In Chapter 9, what caused the destruction of the fish (in Canada, in Maine, and in Yellowstone)?

For many thousands of years, salmon have returned from the Atlantic each year and traveled up the rivers in which they were born to spawn and perpetuate their kind. In 1953 in the Miramichi River of New Brunswick, the salmon migration happened as usual. By spring 1954, these tiny fish, along with their older relatives of the previous year's hatchings, were suddenly besieged by the Canadian government's widespread spraying program, which was meant to combat the spruce budworm. Along with all the insects and most of the birds in the millions of sprayed acres, the entire 1954 hatch of salmon died; five-sixths of the 1953 hatch died; and one-third of the 1952 hatch died. The budworm populations, on the other hand, continued to thrive. Repeated sprayings took place, despite evidence that spraying does not effectively combat budworm. Other places have also killed fish in their attempts to control forest insects. DDT may cause blindness in fish. Even if the fish survive the spraying, the virtual elimination of the insects that they feed on may kill them, or the fish may die some time after the spraying when they draw upon their fat stores for energy and release the DDT stored in their bodies. Efforts to coordinate sprayings to reduce fish mortality have been largely ineffective.