, and larval and juvenile transport from spawning to rearing habitats.
Delta smelt feed exclusively on plankton and most individual fish live only one year.
Although they are restricted to a relatively small geographic range, delta smelt use
different parts of the estuary at different life history stages. Throughout most of their life
span, delta smelt inhabit low salinity habitat, at the interface of inflowing fresh water
from the Sacramento and San Joaquin Rivers and salt water from the Pacific Ocean.
Spawning adults, larvae, and young juveniles are found further upstream in the Delta,
where they are vulnerable to lethal entrainment into federal, state, industrial, and local
agricultural water diversion and export facilities.
As recently as thirty years ago, the delta smelt was one of the most common and
abundant of the pelagic fishes in the estuary. In the early 1980s, its population declined
by more than 80%, leading to a threatened listing under the ESA in 1993. During the
1990s, delta smelt abundance fluctuated and then increased in response to improved
habitat conditions following the 1987-1992 drought. In 2002, the species’ abundance
again declined drastically, dropping more than 80% in just three years. In 2005,
abundance of delta smelt fell to its second consecutive record low and was just 2.4% of
the abundance measured when the species was listed in 1993.
Population viability and extinction risk analyses indicate that delta smelt has fallen below
its “effective population size”, with its present low abundance rendering the species
vulnerable to inbreeding and genetic drift. The analyses, completed three years ago,
predicted a 50% chance that the population would fall below its effective population size
within two years, a prediction fulfilled by recent measurements of the species’ record low
abundance in 2004 and 2005. Other analyses using the most conservative extinction
criterion predicted a 26-30% probability that the delta smelt population would fall to just
800 fish (compared to the present record low population of an estimated 25,000 fish) in
the next 20 years. These high probabilities of extinction for delta smelt exceed criteria
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