Early media reports indicated search and rescue divers were on the scene soon after the alarm was sounded about the missing diver.
The alarm was raised at 1.30 pm.
The media report release was 3.31 pm.
https://au.news.yahoo.com/thewest/wa/a/22245886/diver-missing-off-dawesville/
The deceased diver was on a boat which remained in the area for the remainder of the afternoon.
https://au.news.yahoo.com/thewest/latest/a/22269013/family-gathers-amid-diver-search/
I'd expect that if a pleasure craft could remain anchored in the area for that afternoon the search and rescue divers would have several hours of searching the area where the boat was initially moored.
Media reports stated that the search and rescue divers were deployed on the following day.
https://au.news.yahoo.com/thewest/wa/a/22256264/search-for-diver-continues-into-night/
I expect the media would have reported if the efforts of the search and rescue dive team were seriously affected by the weather conditions prior to the time of the release of these reports. That did not occur.
The original dive location described in media reports where the diver went missing was about 5 km northwest of the Dawesville Cut in 10 m of water. Divers said they stayed within ten metres of the boat.
https://au.news.yahoo.com/thewest/latest/a/22269013/family-gathers-amid-diver-search/
Reports also indicate that the missing man's remains were found near the original dive site.
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The original dive location was near the southern junction of the Five Fathom Bank and Murray Reefs. I've not been that far south but have dived the regions to the north along these reef systems a lot over the years. For me the mystery is how the deceased diver could have evaded the careful search of an area close to the original dive location of a team of divers over a period of even one to two days.
Unless the actual extent of injuries is much greater than is presently being indicated in the media, I'd expect the autopsy would determine if the deceased died from drowning or shark attack, the type of shark responsible for the attack and the approximate time of when the attack occurred.
In any case it now seems police accept the deceased suffered a shark attack. I expect this was self evident from the start.
https://au.news.yahoo.com/thewest/wa/a/22340802/shark-shock-over-divers-death/
In the past Fisheries WA scientists have been able to confirm this within a few days of a fatal attack and identify the type of shark responsible for the attack without the need for an inquest.