Remotely sensed red tide features and their relationship with recreational king mackerel catch off west-central Florida

A strong red tide caused by the toxic dinoflagellate Karenia brevis was present off of the central West Florida Shelf from January through at least November 2005. A new technique to use solar stimulated phytoplankton fluorescence, from the MODIS Fluorescence Line Height (FLH) data product, was used to remotely sense phytoplankton concentrations in the ocean surface. Algorithms to detect frontal features in satellite-derived FLH, chlorophyll concentration, and turbidity images were used to study the linkages between recreational catch of king mackerel (Scomberomorus cavalla or kingfish) and red tides in coastal waters off west-central Florida. The FLH data were used to characterize the spatial distributions of the red tide and its features over the course of 2005. FLH data allowed clear identification of chlorophyll patches as opposed to darker waters related to river discharge along the coast. A Geographical Information System (GIS) tool was used to examine spatial relationships between catch data and ocean fronts, bathymetric features, the presence of baitfish, and the stability of fronts over the three-day period leading up to the tournaments. There was a strong correlation between the presence of baitfish and kingfish catch rates, and catch rates decreased in more turbid waters identified in ocean color imagery. Concurrent with the 2005 red tide event a significant decrease in kingfish catch was found in the fall of 2005 (208 kingfish) compared to spring 2004 (444) and 2005 (538), and fall 2004 (818). Percentages of fishing locations where baitfish were observed also decreased in the fall 2005 (38%) compared to spring 2004 (54%) and 2005 (51%), and fall 2004 (54%). Quantifying the relationships between kingfish catch and its forage is an essential step in forming ecosystem-based management strategies. Satellite data is important in defining ecosystem-scale connections.