Kendall et at: Vertical distribution of eggs and larvae of Theragra chalcogramma 



549 



Response of larvae to wind events 

 and prey distributions 



Increasing winds after 60 hours of sampling 

 during series four prevented further 

 MOCNESS tows, but other observations con- 

 tinued during the storm and documented the 

 deepening of the mixed layer and subsequent 

 changes in microzooplankton distribution 

 (Incze et al., 1990). The path of the drogue, 

 the sequence of CTD data obtained in the 

 area, and limited satellite imagery suggested 

 the presence of an anticyclonic eddy (Incze 

 et al., 1990;Nieman 4 ). The mixed layer depth 

 during the first half of series four was vari- 

 able, but during the last half it deepened, 

 presumably in response to increased winds 

 (Fig. 4). Copepod nauplii of length range 150- 

 350 p, which has been found to be the size 

 range primarily eaten by 5-6 mm walleye pol- 

 lock larvae (Paul et al., 1991 ), had mean depths 

 between 20 and 34 m during series four (Fig. 4 ). 

 Their observed mean depth increased during 

 the storm, but their densities at some depth 

 within the upper 45 m was always greater than 

 15 per liter. Excluding the deep net from the 

 noon tow on day two, the mean 

 depths of larvae in series four were 

 at or 5-10 m below the mixed layer 

 depth and the mean depth of 150- 

 350 urn copepod nauplii. 



Wind, measured hourly aboard 

 the ship during series nine, in- 

 creased from less than 8 m/second 

 during the first six tows of this 

 series to over 12 m/second by the 

 end of the series. The mixed layer 

 was about 25 m deep at the time 

 of the last tow (night) in series 

 nine as opposed to about 10 m dur- 

 ing the previous seven tows 

 (Fig. 9). The greater mean depths 

 of larvae at dusk and night on the 

 second day of sampling compared 

 with the first day of sampling were 

 possibly caused by increased tur- 

 bulence and deepening of the 

 mixed layer (Fig. 10). 



Discussion 



Most walleye pollock eggs in 



Shelikof Strait developed at depths between 150 and 



4 Nieman, D. R. Rosenstiel School of Marine and Atmospheric 

 Science, Univ. Miami, Miami, Florida 33149. Personal commun., 

 February 1993. 



200 m. However, there was considerable variation 

 in the mean depth of eggs among the tows. Mean 

 depth of eggs varied from 153 to 206 m in April (when 

 egg densities were high) and from 20 to 129 m in 



