Development of a catch mortality model

The discarding of non-target species and sizes of fish by commercial fishing vessels is a common practice in many fisheries around the world. Efforts to reduce discarding in North Sea fisheries were initiated over 100 years ago, and were the precursor to development of mesh-selectivity research for many European countries. In most cases mechanical selection through fishing gear modifications has been carried out without research into the survival of fish after escape. In recent years, research into fish mortality after escape has shown that mortalities vary by gear type and species, may be immediate or delayed, and may be due to injuries or stressors associated with capture-escape trauma. Based on this information, a general model of fishing mortality has been developed. Measuring the level of catch, discards and escape mortality associated with each gear type may be one index for assessing the conservation aspects of fishing gears, and may lead to more realistic estimates of induced fishing mortality.