Complex sentence: Strict regulations and greatly reduced fishing quotas introduced in 2000 have since begun to reverse the stock decline, though recovery of the stock is projected to take decades due to the low productivity of the species.
Split into simpler sentences: Strict regulations and greatly reduced fishing quotas introduced in 2000 have since halted the stock decline, and allowed for recovery to begin. Recovery of the stock is projected to take decades, due to the low productivity of the species.