An important aspect of species susceptibility to fishing are the changes in demographic characteristics of populations that fishing might induce. The purpose of this study is to show the short-term effects of fishing on growth and reproduction patterns. This assessment is made through a comparative study of key parameters (mortality, size, age and size at maturity. fecundity) among stocks subject to various levels of exploitation. Data have been assembled for 77 separate (primarily commercial) fish stocks. Trait variation is partitioned into effects attributable to size, phylogeny, and population. High adult mortality appears to lead to short-term apparently plastic changes in age and size at maturity: exploited populations are characterized by earlier age and increased size at maturity. This compensatory response to exploitation may conceal longer term selection effects, and may be worth considering in stock assessments. (C) 1998 International Council for the Exploration of the Sea.