While local Aborigines were excellent swimmers, known to have covered great distances over water, sometimes to escape imprisonment, unlike their counterparts in some other parts of Australia they had no cause to dive in conditions where the tidal range provided all they needed. Many were also succumbing to diseases to which they had not previously been exposed, as well as accidents. This led to recruitment from the convicts on the "Native Prison" on Rottnest Island. Broadhurst was criticised for harsh treatment of at least one indigenous employee, while some pearlers abducted and/or forcibly retained their divers.