FWS, in its memorandum dated March 19, 1996, recommended that the effects analysis of this document also address five listed species that are endemic or have a portion of their range in Mexico. These species were the Yuma clapper rail, southwestern willow flycatcher, desert pupfish, totoaba, and vaquita (Gulf harbor porpoise). The biology and potential effects of the first two species have been discussed previously. The latter three species are discussed below.
The reduction in Colorado River flows below the SIB has had an affect on the historical ecosystem of the delta. However, these reductions have been instituted through an international treaty, and the diversion and use of such treaty water is solely at Mexicos discretion. Except for major flood periods as experienced on the Colorado River in the mid-1980s, little water reaches the delta and the upper Gulf. It is not within Reclamations discretionary authority on the lower Colorado River to augment or make unilateral adjustments to water deliveries to the international border.
Reclamation provided the NMFS a copy of the previous draft (March 1996) of this assessment and will also provide them an official copy of this final BA. The NMFS provided comments on the draft BA via letter dated June 28, 1996. In its letter, NMFS determined that lower Colorado River operations are not likely to adversely affect the vaquita and four listed sea turtles (i.e., green sea turtle, leatherback sea turtle, loggerhead sea turtle, and olive ridley sea turtle). NMFS also requested additional analysis of the biology and factors affecting the endangered totoaba along with a discussion of the United States discretion regarding Mexicos treaty waters.
Description and Life Requisites
The desert pupfish is a small killifish with a smoothly rounded body shape. Adults generally range from 2-3 inches in length. Males are smaller than females and during spawning the males are blue on the head and sides and have yellow edged fins. Most adults have narrow, dark, vertical bars on their sides. The species was described in 1853 from specimens collected in San Pedro River, Arizona. There are two recognized subspecies and possibly a third form (yet to be described). The nominal subspecies, Cyprinodon macularius macularius, occurs in both the Salton Sea area of southern California and the Colorado River delta area in Mexico and is the species of concern, herein. The other subspecies is C.m. eremus and is endemic to Quitobaquito Spring, Arizona.
The desert pupfish was listed as an endangered species on March 31, 1986. Critical habitat for the species was designated at the time of listing and included the Quitobaquito Spring which is in Organ Pipe Cactus National Monument, and San Felipe Creek along with its two tributaries Carrizo Wash and Fish Creek Wash in southern California. All of the former and parts of the latter were in Federal ownership at the time of listing. Reclamation purchased the remaining private holdings along San Felipe Creek and its tributary washes and turned them over to CFG in 1991. All of the designated critical habitat is now under State or Federal ownership.
Desert pupfish are adapted to harsh desert environments and are extremely hardy. They routinely occupy water of too poor quality for other fishes, most notably too warm and too salty. They can tolerate temperatures in excess of 110° F; oxygen levels as low as 0.1 ppm; and salinity nearly twice that of sea water (over 70 parts per thousand [ppt]). In addition to their absolute tolerance of these parameters, they are able to adjust and tolerate rapid, extreme changes to these same parameters (Marsh and Sada 1993).
The fish have a short life span, usually only 2 years, but they mature rapidly and can reproduce as many as three times during the year.
Distribution and Abundance
Desert pupfish inhabit desert springs, small streams, creeks, marshes and margins of larger bodies of water. The fish usually inhabit very shallow water, often too shallow for other fishes. Present distribution of the subspecies C. m. macularius includes natural populations in at least 12 locations in the United States and Mexico, as well as over 20 transplanted populations.
One of the natural populations in Mexico is in the Cienega, a 100,000 acre bowl on the Colorado River delta 60 miles south of the U.S./Mexico border. The area is about 90 percent unvegetated salt flats with a number of small marsh complexes along the eastern edge of the bowl where it abuts an escarpment. The area is disconnected from both the Colorado River and the Gulf (Sea of Cortez), however extreme high tides result in the lower half of the bowl becoming inundated to a level of one foot or less of salt water from the gulf. The marsh areas on the east side are small and are spring fed. The largest marsh complex is on the northeast side where two agricultural drains provide relatively fresh water inflows. The desert pupfish occur in a number of these marsh complexes.
Reclamation biologists discovered this population of desert pupfish in 1974 during preproject investigations for a feature of the Colorado River Basin Salinity Control Project. At that time, the Cienega was being fed by agricultural return flows from the Riito Drain in Mexico which provided about 35 cfs flow. The project feature being investigated was construction of a bypass canal for drain water from WMIDD.
