398 



Fishery Bulletin 101 (2) 



PAMLICO 

 UPPER 



[ [[ 18Mar 



n= 3 



^-U 



MID-LOWER 



* ^ ,* 



n=78 



J^-M 



~i 1 1 1 1 r 



-+- 



n=70 

 n = 47 



10 20 30 40 50 60 70 



Standard length (mm) 



Figure 11 



Atlantic croaker length frequencies in general areas of the Pamlico Sound, NC, estuary by sampling week, March- 

 June 1987. Solid dots represent mean SL. 



previous mortality estimates are likely confounded by emi- 

 gration because measures of declining fish numbers were 

 extended longer into the nursery season (through August, 

 Weinstein and Walters, 1981; through October, Currin et 

 al., 1984; through July, Miller et al., 1985). 



Growth in weight (weight-length relationships) also in- 

 dicated advantages of oligohaline habitats for these fishes. 

 Higher weights per length have been equated with greater 

 fitness (Friedland et al, 1988; Bolger and Connolly, 1989). 

 Improved fitness was suggested by a consistent trend for 

 individuals of both spot and Atlantic croaker in both sys- 

 tems to be heavier per length in the oligohaline creeks. 

 Laboratory experiments on spot (Moser, 1987) resulted in 

 heavier fish per length in freshwater, and the weight differ- 

 ence was attributed to a higher feeding rate in freshwater, 

 rather than water absorption because of osmotic imbal- 

 ance. Spot from oligohahne areas of the James River, VA, 

 were heavier per length compared to those from several 

 other estuaries (McCambridge and Alden, 1984), but the 

 role of salinity in these differences was unclear. Peterson 

 et al. (1999) indicated that reduced salinity itself caused 

 higher growth rates (in weight) for Atlantic croaker in oli- 

 gohaline conditions. 



Growth (in length) rates and size distributions indi- 

 cated that PNA habitats at extreme ends of estuaries were 



equally valuable to both species (with one exception). The 

 exception — depressed spot growth rates in the upper Pam- 

 lico area — did not appear to be correlated with lower sa- 

 linities or temperatures because spot from other areas with 

 low salinity and similar or lower temperatures exhibited 

 higher growth rates. The most obvious difference between 

 upper Pamlico creeks and all other areas was the extremely 

 long (often >100 km) estuarine migration required to reach 

 them. Potential costs involved in such migrations should 

 be examined as should the degree to which the lower spot 

 growth rates persisted into later life. General lack of growth 

 rate variation between oligohaline and polyhaline habitats 

 suggested that salinity (and probably tidal influence) did 

 not affect growth to a degree detectable in the present study. 

 This conclusion is supported by previous studies (Moser and 

 Gerry, 1989; Moser and Hettler, 1989; Miller et al., 2000) 

 despite a general prediction that fish growth rates should 

 be higher in brackish waters (Boeuf and Payan, 2001). 

 The lack of evidence for negative effects of fish density on 

 growth (Ross, 1992) indicated that resources in oligohaline 

 or polyhaline PNAs may not limit these fishes. Currin et al. 

 ( 1984) also suggested that food resources did not limit spot 

 production in middle areas of Pamlico Sound. 



Lack of spatial variation in early estuarine growth rates 

 was also found in the few relevant studies available. Wein- 



