Acting Senior Sergeant Craig Dinnissen said CCTV footage of the incident showed the youth using the BB gun and ''cracking them off in the general direction of seagulls''.
The youth, who was near the Robbie Burns statue with a group of friends, fired five shots in the direction of seagulls - injuring none of them.
''He was just being an idiot,'' Acting Snr Sgt Dinnissen said.
''There was no common sense. These sorts of incidents can lead to armed offenders' callouts ... It was a moment of stupidity.''
A concerned member of the public contacted police.
The BB gun was seized and would be destroyed by police, Acting Snr Sgt Dinnissen said.
The youth was given a pre-charge warning. Black-billed and red-billed gulls are protected native birds.
