Kathleen R. Matthews

RESISTANCE AND RESILIENCE OF ALPINE LAKE FAUNA TO FISH INTRODUCTIONS

This paper reports on the response by amphibians, benthic macroinverte- brates, and zooplankton in naturally fishless alpine lakes to fish introductions and subsequent fish disappearance. We assessed resistance (the degree to which a system is altered when the environment changes) by comparing faunal distribution and abundance in lakes that have never been stocked with fish vs. the distribution and abundance in lakes that have been stocked and still contain fish. We assessed resilience (the degree and rate of a systems return to its previous configuration once the perturbation is removed) by comparing faunal distribution and abundance in lakes that were stocked at one time but have since reverted to a fishless condition (stocked-now-fishless lakes) vs. the distribution and abundance in lakes that have never been stocked. We quantified recovery rates and trajectories by com- paring faunal assemblages of stocked-now-fishless lakes that had been fishless for 5-10, 11-20, and .20 yr. Faunal assemblages in the study lakes had low resistance to fish introductions, but in general showed high resilience. The mountain yellow-legged frog (Rana muscosa), con- spicuous benthic macroinvertebrates, and large crustacean zooplankton (.1 mm) were dramatically reduced in distribution and abundance by fish introductions but generally recovered to predisturbance levels after fish disappearance. Inconspicuous benthic inver- tebrate taxa, small crustacean zooplankton (,1 mm), and rotiferan zooplankton (,0.2 mm) were either unaffected by fish or increased in the presence of fish. For both the benthic macroinvertebrate community and the zooplankton community as a whole, fish disappear- ance was followed by a steady change away from the configuration characteristic of fish- containing lakes and toward that of lakes that had never been stocked. Both communities remained markedly different from those in never-stocked lakes 5-10 yr after fish disap- pearance and converged on the configuration of never-stocked lakes only 11-20 yr after fish disappearance. Recovery was likely facilitated by the winged adult stages of many benthic macroin- vertebrates, resting eggs of zooplankton, and nearby source populations of frogs. However, many frog populations have disappeared since the time that lakes in this study reverted to a fishless condition, and the viability of zooplankton egg banks should decline in fish- containing lakes over time. As a result, faunal resilience may be lower in lakes that revert to a fishless condition today than is suggested by the results of our study. These findings have important implications for the restoration of alpine lake ecosystems.

DEVELOPING PROBABILISTIC MODELS TO PREDICT AMPHIBIAN SITE OCCUPANCY IN A PATCHY LANDSCAPE

Human-caused fragmentation of habitats is threatening an increasing number of animal and plant species, making an understanding of the factors influencing patch occupancy ever more important. The overall goal of the current study was to develop probabilistic models of patch occupancy for the mountain yellow-legged frog (Rana mus- cosa). This once-common species has declined dramatically, at least in part as a result of habitat fragmentation resulting from the introduction of predatory fish. We first describe a model of frog patch occupancy developed using semiparametric logistic regression that is based on habitat characteristics, fish presence/absence, and a spatial location term (the latter to account for spatial autocorrelation in the data). This model had several limitations in- cluding being constrained in its use to only the study area. We therefore developed a more general model that incorporated spatial autocorrelation through the use of an autocovariate term that describes the degree of isolation from neighboring frog populations (autologistic model). After accounting for spatial autocorrelation in patch occupancy, both models in- dicated that the probability of frog presence was strongly influenced by lake depth, elevation, fish presence/absence, substrate characteristics, and the degree of lake isolation. Based on cross-validation procedures, both models provided good fits to the data, but the autologistic model was more useful in predicting patch occupancy by frogs. We conclude by describing a possible application of this model in assessing the likelihood of persistence by frog

Cool Water Formation and Trout Habitat Use in a Deep Pool in the Sierra Nevada, California

Abstract We documented temperature stratification in a deep bedrock pool in the North Fork of the American River, described the diel movement of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta, and determined whether these trout used cooler portions of the pool. From July 30 to October 10, 1992, the main study pool and an adjacent pool were stratified (temperature differences between surface and bottom were as great as 4.5°C) on all but two days. Six rainbow and one brown trout equipped with temperature-sensitive radio transmitters used water with temperatures ranging from 12 to 19.3°C. During the late afternoon, when the widest range of water temperature was available, trout were found in temperatures up to 19.3°C even though cooler (14.5°C) water was available. Radio tracking indicated that fish were significantly more active and had significantly larger home ranges at night; fish were least active during the day. Because we found no evidence of subsurface seepage into the pool and water ...

