This chapter searches for an approach to monitoring the reproductive performance of a generalized high fecundity finfish stock while fishing for juveniles. Current assessments frequently use stock–recruit relationships that require information on the abundance of adult fish, but such data may not be available for fisheries on juveniles. A study of the bioeconomics of a small mesh fishery for juvenile Mediterranean hake showed that a relatively high market price for juveniles plays a significant role in the economic performance of this fishery. Deepwater trawling in the Mediterranean is mainly aimed at red shrimp, but also catches mature fish of several species. The concept of a gnomonic time interval was proposed as a possible way of modelling the progressive decline in natural mortality rates of highly fecund marine organisms throughout life. Research in Northern Europe and North America has shown that there is often a significant mortality of small fish after passing through trawl cod ends.