Abundance exchange models of fish assemblages along the Hudson River Estuary Gradient, New York Nuanchan Singkran and Mark B. Bain ABSTRACT Nuanchan Singkran (corresponding author) Pollution Control Department, Aquatic Ecology and Mathematical Modeling Center Water Quality Management Bureau, Bangkok 10400, Thailand E-mail: ns235@cornell.edu Mark B. Bain Department of Natural Resources, Cornell University, Ithaca, New York 14853, USA The spatially explicit abundance exchange model (AEM) was built for four fish species: winter flounder (Pseudopleuronectes americanus), Atlantic silverside (Menidia menidia), eastern silvery minnow (Hybognathus regius), and striped bass (Morone saxatilis) along the Hudson River estuary gradient, New York. The fish and habitat data during 1974–1997 were used to develop and calibrate the AEM; and the fish data during 1998–2001 was used to validate the model. Preference indexes of fish species for dissolved oxygen, salinity, water temperature, and bottom substrates along the gradient were estimated; and these were used to compute habitat preference (HP) of the associated fish species. The species HP was a key variable in the AEM to quantify abundance and distribution patterns of the associated species along the gradient. The AEM could efficiently predict abundance and distribution patterns of all modeled species except striped bass. The model ability for predicting a local distribution range of a fish species with broad tolerance on changing environment like striped bass should be improved. Key words | distribution, habitat preference, modeling INTRODUCTION In estuaries, gradients of change in physical factors (e.g., salinity, water temperature, and dissolved oxygen) often define the breadth of species distribution in space (Ray & Hayden 1992) and shape species abundance patterns in time. Abun- dance and distribution are influential features indicating population dynamics (Tilman & Kareiva 1997; Turchin 1998) and reflecting habitat utilizations of species (e.g., Winemiller & Leslie 1992; Willis & Magnuson 2000; Jackson et al. 2001; Martino & Able 2003). However, both abundance and distribution are rarely investigated in concert although they are elements of the same problem (Andrewartha & Birch 1954). Studies of species distribution ignore the temporal dimension of population dynamics by taking a snapshot of the spatial density of a population at a certain point in time or by averaging the population density over time. In contrast, studies of abundance ignore the spatial dimension and focus on temporal fluctuations in the number of organisms at a particular point, or the average over a large area (Turchin 1998). In this study, an abundance exchange model was built for four fish species based on fish preferences on changing physical variables along the Hudson River estuary gradient, New York. The objectives of the study were to 1) use key physical habitat variables of the study gradient to model distribution and abundance patterns of fish species in space and time, respectively and 2) explore the local distribution range of each species on the gradient. MATERIALS AND METHODS Hudson River estuary gradient The study gradient started from the river kilometer (RKM) 19 (region 1) in New York City to the RKM 246 (region 12) at Troy’s Federal Dam in Albany, New York State (Figure 1). Water salinity is 18–30 ppt in the lowest zone doi: 10.2166/wst.2008.827 2133 Q IWA Publishing 2008 Water Science & Technology—WST | 58.11 | 2008 Downloaded from https://iwaponline.com/wst/article-pdf/58/11/2133/435892/2133.pdf by guest on 18 November 2018