Lost, A Desert River and its Native Fishes - Sierra Club

Tributaries
Similar changes have occurred to tributary streams.
Historically, surface flow often became intermittent or
totally dried up in the stream‘s lower reaches. Today, that
condition has not only intensified but has become permanent.
Upstream water storage on the Bill Williams and
Gila Rivers has dried up the lower portions of these
streams. On the Salt and Gila Rivers, Roosevelt, Horse
Mesa, Mormon Flat, Stewart Mountain, Bartlett, Horseshoe,
and Coolidge Dams capture water that historically
flowed to the Colorado River and delta. The river channel
through the —Valley of the Sun“ is normally dry except for
a few deep ponds left behind from sand and gravel mining
and an incongruous, 2-mile-long artificial lake. The
river corridor is leveed and highly disturbed, forming little
more than a scar across the valley and state (Figs. 41 and
42). Recent maps seldom show sections of these streams,
testifying to their conspicuous absence.
Fish
Fish found in the lower Colorado River were unique,
having the highest proportion (75%) of endemism in the
Nation. They occurred nowhere else in the world. Only
nine species were native to the lower mainstem river and
they evolved over millions of years in one of the harshest
river environments known. They had learned how to survive
floods, prolonged droughts, extreme temperatures,
and salinities that few other fish could tolerate.
The majority of nonnative fish found in the river
today could not have survived long in the pristine system,
nor could they invade the basin on their own. Nonnative
fish only gained access to the Colorado River when they
were stocked by Europeans. Common carp were imported
to southern Nevada and first noticed in the wild in 1881.
Others soon followed. Bullhead and channel catfish were
stocked in 1894 and by 1910, all had spread through the
lower river and were replacing natives at a rapid pace. By
1930, the majority of native fish had already been replaced
by these three species.
There is little doubt that water control projects sealed
the fate of natives. Dams blocked upstream spawning
migrations, irrigation reduced flows, fish were stranded
in canals and fields, while critical habitat was claimed by
agriculture. The wide, shallow, braided river was squeezed
by levees and further deepened by dredging and the natural
forces of streambed scour. Storage reservoirs captured
floods, reduced sediment, supplied consistent summer
flows to water users, and provided optimal conditions for
recreational fisheries. Deep, cool water habitats benefitted
species like channel catfish, common carp, largemouth
bass, trout, and sunfish that were less tolerant of desert
MUELLER AND MARSH 37
conditions. State and federal game agencies recognized
the recreational potential of this resource and started to
manage these waters to meet an ever-growing angler demand.
Resource agencies sold fishing licenses to fund
their programs and sport fishing generated revenue for
local merchants.
What physically and biologically remains of the river
more closely resembles conditions and fish communities
found in the Upper Mississippi and Missouri River drainage.
Today, the Lower Colorado River has the dubious
distinction of being among the few major rivers of the
world with an entirely introduced fish fauna. The following
section describes the historical fish community, the
decline of the native fishery, and the fishery that exists
today.
The Native Fish Community (Pre-1880)
The river‘s estuary contained more than 75 marine
species, but prior to 1880, only nine freshwater species
were found further upstream in the main river channel
(Table 5). These represented four families (cyprinids,
catostomids, cyprinodontids, poeciliids) of freshwater
fishes and two (mugilids, elopids) marine species that
frequently invaded the lower river.
Evermann and Rutter (1895) reported that —the lower
Colorado is one of the muddiest rivers in America and is
unfit for any but mud-loving species.“ This was especially
true during floods. Fish in the channel were blasted
by suspended mud and sand. Abrasion to their bodies
and gills must have been tremendous. Early reports suggest
that fish were not plentiful in the channel and most
were found in off-channel habitats where conditions were
more hospitable.
Floods were unquestionably important for
maintaining nursery and spawning habitat, but the size
of the fish community not only depended on successful
spawning during wet periods, but also the severity of
droughts. It did not make any difference how many young
fish were produced, if there was not enough water for
them to survive. The influence that drought played in the
native fish community is poorly understood and
unfortunately largely ignored. Researchers and
hydrologists have been fascinated with flood mechanics
and stream morphology but little study has gone into
understanding the long-term biological implications of
droughts and how it must have shaped the fish
community.
The first drought-related fishkill was reported by
Father Garces in 1774œ1776 (Coues, 1900). He reported
observing the remains of thousands of dead fish while
traveling through the delta. At the beginning of the twentieth
century, MacDougal (1917) reported —a windrow of
remains of fish which appeared to be carp,“ that —extended