Exercise conditioning decreases downstream movement of pond-reared razorback suckers released into a stream environment

Despite augmentation stocking efforts, wild populations of razorback suckers ( Xyrauchen texanus ) continue to decline. Endangered razorback suckers are commonly raised in off-channel ponds until maturity (approximately 300 mm TL) and then stocked into the Colorado River or its tributaries. After fish are stocked, they commonly move large distances downstream. We conducted an experiment to determine if downstream dispersal could be reduced through exercise conditioning. Two groups of razorback suckers, exercised and nonexercised, were released into Fossil Creek, Arizona. Prior to release, a subsample from each treatment group was tested in a laboratory flow chamber. Razorback suckers that had been exercise conditioned were able to maintain a position in the flow chamber 2 times longer and at velocities 25 cm · s –1 higher than nonexercised fish. Although the intended method of field data collection via passive-integrated-transponder (PIT) antennas and a remote communication station failed because river otters ( Lontra canadensis ) preyed upon the released razorback suckers, implanted PIT tags were retained in otter scat. Recovered PIT tags enabled distributional analysis, which indicated that exercised razorback suckers did not move as far downstream from the point of release as nonexercised razorbacks. Exercise conditioning may increase overall fitness of pond-reared razorback suckers, and, consequently, increase the effectiveness of augmentation stocking. A pesar de los esfuerzos de repoblación, las poblaciones silvestres del matalote jorobado ( Xyrauchen texanus ) siguen en declive. Los matalotes jorobados, que están en peligro de extinción, se crían en estanques fuera del cauce hasta la etapa adulta (~300 mm) y después son liberados en el Río Colorado o uno de sus afluentes. Los peces suelen desplazarse largas distancias río abajo después de su introducción al río. Llevamos a cabo un experimento para determinar si la dispersión río abajo se podía reducir mediante el acondicionamiento por ejercicio. Dos grupos de matalotes fueron liberados en Fossil Creek, Arizona, uno que había sido acondicionado y otro que no. Antes de liberarlos, examinamos una submuestra de cada grupo en una cámara de flujo en el laboratorio. Los matalotes que habían sido acondicionados por ejercicio pudieron mantener sus posición en la cámara de flujo dos veces más tiempo y a velocidades de 25 cm · s –1 más altas que los peces no acondicionados. Aunque falló el método de colecta de datos mediante antenas de sistema PIT (passive integrated transponder) y una estación remota de comunicación, los matalotes liberados fueron depredados por nutrias de río ( Lontra canadensis ) y las marcas PIT implantadas se quedaron en las heces de las nutrias. La recuperación de estas etiquetas PIT permitió un análisis de distribución que indicó que los matalotes acondicionados no se desplazaron río abajo tan lejos del punto de liberación como los matalotes no acondicionados. El acondicionamiento por ejercicio podría mejorar la condición física de los matalotes jorobados criados en cautiverio y así aumentar la eficacia de la reintroducción.     

Population ecology and reproduction of the Mexican mud turtle ( Kinosternon integrum ) in Tonatico Estado De México

Ecological data directly from the field are important in understanding the life history strategies of kinosternid species in the tropics. Herein we summarize the basic population ecology and life history of Kinosternon integrum in the municipality of Tonatico (southeastern Estado de México, México). From October 2003 to November 2004, we marked a total of 204 turtles and recaptured 118 of them. Mean population size using the Jolly-Seber model was 197 (95% CI 128–416) individuals, with a sex ratio of 1:1.7, biased to females. Males were larger than females in carapace length and plastron length. The reproductive season starts in late June and finishes in late October. The smallest female with oviductal eggs was 122 mm in carapace length. Mean clutch size was 4 eggs ( s = 1.77, range 1–8) and was significantly and positively related to body size. Mean egg length was 30.43 mm ( s = 2.24, range 23.92–35.96), mean width was 16.35 mm ( s = 1.01, range 12.99–18.30), and mean weight was 5.14 g ( s = 0.60, range 3.41–6.57). Mean egg length was significantly and inversely related to clutch size. Relative clutch mass (reproductive effort) was 0.043 ( s = 0.017, range 0.017–0.071), which is the smallest value reported for the genus Kinosternon. Additionally, there was no evidence of a pelvic restriction on egg size in this population. This is the first study that documents basic population ecology and reproductive characteristics for a single population of the most widespread freshwater turtle in Mexico.     

