P a R T Iii Report of the Working Group on Environmental Studies and Monitoring

The main primary variables or conditions which directly affect individual fish and, through these, the abundance of fish populations are: food, predation, temperature, salinity and oxygen concentration. These primary variables are altered by several processes, some of which are described in this report, together with different sources of information on environmental variability and biological characteristics. There is a need for more rigorous approaches to the problem of environmental effects on fishery problems, and some suggestions are made in this respect. The information on environmental variations is of great value for management purposes, particularly when environment has proven to be a major source of fluctuation of fish availability.