Geology topics

Maria C. Dzul

Publications and source records attributed to Maria C. Dzul.

22 records · Page 2Linked to original sources

USGS2017

Incorporating temporal heterogeneity in environmental conditions into a somatic growth model

Evaluating environmental effects on fish growth can be challenging because environmental conditions may vary at relatively fine temporal scales compared to sampling occasions. Here we develop a Bayesian state-space growth model to evaluate effects of monthly environmental data on growth of fish that are observed less frequently (e.g., from mark-recapture data where time between captures can range from months to years). We assess effects of temperature, turbidity duration, food availability, flow variability, and trout abundance on subadult humpback chub (Gila cypha) growth in two rivers, the Colorado River (CR) and the Little Colorado River (LCR), and we use out-of-sample prediction to rank competing models. Environmental covariates explained a high proportion of the variation in growth in both rivers; however, the best growth models were river-specific and included either positive temperature and turbidity duration effects (CR) or positive temperature and food availability effects (LCR). Our approach to analyzing environmental controls on growth should be applicable in other systems where environmental data vary over relatively short time scales compared to animal observations.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2014

Survival, growth, and movement of subadult humpback chub, Gila cypha , in the Little Colorado River, Arizona

Ecologists estimate vital rates, such as growth and survival, to better understand population dynamics and identify sensitive life history parameters for species or populations of concern. Here, we assess spatiotemporal variation in growth, movement, density, and survival of subadult humpback chub living in the Little Colorado River, Grand Canyon, AZ from 2001–2002 and 2009–2013. We divided the Little Colorado River into three reaches and used a multistate mark-recapture model to determine rates of movement and differences in survival and density between sites for different cohorts. Additionally, site-specific and year-specific effects on growth were evaluated using a linear model. Results indicate that summer growth was higher for upstream sites compared with downstream sites. In contrast, there was not a consistent spatial pattern across years in winter growth; however, river-wide winter growth was negatively related to the duration of floods from 1 October to 15 May. Apparent survival was estimated to be lower at the most downstream site compared with the upstream sites; however, this could be because in part of increased emigration into the Colorado River at downstream sites. Furthermore, the 2010 cohort (i.e. fish that are age 1 in 2010) exhibited high apparent survival relative to other years. Movement between reaches varied with year, and some years exhibited preferential upstream displacement. Improving understanding of spatiotemporal effects on age 1 humpback chub survival can help inform current management efforts to translocate humpback chub into new locations and give us a better understanding of the factors that may limit this tributary's carrying capacity for humpback chub.

Arizona↗

USGS2012

Using variance components to estimate power in a hierarchically nested sampling design improving monitoring of larval Devils Hole pupfish

We used variance components to assess allocation of sampling effort in a hierarchically nested sampling design for ongoing monitoring of early life history stages of the federally endangered Devils Hole pupfish (DHP) (Cyprinodon diabolis). Sampling design for larval DHP included surveys (5 days each spring 2007–2009), events, and plots. Each survey was comprised of three counting events, where DHP larvae on nine plots were counted plot by plot. Statistical analysis of larval abundance included three components: (1) evaluation of power from various sample size combinations, (2) comparison of power in fixed and random plot designs, and (3) assessment of yearly differences in the power of the survey. Results indicated that increasing the sample size at the lowest level of sampling represented the most realistic option to increase the survey's power, fixed plot designs had greater power than random plot designs, and the power of the larval survey varied by year. This study provides an example of how monitoring efforts may benefit from coupling variance components estimation with power analysis to assess sampling design.

California↗

USGS2012

Evaluation of otoliths Salt Creek pupfish (Cyprinodon salinus salinus) for use in analyses of age and growth

We collected Salt Creek pupfish (Cyprinodon salinus salinus) from Salt Creek, Death Valley, California, in November 2009 and May 2010. The purpose of our study was to determine whether otoliths displayed interpretable marks that might be used for estimating age and growth. Otoliths exhibited alternating bands of opaque and translucent material. Kendall rank correlation between number of bands on otoliths and length of fish were high for two readers (τ = 0.65 and 0.79) and exact agreement between readers was 51%. Otoliths exhibited 0–5 bands, which provided evidence that longevity of Salt Creek pupfish likely is >1 year. Total length of fish collected in spring and autumn differed for fish with one and three bands on otoliths.

California↗