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<br />
<br />
<br />quite. More cottonwood-willow habitat exists in the
<br />delta than in the riparian forests upstream (Ohmart et
<br />aI., 1988).
<br />
<br />Delta wetlands provide habitat for a number of mam-
<br />mals, including raccoons, skunks, bats, coyotes, bobcats,
<br />muskrats, rabbits, jackrabbits, desert rats, gophers, and
<br />squirrels (Valdes-Casillas et aI., 1998a).
<br />
<br />The tidal zone and near shore marine habitats of the
<br />Gulf of California also support endangered species and
<br />important fisheries. Fish species include catfish, carp,
<br />tilapia, mullet, and largemouth bass, and the last remain-
<br />ing populations of desert pupfish, which still survive in
<br />backwaters and lagoons (Valdes-Casillas et aI., 1998a).
<br />The delta is a negative estuary (where the salinity is
<br />greater than the ocean's due to evaporation that exceeds
<br />precipitation and river flow) that is a rich breeding
<br />ground for marine species and has a significant influ-
<br />ence on fish populations, possibly throughout the entire
<br />Gulf. Reduction of freshwater flows into the Gulf has
<br />reduced the transport of nutrients and changed the char-
<br />acteristics of this critical nursery habitat. Nutrient
<br />concentrations are higher than most of those reported
<br />in the literature for estuaries and negative estuaries,
<br />perhaps due to the strong mixing caused by tides of great
<br />amplitude (Hernandez-Ayon et aI., 1993). The shrimp
<br />fishery has dropped off steeply and other fisheries are
<br />in decline. The totoaba is now virtually extinct, and the
<br />vaquita porpoise is thought to number only a few hun-
<br />dred (Marine Mammal Commission, 1996).
<br />
<br />The loss of upper Gulf fisheries may be the most costly
<br />effect of reduced flows to the delta. Overfishing certainly
<br />contributes to the problem, but scientists have noted a
<br />correlation between shrimp catches and flood flows to
<br />the delta.27 This corroborates anecdotal evidence and
<br />reports from local fishermen that indicate trends such
<br />as a temporary increase in the number of fish species
<br />observed in the mid-1980's after high flood flows
<br />reached the delta (Postel et aI., n.d.).
<br />
<br />THE ENVIRONMENTAL DEFENSE
<br />FUND'S RESEARCH IN THE DELTA
<br />
<br />In 1997 and 1998, staff from the Environmental Defense
<br />Fund, the Environmental Research Laboratory (ERL),
<br />the Instituto Tecnologico y de Estudios Superiores de
<br />Monterrey (ITESM) and the Sonoran Institute conducted
<br />fieldwork to evaluate the potential for restoration of
<br />delta habitat. This was the first serious attempt to study
<br />delta habitat since the restoration of flows. The team
<br />quantified the effects of a flood release of known mag-
<br />nitude, and inventoried vegetation. They were able to
<br />observe the response of vegetation to flows as a basis to
<br />define the amount of water needed to sustain delta eco-
<br />systems. In addition, they assessed the potential for
<br />existing vegetative cover to support wildlife,28 particu-
<br />larly in comparison to the upstream stretches where
<br />current conservation efforts are focused.29 The findings
<br />also serve as a baseline for evaluating the quality and
<br />extent of habitat that could be restored and maintained
<br />with a dedicated supply of water and a program for
<br />managing that water. [Appendix B details the methods used
<br />in this study]
<br />
<br />To conduct its inventory, the research team used
<br />satellite imagery, low-level aerial videography, and
<br />ground surveys to map channels and plant life.
<br />[See Figure 5.] The main (navigable) course of the river
<br />was found by exploring its channels in a small boat
<br />during floods. The team also surveyed the marshlands
<br />supported by agricultural drain water. They assessed
<br />the relative potential and importance of restoring and
<br />managing wetlands in the delta, basing its assessment
<br />on habitat values, degree of environmental threat, and
<br />the importance of each area to local people who use the
<br />wetland resources and may be willing to help protect
<br />them.3D The results of this fieldwork are summarized
<br />below, followed by a number of restoration objectives.
<br />
<br />27 Data correlating shrimp landings at San Felipe, Baja California, the nearest shrimping station to the delta, with discharges from the Colorado River to the
<br />northem Gulf of California show a significant correlation since the resumption of flows (Galindo-Beet et al.).
<br />2. Previous research has inventoried the extent and habitat values of the Cienega de Santa Clara wetland in the southeast portion of the delta and the
<br />wetlands of the Rio Hardy/Rio Colorado confluence. See Glenn et al., 1992, and Glenn et al., 1996.
<br />29 Conservation efforts on the Colorado River are discussed in Chapter 1 .
<br />30 These scientific findings are in manuscript, and will be published (Valdes-Casillas et aI., 1998c), and are presented in a report the North American
<br />Wetland Conservation Council prepared by scientists from ITESM and others (Valdes-Casillas et aI., 1998a).
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