Three new species of the genus Mononchus (Nematoda: Mononchida), and the “real” Mononchus truncatus Bastian, 1865

Mononchus altiplanicus sp. nov. from Chile is characterized by an average body length of 2.68 mm, dorsal tooth apex at about 30% of buccal capsule, transversal ribs anterior to tooth apex, tail on average eight anal body widths long. Mononchus oblongus sp. nov. from France is characterized by an average body length of 1.72 mm, shape and length of the buccal cavity (more elongate than in other congeners), relatively anterior position of the dorsal tooth apex, tail on average 8.2 anal body widths long, and seta-like subterminal caudal papillae. Mononchus medius sp. nov. from the USA is characterized by an average body length of 1.55 mm, posterior location of dorsal tooth apex, subventral ribs anterior to tooth apex, and tail on average 7.7 anal body widths long. Mononchus truncatus is rediagnosed on the basis of type/neotype specimens and those from Hungary. A key to species is provided.     

Aspects of the biology of the flathead chub ( Hybopsis gracilis ) in Montana

Mature flathead chubs ( Hybopsis gracilis ) were present in mid - July and mid - August collections from the Musselshell River, Montana. The estimated numbers of mature eggs present in eight females were 360–753 per female. The smallest mature female and male collected were 113 and 123 mm in total length, respectively. The male to female sex ratio in collections was about 1:1. Only small differences were detected among the length – weight relationships of males and females and samples taken from various seasons and localities in Montana. Observations on size groups, fish associates, and habitat characteristics of flathead chubs are presented.         

Pocket gophers ( Thomomys talpoides ) in successional stages of spruce-fir forest in Idaho

This study examined (1) the relative abundance of the pocket gopher ( Thomomys talpoides ) in four successive stages (1–10, 11–39, 40–79, and 80+ years following disturbance) of spruce-fir forest; (2) the relationship between number of gopher sign (mounds and earth plugs) with gopher density; and (3) a method of sampling pocket gopher populations using a 500 by 4 m strip transect. The number of gopher mounds was significantly correlated with the number of earth plugs. Data were pooled and a categorical log linear analysis used to test for significant differences in pocket gopher sign between the four successive stages. The 1–10 and the 80+ -year-old sites had significantly more gopher sign than the 11–39 and the 40–79 year-old sites. No significant differences were found between the 11–39 and the 40–79-year-old sites, or between the 1–10 and the 80+ -year-old sites. The difference in population densities may be due to understory vegetation differences between the successional stages. There was a significant correlation between amount of gopher sign and gophers caught in each of the study sites. This indicates that counts of pocket gopher sign may be used to estimate pocket gopher density. The strip transect is recommended as the most appropriate method when sampling heterogeneous habitats or when there is cause to suspect gopher populations may be aggregated within the area rather than spaced randomly or regularly.     

Contributions to the life history of Sacramento perch, Archoplites interruptus, in Pyramid Lake, Nevada

