Geology topics

Jay J. Rotella

Publications and source records attributed to Jay J. Rotella.

12 recordsLinked to original sources

USGS2024

Adapting standardized trout monitoring to a changing climate for the upper Yellowstone River, Montana, USA

Objective Long‐term standardized monitoring programs are fundamental to assessing how fish populations respond to anthropogenic stressors. Standardized monitoring programs may need to adopt new methods to adapt to rapid environmental changes that are associated with a changing climate. In the upper Yellowstone River, Montana, biologists have used a standardized, mark–recapture monitoring protocol to annually estimate the abundance of trout since 1978 to assess population status and trends. However, within the past two decades, climate change has caused changes in discharge timing that have prevented standardized monitoring from occurring annually. Methods We investigated the feasibility of using two analytical methods, N‐mixture models and mean capture probability, for estimating the abundance of three trout species in the upper Yellowstone River using the historical long‐term data set; these methods allow abundance to be estimated when a mark–recapture estimate cannot be obtained due to hydrologic conditions. Result When compared with abundance estimates from mark–recapture methods, N‐mixture models most often resulted in negatively biased abundance estimates, whereas mean capture probability analyses resulted in positively biased abundance estimates. Additionally, N‐mixture models produced negatively biased estimates when tested against true abundance values from simulated data sets. The bias in the N‐mixture model estimates was caused by poor model fit and variation in capture probability. The bias in the mean capture probability estimates was caused by heterogeneity in capture probability, likely caused by variable environmental conditions, which were not accounted for in the models. Conclusion N‐mixture models and mean capture probability are not viable alternatives for estimating abundance in the upper Yellowstone River. Thus, exploring additional adaptations to sampling methodologies and analytical approaches, including models that require individually marked fish, will be valuable for this system. Climate change will undoubtedly necessitate changes to standardized sampling methods throughout the world; thus, developing alternative sampling and analytical methods will be important for maintaining the utility of long‐term data sets.

Montana↗

USGS2020

Sources of variation in maternal allocation in a long-lived mammal

1. Life history theory predicts allocation of energy to reproduction varies with maternal age, but additional maternal features may be important to the allocation of energy to reproduction. We aimed to characterize age‐specific variation in maternal allocation and assess the relationship between maternal allocation and other static and dynamic maternal features. Mass measurements of 531 mothers and pups were used with Bayesian hierarchical models to explain the relationship between diverse maternal attributes and both the proportion of mass allocated by Weddell seal mothers, and the efficiency of mass transfer from mother to pup during lactation as well as the weaning mass of pups. Our results demonstrated that maternal mass was strongly and positively associated with the relative reserves allocated by a mother and a pup's weaning mass but that the efficiency of mass transfer declines with maternal parturition mass. Birthdate was positively associated with proportion mass allocation and pup weaning mass, but mass transfer efficiency was predicted to be highest at the mean birthdate. The relative allocation of maternal reserves declined with maternal age but the efficiency of mass transfer to pups increases, suggestive of selective disappearance of poor‐quality mothers. These findings highlight the importance of considering multiple maternal features when assessing variation in maternal allocation.

Journal of Animal Ecology↗

USGS2020

Fort Peck paddlefish population survival and abundance in the Missouri River

Excessive fishing pressure can induce population declines or complete collapse of fisheries. Unless commercial and recreational fisheries for K-selected fishes, or those with slow growth and late maturation, are carefully managed, declines in abundance or fishery collapse is probable. Paddlefish Polyodon spathula, are a K-selected species that experienced historical declines in abundance as a result of habitat degradation and overfishing. Mark-recapture studies are well-suited for long-lived fishes by providing information on population density and vital rates. For sustainable commercial or recreational fisheries targeting species such as the paddlefish, managers require accurate estimates of population vital rates including survival, abundance, and exploitation. We used a Montana Fish, Wildlife & Parks (MFWP) mark-recapture dataset and modified Jolly-Seber (POPAN) models to estimate survival, recapture, probability of entry, and abundance of 8,518 tagged paddlefish over a 25-year period. With many supporting estimates including stable survival (0.92 for females, mean of 0.82 for males), low exploitation rates (means of 2.6% for females and 2.9% for males), and stable abundance estimates (25-year mean of 12,309 individuals for both sexes), the Fort Peck paddlefish population appears to be stable and well-managed over the past 25 years. Presently, this is the only study focused on paddlefish in North America that has estimated survival and abundance for both male and female paddlefish using contemporary analyses. This research provided a unique opportunity to highlight that the effort exerted by management agencies to collect long-term field data is extremely useful to our understanding of fish populations and management.

