Two‐Stage Boosted Regression Tree Model to Characterize Southern Flounder Distribution in Texas Estuaries at Varying Population Sizes

Abstract

Linking trends in fish population abundance to environmental characteristics is often difficult because fish use a variety of habitats throughout their ontogeny and may exhibit large interannual fluctuations in abundance. We developed a two‐stage boosted regression tree model to investigate spatiotemporal patterns of Southern Flounder Paralichthys lethostigma abundance and distribution in Texas estuaries. We used a 36‐year fishery‐independent data set (1977–2012) to correlate distribution with environmental conditions and seasonal or long‐term changes in abundance. Adult Southern Flounder were sampled with gill nets using a random‐stratified design. Predictions of abundance were made to grids of environmental data to identify “hot spots” as well as seasonal or decadal shifts in distribution. Models were fit using cross validation, and variance was estimated using nonparametric bootstrapping. Depth, temperature, distance to a tidal inlet, and salinity were the primary environmental determinants of Southern Flounder distribution and abundance. Because distribution and response to environmental conditions can depend on population abundance, we also developed a standardized index of annual abundance using the same two‐stage boosted regression tree model. The index identifies a long‐term decline in abundance punctuated by recent recovery (possibly in response to management actions). Mapped results identify a coastwide decline in abundance between 1980–1984 and 2005–2009 but the magnitude varied substantially, suggesting disproportionate changes in abundance across the study area. Received April 10, 2015; accepted July 28, 2015

Mesoscale climatic impacts on the distribution ofHomarus americanusin the US inshore Gulf of Maine

“…Final GAMs were also used to project how lobster distribution may change under two thermally contrasting climatologies (Sagarese et al 2014). Predictive fields were interpolated using ordinary kriging to describe spatial variability in lobster catch density (Froeschke and Froeschke 2016;Tanaka et al 2017). Ordinary kriging procedures were conducted via the automap package (Hiemstra et al 2008) and kriged maps were prepared at 0.03 × 0.03 latitude/longitude grid.…”

Predicting the spatial abundance of Ixodes ricinus ticks in southern Scandinavia using environmental and climatic data

“…The repeated CV predictions in a BRT model is the average taken from many models, thus the models tend to overestimate low values and underestimate high values 53 . To overcome this problem, we explored splitting the data into a presence/absence binomial (Bernoulli) BRT model and a log-transformed presence only Gaussian BRT 53,54 , however the resulting ensemble models performed much poorer than the one-model approach and were therefore abandoned.…”

Assessing the relative importance of temperature, discharge, and day length on the reproduction of an anadromous fish (Alosa alosa)

“…The impact of global warming on reproduction will depend on the magnitudes of these environmental changes in the freshwater habitat and on the ability of shads to adapt to them (Foden et al, 2019). However, low abundance will enhance the sensitivity of these populations to environmental stress (Froeschke & Froeschke, 2016;Hidalgo et al, 2011). However, low abundance will enhance the sensitivity of these populations to environmental stress (Froeschke & Froeschke, 2016;Hidalgo et al, 2011).…”

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