148 William F. Hettler, Jr. 



On board the vessel, larvae were preserved in 70% ethyl alcohol. In the 

 laboratory, larvae were sorted by species and counted. Up to 10 larvae of each 

 species from each tow were measured to the nearest 0. 1 mm standard length. Lar- 

 val abundance was calculated as the number per 100 m 3 and plotted as the week- 

 ly mean density (± 1 standard error) of the individual tow densities by inlet and 

 date. Lengths were plotted as the mean standard length of up to 1 20 larvae of 

 each species at each inlet each week (± 1 standard error). 



Wilcoxon rank sum tests were used to compare densities of species 

 between inlets. To examine the relative contribution by inlet for each species, the 

 seasonal weekly density by species for Oregon Inlet and Ocracoke Inlet was 

 compared with data collected during the same period in a separate study at Beau- 

 fort Inlet (Warlen 1994; S. Warlen, NMFS Beaufort Laboratory, personal com- 

 munication). For this comparison, it should be recognized that the Beaufort Inlet 

 study results are used as proxy data in the absence of data collected with the same 

 methods as at Oregon and Ocracoke inlets. In the Beaufort study, a 2-m 2 , 1000- 

 micron-mesh neuston net was fished passively in the tidal current at the surface. 

 In both studies, however, the data were standardized to densities per unit volume 

 by the use of flow meters. 



RESULTS AND DISCUSSION 

 TEMPERATURE AND SALINITY 



The inlets were similar in temperature, except that Ocracoke Inlet 

 warmed at a faster rate after late February than did Oregon Inlet (Fig. 2). Dur- 

 ing February, when abundance of most larval species was low, temperature at 

 both inlets dropped to less than 5C. 



Salinity as high as 33 ppt was observed twice at Ocracoke Inlet, once 

 in late autumn and once in early spring, a time when salinity at Oregon Inlet was 

 about 20 ppt. Salinity at Oregon Inlet was always 5-20 ppt lower than Ocracoke 

 Inlet and in February was as low as 4 ppt. Salinities lower than 10 ppt in Oregon 

 Inlet in combination with low temperatures occurred eight times. The physio- 

 logical consequences of low salinities and temperatures on ocean-spawned lar- 

 vae is only partially known. For example, Brevoortia tyrannus (Atlantic men- 

 haden) larvae died in laboratory experiments at salinities <5 ppt and tempera- 

 tures <5 C. In these experiments, however, 50% mortality in <48 hours also 

 occurred at high salinity (30 ppt) and low temperatures (<5 C) (Lewis, 1966). In 

 other laboratory experiments, Leiostomus xanthurus (spot) were determined to 

 be more cold sensitive at 10 C than Micropogonias undulatus (Atlantic croaker), 

 but test salinities were not given (Hoss et al. 1988). Their study concluded that 

 during severe winters many early arriving larvae in estuaries are killed and that 

 only late arriving larvae survive for recruitment into the fishery. 



Twice at each inlet, the temperature difference between the surface and 

 bottom water equaled or exceeded 1 C in the 7-m-deep channel, but generally 



