FISHERY BULLETIN: VOL. 81, NO. 3 



assumed that leptocephali were quickly captured by 

 the Gulf Stream and carried north and east, and it 

 had been unclear how significant numbers of larvae 

 remained in the southern portion of the eel's range. It 

 is remarkable that a majority of the larvae remained 

 so far south for such a prolonged period of time in 

 the simulations. 



Leptocephalus collections have not been made as 

 systematically north of lat. 30°N as they have to the 

 south, so it is difficult to compare the simulation 

 results with the collection data north of this latitude. 

 Kleckner and McCleave (1980, 1982 6 ) stated that 

 American eel leptocephali are abundant in the Gulf 

 Stream from July through September, and the dis- 

 tributions of leptocephali they presented for these 

 months correspond well with the simulation dis- 

 tributions (Fig. 11). 



Up to about lat. 38°N the simulated concentrations 

 formed wide bands along the coast; however, the 

 simulations did not indicate how leptocephali in the 

 eastern edges of the bands would move west towards 

 the coast. The possibility of a behaviorally based, 

 directed movement cannot be dismissed as un- 

 necessary. Alternatively, it could be that these larvae 

 are transported to Europe, or simply perish. 

 McCleave and Kleckner (1982) demonstrated that in 

 the tidal portion of an estuary American glass eels 

 achieved upstream transport by selectively rising in- 



"Kleckner, R. C, and J. D. McCleave. 1982. Spatial and temporal 

 distribution of American eel larvae in relation to North Atlantic 

 Ocean current system. Unpubl. manuscr., 46 p. Department of Zool- 

 ogy, Murray Hall, University of Maine at Orono, Orono, ME 

 04469. 



AUGUST 8 SEPTEMBER 



ANGUILLA ROSTRATA (0 GROUP) 



I I [ I I I I I I I | I I I I [ I I I I | I I I I I I I l I | I I I I I I I M 

 80° 70° 60° 50° 40° 



Figure 11. — Locations in the North Atlantic Ocean where one or 

 more Anguilla leptocephali have been collected during August and 

 September. Compare with Figures 6 and 7. From Kleckner and 

 McCleave (text footnote 6). 



to the water column during flood tides. This has also 

 been demonstrated for European eels (Creutzberg 

 1961), and it is certainly possible that larval and 

 juvenile eels could utilize this mechanism in offshore 

 tidal areas such as Georges Bank (Magnell et al. 

 1980). 



There are abundant examples in the literature of 

 stochastic events whereby leptocephali could also be 

 transported inshore. Recent examples include Gulf 

 Stream intrusions off St. Augustine, Fla. (Atkinson et 

 al. 1978) and in Onslow Bay (Blanton 1971), Gulf 

 Stream frontal eddies off Jacksonville, Fla. (Yoderet 

 al. 1981), and Gulf Stream intrusions along the New 

 York Bight (Judkins et al. 1980). Cox and Wiebe 

 (1979) discussed the mechanisms by which oceanic 

 plankton are transported into the Mid- Atlantic 

 Bight, such as Gulf Stream warm- core rings and 

 meanders. These meso- and finer scale features all 

 surely transport leptocephali, but they were not 

 directly incorporated into the model, except as their 

 effects were represented with other turbulent 

 motions by the eddy diffusivity terms. It seems 

 maladaptive for leptocephali to rely upon such un- 

 predictable features to facilitate a migration that oc- 

 curs with annual regularity. 



Eastward transport into the North Atlantic on the 

 Gulf Stream was the fourth and final phase evident in 

 the simulations. These last simulation phases may 

 not have accurately represented the eel's migration, 

 because leptocephali begin metamorphosis to the 

 glass eel stage as early as October (Kleckner and 

 McCleave 1980), and it becomes questionable as to 

 whether the eels were still drifting passively. Unless 

 the loss of eels due to transport out into the Atlantic 

 is substantial, it seems that by this point the eels 

 must modify their drift in some way if they are to 

 avoid transport to Europe. A small number of 

 American eel are in fact found in European waters 

 (Boetius 1980). In the passive drift simulations, on- 

 ly a small portion of the larvae entered the Gulf of 

 Maine, although this region also has complicated 

 currents not accurately represented in the model. 

 Meanders of the Gulf Stream will carry some larvae 

 near the northeastern North American coast, as it has 

 for other species (Colton et al. 1962; Markle et al. 

 1980). The transport of leptocephali out into the 

 Atlantic was centered on lat. 40°N, and this agrees 

 well with the results of Richardson (1981), who tracked 

 buoys drifting on the Gulf Stream. 



The European eel spawns in a region of weak and in- 

 determinate currents, and in the simulation this 

 resulted in a slow spreading of the leptocephali 

 throughout the Sargasso Sea. It is clear that if the 

 simulation presented in Figure 9 were continued, the 



498 





