Transactions of the American Fisheries Society 125:803-808, 1996 © Copyright by the American Fisheries Society 1996 Spatial Patterns in Condition and Feeding of Juvenile Weakfish in Delaware Bay PAUL A. GRECAY 1 AND TIMOTHY E. TARGETT University of Delaware, College of Marine Studies, Lewes, Delaware 19958, USA Abstract.—Juvenile weak fish Cynoscion regalis were collected during July 1986 in Delaware Bay. Fish, rang- ing in size from 40 to 84 mm standard length, were analyzed for weight at length as a measure of condition and for gut fullness as a measure of feeding success. These data were compared among collections from the head of the estuary, the midbay region, and the mouth of the estuary. Condition and gut fullness were generally highest in the midbay region, lowest in the upper bay, and intermediate in the lower bay. The proportion of the diet consisting of mysids was also compared among the upper, mid, and lower bay collections. The mysid shrimp Neomysis americana dominated the diet in all bay areas. Despite their ubiquitous distribution throughout the es- tuary, the proportion of the diet consisting of mysids was generally highest in the middle bay, lowest in the upper bay, and intermediate in the lower bay. The upper bay is characterized by high turbidity and low illumi- nation. These turbidity levels frequently extinguish all light on the bottom where juvenile weak fish feed and may reduce prey visibility and feeding success, causing reduced growth and condition in the upper bay. Patterns in feeding and condition suggest that growth rates may also vary spatially. Because feeding and growth are pre- sumed important to survival and recruitment, it is pos- sible that some bay nursery areas may potentially con- tribute more to recruitment. The Delaware Bay estuary is an important spawning and nursery area for weakfish Cynoscion regalis (Colton et al. 1979; Grimes 1984). Dela- ware Bay has a mean depth of 4.2 m, broad shallow marginal areas less than 5.5 m deep, and a deeper (12.2 m) midbay channel (Hulburt 1957). From the mouth to 80 km upstream, temperatures and salinities range from 19 to 27°C and 31.6 to 5.8%o, respectively. The upper limit of saline water is about 120 km from the mouth (Sharp 1984). A turbidity maximum occurs about 80 km upstream from the mouth (Gibbs et al. 1983; Pennock and Sharp 1986; Fisher et al. 1988). Juvenile weakfish shorter than 70 mm standard length (SL) are common in Delaware Bay from July to September (Cole et al. 1988) and are abun- 1 Present address: Department of Biological Sciences, Henson School of Science and Technology, Salisbury State University, Salisbury, Maryland 21801-6837, USA. dant at the head of the estuary where they con- centrate near the bottom (Thomas 1971; PSEGC 1984a). It has been suggested that features such as physicochemical conditions, prey availability, and predators influence the feeding, growth, sur- vival, and recruitment of juvenile fishes (Joseph 1973). Subtle differences among factors that in- fluence feeding and growth in the early life of fishes are believed to have significant effects on survival, recruitment, and year-class strength (Houde 1989; Fogarty et al. 1991). In laboratory investigations, physicochemical factors, such as temperature and salinity typical of estuarine nurs- ery areas like Delaware Bay, were shown to sig- nificantly affect feeding, growth rates, and growth efficiencies of juvenile weakfish (Lankford and Targett 1994). Spatial heterogeneity of factors that influence feeding and growth may be reflected in condition and feeding of juveniles caught in dif- ferent bay areas. Spatial patterns in condition are known for esocids (Craig and Babaluk 1989) in freshwater lakes and for juvenile fishes that occupy estuaries (Sogard 1992). Owing to nutritional prof- itability, differences among habitats may result in spatial differences in growth. The objective of this field investigation was to find out whether juvenile weakfish vary spatially in feeding, size, and con- dition in Delaware Bay. Methods We collected juvenile weakfish with an otter trawl (4.6-m width, 2.5-cm-stretch-mesh body, 19-mm-stretch-mesh cod end, 6.4-mm-mesh cod end liner) during July 1986 at seven stations dis- tributed over 85 km from the mouth of the bay to the Chesapeake-Delaware Canal (Figure 1). We towed the trawl for 10 min at each station and repeated tows until at least 40 juveniles were col- lected. We weighed all fish to the nearest 0.1 g, measured them to the nearest 0.5 mm SL, and later analyzed the entire sample for spatial patterns in length, gut fullness, condition, and dietary com- position. For stomach analysis, we drew a sub- sample from the catch at each station by dividing the catch into 5-mm size-classes (40-44, 45-49, 50-54, 55-59, 60-64, 65-69, and 70-74 mm) and 803