This chapter is the first attempt to describe major changes in the population of marine animals in the seas of Southeast Asia since 1850. Using a wide variety of anecdotal evidence, it begins by building up a picture of populations of fish and other marine animals in the mid 1800s. Having established this as a rough baseline, it argues that only a few fish populations, most notably those of fusiliers, which inhabited coral reefs exploited by Japanese muro ami fishers, underwent significant change before 1940. Beginning in the late 1940s in the Philippines and the 1960s in the Gulf of Thailand, there were dramatic drops in the population of demersal fish, only partially compensated by increases in squids and other species which had been the prey or competitors of these fish. As demersal fish populations fell, fishers turned their attention to various pelagic species, which in turn underwent declines. Fishing rather than pollution was by far the greatest contributor to sharp reductions in the population of most species. Those species occupying the highest trophic levels underwent the greatest declines in population.