Big swells made it difficult for the group to anchor a tyre basket to put their mussels in, so they swam to another group of rocks, he said.
Later, Mr Delamere-Keane saw his friend get into trouble as he tried to swim through rough seas.
"Peeti heard Anaru call out 'Peeti, help me', [and] Peeti started swimming out to Anaru," Mr Ferguson said.
"But by the time Peeti was where he last saw Anaru, Anaru had disappeared under the water."
Mr Gage's friends tried looking for him but, in poor visibility, were forced to return to shore and raise the alarm.
His body was found the next morning by local divers, who could not recover Mr Gage at first because of the heavy weight belt still attached to him.
His father in law, John Wharepapa, later told police that Mr Gage would have only needed to use half the weight.
But his son-in-law had told him that the heavy weights made it "effortless" for him to reach the sea floor when diving.
Mr Wharepapa also said the swells had made diving dangerous.
"I was aware of the weather conditions on the day Anaru drowned and I would not have dived that day because it was so rough."
Mr Gage had been in the process of completing a civil construction course and was described by one local as "a really nice young guy with a couple of tamariki (children)".
He was described as a healthy young man and the exact cause of his death was unable to be ascertained, as his whanau opposed a post-mortem examination being carried out on cultural grounds.
His father, Hori Gage, told today's inquest that the whanau wanted closure and appealed to Coroner Wallace Bain to see the process through as quickly as possible.
Dr Bain described the death as "a tragedy" and called into question the diving conditions and weight belt.
He has reserved his finding.
