Wespestad and Moksness: Growth and survival of Clupea patlssii 



197 



Herring held in the lal^oratory and deprived of food 

 died 21 days after hatching. Larval survival was high 

 until day-19 at which time the number alive had de- 

 creased to 52% (Table 4). Mortality proceeded rapidly 

 at this point, and total mortality was observed in the 

 remaining batch on day-21 of the experiment. 



Length increased in starved herring during the first 

 week from an average of 7.0 mm to 9.4 mm and then 

 remained essentially unchanged for the remainder of 

 the experiment (Table 4). Weight, on the other hand, 

 decreased from 175 ^g on day-1 to 147 f^g near the end 

 of the yolksac stage and to 109 f.ig on day-19 (Table 4). 



Discussion 



The development of Bristol Bay herring larvae in the 

 basin was similar to that reported for other stocks. The 

 average growth of 0.66 mm/day was near the upper 

 end of the range reported from British Columbia and 

 Washington but greater than that observed in aquaria 

 experiments in California (Table 5). Direct comparison 

 is difficult because of the differences in duration of 

 observation periods, but it is likely that the 0.33 

 mm/day reported for San Francisco Bay herring is low 

 due to a diet of Arte7nia nauplii, which have been 



shown to produce poorer gi'owth than natural plankton 

 (Blaxter and Hunter 1982). 



Comparison of our results with otolith ring data 

 (Checkley 1982) indicates that the growth observed in 

 the basin is similar to at-sea growth. The otolith-ring 

 age estimates were 0.78 mm/day and 0.94 mm/day for 

 herring of 82 mm average length and 108 mm max- 

 imum length. These are likely slight overestimates of 

 growth rates since there is a lag time between hatching 

 and ring formation related to yolksac absorption 

 (Messieh et al. 1987, Moksness and Wespestad 1989). 



McGurk (1984) concluded that growth in laboratory 

 experiments is always lower than at-sea growth. The 

 similarity between growth rates observed in the basin 

 and rates estimated from at-sea otoliths suggests that 

 the basin environment resembled natural conditions. 

 Stevenson (1962), Keegen et al. (1986), and McGurk 

 (1984) reported higher growth rates for batches of lar- 

 vae developing at higher temperature. 



Blaxter and Hunter (1982) relate that the growth 

 rate of herring is primarily governed by temperature 

 and food abundance. In Bristol Bay, summer surface- 

 water temperatures are warmest nearshore (10°C and 

 gi'eater) and decrease (7°C or less) a short distance off- 

 shore (Ingraham 1981). That herring growth in the 

 basin was similar to growth observed in field samples 



