Investigating spatial variation and temperature effects on maturity of female winter flounder (Pseudopleuronectes americanus) using generalized additive models

2014 ◽  
Vol 71 (9) ◽  
pp. 1279-1290 ◽  
Author(s):  
Megan V. Winton ◽  
Mark J. Wuenschel ◽  
Richard S. McBride
Keyword(s):  
Spatial Structure ◽  
Spatial Variation ◽  
Clustering Algorithm ◽  
Generalized Additive Models ◽  
Additive Models ◽  
Winter Flounder ◽  
Effect Of Temperature ◽  
Spatial Effects ◽  
Age At Maturity ◽  
Pseudopleuronectes Americanus

Generalized additive models were used to investigate fine-scale spatial variation in female maturity across the three United States’ winter flounder (Pseudopleuronectes americanus) stocks. The effect of temperature on maturity was also investigated. Maturity models explicitly incorporating spatial structure performed better than “traditional” methods incorporating spatial effects by aggregating data according to predefined stock boundaries. Models including temperature explained more of the variability in maturity than those based only on fish size or age but did not improve fit over models incorporating spatial structure. Based on the size- and age-at-maturity estimates from the spatially explicit models, distinct subareas were objectively identified using a spatially constrained clustering algorithm. The results suggested greater variation in size- and age-at-maturity within than between existing stock areas. The approach outlined here provides a method for identifying areas with different vital rates without the need to presume subjective boundaries.

scholarly journals Spatial analysis of the distribution of intestinal nematode infections in Uganda

2004 ◽  
Vol 132 (6) ◽  
pp. 1065-1071 ◽  
Author(s):  
S. BROOKER ◽  
N. B. KABATEREINE ◽  
E. M. TUKAHEBWA ◽  
F. KAZIBWE
Keyword(s):  
Spatial Structure ◽  
Land Surface ◽  
Large Scale ◽  
Spatial Epidemiology ◽  
Generalized Additive Models ◽  
Additive Models ◽  
Spatial Dependency ◽  
Geostatistical Methods ◽  
Semivariogram Analysis ◽  
Intestinal Nematode

The spatial epidemiology of intestinal nematodes in Uganda was investigated using generalized additive models and geostatistical methods. The prevalence of Ascaris lumbricoides and Trichuris trichiura was unevenly distributed in the country with prevalence greatest in southwest Uganda whereas hookworm was more homogeneously distributed. A. lumbricoides and T. Trichiura prevalence were nonlinearly related to satellite sensor-based estimates of land surface temperature; hookworm was nonlinearly associated with rainfall. Semivariogram analysis indicated that T. trichiura prevalence exhibited no spatial structure and that A. lumbricoides exhibited some spatial dependency at small spatial distances, once large-scale, mainly environmental, trends had been removed. In contrast, there was much more spatial structure in hookworm prevalence although the underlying factors are at present unclear. The implications of the results are discussed in relation to parasite spatial epidemiology and the prediction of infection distributions.

Predation on winter flounder (Pseudopleuronectes americanus) eggs by the sand shrimp (Crangon septemspinosa)

2005 ◽  
Vol 62 (7) ◽  
pp. 1611-1625 ◽  
Author(s):  
David L Taylor ◽  
Donald J Danila
Keyword(s):  
Deterministic Model ◽  
Size Structure ◽  
Early Stage ◽  
Winter Flounder ◽  
Spawning Season ◽  
Effect Of Temperature ◽  
Feeding Rates ◽  
Pseudopleuronectes Americanus ◽  
Egg Mortality ◽  
Crangon Septemspinosa

This study estimated rates of sand shrimp (Crangon septemspinosa) predation on winter flounder (Pseudopleuronectes americanus) eggs and examined the effect of temperature on density-dependent mortality of early-stage flounder. In laboratory experiments, shrimp feeding rates on flounder eggs were positively correlated with temperature and shrimp size. Immunological assays of shrimp stomach contents indicated that 7.2% of shrimp collected from the Niantic River (Connecticut) had flounder eggs in their stomachs. Incidence of egg predation was highest in February (20%) and decreased continuously into early April (1.2%). In a deterministic model simulating predator-induced mortality of flounder eggs during a spawning season, shrimp consumed 0.4%–49.7% of the total flounder spawn. Variations in shrimp population abundance and size structure accounted for the greatest variability in egg mortality. Water temperature during the spawning season presumably alters the population dynamics of early-stage flounder. In a long-term survey, the number of yolk-sac flounder larvae in warm years (≥4.3 °C) was depressed at high egg densities, indicating strong compensatory processes that increased egg mortality and limited the abundance of larvae. Failure of flounder to produce strong year-classes of larvae during warm years, possibly resulting from altered trophic dynamics, may explain the inability of stocks to recover from previous overexploitation.

