Effects of Winter Temperature and Flow on a Summer–Fall Nursery Fish Assemblage in the Chesapeake Bay, Maryland

—In temperate estuaries, nearshore nursery fish assemblages are influenced by environmental conditions that are present during and prior to the period of juvenile fish occurrence. An intensively sampled site (Patuxent River estuary) in mesohaline Chesapeake Bay provided 9 years of data for relating previous and current environmental variables with juvenile fish assemblages. Canonical correspondence analysis identified temperature and flow from the previous winter (January–March) and week and year of the assemblage sample as the most influential variables. In contrast, environmental variables at the time of sampling were not identified as important. High summer–fall abundances of Atlantic silversides Menidia menidia, striped bass Morone saxatilis, white perch Morone americana, and Atlantic needlefish Strongylura marina were positively associated with low winter temperatures and high winter flows. High abundances of bluefish Pomatomus saltatrix, spot Leiostomus xanthurus, bay anchovy Anchoa mitchilli, and northern puffer Sphoeroides maculatus were associated with low winter flows and high winter temperatures. The mechanisms by which winter conditions affect the summer–fall nursery fish assemblage were not directly addressed in this study, but winter conditions can affect subsequent spring and summer estuarine production, spawning and recruitment phenology, and distributions of juvenile fishes. Fish assemblages in temperate estuaries are strongly influenced by environmental conditions (Attrill and Power 2002; Austin 2002; Jung and Houde 2003). Temporal and spatial variability in temperature, freshwater flow, salinity, dissolved oxygen, and turbidity are known to influence fish assemblage structure (Gunter 1956; Rogers et al. 1984; Szedlmayer and Able 1996; Marshall and Elliott 1998; Whitfield 1999; Akin et al. 2005). Numerous studies on temperate estuarine assemblage structure have focused on relations between current environmental conditions and assemblage structure (Rogers et al. 1984; Szedlmayer and Able 1996; Wagner and Austin 1999; Kimmerer 2002; Thiel et al. 2003), but the effects of prior environmental conditions have received little attention. However, recent evidence indicates that summer–fall fish assemblages in temperate estuaries are structured by environmental conditions present during the previous winter and spring. Miller et al. (2006) showed that in U.S. mid-Atlantic estuaries, winter climate patterns were closely related to interannual changes in winter and spring freshwater flow. In turn, past studies have shown that spring flow influenced early life stages of estuary-spawning species, such as white perch Morone americana and bay anchovy Anchoa mitchilli (Secor 2000; Jung and Houde 2003; North and Houde 2003). Wood (2000) found that the timing of the winter–spring transition influenced subsequent summer–fall nursery fish assemblage structure in the Chesapeake Bay; coastalspawning species (e.g., Atlantic menhaden Brevoortia tyrannus and spot Leiostomus xanthurus) were associated with warm, dry winter conditions, and anadromous species (e.g., striped bass Morone saxatilis and white perch) were associated with cold, wet winter conditions. Supporting these associations, Hare and Able (2007) showed that winter temperature was positively associated with subsequent abundance of Atlantic croaker Micropogonias undulatus. Similarly, Attrill and Power (2002) showed that the North Atlantic Oscillation Index (NAOI), which primarily affects winter conditions, was the most important factor explaining the annual variation in various diversity indices (e.g., species number and Shannon–Weiner index) and individual species’ abundance and growth in the Thames Estuary, UK. Hurst et al. (2004) showed that the Hudson River estuary fish assemblage structure from late August to November was strongly correlated with river flow during the preceding May–July but was not correlated with river flow during the summer–fall sampling period. Jung and Houde (2003) also showed that the assemblage structure in the main-stem Chesapeake Bay during 1997 was influenced by an anomalously high freshwater input during 1996. Understanding estuarine fish assemblage structure requires the sampling of both temporal and spatial * Corresponding author: [email protected] Received April 27, 2007; accepted January 13, 2008 Published online July 10, 2008 1147 Transactions of the American Fisheries Society 137:1147–1156, 2008 Copyright by the American Fisheries Society 2008 DOI: 10.1577/T07-098.1 [Article]