Biology Reference
In-Depth Information
from some of our species, it's because all the stressors are now operating at
a high level all the time.”
Take the case of the Delta Smelt, a small silver fish no longer than a
finger. It lives in a narrow zone of the estuary between the two pumping
plants that supply millions of Californians with drinking water. The smelt
should be adapted to very variable conditions, yet it seems to be losing its
ability to bounce back.
The droughts of the 1990s, shrinking habitat, and untimely flows were
all bad for the fish. Water exports slowly changed what was once a dy-
namic fresh and salt water mixing zone into a warm, giant lake. Those fish
wandering upstream in search of better habitat, or in response to sudden
changes in turbidity, got ground up in the pumps. Too often these “takes”
occurred before the fish were ready to reproduce—a grim scenario for a
fish that seldom lives past its first birthday. Smelt can't rely on younger or
older generations to buffer the species against environmental catastrophes.
Delta Smelt, a native fish
that once spawned in shal-
lows associated with tidal
rivers and sloughs through-
out the delta. Today's popu-
lation is a tiny fraction of
its historic size due to
human changes to its habi-
tat, including the export of
water. Consequently, this
small, short-lived fish is
frequently blamed for big,
long-lived conflicts over
who gets how much of Cali-
fornia's fresh water. (René
C. Reyes)
On top of these stresses, the food supply for smelt isn't so plentiful any-
more in the estuary. Their staple, plankton, is being eaten by the Asian
Clam, or has become more difficult to catch. The hungry smelt end up
chasing copepod species they never used to eat, using more energy to
catch these aquatic morsels than they gain from the meal. Smelt habitats,
meanwhile, are now tainted with ammonia from sewage outflows, or with
toxic blue-green algae, or with mats of Brazilian water weeds full of preda-
tory Largemouth Bass. These changes have turned the entire world of a
smelt upside down.
The tragedy is that this story isn't limited to the Delta Smelt. A similar
tale can be told for three fish species—Longfin Smelt, Striped Bass, and
Threadfin Shad—although each has a different life history and set of stress-
ors in the estuary, and two are long-established non-natives. Water manag-
