Always good to hear someone talking about conservation.

Regardless of legality, I would think that releasing a blackfish at the dock might just kill it anyway, although not immediately.
There would be a great change in water temperature, salinity, oxygen level, pressure, and general environment in the harbor at the dock versus out on the reef where you caught it. Combine that with the stress of being in a live well for hours.
I know that this is done all the time in freshwater tournaments but I think the change in environment is not as severe in lakes and ponds.