The boat's skipper Zane Wright said the shark had drowned and was dead when they pulled it onto his boat.
Mark Collins and Eddie Bithell had been with Mr Wright on his boat and had taken the deadthresher shark to shore dead.
The three men said they took the shark back out to sea to dispose of it the next day and had decided to surf it on the way out.
Mr Collins had made a film of Mr Bithell riding the shark.
Mr Wright said he regretted filming his friend riding the shark and especially regretted putting the video online without his friend's permission.
Auckland environmentalist Catherine Cassidy said she was disgusted at the video, which she said was brought to her attention by a shark expert in Borneo.
She said she had contacted MPI and asked questions about what rules were in place at game fishing clubs that allowed, "this kind of fishing''.
Ms Cassidy, a zoologist, said the video clearly showed the men claimed the "fun'' of shark surfing.
She said the act was "a shockingly disrespectful attitude to have to some of the rare marine animals in the world''.
"We see people working hard worldwide to establish shark sanctuaries, where every shark counts, and then we acts like this from a so-called developed country. It is heartbreaking and offensive.''
Department of Conservation marine scientist and shark expert Clinton Duffy said the shark was a bigeye thresher. He said the species gad a major decline in numbers in the north Atlantic and north Pacific oceans but was not significantly affected in New Zealand waters.
Tauranga SPCA animal welfare inspector Jason Blair said it wasn't likely the action breached any laws but the SPCA "frowned upon'' mistreatment of animals, dead or alive.
- Additional reporting Bay of Plenty Times