During a two-year period (1976&ndash;1977), 180 Sacramento perch ( Archoplites interruptus ) were sampled from Pyramid Lake, Nevada, on a monthly basis using several capture methods in all lake areas. Age and growth determinations of these fish were inconsistent with previous research on this species. Sacramento perch are entirely carnivorous, adults feeding primarily on tui chub ( Gila bicolor ). Fish accounted for 6 percent of the diet (by volume) of Sacramento perch less than 300 mm fork length, and 98 percent for those exceeding 300 mm. Amphipods, Odonata, and Chironomidae composed 6.3, 5.7, and 1.8 percent, respectively, of the stomach contents by volume for all sizes combined. Females spawned from June to August when water temperatures approached 20 C, and their gonad weight was about 6 percent of the total body weight. A sample of 20 female perch had a mean fecundity of 84,203 eggs. The mean diameter of mature eggs was 0.88 mm. Sacramento perch almost exclusively inhabit the littoral zone of Pyramid Lake. Activity, as indicated by net catches, was greatest during the warm months of May to October. Monthly catches were significantly correlated with temperature (r = 0.577, P < 0.01). No short-term changes in population abundances were observed during 1976&ndash;1977.     

Some spatial and behavioral features of the thirteen-lined ground squirrel

Some relationships between home range, agonistic behavior, and reproductive patterns in thirteen-lined ground squirrels were investigated in Laramie Plains, Wyoming (August 1966&ndash;April 1969). Population size and densities fluctuated seasonally and annually. Adult male (N = 7) home ranges averaged 0.24 ha and were smaller than those of the female (N = 9), which averaged 0.35 ha. Agonistic interactions were more frequent during the natal period (late May&ndash;June) than during the breeding-gestation period (mid April&ndash;May). Most squirrels (86 percent) shared capture sites and had overlapping home ranges. However, a certain degree of spacing existed because of agonistic behavior.     

Observations on woundfin spawning and growth in an outdoor experimental stream

The response of woundfin to different substrates and current speeds was investigated in an outdoor experimental stream. Fish spawned in groups of 15 &ndash; 20 over 5 &ndash; 10 cm rock substrate in a .06 to .09 m/sec current at a depth of 10 cm. Eggs were adhesive on the undersides of the rocks. Fish spawned under these conditions grew to approximately 55 &ndash; 60 mm TL in 5 months.     

Description of a Phyllorhynchus from Cerralvo Island, Gulf of California, Mexico

Phyllorhynchus decurtatus porelli ssp. nov. is described from a single specimen from Cerralvo Island, Gulf of California, Mexico, and is regarded as different from P. d. decuratus on the basis of an increased number of dorsal blotches (41 as compared to 18 &ndash; 33) and an increased number of supralabials (7 as compared to 6), combined with geographical isolation and the high degree of endemism found in other reptiles on Cerralvo Island. &nbsp;     

Daily and seasonal patterns of activity at pygmy rabbit burrows in Utah

The pygmy rabbit ( Brachylagus idahoensis ) is a secretive, obligate sagebrush-steppe resident of the Intermountain West and is one of two rabbits in North America that digs its own burrows. Although the pygmy rabbit has a recorded home range of 0.21&ndash;67.9 ha in relatively high sagebrush cover (21%&ndash;36%), they spend much of their time within 30&ndash;100 m of a burrow system. Due to big sagebrush cover in preferred habitat and the secretive behavior of pygmy rabbits, it is often difficult to study this leporid through direct observation. We used remote cameras to document pygmy rabbit activity at burrow systems in south central Utah from 2006 to 2008. We analyzed photographs from remote cameras for daily and seasonal patterns of activity. Our results suggested that time of day and season were important influences on activity level, while year and site were less so. Pygmy rabbits were active during all time periods of the day, but the greatest activity occurred in the morning, except during winter. Numerous other species were recorded by remote cameras, including other leporids, birds, rodents, reptiles, and terrestrial predators. Remote cameras are a valuable tool in understanding pygmy rabbit behavior, in addition to confirming rabbit presence in areas of interest.     

