Density, Growth, Production, and Feeding Dynamics of Juvenile Weakfish (Cynoscion regalis) in Delaware Bay and Salt Marsh Tributaries: Spatiotemporal Comparison of Nursery Habitat Quality

Abstract

Biomass, growth, production, and feeding of young-of-the-year weakfish were examined in salt marsh tributary and nearshore habitats of Delaware Bay to describe the dynamic nursery habitat function for this species. Weakfish were collected from June through October 2005–2007 at seven sites in Delaware Bay, each with one nearshore bay station and three stations in an adjacent tributary. Weakfish biomass was consistently highest in the mid-bay, with a shifting peak down-bay in the late stages of the nursery period. Specific growth rates (SGR) ranged from − 2.98 to 9.57% mass day −1 and exhibited a seasonal bimodal pattern of the highest growth in early and late summer. This pattern coincided with that of biomass, suggesting an absence of density-dependent effects on growth. SGR declined in mid-summer and appeared to be associated with reduced stomach fullness. Growth was highest at sites in the mid- and lower bay, and lowest in the upper bay. Variation in instantaneous production primarily reflected trends in biomass, although low growth in August exacerbated a mid-summer production decline. Stomach fullness also declined in mid-summer, suggesting low resource availability. In most cases, fish at sites with high biomass, growth, and production had a higher proportion of mysids in the diet. Both tributary and nearshore areas adjacent to large expanses of salt marsh with abundant mysid resources served as the most important nurseries for juvenile weakfish, though importance of each habitat was temporally dynamic. This study presents a novel approach to quantifying dynamic nursery habitat quality for estuary-dependent fishes during their nursery period.