Publications by Year

The authors sampled for fishes at 23 historic and potential Mexican habitats of the endangered desert pupfish, Cyprinodon macularius Baird and Girard. Though pupfish were found at 11 localities, ichthyofaunas of the region were typically dominated by exotics. Desert pupfish was found at two sites from which it had been reported extirpated. One site was found to function as an extensive pupfish refugium from which other species were apparently excluded by water quality. It is concluded that the range of species has been dramatically reduced over the last century by habitat modification and introductions of exotic fishes. Probable continued habitat alterations and limited distribution and population size in natural populations, as well as limited success of reintroduction attempts, require that the species remain considered to be very much endangered

Daily growth increments of otoliths of fishes have been useful in many fishery applications since they have been demonstrated to provide a precise method of ageing individuals and reconstructing individual growth and, possibly, movement or habitat histories. These techniques have not been previously applied to humpback chub, but are believed to have considerable potential for providing knowledge of this difficult to sample and little-understood species. Large temperature and water quality gradients apparently traversed by individuals of this species in the Grand Canyon are of a magnitude likely to produce structural and/or chemical signals in the crystalline calcareous otoliths. If so, since otoliths grow by accretion of daily increments (much like trees develop yearly growth rings), and are stable structures, which unlike scales, are not susceptible to reabsorption except in the most extreme conditions, they retain a structural and chemical chronology of habitats occupied. If the relationships of ambient physical and chemical conditions to otolith structure and composition can be described, a chronology of habitat occupancy and growth for individuals could theoretically be reconstructed with daily precision. Such reconstructions of growth rates, birth dates, movement histories, and possibly, birth place (based on chemistry at otolith formation or during early life), could provide extremely valuable life-history information regarding timing of spawning, cohort recruitment, mortality rates, and data on other population parameters critical for management of this endangered species. The feasibility of using otoliths and opercles of humpback chub for age estimation of individuals has been preliminarily investigated by examining otoliths and opercles from a total of 47 juvenile (ages 0 through 1 +)and 43 adult (estimated ages 2- 23) specimens collected in the Little Colorado River (71 specimens) and mainstream Colorado River (19 specimens) at various places in the Grand Canyon between 1988 and 1992. Studies are continuing, and at this point, due to both sample size and numerous other limitations, and ongoing refinements of techniques, conclusions made here are highly preliminary. Structures prepared and examined included opercles of 35 specimens, one asteriscus from each of 47 specimens and a lapillus from each of 56 specimens. Seventeen specimens were evaluated using all three calcareous structures (lapillus, asteriscus and opercle). The sagitta was also examined, but found to be unsuitable for ageing purposes due to its long, delicate form and irregular increments after the larval/juvenile stage. Additional lapilli have been removed from other available specimens, and a complete inventory of specimens available for further study of calcified structures is provided. Studies of micro-spatial variation in chemical composition of selected lapilli is in progress, using the highly accurate proton probe at the Institute of Geological and Nuclear Sciences in Lower Hutt, New Zealand. This method of analysis shows great promise of overcoming what has been indicated in recent literature to be significant inaccuracies of other techniques (Energy Dispersive X-ray diffraction and Wave Length dispersive X-ray diffraction) used in many of the published studies of microspatial elemental analysis of otoliths.

