Using GIS To Identify Spatial Relationships Among Fish Health, Water Quality And Land Use Data     Sandra Page1, John Young1, Vicki Blazer2 and Laurence Pieper3   1Aquatic Ecology Lab, Leetown Science Center, U.S. Geological Survey; 2National Fish Health Laboratory, Leetown Science Center, U.S. Geological Survey; 3Maryland Department of Natural Resources, Stevensville, MD     Recently, a number of fish health issues in wild fish populations have attracted a great deal of public and political attention. In the Chesapeake Bay and its tributaries, these include ulcerative lesions of menhaden, fish kills attributed to Pfiesteria and skin lesions in striped bass due to Mycobacteria sp. Understanding infectious disease outbreaks in wild populations involves identifying both the cause(s) of the problem and predisposing factors or stressors that may influence the pathogen as well as the host. Using the ulcerative skin lesions of menhaden, we will demonstrate how mapping and GIS can be used to better understand fish disease epizootics. Ulcerative mycosis (UM) of menhaden has been known to occur along the East Coast of the U.S. since the 1980’s and probably the 1970’s. There has been much controversy concerning the cause of these lesions, however we have recently demonstrated that fungal hyphae can be consistently observed in the lesions. The pathogen Aphanomyces invadans can be routinely isolated from lesions or demonstrated by PCR. In addition, lesions can be reproduced in menhaden by injection or bath exposure to A. invadans zoospores. This pathogenic fungus also causes Epizootic Ulcerative Syndrome (EUS), a serious mycotic disease of freshwater and estuarine fishes Asia and Australia. Research in these countries has indicated that correlations exist between some water quality parameters and the occurrence of EUS; however, the relative importance of each water quality parameter has varied from study to study. Moreover, studies on EUS have not typically included the use of mapping techniques to identify spatial correlations between water quality, land use and EUS outbreaks. We are currently using GIS (Geographic Information Systems) as a tool for analyzing spatial patterns in EUS prevalence. Specifically, we have investigated the spatial relationships between ulcer frequency (from Maryland DNR) in menhaden of the Chesapeake Bay watershed and four physical water quality parameters: temperature, salinity, pH, and dissolved oxygen. These parameters were analyzed within the context of the conditions that would most likely support the growth and dispersal of the pathogen. Currently, we are also using GIS to link landscape attributes with ulcer frequency, using data collected by USGS on flood events and nutrient point sources.