Life history of the cui-ui, Chasmistes cujus Cope, in Pyramid Lake, Nevada: a review

The cui - ui, Chasmistes cujus Cope, a member of the sucker family and endemic to Pyramid Lake, Nevada, is listed as endangered by the U.S. Fish and Wildlife Service. Cui - ui was once a major source of sustenance for native Americans, who have inhabited the Lahontan region for at least 11,000 years. The Northern Paiutes developed sophisticated fishing technology to harvest this resource. The original distribution of cui - ui was the ancient Lake Lahontan complex, but as a result of climatic changes it was restricted to the Pyramid &ndash; Winnemucca &ndash; Truckee system by the turn of the 20th century. Transbasin water diversions (1905 to present) have resulted in further restrictions of habitat. The species is now limited to Pyramid Lake and the lower Truckee River. Reproduction is from hatcheries as well as limited natural reproduction. Females produce more than 40,000 2 - mm eggs per year. The normal development is described from the unfertilized egg through 912 hours post - hatching, when the fry are actively feeding and approaching adult body form. The unusual feature of adult cui - ui morphology is the relatively large ventro - terminal mouth, with thin and obscurely papillose lips. Cui - ui grow slowly and may live 18 years or possibly much longer; females generally live longer and attain a greater size than males. The highest adult mortality probably occurs during spawning runs. At this time they are vulnerable to predation, stress, and sometimes environmental degradation. The highest larval mortality probably occurs from predation when they are planted or migrate into the lake. The trophic ecology of the species is poorly understood, but they are known to ingest algae and zooplankton. Spawning behavior is documented. At present, natural reproduction is probably still the limiting factor for the cui - ui population. Cui - ui composed less than one percent of the total fish in Pyramid Lake during 1975&ndash;1977. During 1982 the largest cui - ui spawning run (13,000) in recent years occurred. The activity of cui - ui in the lake closely resembles that of the Tahoe sucker being most active during the spawning season each spring. Cui - ui inhabit the inshore - benthic zone and the pelagic waters of Pyramid Lake ( &nbsp;&nbsp;&nbsp;     

Short-term effects of logging on red-backed voles and deer mice

Clearcutting and selective logging effects on red-backed voles ( Clethrionomys gapperi ) and deer mice ( Peromyscus maniculatus ) were studied (September&ndash;November, 1975; June&ndash;October, 1976) in Bridger-Teton National Forest, Wyoming. Five selective cuts (total 137 ha) removed 57 percent (range 34&ndash;74 percent) of the trees. One clearcut (9.6 ha) eliminate 84 percent of the trees. Soils remained mesic in selective cuts, but became xeric in the clearcut. Snap-trapping indicated that voles were most abundant on the unlogged and selectively cut mesic sites (76 percent of 408 captures), whereas deer mice were more common on the xeric clearcut (80 percent of 60 captures). Species composition remained unchanged on selective cuts following logging (77 percent voles of 256 captures), but changed from predominantly voles to mostly deer mice (80 percent of 60 captures) in the clearcut. Intraspecific age and sex ratios, litter sizes, and morphological measurements were compared between logged and unlogged areas.     

Growth and development of the western harvest mouse, Reithrodontomys megalotis megalotis

Growth rates, gestation period, litter size, reproductive age, sex ratios, and development were studied on 198 litters of Reithrodontomys megalotis megalotis (Baird). Growth was characterized by several standard skull and body measurements and was partitioned into four phases of 1 &ndash; 3, 4 &ndash; 12, 13 &ndash; 22, and 23 &ndash; 70 days. Growth was best described by measurements of tail length, ear length, and dried eye - lens weight. Reproductive activity began as early as 38 days for females and 59 days for males. The gestation period was 22 days, and the mean litter size was 3.83 (range 1 &ndash; 7). Sex ratio was 53.49 percent males to 46.51 percent females. Reproductive efficiency was 53.53 percent. The development of R. m. megalotis was very similar to that of R. m. dychei. Early breeding, postpartum estrous, year - round breeding, high reproductive efficiency, and a short gestation period contribute to a high reproductive potential in R. m. megalotis. &nbsp;     

Length of western tent caterpillar egg masses and diameter of their associated stems

Stems bearing egg masses of the western tent caterpillar ( Malacosoma californicum ), collected in Arizona and northern New Mexico during 1977&ndash;1980, had mean diameters between 2.9 and 4 mm. Mean lengths of the egg masses were consistently between 11 and 14 mm.     

