108 



Fishery Bulletin 101(1) 



DT LMB UMB CT BR MHC MC 



Lower Bay Sites 



Upper Bay Sites 



Figure 7 



Combined overall average catch per unit of effort (CPUE= 

 fish/2 min. tow |±SEM]) of young-of-the-year Atlantic 

 croaker {Micropogonias undulatus) collected by otter 

 trawl at the Dennis Township (DT), Lower Moores Beach 

 (LMB), Upper Moores Beach (UMB), Commercial Town- 

 ship (CT), Browns Run (BR), Mad Horse Creek (MHC) 

 and Mill Creek (MC) marsh sites during the fall ingi'ess of 

 four years 11996-99) and of post-ingress croaker (April to 

 November 1997-99). 



Bay was higher in the upper bay, which has muii sedi- 

 ments in most areas, and was much higher in 1998 than 

 in 1997. The monthly CPUE in the upper bay peaked in 

 July or August, but in the lower bay it peaked in October 

 of both years (Fig. 6). The combined CPUE values in the 

 upper and lower bay zones were different between the two 

 regions in both 1997 and 1998 (P<0.001) and the catches 

 within each region were different between the two years 

 (P<0.001). 



During the summer most YOY were collected in areas of 

 Delaware Bay that had muddy sediments (Fig. 9). In the 

 upper bay zones 7 and 8, which likely have mostly pure 

 mud sediments, YOY were collected at 829f of the stations. 

 In contrast, they were absent in the deeper, large central 

 area of the lower bay that has predominantly sandy and 

 gravelly sediments. However, in the shallow portion of 

 the lower bay, sandy mud, muddy sand, and gravelly mud 

 sediments appear to be distributed on both sides of the 

 bay, and YOY were almost exclusively collected over or 

 near these substrates from April to August, 



Growth 



Although YOY Atlantic croaker showed rapid growth 

 during the summer, there was no evidence of growth 

 during the winter. The median growth rates for YOY 



10000 ' 1997 



1000 



100 

 10 



1 



0,1 



1997  



I — I 

 n = 803 



All 



1996-97Year class 

 1997-98 Year class 



n = 4,001 



H 



-H 



10000 I 1998 



1000 1 

 100 1 n = 3,167 



10 



a. 

 o 



1 



1 



10000 - 1999 



1000 \ 



100 



10 



1 



\l 



1997-98Year class 

 1998-99 Year class 



n= 1,544 



^JJIJ 



1998-1998Year class 

 1999-2000 Year class 



n = 24 



n = 9,378 



0.1 



i_Ll 



APR MAY JUN JUL AUG SEP OCT NOV 

 Montti 



Figure 8 



Catch per unit of effort (CPUE, fish/set) of four year classes 

 of young-of-the-year Atlantic croaker (Micropogonias 

 undulatus) caught each year in the two monthly weir sets 

 across small intertidal creeks at the Dennis Township 

 marsh site in the lower bay during the fall ingress (white 

 bars) and during spring and summer of the following year 

 (black bars). 



Atlantic croaker calculated for two- to five-month periods 

 beginning in May were fast and ranged from 0.5 to 1,.5 

 mm/d (Table 3), They were slightly higher in the bay than 

 in the marshes (avg,=l,2 mm/d in the bay and 0,9 mm/d 

 in the marshes) and were lowest in 1998 when Atlantic 

 croaker were most abundant. The growth rates dropped off 

 in the marshes when calculated from May to September or 

 October (Table 3), The lowest early summer growth rates 

 occurred in the tidal creeks in the lower bay in 1998 when 

 the CPUE was the highest. The gi-owth rates in the upper 

 and lower regions of Delaware Bay were similar in each 

 year, but as in the lower bay marshes, the values were 

 lower in 1998 when YOY were much more abundant. Linear 

 regressions of the median lengths used to calculate these 

 growth rates showed that median length was strongly cor- 

 related to date (P=0.02-0.001) and illustrated the slightly 

 slower growth rates at the lower bay sites in both 1997 

 and 1998 (Fig. 10). These pairs of regression lines were not 

 significantly different (ANCOVA) for upper and lower bay 

 regions of either the marsh sites in 1997 (P=0.1), or in the 

 bay in 1998 (P=0.6), except in 1998, when a lower growth 

 rate was indicated at the lower bay marsh sites (P=0.03). 

 In 1999, a similar linear progi-ession of median lengths was 

 observed in the lower bay marshes (r-=0.98), but sample 

 sizes were too small in the upper bay for growth-rate cal- 

 culations. Although there was no sampling in the winter, 

 the length-frequency distributions indicated that most fish 

 collected in April in the bay and marshes were the same 