Montana↗

USGS2019

Variation of annual apparent survival and detection rates with age, year, and individual identity in male Weddell seals (Leptonychotes weddellii) from long-term mark-recapture data

Exploring age- and sex-specific survival rates provides insight regarding population behavior and life-history trait evolution, but many population studies exclude males. Accordingly, our understanding of how age-specific patterns of survival, including actuarial senescence, compare between the sexes remains inadequate. Using 35 years of mark-recapture data for 7,516 male Weddell seals (Leptonychotes weddellii) born in Erebus Bay, Antarctica, we estimated age- specific annual survival rates using a hierarchical model for mark-recapture data in a Bayesian framework. Our male survival estimates were moderate for pups and yearlings, highest for 2- year-olds, and gradually declined with age thereafter such that the oldest animals observed had the lowest rates of any age. Reports of senescence in other wildlife populations of species with similar longevity occurred at older ages than those presented here. When compared to recently published estimates for reproductive Weddell seal females, we found that peak survival rates were similar (males: 0.94, 95% CI = 0.92-0.96; females: 0.92, 95% CI = 0.93-0.95), but rates declined more rapidly in males. Costs of reproduction for males seem to exceed costs incurred by females, but age-specific reproductive data for males are necessary to fully evaluate survival- reproduction tradeoffs in males. Similar studies on a broad range of species are needed to contextualize these results for a better understanding of the variation in senescence patterns between the sexes of the same species, but our study adds information for a marine mammal species to a research topic dominated by avian and ungulate species.

Population Ecology↗

USGS2019

Size-specific apparent survival rate estimates of white sharks using mark-recapture models

For species that exist at low abundance or are otherwise difficult to study, it is challenging to estimate vital rates such as survival and fecundity and common to assume that survival rates are constant across ages and sexes. Population assessments based on overly simplistic vital rates can lead to erroneous conclusions. We estimated sex and length-based annual apparent survival rates for white sharks (Carcharodon carcharias). We found evidence that annual apparent survival differed over ontogeny in a system with competitive foraging aggregations, from 0.63 (SE = 0.08) for newly recruiting sub-adults to 0.95 (SE = 0.02) for the largest sharks. Our results reveal a potential challenge to ontogenetic recruitment in a long-lived, highly mobile top marine predator, as survival rates for sub-adult white sharks may be lower than previously assumed. Alternatively, younger and competitively inferior individuals may be forced to permanently emigrate from primary foraging sites. This study provides new methodology for estimating apparent survival as a function of diverse covariates by capture-recapture study including when sex assignment is uncertain.

California↗

USGS2019

Application of multistate modeling to estimate salmonid survival and movement in relation to spatial and temporal variation in metal exposure in a large mining-impacted river

We used telemetry and multistate modeling to estimate survival and movement of brown trout Salmo trutta and westslope cutthroat trout Oncorhynchus clarkii lewisi in relation to dissolved copper concentrations in 189 km of the upper Clark Fork River, Montana, a mining-impacted river in western Montana. Annual survival estimates for both brown trout (range, 0.27-0.53) and westslope cutthroat trout (range, 0.001-0.34) over the three-year study were low and variable within the study area, with survival negatively related to level of copper exposure. Survival probability for brown trout and westslope cutthroat trout in the uppermost river segment, where dissolved copper concentrations frequently exceeded acute criteria for aquatic life (range, 31-60 d >13.4 µg·L-1), was 2.1 times and 122 times lower, respectively, compared to survival rates in the lowermost segment that had relatively low dissolved copper (0 d exceedance of acute concentration). Seasonal differences in survival also appeared to be related to copper exposure level. Lowest survival for both species occurred in the spring-summer period when dissolved copper concentrations were elevated coincident with higher discharge. Movement among study segments was generally low, and cutthroat trout in particular showed low movement into the uppermost river segment with the most elevated copper levels. Both species showed high rates of movement into tributaries, which coincided with their respective spawning migrations rather than as an apparent avoidance of elevated copper levels. Our research design provided an uncommon opportunity to directly relate the degree of contaminant exposure to estimates of fish survival and movement at a population-level over a large spatial scale. This linkage between survival rate and level of copper exposure for both brown trout and cutthroat trout in the upper Clark Fork River suggests that additional removal of tailings deposits could improve survival rates.