Desert pupfish were found in the marsh along with mosquitofish, sailfin mollies, carp and red shiners. The bypass canal was completed in 1978 and provided a steady flow of over 150 cfs to the marsh. Based upon aerial surveys, the added inflow caused the marsh to grow from an estimated 300 acres of vegetated area in 1974 to roughly 10,000 acres in 1985. Recent aerial surveys show that while the inflows have continued, the marsh has not continued to grow in size. Desert pupfish continue to exist in the marsh. The fish tend to inhabit the shallow edges of the marsh in vegetated areas.
Desert pupfish from the Cienega were transported to Dexter National Fish Hatchery during May 1983, and many of the transplanted populations in the United States are of this subspecies and stem from this initial transplant.
During preproject investigations in 1974 to 1976, Reclamation biologists observed desert pupfish in the Cienega. Measurements of water quality at that time revealed salinity ranging from 6 ppt inthe irrigation drain inflow to over 80 ppt at the edge of the salt flats. Bypass canal water, which began flowing into the Cienega in 1978, was 3.2 ppt and resulted in rapid expansion of the vegetated areas of the Cienega. Salinity measurements made in 1994 were similar to those made in 1974 and ranged from 4 - 80 ppt. Operation of the YDP at one-third capacity would reduce the flow of drain water coming into the marsh, via the main outlet drain, from 135,000 acre-feet to 108,800 acre-feet. This action may raise the lower end of the salinity range from 4 ppt to 6 ppt which may affect some of the nonnative fish in the marsh and would possibly be a net benefit to the desert pupfish. Since aerial expansion of the marsh has not continued, it is unlikely that available habitat for desert pupfish would change. We conclude, therefore, that operation of the YDP at one-third capacity would not effect desert pupfish in the Cienega.
Description and Life Requisites
The vaquita is a small porpoise and is widely believed to be the most endangered marine cetacean in the world (Klinowska 1991; Taylor and Gerrodette 1993). It is also the only endemic species of marine mammal from the Gulf.
The vaquita is very similar in external morphology to the harbor porpoise (Phocoena phocoena). Based on a very small sample and a maximum recorded total length of about 5 feet, the vaquita may be the smallest of all the delphinoids (Brownell et al. 1987). The pectoral fins are larger and the dorsal fin is higher proportionally to the body length than in any other extant porpoise species (Brownell et al. 1987).
The coloration of adult vaquitas is unique. On the dorsal portion, the color is dark gray, the sides are pale gray, and the ventral surface is white with some pale-gray elongated spots. The porpoise has a large, dark eye spot and lip patches that contrast with the gray background (Ramirez 1993).
Little is known about the reproductive biology of the species. It has been suggested that calving occurs in the spring and mating in late spring or soon thereafter (Vidal 1990). Food habits are also practically unknown; Fitch and Brownell (1968) reported small fish such as grunt (Orthopristis reddingi) and croaker (Bairdiella icistia) from stomach contents and Brownell (1982) also reported squid.
Distribution and Abundance
The geographic distribution of the vaquita appears to be confined to the upper Gulf, representing the most restricted range for any cetacean species (Ramirez 1993). Sightings outside of this region (south of 30° 45' N latitude) may represent occasional departures by some individuals from the center of distribution (Silber and Norris 1991) or temporary extensions in distribution due to climatic changes (Vidal 1990). The region south of Puerto Penasco, Sonora, Mexico, remains insufficiently monitored to further increase the accuracy of population estimates and to establish the southern limit of the geographic range of the species (Ramirez 1993).
The range of the vaquita overlaps that of the endangered totoaba, to which it may be linked ecologically (Ramirez 1993).
A number of factors make the vaquita an extremely difficult species to survey; habitat characteristics such as turbid water, fraction of the time spent at the surface, elusive behavior, and its erratic surfacing mode (Ramirez 1993). Despite these difficulties, and biases in collection of survey data, it is clear that the species is rare (between 224 to 855 individuals) (Barlow et al. in press). Barlow et al. (in press) expect that with current levels of mortality, a low reproductive potential, and a low population estimate in 1993 of 224, the species will continue a decreasing trend in abundance into the future.
