Construction of discard estimates from survey and market samples

Most stock assessments in the North Sea, like those of plaice and sole, are currently based on catch statistics of landings into ports and not on the catch by the fleets. Discarding is the process where part of the catch (usually undersized fish) is thrown back into the sea immediately after being caught. The survival of discarded fish is very low. Not taking discards into account in a stock assessment could lead to underestimation of the fishing mortality, mostly on the youngest ages. This could lead to systematic differences in catch forecasts and errors in the estimation of incoming year classes