Ross: Relative value of different estuanne nursery areas for juvenile manne fishes in North Carolina 



395 



Cape Fear area were usually significantly shorter (P<0.05) 

 than those from other areas, and Atlantic croaker from the 

 lower Cape Fear were significantly longer (P<0.05) than 

 those of other areas. 



Atlantic croaker collected from the upper Pamlico creeks 

 were significantly larger {P<0.05) on all sample dates than 

 those occupying any area of the Cape Fear during the same 

 weeks. Within the Pamlico, upper and mid-lower mean SLs 

 were the same (P>0.05) except in the last week when mid- 

 lower mean SL was significantly larger (P<0.05). 



Growth Atlantic croaker ( 12-35 mm SL, n =383 ) ages esti- 

 mated from otoliths ranged from 62 to 234 days, and all 

 age-SL relationships (Fig. 12) were significant (P<0.0001). 

 Residuals of these regressions exhibited no pattern: there- 

 fore, the growth models appeared to be appropriate. The 

 instantaneous daily growth rates within each system 

 were not significantly different (analysis of covariance, 

 P<0.05) between upper and lower areas (Fig. 12). Between 

 systems, upper Pamlico Atlantic croaker grew more slowly 

 than those from the upper Cape Fear (P<0.05). Overall age- 

 length relationships for upper and lower Cape Fear com- 

 bined and for the upper and lower Pamlico Atlantic croaker 

 combined were the following: for Cape Fear — log, gSL = 

 0.915 -I- 0.0027{age ), r2=0.87, n=229: for Pamlico— logj^SL = 

 0.970 -I- 0.0024(age), r2=0.87, n=158. 



The above combined equations for each system were 

 used to calculate age-specific absolute and relative Atlan- 

 tic croaker growth rates (Table 4). Early absolute Atlantic 



croaker growth rates in the Cape Fear system increased 

 most rapidly in ages <105 days, averaging 0.085 mm/d 

 (Table 4). After this age. Cape Fear growth rates increased 

 at a steady, slow rate, reaching 0. 19 mm/d by age 215 days. 

 Relative Atlantic croaker growth rates in the Cape Fear 

 were constant over the whole age range at about 0.63 %/d 

 SL. The larger Pamlico system Atlantic croaker exhibited 

 similar absolute growth rates to Cape Fear fish and these 

 increased rapidly from 0.077 mm/d between ages 60 and 65 

 d to 0.106 mm/d between ages 120 and 125 d to 0.175 mm/d 

 between ages 210 and 215 d (Table 4). Relative growth 

 rates were less than those from the Cape Fear and were 

 constant around 0.56 %/d SL. 



Weight-length relationships for Atlantic croaker were 

 highly significant in all areas (P<0.G001 ) (Table 3). In both 

 systems fish from upper area creeks exhibited significantly 

 larger (P<0.05) weights per length than those from other 

 areas, particularly at the larger sizes (Fig. 13). Slopes of 

 middle and lower Cape Fear weight-length relationships 

 were not significantly different from each other (P>0.05). 



Mortality Catch curves used to estimate Atlantic croaker 

 mortality rates were calculated by using ages >125 days. 

 All regression slopes were significantly different from zero 

 (P<0.0001), although the relationship was more variable 

 for the mid-lower Pamlico area because of the small sample 

 size. Instantaneous mortality rates for Atlantic croaker in 

 the nursery creeks ranged from 0.008 to 0.038 (Fig. 14). 

 Atlantic croaker in the upper and mid-lower Pamlico 