Any effect analysis of present-day river operations on the vaquita is severely hampered by the lack of data on the biology of the species, ecological interactions and effects of pre-dam freshwater flows into a marine environment, and the impacts the subsequent reduction in flows and sediment had on the flora and fauna of the Gulf.
Ramirez (1993) identified three actual and potential impacts to the vaquita: incidental mortality caused by fishery activities, reduced Colorado River flows into the gulf, and pollution from various sources associated with Colorado River flows into the gulf.
Vaquita have been killed in gillnets set for totoaba which has been a commercially important fishery in the gulf. Although the totoaba fishery was banned in 1975, it has continued illegally, further endangering both the totoaba and the vaquita. Vidal et al. (1991) estimated that a minimum of 95 vaquitas died in gillnets between 1985 and 1990, for an average mortality of 15.3 animals per year. This incidental loss can not be sustained by the population (Ramirez 1993). Shrimp trawling may also impact the vaquita through the direct depletion of an existing food source (shrimp) and by disrupting the benthos and associated foodweb.
Reduced flow into the upper gulf may have contributed to an alteration of the vaquitas habitat (Brownell 1982, Ramirez 1993). This reduction in freshwater flow and sediments caused by construction of Hoover Dam and other facilities may have caused alterations in food webs and biological diversity. This is, however, a hypothesis with little supporting data. In fact, some evidence suggests that the Colorado River delta behaves as a very fertile coastal lagoon, supporting abundant populations of crustaceans and mollusks (Alvarez-Borrego 1992), and substantial numbers of bottlenose dolphins utilize the delta (Silber 1990, Ramirez 1993).
Concern has been raised about the concentration of organochlorine pollutants and fertilizers in the agricultural return flows that make their way into the Colorado River and eventually into the gulf. Some of these pollutants have made it into the Gulf, but samples taken from vaquita suggest that organochlorine and heavy metal concentrations are lower than in marine mammals elsewhere (Ramirez 1993).
According to Rojas-Bracho and Urban-Ramirez (n.d.) the data suggest that pollution and reduced or null freshwater flow from the Colorado River are not significant factors in threatening the immediate survival of the vaquita, whereas commercial fishing might be the most critical factor affecting continued survival.
Until further studies and data prove otherwise, Reclamations routine operation and maintenance activities along the lower Colorado River will not affect the vaquita.
The totoaba is a fish endemic to the Gulf, Mexico. On May 21, 1979, the totoaba was listed as endangered pursuant to the Endangered Species Act (44 FR 99). This international species was included in this assessment at the suggestion of the FWS and a number of public stakeholders.
Description and Life Requisites
Totoaba are large schooling fish that undertake a seasonal migration within the Gulf and may live to 25 years of age (Cisneros-Mata et al. 1995). Totoaba are the largest of the sciaenid fish, with a maximum reported weight of over 100 kg and a length of over 2 meters (Flanagan and Hendrickson 1976). Adults spawn in the shallow waters of the Colorado River delta in the upper Gulf where they remain for several weeks before migrating south. Juveniles are thought to emigrate south after spending 2 years in the upper Gulf, which is considered their nursery ground (Flanagan and Hendrickson 1976).
Juvenile fish eat small benthic organisms, mainly crabs and fish, amphipods, and shrimp; adults eat larger more pelagic items, such as sardines and adult crabs (Flanagan and Hendrickson 1976, Cisneros-Mata et al. 1995). Many aspects of the biology and ecology of this species are unknown.
Distribution and Abundance
The totoaba is thought to have ranged from the mouth of the Colorado River to Bahia Concepcion on the west coast of the Gulf and to the mouth of the El Fuerte River in the east (Jordan and Everman 1896 cited in Berdegue 1955). Historically, millions of totoaba migrated north in the spring to spawn at the mouth of the Colorado River (Gause 1969).
The first commercial harvesting of totoaba began in the early 1890s and by 1942, annual catches peaked at 2.3 million kg. In 1975, the catch had declined to 59,142 kg (Lagomarsino 1991). Beginning as early as 1940, the Mexican government imposed restrictions on the commercial fishery for totoaba, and in 1975, the government designated totoaba as endangered and declared an indefinite prohibition on all types of commercial and recreational fishing (Flanagan and Hendrickson 1976).