Age, growth, and food habits of tui chub, Gila bicolor, in Walker Lake, Nevada

At Walker Lake, Nevada, tui chub were collected 1975&ndash;1977 for analysis of age, growth rate, and food habits. The fork length (FL) &ndash; scale radius (SR) relationship was linear and described by the equation FL = 4.44 + 3.17 (SR). Age I, II, III, and IV chub were 116, 176, 218, and 242 mm fork length, respectively. Maximum longevity was six years. The length weight relationship was defined by the log transformed linear equation log weight = - 4.65 + 2.93 (log FL). Chub collected from pelagic regions ate mostly zooplankton, whereas chub collected from littoral areas had a diet of zooplankton and benthic organisms. &nbsp;&nbsp;&nbsp;     

Emergence of adult pandora moths in Arizona

Adult pandora moths began emerging in late July, and peak daily emergence occurred during 10&ndash;15 August. The mean density of moths emerging per 929 cm 2 of ground surface ranged from 0.1 to 2.4. The ratio of emerging males to females varied from 3&ndash;4:1 during the initial days of emergence to 1:1.5 during the last 10 days of August. Postemergence behavior is described and discussed in relation to egg mass deposition and species survival. &nbsp;&nbsp;&nbsp;     

Deer mouse ( Peromyscus maniculatus ) home-range size and fidelity in sage-steppe habitat

Within a species, home-range size can vary due to factors such as sex, mass, age, and breeding condition of individuals as well as habitat type, food availability, population density, and season. The objectives of this study were to estimate home ranges of deer mice ( Peromyscus maniculatus ) in sage-steppe habitat and to test the hypothesis that several factors (sex, mass, reproductive status, and seasonality) affect home-range size. We also tested the hypothesis that deer mice exhibit home-range fidelity over time. Passive integrated transponder (PIT) technology was used to estimate home ranges in June and September 2006. Home-range estimates varied from 360 m 2 to 5868 m 2 (65 individuals, 753 observations). Home-range size increased by approximately 60% from June to September. Besides seasonality, none of the other predictors of home range were informative in explaining the variation in home range. Deer mice recaptured in September (3 months after initial capture) had high fidelity in home-range use (42.1% [SE = 8.4%] overlap with 74.1% [SE = 8.7%] area conserved; n = 9). All animals for which home range was estimated in both seasons retained some fraction of their June home range in September. Results support the use of combined location data collected over long periods, such as weeks or months, to estimate home range for deer mice. The results have implications for deer mouse&ndash;pathogen ecology, particularly with respect to modeling transmission of Sin Nombre virus&mdash;a pathogen that is directly transmitted by deer mice.     

Black-tailed prairie dog population dynamics at Scotts Bluff National Monument, Nebraska: a 28-year record

