The End of the Line by Charles Clover. Tipped off to this by my brother. Bruv' might not immediately strike you as the conservation type ("the sushi buffets in Kuwait are the best!") so when he says "this book changed how I eat seafood" I listen. There is a related movie coming out, as below. Village Voice interview with Charles Clover; May 1st 2009.
Alternatively you can read Cod which focuses strictly on cod and it's currency-like place in history, as well as its worldwide decimation. Can you imagine the scenes in Gloucester etc where you could at one time (1800's) practically walk across the backs of mammoth cod to get to shore... awesome.
