Ross: Relative value of different estuanne nursery areas for juvenile marine fisfies in North Carolina 



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Standard length (mm) 



Figure 10 



Atlantic croaker length frequencies in general areas of the Cape Fear, NC, estuary by sampling week, March-June 1987. Solid dots 

 represent mean SL. 



Walters (1981) found consistently high mortality for spot 

 in polyhaline creeks during two years, but variable mortal- 

 ity between years (one year higher, one year lower) in low 

 salinity regions. Mortality rates reported in the present 

 study may not be affected by fish density (Ross, 1992), and 

 it is unlikely that starvation (Currin et al., 1984) played a 

 major mortality role. Predation may cause most of the PNA 

 natural mortality; it was previously proposed that preda- 

 tion rates were lowest in oligohaline habitats because these 

 areas contained relatively fewer predators (Weinstein and 

 Walters, 1981; Currin et al., 1984; Miller et al., 1985). This 

 hypothesis continues to lack direct, convincing evidence. 

 Predators in oligohaline habitats (e.g. southern flounder, 

 catfishes, gar, striped bass, etc.) may, in fact, be just as 

 numerous near the upriver nurseries (author's pers. obs.; 

 Patrick and Moser, 2001; Moser"*) as marine predators are 

 around polyhaline creeks. Also, because water levels in the 

 upriver creeks, especially in the Pamlico, do not vary as 

 much as in polyhaline areas, predators may have more op- 

 portunity to use these creeks (Currin et al., 1984). 



* Moser, M. L. 1998. Personal commun. NW Fisheries Science 

 Center, NMFS, 2725 Montlake Blvd., Seattle, WA 98112 . 



One alternative explanation for lower mortality esti- 

 mates in upriver PNAs is that mortality could be related, 

 perhaps indirectly, to ambient salinity. Although freshwa- 

 ter conditions probably do not increase mortalities of these 

 fishes (Moser and Hettler, 1989), there may be negative 

 effects of high salinity on survival that have not been in- 

 vestigated. Moser and Hettler (1989) reported that spot 

 exhibited the highest respiration rates in high salinity 

 conditions, which suggest increased stress. 



Another potential explanation is that fishes may leave 

 high salinity areas more rapidly than freshwater areas. 

 Although 1 attempted to minimize effects of emigration on 

 mortality estimates by limiting the analyses to the period 

 before mid-June, the mortality rates 1 calculated could have 

 contained an unknown effect of emigration. Other studies 

 (Weinstein, 1983; Weinstein and O'Neil, 1986; Miller and 

 Able, 2002; author's pers. obs. ) supported my assumption 

 that emigration of spot and Atlantic croaker from PNAs 

 was negligible at least through June. Such early habitat 

 fidelity seems to be a common trait among juvenile fishes 

 (Rountree and Able, 1992; Ross and Lancaster, 2002). Many 

 individuals of OWS juvenile fishes leave PNAs by July 

 (Ross, 1988; NC Division of Marine Fisheries^); therefore, 



