Glenn F. Black
Salton Sea Populations
Although quantitative data are lacking, the desert pupfish was regarded by various observers as "abundant" at the Salton Sea, especially in shallow shoreline pools in 1961. However, this survey of the shoreline pools has shown that the abundance of desert pupfish was low and that the sailf in molly has apparently displaced the pupfish and become the dominant littoral inhabitant. Harrington and Harrington (1961) indicated that food items of the sailfin molly and C. variegatus, a close relative of the pupfish, were similar in a subtropical salt marsh. It is probable that the food habits of the sailf in molly and desert pupfish are also similar, but further work needs to be done to establish that competition exists.
The ability of sailfin mollies to withstand high salinities such as occur in the shoreline pools has also been documented (Barlow 1958b). Schoenherr (1979) speculates that dramatic rises in the level of the Salton Sea since 1975 may have interfered with nesting of desert pupfish and favored reDroduction of sailf in mollies, but I believe the principal factor causing a significant decline in pupfish numbers and distribution within the shoreline poo1s is more likely to have been direct competition with the sailfin molly for food and living space.
My curve's show that the longjaw mudsucker is more abundant than the desert pupfish within shoreline poo1s. Walker (1961) reported that mudsuckers occasidnally eat pupfish, however, he found no evidence that pupfish numbers were affected by their presence.
Surveys of the irrigation drains show that desert pupfish numbers also were low in this habitat and that the sailf in molly was again the most abundant species sampled. African cichlids and crayfish were also more abundant than desert pupfish in the irrigation drains.
Nichols (Cal Poly, Pomona, pers. commun.) and Cox (1972) showed that juvenile Zill's cichlid and desert pupfish have similar food preferences. Nichols also found as much as 24.6% of the diet of adult Zill's cichlids consisted of unidentified fish and their eggs in one of the irrigation drains at the Salton Sea. Thus, this species may also prey on desert pupfish as well as compete with it for food. Laboratory and field studies of interactions between desert pupfish and Zill's cichlids during the spawning season of the former, indicate that the male pupfish expends significantly more time defending a nest when Zill's cichlids are present than when they are not (M. Matsui, Occidental College, pers. commun.). This behavioral interference resulted in the eggs being unguarded for short periods of time, thus being more susceptible to predation. Similar effects were demonstrated for molly-pupfish interactions.
Schoenherr (1979) states that in an area of one irrigation drain where pupfish formerly abounded,.Zill's cichlids are now co~on. Though this species was not introduced into the irrigation drains until 1971 (Moyle 1976) and thus may not have been directly responsible for the decline of the desert pupfish, evidence from the quarterly surveys and the previously mentioned sources indicates that the cichlid may be helping to keep desert pupfish populations depressed.
Since crayfish also were more abundant in the irrigation drains than pupfish and have been identified as predators of demersal fish eggs (G. Capelli, College of William and Mary, pers. commun.), they also may be limiting pupfish numbers and distribution. Pister (Calif. Dep. Fish and Game, Bishop, pers. commun.) believes crayfish and mosquitofish are responsible for the recent elimination of the Owens pupfish, C. radiosus, from a refugium in Warm Springs near Big Pine, California.
Despite the fact that mosquitofish were sampled in very small numbers from the irrigation drains and tributaries to the Salton Sea, they were more numerous than the traps indicated. Their diet has been described by several authors (Harrington and Harrington 1961, Walters 1976) and is much like that of the desert pupfish (Walters 1976,. Moyle 1976). Minckley and Deacon (1968) and Deacon and Bunnel (1970) stated that the introduced mosquitofish has been responsible for eliminating many cyprinodonts in the southwest. It is doubtful whether mosquitofish alone have had much of an impact on resident desert pupfish populations at the Salton Sea. Both species were reported as "quite abundant" from the shoreline pools along the shore and in one nearby spring by Coleman in 1929, long before pupfish numbers were on the decline. Also, there are several populations of C. n. armogosa and C. n. nevadensis that coexist with mosquitofish (E. P. Pister, pers. commun.). However, together with the sailfin molly, Zills cichlid, and the crayfish all four species probably compete for food, space, aria possibly even prey upon the desert pupfish or their eggs to the extent that pupfish abundance and distribution have declined to a precariously low level. Without comparable survey data. before 1978, it is impossible to say whether desert pupfish populations will remain at present levels or decline further.
