Nichol and Somerton: Tidal stream transport of Lepidopsetta polyxystra in the eastern Bering Sea 
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Migration path of one female northern rock sole ( Lepidopsetta polyxystra ), tagged 
and recaptured in the eastern Bering Sea, released in 2003 and captured in 
2004. The migration path is based on current velocity vectors predicted during 
periods when the northern fish underwent excursions away from the bottom. 
Circles identify the release and recovery positions. Gray lines with numbers 
indicate the bathymetric contours (m). Months are indicated by the alternating 
black and white paths. 
sole, this behavior is common among various flatfish 
species and juvenile northern rock sole. Nighttime ver- 
tical excursions have been reported for a variety of 
flatfishes from postlarval through adult stages (e.g., De 
Veen, 1967; Weinstein et ah, 1980; Cadrin and West- 
wood, 2004; Hunter et ah, 2004). Nighttime periods are 
thought to offer flatfishes a reduced risk of predation 
by visual predators (Burrows, 1994). In laboratory ex- 
periments, the swimming activity of juvenile northern 
rock sole (20-40 mm TL) away from the bottom oc- 
curred most often during nighttime (Hurst and Duffy, 
2005). This activity involved vertical excursions to the 
surface, followed by horizontal swimming and gliding. 
It follows that, like adult northern rock sole, juveniles 
undergo vertical excursions away from the seafloor 
for the purpose of horizontal migration. Considering 
northern rock sole juveniles inhabit areas with tidal 
influence, it follows that they also use tidal currents for 
transport. Although it is unlikely that small juveniles 
migrate extensive distances, as some adults do, juve- 
niles may use tidal current for short-term migrations 
as a mechanism to locate better feeding grounds within 
nursery areas (Hurst and Duffy, 2005). We believe 
that at least some adult northern rock sole employ this 
