Relationships between Juvenile Winter Flounder and Multiple-Scale Habitat Variation in Narragansett Bay, Rhode Island

Abstract

A rapid random sampling method was used to relate densities of juvenile winter flounder Pseudopleuronectes americanus to multiple scales of habitat variation in Narragansett Bay and two nearby coastal lagoons in Rhode Island. We used a 1-m beam trawl with attached video camera, continuous global positioning system track overlay, and continuous recording YSI sonde to sample 163 sites in June and July 2002 and 2003. The YSI sonde recorded temperature, salinity, dissolved oxygen, depth, turbidity, and chlorophyll a throughout the tow, while the video camera recorded other habitat characteristics. Habitat patterns at larger spatial scales were assessed with aerial imagery and charted depth data. We caught 25 species and 977 fish, almost twice as many fish being captured in 2002 (596) as in 2003 (381). Winter flounder was the most common species in both years, comprising 60.2% of the catch in 2002 and 33.6% of the catch in 2003. Total fish and winter flounder were three times more abundant in the coastal lagoons than in the bay. We used stepwise multiple regression to develop a general model (all variables, including those affecting catch efficiency) and a habitat model (only habitat variables) describing the relationship between habitat quality and juvenile winter flounder density. The results of the stepwise regression on the general model explained only about 25% of the variability in catch, but they suggested that winter flounder densities were higher at sites in coves and that densities increased with human population density, greater percentages of algal cover, and higher percentages of mud. Densities were negatively correlated with dissolved oxygen and chlorophyll a. In the habitat model (r ² = 0.16), densities were higher in coves, at sites with marsh or beach edges, and at sites with human disturbance. Similar to the general model, densities increased with algal cover and decreased with dissolved oxygen. At larger spatial scales, shorelines dominated by beaches and habitat diversity (as calculated by Simpson's diversity index) were positively correlated with higher juvenile winter flounder densities. Overall, the results suggested that juvenile winter flounder were most abundant in coves and upper estuaries. We conclude that these areas may provide beneficial nursery habitat for winter flounder despite apparent human disturbance.