San Felipe Creek Population
The only viable population of desert pupfish remaining in California is within the 7.2 km to 9.7 km of permanent water along San Felipe Creek fed by several desert springs. This is the only natural habitat within the historical range of this species which currently supports a pupfish population. There are some exotic species (sailf in molly, shortfin molly, and the mosquitofish) present in the Creek, but presently they are not abundant. These exotics probably gained access to the permanent water during periods of heavy rainfall when flooding occurs that connects this portion of San Felipe Creek to the Salton Sea. These exotics also successfully reproduce in the Creek, but presently makeup only a minor percentage of the fishery. At present it appears this natural desert creek is marginal habitat for the exotic species. Installation of a low spillway or drop 15 to 30 cm high would prevent further upstream movement of unwanted exotic fish species. Maintenance of the barrier to remove siltation would be necessary every spring.
The National Park Service designated the marsh areas within the San Felipe Creek as a National Natural Landmark in 1971, and in 1974 the Heritage Conservation and Recreation Service identified lower San Felipe Creek as one of the last natural streams in the Colorado Desert. The U. S. Bureau of Land Management (BLM) has designated this land as the San Sebastian Marsh Outstanding Natural Area (Figure 8), and recommended in its Yuha Desert Management Framework Plan (1975) that 12 sections of private land within the natural area be acquired "in order to maintain the integrity and long-term stability of these environmentally sensitive areas". Currently BLM manages public lands in the natural area under a 1920 agreement with the Water and Power Resource Service (Bureau of Reclamation), which owns approximately five sections within the natural area.
The historical range of the desert pupfish extended over a broader area than at present. Except for San Felipe Creek, all original spring habitats have been lost. The population in the Salton Sea possibly originated from inundation of springs in the Salton Sink by the rising of the Salton Sea, or from populations present in the Colorado River at the time the Sea was formed. The Salton Sea and its agricultural drains, however, supply only marginal conditions for continued survival of the pupfish. The Sea itself has changed dramatically over the past 20 years, not only in salinity, but also in depth and species comvosition. The agricultural drains are poor pupfish habitat. The Imperial Irrigation District has plans for either filling, scraping, or concrete-lining these drains. During the quarterly surveys one complete drain (McKinley Street) was completely filled in oetween the su~er survey and fall surveys. Obviously, the drains cannot be regarded as secure pupfish habitat.
The present work as well as several references describe various aspects or the physical habitat characteristics necessary for the desert pupfish (Moyle 1976, Soltz and Naiman 1978). The habitat characteristics generally favorable to desert pupfish include: (1) a sand-silt substrate; (2) an abundance of rooted aquatic plants and filamentous algae; (3) relatively shallow water (30 cm or less in depth); (4) a minimal surface flow (< 1.0 cfs); and (5) water temperatures above freezing during the winter.
FIGURE 8. San Felipe Creek and San Sebastian Outstanding Natural Area, Imperial County, California.
An additional threat to the pupfish residing within the drains, sea proper, and permanent tributaries, is exposure to agricultural pesticides. There are sufficient examples of fish kills resulting from agricultural pesticide exposure in the Imperial Valley (Calif. Dep. Fish and Game, unpubl. records). Certainly any area providing refuge for the desert pupfish should have minimal pesticide use. One area which meets all of the above criteria and has an abundant pupfish population is San Felipe Creek, however, there are threats to this habitat also.
Lower San Felipe Creek and the lands bordering it have been zoned as open space in the Imperial County General Plan of 1973. This designation allows land to be developed for agriculture, which includes crop and tree farming and livestock, without any permit. In another part of the plan a stated goal and objective is "to preserve unique plant and wildlife by identification and preservation of natural habitats." Under a section called selected critical habitats, the plan says, "the following list of rare and endangered wildlife includes species not designated as rare or endangered according to the U. S. Department of the Interior, but whose habitats are threatened. It is planned that by timely and effective preservation measures these species will not become so classified: Fish - Desert Pupfish - San Felipe Creek Area." Another portion of the plan says, "Recommendation: Notify any agency responsible for protecting plant and wildlife before approving a project which would impact on rare or unique plant or wildlife habitat."
