This eventually caused over-harvesting of the shallows and a shortage of shell. This led the industry into its second stage and a transition took place from wading in the shallows into the use of "skin divers" (unassisted by the emerging technology of breathing apparatus). In most cases, however, the transition from wading to diving took place during 1868. While Broadhurst and a few other proprietors experimented, during the 1860s, with the use of breathing apparatus by professional divers, it proved at the time to be expensive, unreliable and dangerous.