demography in a way that would affect yield and concern managers? How effective can management be in detecting and countering these effects? Recently, promising strides have been made to address the first question but the evidence is still largely circumstantial [e.g., Hard et al. (2008)]. The other questions have seldom been addressed directly except through simulation [e.g., Bromaghin et al. (2008) and Hard et al. (in press)].
Sustainable exploitation requires that phenotypic changes induced by harvest do not appreciably reduce yield and viability. Although we cannot be certain that many of the observed phenotypic trends in a variety of exploited animals are solely the result of exploitative selection, it would be imprudent to assume that such selection has not had an effect. The coupling of such trends with evidence for reduced productivity and yield is reason enough to adopt a risk-averse approach in considering sustainable harvest practices. One means of maintaining viability is by reducing selectivity in exploitation; assuming that the level of exploitation is not so high that it poses excessive demographic risk, reducing selectivity ameliorates the potential for selection to erode viability through phenotypic evolution. It also maintains the opportunity for natural and sexual selection to maximize reproductive fitness. Sustainable harvest practices require adequate monitoring of traits that are sensitive to selection and influence viability (Allendorf et al., 2008), and promote management that maintains breeding populations that are large and diverse enough to foster the full range of phenotypes that natural and sexual selection can act on (Hutchings and Rowe, 2008). Moreover, sustainable management strategies should adapt quickly and appropriately to detected changes (Kuparinen and Merilä, 2007).
Recovery after relaxation, or even reversal, of selective harvest is likely to be slower than the initial accumulation of harmful genetic changes (Heino, 1998). This is because harvesting can create strong selection differentials, whereas relaxation of this selective pressure will more often produce weaker selection in the opposing direction (Swain et al., 2007). De Roos et al. (2006) used an age-structured fishery model to show that exploitation-induced evolutionary regime shifts can be irreversible under likely fisheries management strategies such as belated or partial fishery closure. Swain et al. (2007) concluded that human-induced adaptation to fishing may be a primary reason for lack of recovery of northwest Atlantic cod because harvest has been reduced after the collapse of this