Geology topics

Research about Lake Clark National Park and Preserve

Source-linked reports with geographic coverage including Lake Clark National Park and Preserve.

4 recordsLinked to original sources

USGS2022

Integrating distance sampling survey data with population indices to separate trends in abundance and temporary immigration

Managers rely on accurate estimators of wildlife abundance and trends for management decisions. Despite the focus of contemporary wildlife science on developing methods to improve inference from wildlife surveys, legacy datasets often rely on index counts that lack information about the detection process. Data integration can be a useful tool for combining index counts with data collected under more rigorous designs (i.e., designs that account for the detection process), but care is required when datasets represent different population processes or are mismatched in space and time. This can be particularly problematic in cases where animals aggregate in response to a spatially or temporally limited resource because individuals may temporarily immigrate from outside the study area and be included in the abundance index. Abundance indices based on brown bear ( Ursus arctos ) feeding aggregations within coastal meadows in early summer in Lake Clark National Park and Preserve, Alaska, USA, are one such example. These indices reflect the target population (brown bears residing within the park) and temporary immigrants (i.e., bears drawn from outside the park boundary). To properly account for the effects of temporary immigration, we integrated the index data with abundance data collected via park-wide distance sampling surveys, the latter of which properly addressed the detection process. By assuming that the distance data provide inference on abundance and the index counts represent some combination of abundance and temporary immigration processes, we were able to decompose the relative contribution of each to overall trend. We estimated that the density of brown bears within our study area was 38–54 adults/1,000 km 2 during 2003–2019 and that abundance increased at a rate of approximately 1.4%/year. The contribution of temporary immigrants to overall trend in the index was low, so we created 3 hypothetical scenarios to more fully demonstrate how the integrated approach could be useful in situations where the composite trend in meadow counts may obscure trends in abundance (e.g., opposing trends in abundance and temporary immigration). Our work represents a conceptual advance supporting the integration of legacy index data with more rigorous data streams and is broadly applicable in cases where trends in index values may represent a mixture of population processes.

Alaska↗

USGS2020

Lake trout growth is sensitive to spring temperature in southwest Alaska lakes

In high‐latitude lakes, air temperature is an important driver of ice cover thickness and duration, which in turn influence water temperature and primary production supporting lake consumers and predators. In lieu of multidecadal observational records necessary to assess the response of lakes to long‐term warming, we used otolith‐based growth records from a long‐lived resident lake fish, lake trout ( Salvelinus namaycush), as a proxy for production. Lake trout were collected from seven deep, oligotrophic lakes in Lake Clark National Park and Preserve on in southwest Alaska that varied in the presence of marine‐derived nutrients (MDN) from anadromous sockeye salmon ( Oncorhynchus nerka) . Linear mixed‐effects models were used to partition variation in lake trout growth by age and calendar‐year and model comparisons tested for a mean increase in lake trout growth with sockeye salmon presence. Year effects from the best mixed‐effects model were subsequently compared to indices of temperature, lake ice, and regional indices of sockeye salmon escapement. A strong positive correlation between annual lake trout growth and temperature suggested that warmer springs, earlier lake ice break‐up, and a longer ice‐free growing season increase lake trout growth via previously identified bottom‐up increases in production with warming. Accounting for differences in the presence or annual escapement of sockeye salmon with available data did not improve model fit. Collectively with other studies, the results suggest that productivity of subarctic lakes has benefitted from warming spring temperatures and that temperature can synchronise otolith growth across lakes with and without sockeye salmon MDN.

Alaska↗

USGS2018

Influences of landscape heterogeneity on home-range sizes of brown bears

Animal space use is influenced by many factors and can affect individual survival and fitness. Under optimal foraging theory, individuals use landscapes to optimize high-quality resources while minimizing the amount of energy used to acquire them. The spatial resource variability hypothesis states that as patchiness of resources increases, individuals use larger areas to obtain the resources necessary to meet energetic requirements. Additionally, under the temporal resource variability hypothesis, seasonal variation in available resources can reduce distances moved while providing a variety of food sources. Our objective was to determine if seasonal home ranges of brown bears ( Ursus arctos ) were influenced by temporal availability and spatial distribution of resources and whether individual reproductive status, sex, or size (i.e., body mass) mediated space use. To test our hypotheses, we radio collared brown bears ( n = 32 [9 male, 23 female]) in 2014–2016 and used 18 a priori selected linear models to evaluate seasonal utilization distributions (UD) in relation to our hypotheses. Our top-ranked model by AIC c , supported the spatial resource variability hypothesis and included percentage of like adjacency (PLADJ) of all cover types (P < 0.01), reproductive class (P > 0.17 for males, solitary females, and females with dependent young), and body mass (kg; P = 0.66). Based on this model, for every percentage increase in PLADJ, UD area was predicted to increase 1.16 times for all sex and reproductive classes. Our results suggest that landscape heterogeneity influences brown bear space use; however, we found that bears used larger areas when landscape homogeneity increased, presumably to gain a diversity of food resources. Our results did not support the temporal resource variability hypothesis, suggesting that the spatial distribution of food was more important than seasonal availability in relation to brown bear home range size.

Alaska↗

USGS2018

Sex-specific variation in denning by brown bears

Denning characteristics of brown bears ( Ursus arctos ) have been described in numerous studies; however, population specific factors (i.e., landscape characteristics and climate) can greatly influence the location and timing of denning. Our objective was to evaluate den-site characteristics and denning chronology for male and female brown bears in Lake Clark National Park and Preserve, Alaska. We used maximum entropy modeling to characterize attributes of den sites and generalized linear mixed models to compare denning chronology between males and females. We located 70 den sites (19 male and 51 female) and documented den entrance ( n = 61 [15 male and 46 female]) and emergence ( n = 60 [13 male and 47 female]) dates for bears from fall 2014 to spring 2017. The best performing model for estimating probable male den-site use (AUC = 0.862) was most influenced by slope (79.5%). The most parsimonious female model (AUC = 0.910) included elevation (49.3%), slope (43.1%), and aspect (7.6%). Female brown bears on average denned at higher elevations (868, SE = 190 m) than males (762, SE = 195 m) ( F 1,73 = 4.08, P = 0.047). Additionally, female bears entered dens 8 days earlier than males (SE = 12.82; 20 and 28 October, respectively, P = 0.04), and although not significant ( P = 0.09), average female den emergence dates were 7 days (SE = 15.14) later than males. With the potential for increased human activities (i.e. resource extraction and associated access), gaining an understanding of population specific denning requirements is essential for developing future management actions. Our results provide valuable information that will allow decision makers to structure future development in a way that avoids habitats important for denning, and allows for reduced disturbance of winter den sites.

Alaska↗