I too have recently read this
[ame="http://www.amazon.co.uk/Underwater-foraging-instructional-sustainable-spearfishing/dp/1484904591"]Underwater foraging - Freediving for food: An instructional guide to freediving, sustainable marine foraging and spearfishing: Amazon.co.uk: Ian Donald: Books@@AMEPARAM@@http://ecx.images-amazon.com/images/I/51kRo4-NfHL.@@AMEPARAM@@51kRo4-NfHL[/ame]
I found it pretty well written, quite informal and relaxed, though I feel it didn't really cover anything in any particular depth. The book is essentially in two parts, first is just general freediving including a quick history, technique, equipment and safety. The second part is about foraging and diving for food, again equipment, safety, technique etc and descriptions of fish, shellfish, seaweed etc.
I primarily bought this book as it was sold as describing hunting technique, however, this was very thin e.g. the section on the location and technique for bass was 8 lines long and the bass section was the most comprehensive.
I'd say this is a good book for someone trying spearfishing for the first time with no freediving experience , however, I don't think there's anything in it for for someone with more than one season of spearing experience.