The effects of large-scale, environmentally driven changes on the distribution and abundance of fish populations have been a major source of concern for fishery scientists and managers for decades, particularly those dealing with the assessment and management of small pelagic fisheries. While much still needs to be investigated and elucidated, significant progress has been made in describing and understanding the primary aspects of observed large-scale changes in small pelagic fish production and the most likely causal mechanisms, climate–fish abundance interactions, patterns of change, species interactions, and many other important issues. A newer and additional difficulty is that global climate change is altering the structure and functioning of marine ecosystems, which in turn affects availability of ecological resources and benefits, changes the magnitude of some feedbacks between ecosystems and the climate system, and will affect economic systems that depend on marine ecosystems. Newer questions and uncertainties have to be faced. For instance, will there be an increase in variability from season to season and year to year? Predictions of such changes in the future are likely to be less reliable than they may have been in the past, given that the past will become less useful as a guide to the future.