Black-tailed prairie dogs, Cynomys ludovicianus, now inhabit a small fraction of their original range in the Great Plains. We monitored a population of black-tailed prairie dogs at Scotts Bluff National Monument, Nebraska, from colonization in 1981 until 2009 (28 years). Colony boundaries were mapped by delineating clip lines and active burrows; population densities were estimated via visual counts. Estimates of total population size revealed 4 distinct periods of changing dynamics: (1) a linear increase, (2) a decline and prolonged depression, (3) an exponential increase, and (4) a period of high variability. Area occupied revealed similar, although less-defined trends, whereas densities fluctuated greatly (8&ndash;80 individuals &middot; ha &ndash;1 ). Even after almost 30 years, this population remains relatively small. Decreases in the population may have been due, in part, to predation by badgers, although sylvatic plague cannot be ruled out. Black-tailed prairie dogs are recognized as keystone grassland species, and attempts are underway to reintroduce them to parts of their historic range. Our data suggest that black-tailed prairie dogs possess high potential for rapid population growth and decline, regardless of colony size. Therefore, either human-assisted or natural dispersal events may be important in establishing colonies in suitable habitat. El perrito de pradera de cola negra, Cynomys ludovicianus, habita en una peque&ntilde;a fracci&oacute;n de su distribuci&oacute;n original en las Grandes Llanuras. Monitoreamos una poblaci&oacute;n de perritos de pradera de cola negra en Scotts Bluff National Monument, Nebraska, por 28 a&ntilde;os, desde la colonizaci&oacute;n en 1981 hasta 2009. Trazamos los l&iacute;mites de las colonias usando de referencia las l&iacute;neas de ramoneo y las madrigueras activas, y estimamos la densidad de las poblaciones mediante un recuento visual. Los estimados de poblaci&oacute;n total revelaron cuatro per&iacute;odos distintos de din&aacute;micas cambiantes: (1) un aumento lineal, (2) una disminuci&oacute;n y depresi&oacute;n prolongada, (3) un aumento exponencial y (4) un per&iacute;odo de alta variabilidad. El &aacute;rea ocupada revel&oacute; tendencias similares, aunque menos definidas, mientras que las densidades fluctuaron mucho (8&ndash;80 individuos &middot; ha &ndash;1 ). A&uacute;n despu&eacute;s de casi 30 a&ntilde;os, esta poblaci&oacute;n permanece relativamente peque&ntilde;a. Los decrementos en la poblaci&oacute;n pueden haber sido provocadas en parte por la depredaci&oacute;n por tejones, aunque no se puede descartar como causa la plaga silv&aacute;tica. El perrito de pradera de cola negra se considera una especie clave de la pradera, y est&aacute;n en proceso esfuerzos por reintroducirlos en partes de su distribuci&oacute;n hist&oacute;rica. Nuestros datos indican que los perritos de pradera de cola negra tienen alto potencial de crecimiento y disminuci&oacute;n de su poblaci&oacute;n, sin importar el tama&ntilde;o de la colonia. Por lo tanto, los eventos de dispersi&oacute;n, ya sean naturales o con asistencia humana, podr&iacute;an ser importantes para establecer colonias en h&aacute;bitats adecuados.     

Distribution and dynamics of waterbird habitat during spring in southern Oregon–northeastern California

The southern Oregon&ndash;northeastern California and extreme northwestern Nevada (hereafter &ldquo;SONEC&rdquo;) region provides critical spring migration habitat for waterfowl and other waterbirds in the Pacific Flyway. Information on the dynamics and distribution of waterbird habitats in SONEC during spring is needed to guide conservation efforts in the region. We grouped 1992 National Land Cover Data classes into 5 potential waterbird habitat types and used Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper Plus satellite imagery to map flooding of these habitat types in SONEC during February&ndash;May, 2002 and 2003. SONEC included 13,727 km 2 of potential waterbird habitat comprised of grasslands (37.1%), pasture/hay (24.6%), marsh (15.9%), open wetland (11.8%), and croplands (10.6%). On average, 11.9% of this potential habitat was flooded during spring; but the percentage, area, and composition varied within and among years and subregions. Total flooding increased from 693 km 2 in February to 2099 km 2 in April during 2002 and from 1630 km 2 in February to 2125 km 2 in May during 2003. Open wetland comprised 58%&ndash;74%, marsh 8%&ndash;18%, pasture/hay 4%&ndash;11%, grassland 4%&ndash;17%, and cropland 3%&ndash;8% of the flooded habitat in SONEC. Satellite imagery and land-use data provided useful estimates of waterbird habitat availability in SONEC during spring, but other methods should be tested to more accurately measure flooding of densely vegetated habitats such as marsh. With &#60;12% of the potential habitat flooded on average during spring, conservation programs have ample opportunity to improve the SONEC landscape for migrating waterbirds.     

