Wespestad and Moksness: Growth and survival of Clupea pallasii 



193 



Salinity during the experiment ranged from 30.6 to 

 32.7 ppt (Fig. 2b). The lowest salinity values were re- 

 corded at the start of the experiment followed by a 

 slight increase throughout the experiment. The in- 

 crease in salinity was attributed to evaporation and in 

 flow of a small amount of denser water pumped into 

 the basin to offset losses from evaporation and leakage. 



Oxygen levels were checked periodically during the 

 experiment. The lowest levels were recorded on day-12 

 at 70% saturation. At other times oxygen saturation 

 was near 100%. 



Zooplankton 



Calanoid copepod adults and nauplii were the primary 

 component of the zooplankton in the basin, constituting 

 26% and 68% of the number of organisms in pump 

 samples, respectively (Fig. 3a). Adult copepod abun- 

 dance was greatest when the herring larvae were in- 

 troduced into the basin; it then declined rapidly (Fig. 

 4a). Copepod nauplii were also at greatest abundance 

 in the beginning and declined over time from a peak 

 of over 100/L to less than 1/L (Fig. 4b). 



The other plankton species taken in pump and net 

 samples were present at much lower densities (Fig 4c). 

 The non-copepod zooplankton were primarily harpacti- 

 coid copepods, Littorina littorea veligers, crab {Cancer 

 ■pagurns) zoea, and cladocera (Bosmina sp., Evadne sp., 

 and Podon sp.). Ephyra sp. hydromedusa were abun- 

 dant in the first days of sampling and then declined 

 rapidly. 



Feeding 



Herring larvae in the basin fed primarily on copepod 

 eggs, nauplii, and adults (Fig. 3b). Other items found 

 in the diet were L. littorea veligers, crab zoea, and 

 chiromomid larvae which occurred in the basin sedi- 

 ments. Food items were found in the gut within a few 

 days of release into the basin. Within the first 5 days 

 of release, 12% of the larvae contained food items 

 (Table 1). 



a. 12 



E 



A 



16 Togiak 



-1 9 12 13 14 16 19 21 24 30 37 48 50 



Days since hatching 



-1 9 12 13 14 16 19 21 24 30 37 48 50 



Days since hatching 



Figure 2 



(A) Water temperature in tlie 2000-m' basin. Fl^devigen Biological 

 Station, Norway, at 0, 2, and 3 ni compared with observed tempera- 

 ture at 2 m in Togiak Bay, Alaska. (B) Salinity (ppt) in the 2000-m' 

 basin at 0. 2, and 3 m. 



The items observed in the gut during the first week 

 were primarily copepod nauplii and eggs. The propor- 

 tion of larvae with food doubled in the second week; 

 eggs and nauplii continued to be major items, but small 

 copepods were also found (Table 1). From day- 13 to 



i^'ciidMijiij riaupiii 



Veligers & zoea 

 Other 



Calanoid adults Calarioid adults 



a, plankton samples • ■•'-^'ns 



Figure 3 



Comparison of (a) species composi- 

 tion in plankton samples and (b) 

 food items consumed by Pacific 

 herring larvae. 



