Complex sentence: The fishery in particular suffered a sharp decline due to overfishing in the 1990s, while mineral resources (notably coal) also declined at about the same time and the forestry industry suffered major declines in the past decade as the demand for paper declined.
Split into simpler sentences: The fishery in particular suffered a sharp decline due to overfishing in the 1990s, while mineral resources (notably coal) also declined at during the same period. The forest industry suffered major declines in the past decade as the demand for paper declined.