Between 1981 and 1990, more than 11 million hatchery-produced razorback suckers (Xyrauchen texanus) and 750,000 Colorado squawfish (Ptychocheilus lucius) were stocked to historic ranges in the Verde and Salt rivers in Arizona, where natural populations had been extirpated. Efforts to date have focused on broad-scale stockings and general fish surveys to evaluate success. Only 519 razorbacks and 444 squawfish were taken in several years of intensive electrofishing and netting surveys during all seasons throughout large segments of both rivers. Survival of razorbacks appears better in the upper Verde River than in the Salt River, while squawfish appear to fare better in the Salt River than do razorbacks. Most recaptures of either species were taken within weeks of stockings; relatively few individuals were verified to have lived more than a few months in the wild. Large populations of razor backs have not established in mainstreams, although groups have persisted in small, isolated, peripheral habitats where emigration is blocked or impeded. Despite growth to maturity of at least some razorbacks, no evidence of wild reproduction was found. The few squawfish known to have over-wintered in the wild were also taken from a habitat closed to downstream emigration. Proximate impediments to large-scale successful recruitment of stocked individuals to wild populations clearly include predation, principally by exotic flathead catfish and smallmouth bass, and coincident inability of hatcheries to produce large numbers of individuals for release at sizes large enough to escape predation. Despite limited success, it is recommended that stockings of both species continue for two reasons. Large-scale field experiments easily accomplished under the “experimental, non-essential” designation with readily available hatchery fish can elucidate mechanisms of recruitment failure for hatchery stock. These should emphasize experimental analyses of factors affecting mortality, movements and habitat use of stocked fish. Effects of fish condition, transport and stocking stress, size, stocking season, and parasites are other variables which need research. Along with experiments, continued stockings, especially in the case of razorbacks, even with low recruitment rates, appear very likely to contribute to establishment of long-lived populations, and are therefore recommended for both species. Stockings should be as extensive as possible, and focus on releases to closed, peripheral riverine and reservoir habitats (e .g. isolated backwaters), preferably with low or reduced predator populations. While direct stocking of larger individuals would likely increase survival rates in the wild, absolute numbers stocked would remain small given existing facilities . Stockings of far greater numbers of small individuals to such isolated, “wild” habitats and subsequent “wild” growth there prior to release, via either natural or artificial mechanisms, to larger, adjoining habitats, will likely prove to be the most economical and successful approach to establishing multiple, new populations oflong-lived individuals. Recommendations for immediate habitat management actions for both species include manipulations of predator populations and maximization of availability of backwater habitats. A broad-scale, annual field monitoring effort should continue, but most importantly the program should shift to emphasize experimental research. Effectiveness of the reintroduction program could be greatly improved by high-level administrative adjustments with particular attention to development of program objectives, coordination among production, research and monitoring components and frequent evaluation of progress toward objectives.

Meda fulgida (Pisces: Cyprinidae) is a species endemic to the Gila River basin of Arizona, Mexico, and New Mexico. The extent of geographic variation in morphology within this species has not been explored although evidence indicates that subpopulations have long been isolated. We examined samples from the four restricted areas within the Gila River basin where subpopulations persist, and used principal components analysis, regression against PC1 (to eliminate variation due to size), and ANOVA to demonstrate that individuals from the Verde River (Arizona) have smaller mouths in proportion to body length as compared to individuals from Aravaipa Creek (Arizona). Subpopulations from New Mexico and Eagle Creek in Arizona have intermediate measurements. Additional analyses confirm that females have shorter pre-pectoral measurements, greater mid-body size, and shorter pectoral fins than do males. /// Meda fulgida (Pisces: Cyprinidae) es una especie endémica del Rio Gila en Arizona, México, y Nuevo México. Lo amplio de la variación geográphica de la morfología de esta especie no ha sido explorada, aunque pruebas indican que subpoblaciones han sido largamente aisladas. Nosotros examinamos muestras provenientes de las cuatro áreas restringidas dentro del Rio Gila donde persisten subpoblaciones, y usamos análisis de componentes principales, regresión encontra del PC1 (para eliminar la variación debida al tamaño), y ANOVA para demonstrar que individuos provenientes Rio Verde (Arizona) tienen la boca más pequeña en proporción a la longitud del cuerpo en comparación con individuos provenientes del Arroyo Aravaipa (Arizona). Subpoblaciones de Nuevo México y Arroyo Eagle (Arizona) tienen una medida intermedia. Análisis adicionales confirman que las hembras tienen medidas prepectorales más cortas, mayor tamaño en la mitad del cuerpo, y aletas pectorales más cortas que los machos.