Montana↗

USGS2018

Variation in the vital rates of an Antarctic marine predator: the role of individual heterogeneity

Variation in life‐history traits such as lifespan and lifetime reproductive output is thought to arise, in part, due to among‐individual differences in the underlying probabilities of survival and reproduction. However, the stochastic nature of demographic processes can also generate considerable variation in fitness‐related traits among otherwise‐identical individuals. An improved understanding of life‐history evolution and population dynamics therefore depends on evaluating the relative role of each of these processes. Here, we used a 33‐yr data set with reproductive histories for 1,274 female Weddell seals from Erebus Bay, Antarctica, to assess the strength of evidence for among‐individual heterogeneity in the probabilities of survival and reproduction, while accounting for multiple other sources of variation in vital rates. Our analysis used recent advances in Bayesian model selection techniques and diagnostics to directly compare model fit and predictive power between models that included individual effects on survival and reproduction to those that did not. We found strong evidence for costs of reproduction to both survival and future reproduction, with breeders having rates of survival and subsequent reproduction that were 3% and 6% lower than rates for non‐breeders. We detected age‐related changes in the rates of survival and reproduction, but the patterns differed for the two rates. Survival rates steadily declined from 0.92 at age 7 to 0.56 at the maximal age of 31 yr. In contrast, reproductive rates increased from 0.68 at age 7 to 0.79 at age 16 and then steadily declined to 0.37 for the oldest females. Models that included individual effects explained more variation in observed life histories and had better estimated predictive power than those that did not, indicating their importance in understanding sources of variation among individuals in life‐history traits. We found that among‐individual heterogeneity in survival was small relative to that for reproduction. Our study, which found patterns of variation in vital rates that are consistent with a series of predictions from life‐history theory, is the first to provide a thorough assessment of variation in important vital rates for a long‐lived, high‐latitude marine mammal while taking full advantage of recent developments in model evaluation.

Ecology↗

USGS2014

Environmental correlates of temporary emigration for female Weddell seals and consequences for recruitment

In colonial-breeding species, prebreeders often emigrate temporarily from natal reproductive colonies then subsequently return for one or more years before producing young. Variation in attendance–nonattendance patterns can have implications for subsequent recruitment. We used open robust-design multistate models and 28 years of encounter data for prebreeding female Weddell seals ( Leptonychotes weddellii [Lesson]) to evaluate hypotheses about (1) the relationships of temporary emigration (TE) probabilities to environmental and population size covariates and (2) motivations for attendance and consequences of nonattendance for subsequent probability of recruitment to the breeding population. TE probabilities were density dependent (β&circ; BPOP = 0.66, = 0.17; estimated effects [β] and standard errors of population size in the previous year) and increased when the fast-ice edge was distant from the breeding colonies (β&circ; DIST = 0.75, = 0.04; estimated effects and standard errors of distance to the sea-ice edge in the current year on TE probability in the current year) and were strongly age and state dependent. These results suggest that trade-offs between potential benefits and costs of colony attendance vary annually and might influence motivation to attend colonies. Recruitment probabilities were greatest for seals that consistently attended colonies in two or more years (e.g., = 0.56, SD = 0.17) and lowest for seals that never or inconsistently attended prior to recruitment (e.g., = 0.32, SD = 0.15), where denotes the mean recruitment probability (over all years) for 10-year-old seals for the specified prebreeder state. In colonial-breeding seabirds, repeated colony attendance increases subsequent probability of recruitment to the adult breeding population; our results suggest similar implications for a marine mammal and are consistent with the hypothesis that prebreeders were motivated to attend reproductive colonies to gain reproductive skills or perhaps to optimally synchronize estrus through close association with mature breeding females.

Ecology↗

USGS2014

Drivers of waterfowl population dynamics: from teal to swans

Waterfowl are among the best studied and most extensively monitored species in the world. Given their global importance for sport and subsistence hunting, viewing and ecosystem functioning, great effort has been devoted since the middle part of the 20th century to understanding both the environmental and demographic mechanisms that influence waterfowl population and community dynamics. Here we use comparative approaches to summarise and contrast our understanding of waterfowl population dynamics across species as short-lived as the teal Anas discors and A.crecca to those such as the swans Cygnus sp. which have long life-spans. Specifically, we focus on population responses to vital rate perturbations across life history strategies, discuss bottom-up and top-down responses of waterfowl populations to global change, and summarise our current understanding of density dependence across waterfowl species. We close by identifying research needs and highlight ways to overcome the challenges of sustainably managing waterfowl populations in the 21st century.

