Bull. Jpn. Soc. Fish. Oceanogr. 74(sp), Page 84-89, 2010   Fisheries-induced life history evolution Yuu Katsukawa*,† and Yoshiro Watanabe* * Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan † Faculty of Bioresources, Mie University, 1577 Kurima-machiya, Tsu, Mie 514-8507, Japan e-mail: yu@aori.u-tokyo.ac.jp Most fisheries target large individuals, so that fisheries-induced mortality is highly size selective. Therefore, selective pressures drive the evolution of life histories. Changes in life history traits, such as age and size at maturation, fecundity and growth rate, have reported in heavily exploited and declining fish stocks. Decreasing age and size at maturation impact on yields, population dynamics and productivity of fish population. Two non-exclusive hypotheses that may account for the maturity changes are (1) the compensatory response hypothesis and (2) the evolutionary response hypothesis. Firstly, the compensatory response hypothesis predicts that reduced stock size resulting from exploitation leads to faster growth and hence earlier maturity as a phenotypic plastic response to environmental change. Secondly, the evolutionary response hypothesis predicts that intensive exploitation causes selection for early maturation, since few late-maturing phenotypes survive until first spawning. Probabilistic maturation reaction norm (PMRN) has been developed as a new statistical tool to disentangle plastic and genetic effects in the absence of genetic data. PMRN can be estimated from time-series data for commercially fished stocks. Evolutionary response in life history traits can be expected to be seen on a decadal time scale. The controlled experimental manipulation demonstrated that harvesting causes significant maturation evolution within just a few generations. Theory predicts that selective harvest spoils the adaptive life history and increases the temporal variability in population dynamics. Depletion of larger and older fish will restrain the evolutionary and demographic changes that are evolutionally developed by each species or populations. The importance of maternal effects to fisheries management is becoming recognized among fisheries scientists and managers. In order to manage the fish stocks, we need comprehensive knowledge on their reproduction and continuous monitoring of their status as well as their ambient environment. Key words: anthropogenic change, life-history evolution, phenotypic plasticity, reaction norm, maturation