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.

El charalito sonorense, Gila ditaenia, fue incluido como especie amenazada en la lista de especies en peligro de extinción en 1986 por el United States Fish and Wildlife Service. Esta especie, endémica de la cuenca del Río de la Concepción cuya mayor parte se encuentra en Sonora, se distibuye en E. U. sólo en Sycamore Creek cerca de Nogales, Arizona. Uno de los motivos para considerar a la especie dentro de la lista fue la incertidumbre que existía en cuanto a su estatus, distribución y abundancia en México. El uso de pesca eléctrica cronometrada en 17 localidades y el muestreo con redes en ocho ambientes lénticos en Sonora, revelaron que el charalito se encuentra empliamente distribuido (16 de las 17 localidades con agua corriente) y es la especie más abundante en biomasa, y con mayor frecuencia numérica. A pesar de haber encontrado siete especies exóticas, los peces nativos dominaron en las comunidades de arroyo a lo largo de la cuenca (total en número = 99.7%, y biomasa = 96.9%), mientras que en los represos se encontraron peces exóticos en su totalidad. El estatus de especie amenazada de extinción es apropiado si se considera sólo a la población periférica y aislada geográficamente que existe en Arizona, pero es evidente que hasta la fecha, la especie en general está relativamente segura. Las actividades de manejo recomendadas en un futuro próximo son: monitoreo periódico y análisis taxonómico dirigido a las relaciones de la población de Arizona hacia otros demos, y el grado de introgresión genética con el charalito Yaqui G. purpurea, considerada por el United States Fish and Wildlife Service como especie en peligro de extinctión (1984). /// The Sonora chub, Gila ditaenia, was listed as threatened by the United States Fish and Wildlife Service in 1986. This species, endemic to the Río de la Concepción drainage, the major part of which is in Sonora, occurs in the United States only in Sycamore Creek near Nogales, Arizona. One of the motives for listing of the species as threatened was uncertainty regarding its status, distribution and abundance in México. Use of timed electrofishing in 17 lotic sites and seining in eight lentic habitats in Sonora revealed that the chub is widely distributed (16 of 17 lotic sites) and is the most abundant species in biomass and, frequently, in terms of numbers as well. Despite finding seven exotic fish species, native fishes dominated stream collections throughout the basin (99.7% of total numbers; 96.9% of total biomass), while impoundments harbored totally exotic ichthyofaunas. Threatened status is appropriate for Sonora chub if only the peripheral and geographically isolated population in Arizona is considered; however, it is evident that the species in general is presently relatively secure. Recommended future management activities are periodic monitoring and taxonomic analysis directed at determination of relationship of the Arizona population to that of others and the extent of genetic introgression by the endangered Yaqui chub, Gila purpurea (United States Fish and Wildlife Service, 1984).

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

Morphometric analyses of Agosia chrysogaster (Girard) indicated a northern morph native to Bill Williams, Gila, Sonoyta and de la Concepcion basins of Arizona, New Mexico and Sonora, and a southern form from Willcox Playa of Arizona and Rios Sonora, Yaqui, Mayo, Fuerte and Sinaloa of Sonora and Sinaloa, Mexico. The latter is smaller, and less sexually dimorphic, but has longer pre and postdorsal body lengths. Populations in the geographically intermediate Rios Sonoyta and Sonora are morphologically intermediate. Males differ more between morphs than do females. Meristic characters show considerable overlap between morphs, but the northern form has higher mean lateral line scale counts. Highly tuberculate nuptial males, characteristic of the northern morph, were not found in the south, nor were "spawning" pits characteristic of breeding activities of the former. Morphs differ on a multivariate axis on which temporal variation at single localities is also reflected. Distances among some intra locality samples on this axis were greater than least inter morph distances. Measures of morphological dissimilarity were weakly correlated with inter sample differences in elevation, latitude, and longitude, but more highly correlated with an index of hydrologic isolation among localities. Differentiation among basins thus appears to reflect hydrographic isolation, rather than ecological conditions. Electrophoretic data on A. chrysogaster produced relationships patterns largely incongruent with results of the morphological analyses, and with unexpected geographic area relationships.

Subadult and adult fishes from the Gila River drainage in New Mexico and Arizona were tagged, released, and recaptured from April 1983 through May 1985. Numbers of tagged and recaptured fish were dominated by desert mountain sucker, Pantosteus clarki, and Sonora sucker, Catostomus insignis. Fishes were presumed to be sedentary as only two of 53 recaptures were made outside of original release sites. The relatively large habitats and comparatively cool thermal regime of the study area are believed to be the primary reasons for the apparent lack of movement. Growth rates of recaptured fishes were low and indicated that desert mountain and Sonora suckers grow slowly after reaching adult size.

A vicariance hypothesis of New World biogeography involving transport of living biota on fragments of an ancestral landmass to present positions ranging from southern Alaska to northern South America is developed. Geological, as well as biogeographical, ecological, and systematic data from plethodontid salamanders provide correlative support for the model. Other groups appear to have similar biogeographic histories and, along with further geological data, could provide means of corroboration of this hypothesis. Active biotic dispersal between the American continents before Pliocene closure of the Panamanian isthmus may have been less prevalent than previously believed, and tectonic transport may have dispersed many organisms. If corroborated, geologists may be provided a new method of analyzing relationships among “suspect terranes” using phylogenetic analyses of living biota, and biologists may be required to reassess previous concepts of New World historical biogeography.

The term cienega is here applied to mid-elevation (1,000-2,000 m) wetlands characterized by permanently saturated, highly organic, reducing soils. A depauperate flora dominated by low sedges highly adapted to such soils characterizes these habitats. Progression to cienegais dependent on a complex association of factors most likely found in headwater areas. Once achieved, the community appears stable and persistent since paleoecological data indicate long periods of cienegaconditions, with infrequent cycles of incision. We hypothesize the cienega to be an aquatic climax community. Cienegas and other marshland habitats have decreased greatly in Arizona in the past century. Cultural impacts have been diverse and not well documented. While factors such as grazing and streambed modifications contributed to their destruction, the role of climate must also be considered. Cienega conditions could be restored at historic sites by provision of constant water supply and amelioration of catastrophic flooding events.

The endangered Sonoran topminnow P. occidentalis has steadily declined in distribution and abundance in the past several decades, and currently survives in the United States only in several isolated localities in southern Arizona. This reduction is correlated with, and primarily attributed to, habitat destruction, and introduction and establishment of mosquitofish Gambusia affinis and other exotic fishes. Topminnows have characteristically been reduced in number or replaced within a year or two of introduction of non-native fishes. Other native fishes have experienced similar declines after introduction of exotics, and much of the endemic western ichthyofauna may be vulnerable to extirpation in this manner. Predation by introduced fishes on natives appears to be a likely mechanism of replacement