Miller et al.: Distribution, abundance, and growth of Micropogonias undulatus 



101 



of growth in estuaries along the Atlantic coast and 102- 

 250 mm TL in the Gulf of Mexico (Knudsen and Herke, 

 1978), but only a few studies have reported seasonal 

 growth rates (Hansen. 1969; Knudsen and Herke, 1978). 

 Length-frequency based growth rate estimates for the 

 first year of growth for YOY along the Atlantic coast have 

 ranged from 0.32 to 0.41 nim/d ( Knudsen and Herke, 1978). 

 However, these were based on the entire year, including the 

 larval and early juvenile period when analysis of otolith 

 daily growth rings indicates much slower growth rates of 

 0.18-0.41 mm/d during the fall and winter months (Nixon 

 and Jones, 1997). Length-frequency data from estuarine 

 nursery areas clearly indicate that most growth occurs 

 during the spring and summer months (Haven, 1957; Chao 

 and Musick, 1977; Ross, 1988; Able and Fahay 1998). 



Despite various studies of YOY Atlantic croaker in some 

 areas of the Atlantic and Gulf coasts, there is relatively 

 little known of their early life history near the northern 

 part of their range in the MAB and this is especially true 

 for Delaware Bay. Our four-year study used extensive 

 collections in Delaware Bay and in adjacent tidal marsh 

 creeks to describe the timing of Atlantic croaker ingress, 

 their seasonal abundance and size, growth rates, and the 

 timing of their egress out of the marshes. 



Methods 



Study sites 



Delaware Bay is the estuary of the Delaware River and 

 encompasses about 1878 km^ of open water along the 

 southern edge of New Jersey and the northern edge of 

 Delaware (Fig. 1). It has a relatively deep area (10-30 m) 

 in the middle of the lower bay, bordered by narrow shoals 

 and flanked by extensive tidal flats and salt marshes, 

 which contain an additional 85.5 km- of open water in 

 tidal creeks bordered by approximately 640 km- of marsh- 

 plain area. Depending on the amount of river discharge, 

 salinities range from 30-31%f at the mouth of the bay, to 

 1-10'^f in the lower Delaware River (Table 1; Cronin et al., 

 1962; Garvine et al., 1992). 



Ichthyoplankton survey 



Catch data from an ichthyoplankton survey (Table 2) was 

 used to analyze the distribution, abundance, and size of 

 larval Atlantic croaker in Delaware Bay and the lower 

 Delaware River from April to October 1996. Sampling was 

 performed during daylight hours once a month in April 

 and October and twice a month from May to September 

 Each sampling period included one tow at 70 randomly 

 selected stations distributed among eight designated sam- 

 pling zones (Fig. 1). Samples were collected with a 1-m 

 diameter plankton net (0.5-mm mesh) deployed with a 

 depressor in single stepwise oblique tows from the surface 

 to the bottom. Tows were made at a speed of 1.4-1.9 knots 

 for four to six minutes in the direction of the tidal flow. Up 

 to 50 individuals were measured to the nearest millimeter 

 total length (TL) from each sample. 



DELAWARE 



4 



15 km 



Scale 



Figure 1 



Locations of salt marsh tidal creek sampling sites (1996-99) and 

 designated sampling zones (1-8) in the Delaware Bay and in the 

 lower Delaware River for the ichthyoplankton (April-October 

 1996) survey and the otter trawl (April-October 1996-98) survey. 

 The heavier line across the bay indicates the boundary between 

 the upper (5-8) and lower ( 1-4) sampling zones and marsh sites. 



Otter trawl survey 



We used catch data from a three-year otter trawl survey 

 (Table 2) to analyze the distribution, abundance, and 

 growth of settled YOY Atlantic croaker in Delaware Bay 

 and the lower Delaware River Sampling was performed 

 during daylight hours twice a month from April to Octo- 

 ber in 1996 and once a month in 1997 and 1998, at 40 

 stations divided up among the same eight sampling zones 

 of the ichthyoplankton survey (Fig. 1). Station locations 

 were selected by using a stratified random sampling 

 design from a grid of 1002 stations, excluding the stations 

 over the deepest water near the mouth of the bay in zone 

 1. There were eight stations sampled each month in zone 

 3, six in zone 4, and four in all the other zones. Trawling 

 was done with 4.9-m otter trawls (6 mm stretched codend 

 mesh), made against the prevailing direction of the tide 

 at a speed of 1.8 m/sec for 10 minutes. Up to 100 individu- 

 als were measured from each sample. For presentation 



