Can ultraviolet radiation influence cod Gadus morhua L. year class strength: a model study

To simulate the UVR dose that eggs and larvae of cod Gadus morhua receive during spring in Lofoten, the main spawning area of north-east Arctic cod, a model driven by wind, tides and surface heat flux was applied. The model was forced using in situ measured hydrographical data while underwater UVR doses were calculated using satellite data, ozone measurements, meteorological data and in situ diffuse extinction coefficients. The model was run with data from 1934 to the present and indicated that UVR induced mortality has little effect on cod year class strength. When thin ozone layers and slack winds coincide with meagre phytoplankton stocks, UVR induced mortality may be harmful to eggs and larvae. As these events are highly episodic, and since the spawning period of cod is long ( c. 3 months), they are believed to have only a minor influence on the overall survival of cod eggs and larvae.