Nichol and Somerton: Tidal stream transport of Lepidopsetta polyxystra in the eastern Bering Sea 
231 
140 
120 - 
100 - 
<10 10-20 20-30 30-40 40-50 >50 
B 
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<10 10-20 20-30 30-40 40-50 >50 
Current speed (cm/s) 
Figure 7 
Angle difference between observed and predicted (model) near- 
bottom tidal current directions at the mooring site near the 
northern fish (A) and at the mooring site near the southern 
fish (B) in the eastern Bering Sea, plotted at different observed 
current speeds. The y-axis is expressed as the mean absolute 
value of the angle difference between observed and predicted 
current directions (in degrees). Error bars indicate 25 th and 75 th 
percentiles. Percentages next to the means (circles) indicate the 
percentage of time that each grouping of observed current speed 
represented during the 193 days of collection. 
Figure 8 
Comparison of observed and predicted (model) 
near-bottom tidal current speeds at the northern 
(A) and southern (B) mooring sites in the east- 
ern Bering Sea. Predicted speed is presented as 
the component of the model speed projected in 
the observed direction, MS 0 cos(0), where MS 0 = 
the model-predicted speed in the observed 
direction, and d = the angle difference between 
observed and predicted current directions. The 
line indicates a 1:1 ratio. Model estimates of 
speed do not include residual (e.g., baroclinic) 
effects that may have been present in observed 
current speeds. 
they frequently approach the surface (De Veen, 1967; 
Greer Walker et al., 1980). By comparison, the northern 
rock sole examined here only occasionally approached 
the surface; most vertical excursions occurred in the 
bottom half of the water column. Even during periods 
of active migration (e.g., January; northern fish), ver- 
tical excursions averaged only 2.6 hours in duration 
and were a maximum extent of 11.6 m away from the 
bottom. These vertical excursions could be of interest 
to fishery managers if they affect fish availability to 
bottom trawl surveys (Hunter et al., 2004b). However, 
the northern rock sole excursions were particularly 
infrequent during summer daylight hours when the 
bottom trawl surveys of the eastern Bering Sea are 
