Spatial and Temporal Variation in Egg Production of Calanus finmarchicus on Georges Bank: Implications for the Productivity of Prey of Cod and Haddock Larvae

Jeffrey Runge, Ted Durbin, S. Plourde and Y. Gratton

As part of the U.S. GLOBEC Georges Bank program, egg production rates of Calanus finmarchicus and of other common copepod species were estimated between January and June, 1995. Female C. finmarchicus were spawning continuously during this period. The wt-specific rate was highest in February-March (10.5% d-1); at other times it varied between 5.5% d-1 in January to 8% d-1 in June. C. finmarchicus was capable of sustaining egg production under most environmental conditions in the Georges Bank region. Measurements of egg production rate by shipboard incubation during process cruises were used to calibrate a reproductive index based on the proportion of females in preserved samples carrying oocytes in advanced stages of vitellogenesis. The product of the female-specific egg production rate determined from this relationship and the female abundance estimated from net tows yields the population rate of egg production during the broadscale cruises, which sampled a grid of ~40 stations monthly during the same January-June period. In April and May, the period of highest abundance of fish larvae on the southern flank of Georges Bank, the daily input of Calanus eggs into the water column (eggs m-2 d-1) varied by almost two orders of magnitude. The total copepod egg (naupliar) production on the southern flank during this period varied from 1- 80 mgC m-2 d-1, of which the proportion contributed by Calanus ranged between 25-80%. This variability in prey field production may have a significant impact on the growth rates of fish larvae as they are transported along the southern flank corridor.