Recently two actions have been taken which could threaten the continued integrity of this area: First, the approval by the Imperial County Board of Supervisors of a proposal to subdivide a section of land adjacent to San Felipe Creek (Sec. 21, T. 12 5., R. 11 E.) for housing. The second action is agricultural development with associated ground water pumping of 17 sections (Sec. 13, 15, 19, 23, 25, 27, 29, 36, and east 1/2 section of 21 - T. 12 5., R. 10 E.; Sec. 19, 21, 27, 29, 31, 33, 35 - T. 12 5., R. 11 E.; and Sec. 1 - T. 13 5., R. 11 E.) of land immediately adjacent to San Felipe Creek. This second action is in compliance with the Imperial County General Plan, but both of these actions are incompatible with the previously stated concerns of the County for the preservation of San Felipe Creek and the desert pupfish. Currently there is little hydro-logical background data to predict. the potential impact of irrigating these sections of land from ground water sources adjacent to the Creek. However, it is known from similar experiences elsewhere that ground water pumping could have a detrimental effect on surface water levels within San Felipe Creek and ultimately impact the desert pupfish.
Desert pupfish no longer occur within their known historic range along the Colorado River and within numerous springs in the Salton Sink area. Pupfish presently occur, however, in three habitat types: (1) artificial refugia; (2) marginal habitats in and around the Salton Sea; and (3) a natural desert spring habitat in the San Felipe Creek drainage.
Desert pupfish have become established in all five temporary refugia into which they have been introduced. It is estimated that pupfish number approximately 1,000 individuals at Palm Canyon refugium. 100 fish at Living Desert Reserve, 30 individuals at Arrowweed Sorin~. 200 fish at Palm Spring refugium. and 200 individuals at the Visitor Center refugium. These refugium populations will help insure the continued existence of the desert pupfish, but like populations of other endangered species in zoos and similar artificial environments, they contribute nothing to the wild gene pool which must continue to respond to natural selective forces if the species is to persist as a viable component of a natural ecosystem.
As this report shows, the abundance of desert pupfish at various locations in and around the Salton Sea is relatively low and probably greatly reduced from historical times. The introduced exotic fish species probably have adversely affected once abundant pupfish through competition, predation, and behavioral interference. The limited populations around the Salton Sea appear to be occupying habitat marginally suited for pupfish. The agricultural drains support the largest number of pupfish within the Salton Sea system, however, current maintenance operations by the irrigation districts could further reduce or eliminate pupfish from these drains.
The historic distribution of the dese~ pupfish in their native habitat has been reduced to only San Felipe Creek. However, this habitat is presently threatened by residential anAi agricultural development on contiguous land. There is also a limited number of exotic fish species occurring in this same area of San Felipe Creek. This one prime pupfish area should be protected from further habitat loss or damage as well as further invasion by exotic fish species.
The available information strongly supports that the desert pupfish qualifies as an endangered species. The survival of the desert pupfish in California is in immediate jeopardy due to loss of a significant portion of its original habitat; the present or threatened destruction or modification of its existing habitat; and predation, competition, ahd behavioral interference by introduced exotic species.
The following actions should be taken to prevent extirpation of the desert pupfish from its limited natural range:
1. List the desert pupfish as an endangered species by both the State and Federal government.
2. Conduct hydrologic studies to determine the location of the ground water source/sources supplying permanent water portions of San Felipe Creek and determine the effects of ground water pumping on the surface flow in the Creek.
3. Request the Imperial County Board of Supervisors to zone land in and adjacent to San Felipe Creek in a category which excludes any type or development, which could be detrimental to the integrity of the habitat.
4. Request WPRS and/or BLN to acquire the remaining portions of private land in and adjacent to San Felipe Creek.
5. Investigate the feasibility of installing and maintaining a concrete spillway or drop east of State Highway 86, downstream from the permanent water, to prevent the upstream movement of exotic species during periods of flood.
6. Eradicate exotic fish species within the permanent water sections of San Felipe Creek.
7. Conduct biannual surveys of all known habitats to monitor any change in population abundance and distribution.
8. Obtain biological data necessary to effectively manage the species.
9. Establish a minimum of six refugia in areas far enough removed from one another geographically such that some catastrophic event would not exterminate all the refugia populations.