Devries

Bio: Devries is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 715 citations.

Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods

Abstract: Many calcified structures produce periodic growth increments useful for age determination at the annual or daily scale. However, age determination is invariably accompanied by various sources of error, some of which can have a serious effect on age-structured calculations. This review highlights the best available methods for insuring ageing accuracy and quantifying ageing precision, whether in support of large-scale production ageing or a small-scale research project. Included in this review is a critical overview of methods used to initiate and pursue an accurate and controlled ageing program, including (but not limited to) validation of an ageing method. The distinction between validation of absolute age and increment periodicity is emphasized, as is the importance of determining the age of first increment formation. Based on an analysis of 372 papers reporting age validation since 1983, considerable progress has been made in age validation efforts in recent years. Nevertheless, several of the age validation methods which have been used routinely are of dubious value, particularly marginal increment analysis. The two major measures of precision, average percent error and coefficient of variation, are shown to be functionally equivalent, and a conversion factor relating the two is presented. Through use of quality control monitoring, ageing errors are readily detected and quantified; reference collections are the key to both quality control and reduction of costs. Although some level of random ageing error is unavoidable, such error can often be corrected after the fact using statistical (‘digital sharpening)’ methods.

Graphical and Statistical Methods for Determining the Consistency of Age Determinations

Abstract: Many laboratories rely on periodic rereading of reference collections of scales or otoliths to ensure that their age readers remain consistent in their age interpretations, both through time and with other age readers. Measures of both systematic difference (bias) and precision are required for this purpose, because measures of bias are not suitable as measures of precision, and vice versa. Using data from an age comparison study of haddock Melanogrammus aeglefinus for demonstration purposes, we evaluated a variety of graphical and statistical approaches for making paired age comparisons from the standpoint of both detecting age differences and assessing precision. Parametric and nonparametric matched-pair tests, regression analysis, analysis of variance, and age difference plots were all capable of detecting systematic over- or underaging. However, only the age bias plot was sensitive to both linear and nonlinear biases. The coefficient of variation (CV = SD/mean) was a robust measure of precisi...

Nitrogen and phosphorus excretion by detritivorous gizzard shad in a reservoir ecosystem

Abstract: The detritivorous fish, gizzard shad (Dorosoma cepedianum), provides nutrients to phytoplankton in reservoirs by ingesting organic detritus associated with sediments and excreting substantial quantities of nutrients such as N and P in soluble forms that are highly available to phytoplankton, We estimated nutrient excretion by gizzard shad in a eutrophic reservoir (Acton Lake, Ohio) during April-October 1994 by measuring N and P excretion of fieldcaught fish (n = 135). Excretion rates were then extrapolated to nutrient release by the gizzard shad population using quadrat rotenone biomass estimates, electrofishing surveys, and historic seasonal trends. N and P excretion were positively correlated with fish wet mass and temperature, but mass-specific excretion declined with increasing fish mass. Lakewidc gizzard shad biomass in July 1994 was 417 kg ha -I, Our estimates of nutrient excretion by the gizzard shad population ranged from 0.487 to 0.769 pmol NH,-N liter-’ d-l and 0.022 to 0.057 pmol soluble reactive phosphorus liter -I d .I, with the highest excretion occurring during mid-summer through early fall. The low N : P ratio at which gizzard shad excrete [mean molar N : P = 16.75 (kO.89 SE)] may alter phytoplankton community composition, favoring cyanobacteria. Our results indicate that nutrient excretion by detritivorous fish can be an important source of nutrients to open waters, especially when other sources of nutrients are reduced.

Effects of introduced lake trout on native cutthroat trout in yellowstone lake

Abstract: The establishment of a reproducing population of nonnative lake trout (Salvelinus namaycush) poses a serious threat to the integrity of the Yellowstone Lake ecosystem, particularly to the indigenous cutthroat trout (Oncorhynchus clarki bouvieri). We used standard fisheries techniques to quantify the population-level impact resulting from this introduction, while the U.S. National Park Service (NPS) developed a program to control their numbers. Lake trout diets, thermal history, growth, and size structure were incorporated into a bioenergetics model to estimate the predatory impact of introduced lake trout and to evaluate the effectiveness of the NPS lake trout control program. Population size structures were estimated from catches of fish in gill nets that were corrected for mesh size selectivity. Lake trout abundance was estimated using virtual population (cohort) analysis, and cutthroat trout abundance was estimated using hydroacoustics. Juvenile cutthroat trout were highly vulnerable to predation, and ...

Growth and longevity in freshwater mussels: evolutionary and conservation implications

Abstract: The amount of energy allocated to growth versus other functions is a fundamental feature of an organism’s life history. Constraints on energy availability result in characteristic trade-offs among life-history traits and reflect strategies by which organisms adapt to their environments. Freshwater mussels are a diverse and imperiled component of aquatic ecosystems but little is known about their growth and longevity. Generalized depictions of freshwater mussels as ‘long-lived and slow-growing’ may give an unrealistically narrow view of life-history diversity which is incongruent with the taxonomic diversity of the group and can result in development of inappropriate conservation strategies. We investigated relationships among growth, longevity, and size in 57 species and 146 populations of freshwater mussels using original data and literature sources. In contrast to generalized depictions, longevity spanned nearly two orders of magnitude, ranging from 4 to 190 years, and the von Bertalanffy growth constant, K , spanned a similar range (0.02–1.01). Median longevity and K differed among phylogenetic groups but groups overlapped widely in these traits. Longevity, K , and size also varied among populations; in some cases, longevity and K differed between populations by a factor of two or more. Growth differed between sexes in some species and males typically reached larger sizes than females. In addition, a population of Quadrula asperata exhibited two distinctly different growth trajectories. Most individuals in this population had a low-to-moderate value of K (0.15) and intermediate longevity (27 years) but other individuals showed extremely slow growth (K = 0.05) and reached advanced ages (72 years). Overall, longevity was related negatively to the growth rate, K ,a ndK explained a high percentage of variation in longevity. By contrast, size and relative shell mass (g mm −1 shell length) explained little variation in longevity. These patterns remained when data were corrected for phylogenetic relationships among species. Path analysis supported the conclusion that K was the most important factor influencing longevity both directly and indirectly through its effect on shell mass. The great variability in age and growth among and within species shows that allocation to growth is highly plastic in freshwater mussels. The strong negative relationship between growth and longevity suggests this is an important trade-off describing widely divergent life-history strategies. Although life-history strategies may be constrained somewhat by phylogeny, plasticity in growth among populations indicates that growth characteristics cannot be generalized within a species and management and conservation efforts should be based on data specific to a population of interest.