Powles and Warlen; Recruitment season, size, and age of /^Dyu/Z/o /os^/o/o entering an estuary near Beaufort 



305 



The difference in estimated mean age of 8 days from 

 glass-eel growth zones at two North Carolina locations 

 about 9.5 km apart implies that upriver movement was 

 about 1 km a day, much of which could be tidal. We do not 

 know whether or not this rate of movement is reasonable 

 or tjrpical. 



The mean age from our glass-eel growth zones on oto- 

 liths of glass eels agreed with the ages determined from 

 other glass eels collected in North Carolina (Wang and Tz- 

 eng, 1998). 



Finally, the apparent total ages and glass-eel ages from 

 North Carolina, New Jersey, and New Brunswick support 

 the hypothesis that eels are progressively older to the 

 north, and are consistent with their greater distance from 

 the Sargasso Sea. 



Total age estimates of glass eels can be compared with 

 those from two other studies of American eel. Our average 

 total age of glass eels from Black Creek (175 d) was 14% 

 older than the 153 d that Budimawan (1996) found for the 

 same location, date, and year. On the other hand, estimated 

 total ages of glass eels were considerably less (20-22'>; ) than 

 the ages obtained by Wang and Tzeng (1998) for eels from 

 the same general areas (but different dates). Because ages 

 from glass-eel growth zones (as opposed to total age) were in 

 very close agreement with those of Wang and Tzeng (1998), 

 one assumption for this inconsistency in total age is a dif- 

 ference in intei-preting age in either the leptocephalus or 

 metamorphic zone. It is also possible that increments <0.3 p 

 wide may not have been distinguishable by light microscopy, 

 which could account for our ages being younger than those of 

 Wang and Tzeng ( 1998), who used SEM. Antunes and Tesch 

 1 1997) have also suggested that these two methods of otolith 

 observation may produce different results. It is conceivable 

 that increments in the leptocephalus growth zone may be 

 laid down in fewer numbers in some seasons, but it seems 

 unlikely that low water temperatures would cause a cessa- 

 tion of otolith increment deposition, because the Gulf Stream 

 top 200-m layer (the assumed habitat of leptocephali ) main- 

 tains an annual temperature above 16°C (Stommel, 1965). 

 Absorption of increments during metamorphosis ( Cieri and 

 McCleave, 2000) is possible, but our studies could not shed 

 any light on this proposed phenomenon because all lepto- 

 cephali had metamorphosed before reaching North Caroli- 

 na. Obviously, there is consistent agreement among authors 

 in incremental counts of glass-eel growth zones, which are 

 wide and clear, and therefore easy to count. 



Regardless of the discrepancy in age estimates of larval 

 eels, evidence from the rate of transport of other species 

 in the Gulf Stream suggests that once they have reached 

 the Gulf Stream, it is possible for leptocephali to reach 

 the continental shelf of North Carolina in about 110 days. 

 A NOAA (National Oceanic and Atmospheric Administra- 

 tion) sea drifter released in 1996 west of the western edge 

 of the Sargasso Sea in 1996 and travelling just inside the 

 western front of the Gulf Stream at 100 m depth reached 

 the North Carolina outer continental shelf in 50 days. Its 

 release site appears to overlap stations where leptocephali 

 of A. rosti-ata were captured (Wippelhauser et al., 1985; 

 Kleckner and McCleave, 1985). Larvae of several fish spe- 

 cies from Florida waters are known to reach the area off- 



shore North Carolina in 25-30 d (Hare and Ahrenholz).! 

 For example, larval Atlantic menhaden (Brevoortia tyrcin- 

 nux) that spawned offshore from Beaufort in an area close 

 to the path of the sea drifter reached the estuary near 

 Beaufort, North Carolina, in an average of 60 d (Warlen, 

 1994). This estimate of across-continental shelf transport, 

 when added to the 50 d of travel for the sea drifter, gives an 

 elapsed time of 110 d. This estimate of transport duration 

 may prove to be useful in the future. 



McCleave et al. (1998) surmised that leptocephali of the 

 European eel (virtually identical in physical structure to 

 A. rostfata ) do not actively .swim toward land during their 

 migration to Europe. Granted that the age increments in 

 the larval zone of the otolith of American eels may not ac- 

 curately depict early life-history duration (Cieri and Mc- 

 Cleave, 2000), the consistency of recruited lengths and 

 glass-eel ages over the years from 1985 to 1995 is note- 

 worthy. In addition, the annual recruitment seasons and 

 sizes observed in coastal North Carolina and New Jersey 

 regions (Able and Fahay, 1998) reveal a remarkably consis- 

 tent sequential latitudinal pattern. It appears that current 

 data on seasonal recruitment of young eels should contin- 

 ue to be used to examine temporal relationships between 

 geographical areas and oceanic transport times from the 

 spawning area (Sargasso Sea) to the estuaries. 



Acknowledgments 



We thank Betsy Laban for sectioning and for instruction 

 in processing initial samples of otoliths. Beverley Powles 

 removed and prepared the remainder of our otoliths. 

 Dick Peterson, Department of Fisheries and Oceans, St, 

 Andrews, procured our New Brunswick sample. Kenneth 

 Able furnished the New Jersey sample. Dean Ahrenholz 

 provided advice and aging facilities at the Beaufort Labo- 

 ratory. We also thank Trent University for research support 

 and facilities. The (then) Director of the Beaufort Labora- 

 tory, Bud Cross, offered facilities to the senior author, and 

 Director Don Hoss suggested valuable comments on the 

 manuscript. A number of other staff members, were very 

 helpful: in particular Curtis Lewis (figures), David Colby 

 ( statistics ), Peter Hanson ( SAS ), Patti Marraro ( literature), 

 Jon Hare (seabed drifter, oceanographic current patterns), 

 Jeff Govoni (manuscript), and Allyn Powell (anguillid biol- 

 ogy). Martin Castonguay offered helpful comments, as did 

 Raymonde Lecomte. Yves Desaunay provided information 

 on the "transition ring" in the European eel, and Jim 

 McCleave offered many obsei-vations and suggestions. We 

 also thank the anonymous referees of the manuscript. 



Literature cited 



Able, K. W., and M. P. Fahay. 



1998. The first year in the life of estuarine fishes in the 

 Middle Atlantic Bight: chapter 6. Anguilla rostrata (Le- 



' Hare,J.,andD. Ahrenholtz. 1996. Personal comniun. Center 

 for Coastal and Fisheries and Fisheries Habitat Research, 101 

 Pivers Island Road, Beaufort, NO 28516-9722. 