The mission of the Desert Fishes Council is to preserve the biological integrity of North America’s desert aquatic ecosystems and their associated life forms, to hold symposia to report related research and management endeavors, and to effect rapid dissemination of information concerning activities of the Council and its members.

From caves and springs in northern Mexico (Tamaulipas and Coahuila), mostly explored by diving, seven species of stigobitic and troglomorphic cirolanids were sampled: four species of Speocirolana Bolivar (one of them, interesting in several respects, described s new), the two known species of Sphaerolana Cole & Minckley, and Cirolanides texensis Benedict. For all six already known species, the localities are new, and aditional information is provided on their morphology, variability, and relationships. With 15 described species, Mexico has a quite remarkable and varied assemblage of subterranean Cirolanidae, pointing to quite diverse marine ancestors.

The mission of the Desert Fishes Council is to preserve the biological integrity of North America’s desert aquatic ecosystems and their associated life forms, to hold symposia to report related research and management endeavors, and to effect rapid dissemination of information concerning activities of the Council and its members.

The Cuatro Ciénegas Basin has been surveyed for fish, snails, plants and terrestrial invertebrates, but there has been no published survey of other aquatic invertebrates. We conducted regional surveys of aquatic macroinvertebrates in June and July of 1999 to determine which abiotic and biotic factors influence their distribution and to understand in which habitats they are potentially important components of the food web. Habitats sampled include lagunas, pozas, rios, canals, and springs. Possible endemic species will be presented. Predatory taxa were Odonata and Megaloptera. Herbivorous taxa were primarily Chironomidae, Ephemeroptera, and Amphipoda. Biotic and abiotic factors influencing abundance and distribution will be discussed. The hypothesis that Cuatro Ciénegas Basin has lower diversity and abundances of aquatic macroinvertebrates than similar aquatic habitats will be considered.

Cichlasoma minckleyi, an endemic cichlid in Cuatro Cienegas, has a trophic polymorphisim. The two common morphs, (detritivore and molluscivore), differ in pharyngeal tooth morphology. Diet studies suggest strong overlap between the morphs. We used stable isotopes to test whether the morphs have different diets. Stable isotopes offer two advantages over diet studies by allowing for large non-destructive samples and providing a temporally integrated assessment of diet. We collected fish from eight habitats and determined their morphology using an otoscope and took a small fin clipping for isotope analysis. Morphs differed in d13C, indicating that they have different food sources, but did not differ in d15N, suggesting that they occupy similar trophic positions. Differences in isotope values among sites did not correlate with the Hemichromis invasion.

The highly endemic aquatic biota of Cuatro Ciénegas was thoroughly surveyed 20-30 years ago, but more recent inventories are lacking. Human-induced habitat alterations have continued since these early surveys, but the area was recently protected by federal decree. Hydrologic alterations (primarily water diversions) and recent introductions of exotic fishes and snails will likely impact the aquatic ecosystems. Knowledge of inter-specific and habitatorganism interactions will be needed to formulate management plans. In summer of 1999 we began a re-survey of the aquatic biota and water chemistry and will compare our preliminary results to historic data from museum collections. Stable isotope studies will help us describe foodweb interactions, and in situ experiments will help us understand interactions between exotic and native organisms.

Cichlasoma minckleyi is a polymorphic cichlid endemic to the Cuatro Cienegas basin in Coahuila Mexico. The two most common morphs (papilliform and molariform) differ in pharyngeal dentition. Understanding how and if morphs segregate among habitat types might prove useful in understanding cichlid diversification, and such information will be necessary for long term management of this species. Fish were captured in Mojarral Oeste (now also called Poza Azul), a clear spring fed pool with at least 5 discrete habitat types, identified by morph, tagged, released, and observed in situ one to two days later. Data were taken on habitat preference and feeding behaviors for each individual. Initial results indicate differences in habitat preferences between morphs. Future observations will encompass other seasons.