The sharks were seen between 20 and 50 metres from the shore at beaches near Gerroa, Currarong, Jervis Bay and to the north of Mollymook by the Bendigo Bank Aerial Patrol.

Several of the beaches were not patrolled from the shore.

At popular Blenheim Beach near Vincentia, swimmers left the water after seeing the shark from the shoreline.

Aerial patrol crew believed the shark was a bull shark because of its shape and rounded, stubby nose.

Bendigo Bank Aerial Patrol general manager Harry Mitchell said the sightings contradicted the findings of a recent report by the Department of Primary Industries that aerial surveillance of shark movements was ineffective.

"It's all about helping to maximise public safety by mitigating risk at patrolled and unpatrolled beaches using all of the resources available," Mr Mitchell said.

"The department continues to promote the effectiveness of its shark meshing programme despite costs of $1.4 million dollars with a confirmed shark kill of 70 sharks in the 12-month period; an average of $20,000 per shark killed on its nets.

"In the same period, the aerial patrol sighted 138 sharks close to beaches with its total budget for the year at under half a million dollars; an average of $3600 per shark sighting with no harm whatsoever to the shark."

Mr Mitchell urged swimmers to be vigilant for shark activity as water temperatures increased and fish shoals became more abundant along the coast during summer months.