Doc conservation services manager David Agnew said two of the three most recent attacks had resulted in the deaths of two fur seals.
In one of those cases, near Brighton, the owner had been facing a court appearance until she settled out of court and made a $700 donation to the Sea Lion Trust.
In the other, Doc did not have enough information about the identity of the owner to proceed with a prosecution, but it did issue a formal warning.
It was illegal to ''disturb'' marine mammals, and that disturbance could mean anything from ''hassling'' a marine mammal to killing it, Mr Agnew said.
The penalty for such an offence could go as high as a $250,000 fine or two years' imprisonment and the destruction of the dog.
''We use our discretion in terms of - was it intentional, what efforts were made to restrain the dog ... in deciding whether there's intent or negligence.''
Corstorphine resident Ed Baker, who witnessed yesterday's attack, said he was ''incensed by it''.
He was walking along St Kilda Beach when he saw a woman with four dogs suddenly run after the dogs into the dunes.
''I saw them attacking something in the dunes,'' he said.
As he arrived, Mr Baker saw a female sea lion roll down out of the dunes with two of the dogs still hanging on to her.
''I took a big stick and I ran to [the sea lion] and I scared the dogs off her,'' he said.
''It was horrendous.''
Mr Baker said he did not get a chance to inspect the sea lion for wounds before she went back into the ocean, but he knew she was injured because the dogs' mouths were ''covered in blood''.
He had seen dog attacks like it before, and was sick of it.
''I've been walking the beach a long time, and this is not the first time I've seen [something like] this.''
Mr Baker said he told the woman she should have had her dogs under control, but she replied that it was not her fault.
''I said, 'yes it is'.''
The woman was clearly upset by what had happened and had tried to stop her dogs from attacking the sea lion, but that was no excuse, he said.
''If you can't control your animal, don't take it on the beach.''
Mr Baker, a dog owner, said while he sometimes took his dog off-leash along the beach, it was only because he was always in control.
But ''if they banned dogs from the beach, I would adhere to it''.
Mr Agnew said he hoped people would learn from the attacks and keep their dogs under control.
''You never know when you're going to come across a vulnerable marine mammal,'' he said.
''And if it hurts something, you're responsible.''