Despite conservation efforts the totoaba population has continued to decline. Cisneros-Mata et al. (1995) review a variety of human activities that may have affected the totoaba population: prerecruits (egg to 1 year) may have been affected by decreased fresh-water input from the Colorado River, juveniles (1 to 2 years of age) by shrimp harvesting, pre-adults (3 to 5 years) by sport fisherman, and adults (6 years of age and older) by commercial fishing and poaching.
Despite the closure of the fishery, illegal exploitation continued. It is believed that the incidental catch of juvenile totoaba in the shrimp trawling fishery is the principal factor effecting the recovery of the species (Barrera 1990). Much of the illegal gillnetting for totoaba occurs during the spawning migration. As a result, gravid fish are being fished out of the population.
Modification of the flows and water quality of the Colorado River are commonly identified as primary factors contributing to the decline of the totoaba population. Fifty percent of the freshwater flow into the Gulf was from the Colorado River (Silber 1990). Since the delta is no longer subject to annual flooding, totoaba spawning and nursery grounds are considered to have been reduced (Lagomarsino 1991). It is speculated that the salinity gradient formed by spring-flood waters mixing with the saline water of the upper Gulf may have provided an environmental cue for migrating adults to locate their spawning grounds. Loss of the gradient due to the hyper salinity of irrigation return flows into the Gulf may adversely influence existing spawning migrations (Lagomarsino 1991). Cisneros-Mata et al. (1995) also believe that historical Colorado River flows probably had a two-fold effect in the upper Gulf by enhancing habitat for prerecruits and juvenile totoaba by increasing the carrying capacity (addition of nutrients and volume) and regulating water temperatures and salinity.
Cisneros-Mata et al. (1995) indicate that the negative impact on totoaba "due to decreased flow from the Colorado River may be questionable because the claimed effects would have caused extinction of totoaba over 40 years time." Lagomarsino (1991) believes that the loss of adequate spawning and nursery ground areas due to decreased Colorado River flows has probably led to the decline in the growth rate of the population. She also acknowledges that the unregulated taking of juvenile and adult totoaba may seriously influence the recovery of this species. Flanagan and Hendrickson (1976) concluded that over fishing explained the decline of the totoaba population better than habitat alteration.
It is clear that protection of the adults is necessary for recovery of the stock. However, because of a potentially reduced carrying capacity and growth rate, the population of totoaba may never reach historical proportions (Cisneros-Mata et al. 1995).
The regulation of the Colorado River through construction and operation of river facilities and an international treaty probably have had an impact on the spawning habitat of totoaba. The current status of the totoaba population is nonexistent and general biological and ecological data is very sparse, especially on the salinity and temperature tolerance of early life stages. However, we believe that until this information becomes available, it is prudent to conclude that the non-discretionary water management on the river may affect the totoaba through possible degradation of spawning grounds. Reversal of this trend (if so documented) will be critical to the survival of the species, but unless there is containment and/or elimination of illegal and incidental harvesting, the species will continue to be listed as endangered despite any efforts to re-create past flows.
In its letter of June 28, 1996, the NMFS concluded that Reclamation may have limited discretion in taking actions necessary to remedy potential habitat problems; and if that were true, it is possible that a section 7 consultation may not be needed on the totoaba. However, before it could render a determination, NMFS required additional information on four issues. This information is provided in the following paragraphs.
The United States ability to reverse conditions in the Colorado River delta is virtually nonexistent. The reasons for this involve an international treaty and U.S. restrictions. The waters of the Colorado, once delivered to Mexico, as agreed upon in the Mexican Water Treaty of 1944, are the exclusive property of the sovereign nation of Mexico. Further, this treaty contains no provisions requiring Mexico to provide water for environmental protection nor any requirements relating to Mexicos use of that water. Finally, a Supreme Court decree in 1964 enjoined Reclamation from releasing water to Mexico in excess of the quantity identified in the 1944 treaty except for flood control purposes.
Acting through IBWC, Reclamation and its counterpart in Mexico have developed a forum for the exchange of technical information. Any efforts to discuss releasing flows into the upper Gulf with the Mexican government would be subject to the protocol set forth by IBWC and the Mexican Water Treaty. A copy of this biological assessment will be provided to the U.S. Section of the IBWC, who in turn will provide it to the Mexican Section of the IBWC (IBWC letter dated May 21, 1996).
It is Reclamations conclusion that since the United States has no authority (or discretion) regarding the flow of water to the Colorado River delta, a section 7 consultation on the potential effects of its lower Colorado River operations and maintenance on the endangered totoaba is not required.