Livestock Grazing, Golden Trout, and Streams in the Golden Trout Wilderness, California: Impacts and Management Implications

Abstract Impacts of livestock grazing on California golden trout Oncorhynchus mvkiss aguabonita and their habitat were studied inside and outside of livestock exclosures in the Golden Trout Wilderness, California. In two consecutive years, the majority of stream physical characteristics showed large differences between grazed and ungrazed areas, and the directions of these differences were consistent with the recovery of exclosed streams and riparian areas from impacts caused by livestock grazing. Ungrazed areas consistently had greater canopy shading, stream depths, and bank-full heights and smaller stream widths than grazed areas. California golden trout were very abundant in the study sites; their densities and biomasses were among the highest ever recorded for stream-dwelling trout in the western United States. California golden trout density and biomass per unit area were significantly higher in ungrazed than in grazed areas in three of four comparisons. Differences between grazed and ungrazed areas ...

Garter snake distributions in high-elevation aquatic ecosystems: Is there a link with declining amphibian populations and nonnative trout introductions?

Abstract The dramatic amphibian population declines reported worldwide likely have important effects on their predators. In the Sierra Nevada, where amphibian declines are well documented and some are closely tied to the introduction of nonnative trout, the mountain garter snake, Thamnophis elegans elegans, preys predominately on amphibians. We surveyed 2103 high-elevation lakes in the Sierra Nevada, quantified the distributional relationship between the mountain garter snake and anuran amphibians (Pseudacris regilla, Rana muscosa, and Bufo spp.) and used this information to evaluate the possibility that amphibian declines lead to declines of garter snakes. We observed a strong association between amphibian presence and garter snake presence. The probability of finding snakes in lakes with amphibians was 30 times greater than in lakes without amphibians. Lakes with snakes had higher numbers of amphibians within 1 km (mean = 4018.8) than did lakes without snakes (mean = 642.1). On a landscape scale, in Kings Canyon National Park (where 40% of larger lakes contain nonnative trout) amphibians were found in 52% of lakes, and 62 garter snakes were found in 33 of the 1059 lakes surveyed. In contrast, in the John Muir Wilderness (JMW; where 80% of larger lakes contain nonnative trout), amphibians were found in 19% of lakes, and no snakes were found in any of the 1044 lakes surveyed. Based on these data, we suggest that the introduction of nonnative trout has led not only to the decline of amphibians but also to the decline of garter snakes. This study supports the hypothesis that the presence of amphibians is a prerequisite for garter snake persistence in high-elevation portions of the Sierra Nevada and that the introduction of trout into an ecosystem can have serious effects, not just on their prey but also on other predators in the ecosystem.

EFFECTS OF STREAM CHANNEL MORPHOLOGY ON GOLDEN TROUT SPAWNING HABITAT AND RECRUITMENT

Populations of stream-dwelling salmonids (e.g., salmon and trout) are gen- erally believed to be regulated by strong density-dependent mortality acting on the age-0 life stage, which produces a dome-shaped stock-recruitment curve. Although this paradigm is based largely on data from anadromous species, it has been widely applied to stream- resident salmonids despite the fact that the processes limiting or regulating stream-resident populations remain poorly understood. The purpose of the present study was to determine whether stream channel morphology affects the availability of spawning habitat for Cali- fornia golden trout, and whether spawning habitat availability influences the production of age-0 trout and recruitment into the adult population. Wide stream reaches contained significantly more spawning habitat and a higher density of nests and age-0 trout than did narrow reaches. In contrast to the idea that salmonid populations are regulated by density-dependent mortality of age-0 fish, we found that the mortality of age-0 trout was largely density independent. In addition, over most of the range of observed fish densities, the density of a particular cohort was positively correlated between years for age-0, age-1, and age-2 trout. Therefore, our golden trout study population was limited by spawning habitat, with spawning habitat availability influencing the pro- duction of age-0 trout as well as recruitment into the adult population. Grazing by cattle has widened the study streams, and our current findings help to explain why stream sections subject to grazing had more spawning habitat and higher golden trout densities than ungrazed sections. Individual growth rates of golden trout are apparently negatively density dependent, and these grazing-related increases in trout density have likely resulted in decreased growth rates. Our study demonstrates that it is only by gaining an understanding of how processes operate that we will be able to predict the effects of habitat alteration on populations.

