Abstract

This thesis investigates the coupling between climate, hydrography and recruitment variability of fishery resources off West Greenland with special emphasis on cod and shrimp recruitment. The main hypothesis investigated is, that the variability of these stocks at West Greenland is highly controlled by advection of water masses into the area during their pelagic stages. This hypothesis is investigated through three different studies:

1. A review of the past 50 years of climatic conditions off West Greenland is given based on hydrographic and atmospheric observations off West Greenland. Relationships between the past variations in fisheries resources, hydrographic conditions, and the large-scale climatic conditions, expressed by the North Atlantic Oscillation (NAO), are found. A reduction of the inflow of heat and salt to the West Greenland area during positive NAO phase from the late 1960s until the mid 1990s reduces the recruitment of cod larvae from Iceland. Mature cod migrated out of the area reducing the predator pressure on the shrimp stock. By-catches of cod by the shrimp fishery contributed to keeping the predation pressure low.
2. Shrimp larvae transport from larval release to settling at the bottom is studied, using a particle-tracking model forced by a high resolution ocean circulation model. Residual anticyclonic eddies are generated around the shelf banks north of 64°N which largely affect the retention times at the shelf banks. Similar, plankton distributions were related to the physical environment described by observations and the same ocean circulation model. Areas of permanent upwelling west of the shelf banks found in the model are suggested to increase the productivity of plankton.
3. Transport of cod eggs and larvae from the Southwest Icelandic spawning grounds to the Greenland waters is studied for the period 1948–2001 using model based particle tracking forced by a regional nested ocean model with horizontal resolution of 20–25 km. Surprisingly, no relation was found between the drift of recruits from Iceland to Greenland and the observed year class strength of West Greenland cod. However, we can not reject the hypothesis. A validation of the ocean model against observations reveals that the model is far from perfect and even lacking important events as the Great Salinity Anomaly in the late 1960s in Greenland waters. Results from the drift model suggest that the drift of cod larvae towards Greenland is very sensitive to the position of the spawning grounds.

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