How are natural sponges harvested?
This site looks like a first hand observation but it may prove useful to you.
http://www.associatedcontent.com/article/432557/natural_sponges_harvested_at_tarpon.html?cPage=2
http://www.associatedcontent.com/article/432557/natural_sponges_harvested_at_tarpon.html?cPage=2