Wildfowl↗

USGS2013

Relative contribution of lipid sources to eggs of lesser scaup

Studies of how birds mobilize nutrients to eggs have traditionally considered a continuum of possible allocation strategies ranging from income breeding (rely on food sources found on the breeding grounds) to capital breeding (rely on body reserves stored prior to the breeding season). For capital breeding, stored body reserves can be acquired either on or away from the breeding grounds, but it has been difficult to quantify the relative contribution of each, precluding identification of key habitats for acquiring nutrients for clutch formation. During 2006–2009, we explored the importance of spring-staging habitats versus breeding-area habitats for egg-lipid formation in female lesser scaup Aythya affinis using stable carbon (δ 13 C) isotope analyses. Although δ 13 C values for abdominal lipid reserves brought to the breeding grounds overlapped those of local amphipods, we were able to quantify the importance of local plant carbohydrates (seeds of emergent wetland plants) to the production of eggs. We compared the importance of local wetland seeds (overall δ 13 C: −29.1 ± 0.9‰ SD) to combined lipid stores and lipids from local amphipods (overall δ 13 C: −23.8 ± 2.2‰). Local seeds and stored body lipids contributed equally to egg lipid formation across years but we found evidence of annual variation in their relative importance. Wetland seeds contributed 39% (SE = 10%) to egg lipid production, and the importance of this source varied by year (90% CI = 47–75% in 2006, 13–42% in 2007, 29–65% in 2008, and 7–30% in 2009). In contrast to earlier studies that suggest lesser scaup predominantly employ a capital breeding strategy, our results suggest that in some years females may attain half of their energy for clutch formation from foods on the breeding grounds.

Journal of Avian Biology↗

USGS2011

Endogenous contributions to egg protein formation in lesser scaup Aythya affinis

Lesser scaup Aythya affinis populations have declined throughout the North American continent for the last three decades. It has been hypothesized that the loss and degradation of staging habitats has resulted in reduced female body condition on the breeding grounds and a concomitant decline in productivity. We explored the importance of body (endogenous) reserves obtained prior to arrival on the breeding ground in egg protein formation in southwestern Montana during 2006–2008 using stable-carbon (δ 13 C) and nitrogen (δ 15 N) isotope analyses of scaup egg components, female tissue, and local prey items. From arrival on the breeding grounds through the egg-laying period, δ 15 N values of scaup red blood cells decreased while δ 13 C values became less variable; a pattern consistent with endogenous tissues equilibrating with local (freshwater) dietary sources. In 2006 and 2008, isotopic values for egg albumen and yolk protein indicated that most (>90%) protein used to produce these components was obtained on the breeding grounds. However, in 2007, a year with an exceptionally warm and dry spring, endogenous reserves contributed on average 41% of yolk and 29% of albumen. Results from this study suggest that female scaup can meet the protein needs of egg production largely from local dietary food sources. This highlights the importance of providing high-quality breeding habitats for scaup. Whether this pattern holds in areas with similar breeding season lengths but longer migration routes, such as those found in the western boreal forest, should be investigated.

Montana↗

USGS2005

Effects of tag loss on direct estimates of population growth rate

The temporal symmetry approach of R. Pradel can be used with capture– recapture data to produce retrospective estimates of a population's growth rate, λ i , and the relative contributions to λ i from different components of the population. Direct estimation of λ i provides an alternative to using population projection matrices to estimate asymptotic λ and is seeing increased use. However, the robustness of direct estimates of λ i to violations of several key assumptions has not yet been investigated. Here, we consider tag loss as a possible source of bias for scenarios in which the rate of tag loss is (1) the same for all marked animals in the population and (2) a function of tag age. We computed analytic approximations of the expected values for each of the parameter estimators involved in direct estimation and used those values to calculate bias and precision for each parameter estimator. Estimates of λ i were robust to homogeneous rates of tag loss. When tag loss rates varied by tag age, bias occurred for some of the sampling situations evaluated, especially those with low capture probability, a high rate of tag loss, or both. For situations with low rates of tag loss and high capture probability, bias was low and often negligible. Estimates of contributions of demographic components to λ i were not robust to tag loss. Tag loss reduced the precision of all estimates because tag loss results in fewer marked animals remaining available for estimation. Clearly tag loss should be prevented if possible, and should be considered in analyses of λ i , but tag loss does not necessarily preclude unbiased estimation of λ i .

Ecology↗