This project addresses a hypothesis linking spatial/temporal variability in copepod productivity and the growth and survival of cod and haddock larvae on Georges Bank. It represents a synthesis of survey results and process observations conducted prior to and during the U.S. CLOBEC Georges Bank Program, and uses a recently-developed biophysical, individual-based model (IBM) of cod and haddock larvae to investigate the importance of variation in copepod prey field production relative to other factors, including circulation, temperature, turbulence and light, that potentially contribute to the success or failure of recruitment into Georges Bank fish stocks. Cod and haddock larvae on Georges Bank feed primarily on the eggs and nauplii of the dominant copepod species. The vertically-integrated copepod egg production (VIP), in terms of eggs m-2 d-1 or mg-C M-2 d-1) is therefore an index of the daily production of larval fish prey. Research during earlier phases of the Georges Bank program showed that, over three-month periods, the total copepod VIP can vary by 1-2 orders of magnitude on the southern flank of Georges Bank; with Calanus finmarchicus being a dominant influence on the pattern of total copepod VIP. These data suggest that variability in Calanus and total copepod egg production is potentially a major influence on the availability of prey to fish larvae on Georges Bank. However, there is little knowledge about inter-annual variation in both the magnitude and spatial structure of total and Calanus egg production. Dr. Werner and associates suggest that the pattern and magnitude of total egg production on Georges Bank is highly variable from year to year. If a high abundance and sufficient nutrition for Calanus females is set up in some years on the northeast peak and southern flank, food conditions for fish larvae could increase by an order of magnitude or more, with consequent dramatic improvement in their growth and survival. Based on these considerations, the investigators put forward the following, three-part hypothesis: (1) the spatial, seasonal and inter-annual variation in the total VIP (all dominant copepods) is substantial (i.e., orders of magnitude), (2) there is a significant relationship between the VIP and growth and survival of fish larvae on the eastern and southern flanks and (3) variability in the productivity of Calanus finmarchicus influences the growth and survival of cod and haddock larvae on Georges Bank. The hypotheses will be tested by a combined synthesis and modeling study.
