Tidal tributaries and nearshore areas as nursery habitat for juvenile sciaenid fishes and other estuarine nekton in Delaware Bay and the Delaware Coastal Bays

Estuaries have been widely recognized to contribute significantly to the productivity of coastal fisheries. Numerous species, often described as estuary-dependent, use estuarine habitats as nurseries during their early life stages. The physicochemical and biological attributes of estuarine nursery habitats stimulate rapid growth and enhance survival of young fishes, improving the chances of successful recruitment to the adult population. However, estuaries are often subject to anthropogenic alterations and severe impacts on water quality, which threaten the value of these habitats as nurseries. Identification and conservation of the most functionally important nurseries is, therefore, critical for fishes to maintain the productivity needed to contribute ecologically to aquatic ecosystems. In this study, I examined the use of tidal tributaries and nearshore areas as nursery habitat for several young-of-the-year (YOY) estuary-dependent fishes and other estuarine nekton, as well as the functional role of these habitats as nurseries for YOY weakfish (Cynoscion regalis ) in particular to gain a better understanding of the dynamics of estuarine habitat quality.;Chapter 1 is an introduction to the concept of estuaries as nursery habitats, the importance of identifying essential fish habitat, and the environmental conditions and biological interactions that ultimately determine fish habitat quality. Chapter 1 also provides background information regarding fish usage of Delaware Bay and the Delaware Coastal Bays, with particular focus on YOY of the family Sciaenidae, and outlines the overall objectives of this study.;Chapter 2. I investigated the spatiotemporal patterns of numerical and biomass density of YOY sciaenid fishes collected from tidal tributary and nearshore habitats in Delaware Bay to better define nursery habitat quality for the early life stages of fishes in this family. Results illustrate patterns of nursery habitat use by sciaenids in Delaware Bay, how these patterns vary among species, and how these patterns can be temporally variable. In general, sites in the upper bay appear to provide YOY Atlantic croaker with the most important nursery habitats, while the Simons site in the upper-mid bay appears to be the most valuable for YOY weakfish. The observed spatial partitioning of preferred nursery habitats between species seemed to be directly related to differences in salinity preference.;Chapter 3. To gain a better understanding of the functional value of these tidal tributary and nearshore areas as nurseries, I examined the spatial and temporal patterns of YOY weakfish biomass, growth, production, and food habits at the same sites in Delaware Bay over the same three nursery seasons (2005-2007). The results of this study suggest that the Simons and Mispillion sites in the upper-mid and lower bay, and the nearshore habitats of these sites in particular, provide the most functionally important nurseries for YOY weakfish in Delaware Bay. The good growth, high biomass and high production at both of these sites appear to be primarily driven by a combination of optimal physicochemical conditions and a productive forage base. However, reduced resource availability in mid-summer had profound effects on the productivity of these and other nursery habitats in Delaware Bay, reducing the overall quality of nurseries during that time period.;Chapter 4. In this chapter, I used quantitative sampling to examine the seasonal and spatial dynamics of the shore zone and shallow subtidal fish and blue crab (Callinectes sapidus) assemblage structure across a gradient of anthropogenic and oceanic influence in three adjoining marsh creeks in the Delaware Coastal Bays. Results of this study indicate that the shore zone of marsh creeks in the Delaware Coastal Bays provides valuable habitat to fish and blue crabs, but variations in anthropogenic influence can affect habitat quality and alter the associated fish and blue crab assemblage. (Abstract shortened by UMI.)...