A Telemetric Study of the Movement Patterns and Habitat Use of Rana muscosa, the Mountain Yellow-legged Frog, in a High-elevation Basin in Kings Canyon National Park, California

S.–In a high-elevation (3470 m) lake basin (upper Dusy Basin) in Kings Canyon National Park, California, we used radio transmitters on 24 mountain yellow-legged frogs (Rana muscosa ) to gather basic information on their movement patterns. Rana muscosa have declined throughout their range in the Sierra Nevada and restoration plans require information on their movement ecology. Our study indicates that R. mus cosa had different movement patterns and habitat associations during the 1997 summer period (August and September) compared to October when winter dormancy began. In August, visual surveys found frogs in 10 of the 11 lakes in upper Dusy Basin. During August most tagged frogs moved little (mean movement 77 to over five day periods) and all were found in the lake or adjacent stream where they were originally tagged. During September, movement increased compared to August Frogs moved from the original capture lake mean distances of 145 m,and moved cumulative distances of 315-466 m. By October, frogs were again sedentary (mean distance moved 43 mt and frogs were found in three of the 11 lakes in the basin. Moreover, mean home ranges (adaptive kernel 90% contours) also were different throughout the summer and were highest for frogs tracked during September (5336.2 m2) compared to August (385 m2, and October (52.8 m2. Before this study it was assumed that R. muscosa over-wintered in the deepest portion of the lake, However, most lakes were frozen when our study ended, and tagged frogs were found nearshore under ledges and in deep underwater crevices suggesting that at least some R. muscosa over-winter in these nearshore areas. In this study, we found R. mus cosa in different aquatic habitats over the course of their activity period and that they readily moved between these habitats using both aquatic and overland pathways. The movements appear to be associated with seasonal migrations between summer and over-wintering sites. fish stocking still occurs , mountain ye l l ow-l eg ged frogs were found in only 5% of the lakes (Matthews and Knapp, 1999). In contrast, Kings Canyon National Park, where fish stocking was terminated in the late 1970s, had frogs in 35% (379 of 1083) of the sampled lakes. Presumably, pred ation on tadpoles and young frogs has caused the elimination of R. muscosa from the majority of lakes inhabited by introduced fish (Bradford, 1989; Hayes and Je n n i n g s , 1986; Knapp and Matthews, in press). Remaining populations have become increasingly isolated and, therefore, are more susceptible to local extinctions without the o p p o rtunity for re c o l o n i z ation from neighbori n g populations (Bradford et a]., 1993), especially if movement is minimal. Rana muscosa inhabits high-elevation (1370 to 3660 m) lakes and streams in the Sierra Nevada (Zweifel, 1955; Mullally and Cunningham, 1956). Due to the extreme environment encountered at high elevations (e.g., long winters, sustained freezing, and low temperatures), frogs may only be active for a few months during the summer after snowmelt and before the winter freeze.Tadpoles over-winter for at least two to three years (Zweifel, 1955; Cory, 1963, Bradford et al., 1993) and adults, like other anurans, presumably perform migrations to locate suitable areas for reproduction, feeding, and over-wintering (Baker, 1978; Sinsch, 1990). During the summer, tadpoles and adults seek the wa rmest therm a l regimes (Bradford, 1982) and presumably feed to store fat reserves for winter dormancy that can last up to nine months (Bradford, 1983). Despite the information describing population declines, habitat use information on R. muscosa is lacking or speculative. Rana