Sentence:  For two decades the <WSD>bonanza</WSD> on Scotland's west coast continued. An occupation that had been seasonal and modestly profitable became year-round and lucrative. Baskets of herring put televisions into fishermen's cottages and cars outside their doors. But fish, like oil and gas, with which Scotland's continental shelf is also well-endowed, are not in unlimited supply. 
Meaning of the word marked with <WSD> tags:  Anything which is a mine of wealth or yields a large income or return.