SMITH ET AL: DIEL MOVEMENTS OF LARVAL FLOUNDER 



at 2200 and 0100 h might have fed after dark or 

 they might have stopped feeding after sunset. 

 Further study is needed to determine whether yel- 

 lowtail flounder larvae feed at night. 



After analyzing 10 yr of drifter releases, Bum- 

 pus (1973) reported that surface currents in the 

 Middle Atlantic Bight occasionally reach speeds of 

 15 mi/day (27 km/day), but they are usually less 

 than 10 mi/day ( 18 km/day). He estimated bottom 

 drift at 0.5±0.2 mi/day (0.9±0.4 km/day) and 

 speculated that circulation near bottom was so 

 random and sluggish that it was unrealistic to 

 derive drift rates of bottom water from his data, 

 except from nearshore releases, which stranded 

 within a reasonable time frame. Howe (1962) con- 

 cluded that coastal circulation between Cape Cod 

 and New York was largely attributable to short- 

 term wind effects and that waters inside the 90-m 

 isobath were comparatively stagnant during the 

 first half of the year. The sluggish performance of 

 our drogue supports Howe's results and indicates 

 that the velocity of middepth drift at the time and 

 location of our study was similar to Bumpus' de- 

 scription of bottom circulation. 



Returns from drift bottle releases indicate that 

 surface water generally moves westward off Long 

 Island then southward along the Middle Atlantic 

 States (Bumpus and Lauzier 1965). However, both 

 Norcross and Stanley (1967) and Bumpus (1969) 

 found evidence of surface current reversals in the 

 Middle Atlantic Bight during the summer, and 

 Doebler (1966) showed that the direction of sur- 

 face water transport off Delaware responded 

 rapidly to changes in wind direction. On the basis 

 of these reports, we assume that the brisk south to 

 southwest wind during the first 48 h of our study 

 propelled surface water towards southern New 

 England. Although yellowtail flounder larvae 

 were not at the surface during the day, 44% of our 

 night catches were taken at the surface during the 

 first two nights. During this time wind probably 

 influenced their horizontal displacement. By pas- 

 sing the 15 h of daylight at subsurface depths, it 

 appears from the net drift of our drogue that the 

 larvae were transported in the opposite direction 

 to that at night. 



Assuming that our drogue's erratic and sluggish 

 drift is representative of middepth circulation off 

 Long Island in the spring, when spawning by yel- 

 lowtail flounder peaks, and that effects of spring 

 and summer winds on circulation are usually lim- 

 ited to a few days at a time, we conclude that wind 

 driven currents in the study area do not play a 



major role in dispersing the larvae. Our conclusion 

 is supported by Royce et al. (1959). Similarities in 

 patterns of distribution between eggs and larvae 

 led them to conclude that larvae were demersal 

 before much horizontal drift occurred. It seems 

 worth noting here that the smallest larvae, those 

 least able to swim with directed movements, did 

 not ascend to the surface at night. They remained 

 below the shallow thermal gradient, where they 

 were unaffected by wind-driven circulation. 



Whether or not our interpretation of the effects 

 of currents on the distribution of yellowtail floun- 

 der larvae is correct, it is clear to us that research- 

 ers must investigate the diel movements of larvae 

 they are studying before hypothesizing on how 

 circulation affects the distribution and survival of 

 young fishes. It is common practice to overlook or 

 ignore larval behavior and relate the transport of 

 larvae from both day and night collections by ob- 

 liquely towed nets to surface circulation. In many 

 cases, this oversight produces an exaggerated es- 

 timate of the distance larvae are transported and, 

 perhaps, an erroneous estimate of the direction of 

 transport. 



LITERATURE CITED 



AHLSTROM, E. H. 



1959. Vertical distribution of pelagic fish eggs and larvae 

 off California and Baja California. U.S. Fish Wildl. Serv., 

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 BIGELOW, H. B., AND W. C. SCHROEDER. 



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1974. Efficency test on four high-speed plankton samplers. 

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Bumpus, D. F. 



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