muscosa is highly aquatic and reportedly is never found more than two or three jumps from water (Mullally and Cunningham, 1956; Stebbins, 1985) suggesting that movement is restricted to a q u atic pat h ways. And although never dire c t ly observed, R. muscosa is believed to over-winter in the deepest portions of lakes below the ice,thus re q u i ring lakes >4 m deep for surv ival (Bra d fo rd, 1 9 8 3 ) . Our study was designed to gather quantitative information on R. muscosa movements and habitat use during summer and fall. With this information, we should be able to more effectively restore some of their habitat in the Sierra Nevada. Movement distances and ranges will also be important for predict ing recolonization. patterns and for metapopulation a n a lysis (Hanski and Gilpin, 1997). Duri n g August-October 1997, we used telemetry to determine R. muscosa home ranges, their movement between lakes, and typical habitat associations during the summer and fall as lakes began to freeze. MATERIALS AND METHODS Study Area.–The study was conducted in upper Dusy Basin, Kings Canyon National Pa rk , C a l i fo rnia (Latitude 37°5’40”, L o n gi t u d e 118°33’45’) at an elevation of 3470 m (Fig. 1). The site supports a large population of R. muscosa of varying age classes. The glacially formed granite basin supports alpine fell field vege t ation with low-growing herbaceous plants, dwarf shrubs, and few krummholzed white-bark pines (Holland and Keil, 1995). There are a series of streams, lakes, and ponds in the basin that are fed by snowmelt. The study area covers approximately 0.75 km2. Our study focused on 11 lakes and ponds in Dusy Basin. All lakes and streams within the study area have been numbered and mapped using a Trimble Pro XL GPS system accurate to 1 m. Only lakes 1 and 3 (all water bodies being considered lakes) support self-sustaining populations of trout. Fish were also found in some of the connected creeks. This scenario will likely be typical of future refuges in National Forest Wilderness areas where, after re-introductions of mountain yellow-legged frogs, self-sustaining fish populations will likely persist in large lakes despite fish stocking changes. Lakes ranged in size from 114 m2 to 5.3 ha and were 0.25 to 10 m deep. Field Techniques.–We attached radio transmitters (Holohil Systems Ltd.; BD-2 transmitters; 15 mm X 7 mm X 4 mm thick) to 24 R. muscosa (snout-vent length > 55 mm) and documented movement from August 2-October 28,1997 (Table 1). We tagged frogs larger than 55 mm to minimize possible effects of transmitter weight. To at t a ch radio tra n s m i t t e rs , a wa i s t-belt made of alum i num ball or beaded chain was used, similar to that used on the Califo rnia re d l egged frog, Rana auro ra d ray t o n i i ( R at h bun and Murp h ey, 1996). The total weight of the at t a ched transmitter and belt was ap p roxi m at e ly 1.5 g, wh i ch is below the 10% rule that at t a ched objects not exceed 10% of body mass (Heye r et al., 1994). Frogs we re hand-c ap t u re d, we i g h e d, m e a s u re d, t agge d,and then released at the cap t u re site. S ex was determined by the enlarged nuptial pad at the base of the inner-most fi n ger found in adult males ( S t ebb i n s , 1985). The transmitter bat t e ries lasted ab o u t one month. To monitor movements over Au g u s t , S ep t e m b e r, and October, we tagged frogs in three diffe rent gro u p s : G roup one consisted of 12 frogs monit o red from 2 Au g u s t-25 Au g u s t , group two consisted of nine frogs monitored from 3 Sep t e m b e r-30 Sep t e m b e r, and group three consisted of three frogs monitore d f rom 3 October through 28 October. We attempted to re m ove tra n s m i t t e rs and belts just befo re the bat t e ry ex p i re d. After frogs we re tagged they we re re l o c ated on K. MATTHEWS AND K. POPE 616