Retrospective evaluation of the effects of human disturbance and goldfish introduction on endangered Pahrump poolfish

Life history data for Pahrump poolfish ( Empetrichthys latos latos ) collected from 1937 to 1975 were organized and analyzed to improve our understanding of changes caused by human habitat disruption and introduced goldfish ( Carassius auratus ) at Manse Spring, Nevada. Pahrump poolfish twice demonstrated their ability to recover numerically from a population crash. The first crash followed a November 1961 introduction of a few goldfish and subsequent removal of vegetation by local ranch children intent on turning Manse Spring into a swimming hole. The second crash followed another major habitat disturbance resulting from an unsuccessful attempt to eradicate goldfish in July 1967. Each crash (1962&ndash;1963 and 1967&ndash;1968) reduced the poolfish population to fewer than 50 adults and was followed by a population recovery to more than 1000. Following the first habitat disruption, changes in poolfish population structure and poolfish diet were observed. These changes caused an increased mortality rate, resulting in disappearance or decline in relative abundance of larger poolfish size classes with a commensurate reduction in production of mature eggs by the population. We detected no additional changes in life history characteristics that could be associated with the second population crash and recovery. We concluded that removal of vegetation in the summer of 1962 and the more extreme habitat disruption and fish handling in June&ndash;July 1967 were human-induced pulse disturbances resulting in poolfish population crashes. We also concluded that the changes in poolfish life history characteristics resulted principally from press disturbances attributable to goldfish. Los datos sobre la historia de vida del pez de poza Pahrump ( Empetrichthys latos latos ), recopilados entre 1937 y 1975, fueron organizados y analizados para ayudar a entender los cambios cusados por la perturbaci&oacute;n antropog&eacute;nica del h&aacute;bitat y por la introducci&oacute;n del carp&iacute;n dorado ( Carassius auratus ) a Manse Spring, Nevada. En dos ocasiones, los peces de poza Pahrump demostraron la habilidad de reponerse num&eacute;ricamente despu&eacute;s de descensos abruptos de la poblaci&oacute;n. El primero fue en noviembre de 1961, despu&eacute;s de la introducci&oacute;n de algunos carpines dorados y subsecuente remoci&oacute;n de vegetaci&oacute;n por ni&ntilde;os de ranchos locales con la intenci&oacute;n de convertir Manse Spring en una poza para nadar. El segundo descenso ocurri&oacute; luego de otra perturbaci&oacute;n de h&aacute;bitat resultado de un intento fallido por erradicar el carp&iacute;n dorado en julio de 1967. Cada descenso (1962&ndash;1963 y 1967&ndash;1968) redujo la poblaci&oacute;n de peces de poza a menos de 50 adultos; y fue seguido por una recuperaci&oacute;n de la poblaci&oacute;n a m&aacute;s de 1000. Despu&eacute;s de la primera perturbaci&oacute;n del h&aacute;bitat y descenso en la poblaci&oacute;n de peces de poza, se observaron cambios en la dieta y la estructura de la poblaci&oacute;n. Aparentemente, estos cambios ocasionaron un ascenso en la tasa de mortalidad, causando la desaparici&oacute;n o disminuci&oacute;n de la abundancia relativa de peces de poza de clases de mayor tama&ntilde;o, con una reducci&oacute;n proporcional en la producci&oacute;n de huevos maduros. No detectamos cambios adicionales en las caracter&iacute;sticas de historia de vida que pudieran estar asociados con el segundo descenso y recuperaci&oacute;n de la poblaci&oacute;n. Concluimos que la remoci&oacute;n de vegetaci&oacute;n en el verano de 1962, y la a&uacute;n mayor perturbaci&oacute;n del h&aacute;bitat y manejo de peces en junio/julio de 1967, fueron perturbaciones inducidas por el humano a modo de &ldquo;pulso&rdquo; que provocaron descensos de la poblaci&oacute;n de peces de poza, y que los cambios en las caracter&iacute;sticas de historia de vida de los peces de poza resultaron principalmente de la presi&oacute;n por la alteraci&oacute;n atribuida a los carpines dorados.