scholarly journals Evaluation of the Performance of Smoothing Functions in Generalized Additive Models for Spatial Variation in Disease

2015 ◽  
Vol 14s2 ◽  
pp. CIN.S17300 ◽  
Author(s):  
Umaporn Siangphoe ◽  
David C. Wheeler
Keyword(s):  
Spatial Variation ◽  
Disease Risk ◽  
Generalized Additive Models ◽  
Elevated Risk ◽  
Additive Models ◽  
Risk Area ◽  
Study Region ◽  
Risk Levels ◽  
Permutation Methods ◽  
Smoothing Functions

Generalized additive models (GAMs) with bivariate smoothing functions have been applied to estimate spatial variation in risk for many types of cancers. Only a handful of studies have evaluated the performance of smoothing functions applied in GAMs with regard to different geographical areas of elevated risk and different risk levels. This study evaluates the ability of different smoothing functions to detect overall spatial variation of risk and elevated risk in diverse geographical areas at various risk levels using a simulation study. We created five scenarios with different true risk area shapes (circle, triangle, linear) in a square study region. We applied four different smoothing functions in the GAMs, including two types of thin plate regression splines (TPRS) and two versions of locally weighted scatterplot smoothing (loess). We tested the null hypothesis of constant risk and detected areas of elevated risk using analysis of deviance with permutation methods and assessed the performance of the smoothing methods based on the spatial detection rate, sensitivity, accuracy, precision, power, and false-positive rate. The results showed that all methods had a higher sensitivity and a consistently moderate-to-high accuracy rate when the true disease risk was higher. The models generally performed better in detecting elevated risk areas than detecting overall spatial variation. One of the loess methods had the highest precision in detecting overall spatial variation across scenarios and outperformed the other methods in detecting a linear elevated risk area. The TPRS methods outperformed loess in detecting elevated risk in two circular areas.

scholarly journals Do environmental factors affect recruits per spawner anomalies of New England groundfish?

2005 ◽  
Vol 62 (7) ◽  
pp. 1394-1407 ◽  
Author(s):  
Jon Brodziak ◽  
Loretta O'Brien
Keyword(s):  
Environmental Factors ◽  
New England ◽  
Gulf Of Maine ◽  
Generalized Additive Models ◽  
Additive Models ◽  
Winter Flounder ◽  
Water Volume ◽  
Melanogrammus Aeglefinus ◽  
Georges Bank ◽  
Yellowtail Flounder

Abstract We evaluated the influence of environmental factors on recruits per spawner (RS) anomalies of 12 New England groundfish stocks. Nonparametric methods were used to analyse time-series of RS anomalies derived from stock-recruitment data in recent assessments. The 12 stocks occur in three geographic regions: the Gulf of Maine (cod Gadus morhua, redfish Sebastes fasciatus, winter flounder Pseudopleuronectes americanus, American plaice Hippoglossoides platessoides, witch flounder Glyptocephalus cynoglossus, and yellowtail flounder Limanda ferruginea), Georges Bank (cod, haddock Melanogrammus aeglefinus, and yellowtail flounder), and Southern New England (summer flounder Paralichthys dentatus, yellowtail flounder, and winter flounder). Randomization tests were applied to detect years when RS anomalies were unusually high or low for comparison with oceanographic conditions such as the 1998 intrusion of Labrador Subarctic Slope water into the Gulf of Maine region. Randomization methods were also used to evaluate the central tendency and dispersion of all RS anomalies across stocks. Average RS anomalies were significantly positive in 1987 across stocks and regions, indicating that environmental forcing was coherent and exceptional in that year. Responses of RS values of individual stocks to lagged and contemporaneous environmental variables such as the North Atlantic Oscillation (NAO) index, water temperature, windstress, and shelf water volume anomalies were evaluated using generalized additive models. Overall, the NAO forward-lagged by 2 years had the largest impact on RS anomalies. This apparent effect is notable because it could provide a leading indicator of RS anomalies for some commercially exploited stocks. In particular, the three primary groundfish stocks on Georges Bank (cod, haddock, and yellowtail flounder) all exhibited positive RS anomalies when the NAO2 variable was positive.

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