Effects of Nonnative Trout on Pacific Treefrogs (Hyla regilla) in the Sierra Nevada

Abstract We used analyses based on surveys of > 1700 water bodies in a 100,000-ha area in the John Muir Wilderness (JMW) and Kings Canyon National Park (KCNP) to determine the influence of nonnative trout on the distribution and abundance of Hyla regilla in the High Sierra Nevada. At the landscape scale (JMW compared to KCNP), a negative relationship between trout and frogs in lakes was evident. In the JMW study area where trout are more abundant, only 7.2% of all water bodies contained H. regilla versus 26.6% in the KCNP study area. Also, the percentage of the total water body surface area containing H. regilla was 19.4 times higher in the KCNP study area than in the JMW study area. Hyla regilla were most abundant in portions of KCNP where the probability of finding lakes with trout is lowest and least abundant in the northern part of the JMW where the probability of finding lakes with trout is highest. At the water body scale, after accounting for the effects of all significant habitat and isolation variables, the odds of finding H. regilla in water bodies with no trout was 2.4 times greater than in water bodies with trout, and the expected number of H. regilla in water bodies with H. regilla and without trout was 3.7 times greater than in water bodies with both H. regilla and trout. Hyla regilla were significantly more likely to be found at the lower elevations (3000–3400 m) compared to higher elevations (3400–3800 m) and in shallow water bodies with high percentages of silt in near-shore habitats. Our study demonstrates a negative relationship between fish presence and H. regilla distribution and abundance in lakes and suggests that H. regilla has declined in portions of the High Sierra with high numbers of trout-containing lakes. It adds an additional native species to the mounting evidence of landscape-scale declines of native species resulting from the introduction of predatory fish.

Movement Ecology and Seasonal Distribution of Mountain Yellow-Legged Frogs, Rana muscosa, in a High-Elevation Sierra Nevada Basin

Abstract Movement ecology and seasonal distribution of mountain yellow-legged frogs (Rana muscosa) in Dusy Basin (3470 m), Kings Canyon National Park, California, were characterized using passive integrated transponder (PIT) surveys and visual encounter surveys. We individually PIT-tagged 500 frogs during the summers of 1997 and 1998 and monitored these individuals during seven recapture surveys in 1997 and 15 recapture surveys in 1998 from the time they emerged from overwintering in July until the lakes froze for the winter in October. Probability of movement between lakes was associated with abundance of Hyla regilla larvae in the different lakes of origin, activity of the frogs (overwintering, breeding, feeding), and time of year. Overland movements exceeding 66 m were observed in 17% of the tagged frogs. Movement between lakes 1 km apart was detected. Site fidelity from 1997 to 1998 was high, and 97% of the tagged frogs recaptured in October of both years were found in the same overwintering lakes. Frogs were more narrowly distributed in spring and fall than in summer. Summer frog densities (number per meter of shoreline) were positively related to water temperature, air temperature, maximum lake depth, and presence of H. regilla larvae and negatively related to presence of trout. Mountain yellow-legged frogs use a range of aquatic sites throughout their activity period, and basins with a variety of deep lakes and shallow ponds may be the most appropriate reserves for this declining species.

A Skeletochronological Study of the Age Structure, Growth, and Longevity of the Mountain Yellow-legged Frog, Rana muscosa, in the Sierra Nevada, California

Abstract We used skeletochronology to determine the ages of 149 (74 females, 44 males, and 31 juveniles) Mountain Yellow-legged Frogs (Rana muscosa) from 13 locations (elevation 1509–3501 m) throughout their current range in the Sierra Nevada mountains of California. Lines of arrested growth (LAGs) from excised toe bones were distinct in these high elevation frogs, and each LAG was assumed to represent one year of age. Females ranged in age from 0–10 years (mean  =  4.1 years) and males from 0–8 years (mean  =  4.0 years). The skeletochronological age was that of the post-metamorphic frog and did not include the tadpole stage. Mountain Yellow-legged Frogs spend 3–4 years as tadpoles, but no age markers are found in their cartilaginous skeletons; thus, their total age, if both tadpole and post-metamorphic stages were included, would range up to 14 years. Females were significantly longer (snout–vent length: SVL) than males and had greater mean mass, but there was no difference in the mean ages. Juvenile frogs of unknown sex ranged in age from 0–3. The von Bertalanffy growth curve demonstrated that female SVLs were larger than males for all ages. Using a semi-parametric growth model, we also found that elevation within the Sierra Nevada range was an important variable in the relationship between SVL and age; frogs from lower elevation sites were consistently larger at a given age when compared to higher elevation sites. For each increase of 1000 m in elevation, the estimated length (on average) decreases by 8.7 mm. This is the first age determination study of a Sierra Nevada amphibian, and compared to other anuran species, Mountain Yellow-legged Frogs were found to be relatively long-lived, which will have implications for restoration and recovery plans.