Te Puke was the only Western Bay area to buck the trend, with a 27 per cent increase in bus use to 12,217 journeys - the biggest percentage increase on the network.
Bus use in Rotorua dropped 10 per cent, while the core services in the Eastern Bay of Plenty were 9 per cent more popular than the year before.
In his report, council senior transport operations officer Mike Furniss said bus service reliability was a "major issue" in Tauranga.
In the year to March, 802 trips were delayed by more than 20 minutes, with traffic to blame in 78 per cent of cases.
Four of the city's 12 routes - 1, 2, 36 and 40 - accounted for almost three quarters of delayed trips.
Despite being only nine months into the financial year, the number of complaints about late or missing buses in Tauranga have already eclipsed the totals for each of the full previous years.
And in mystery shopper ratings, "punctuality and reliability" was the only part of the service to drop below 80 per cent. Mystery shoppers rated other aspects of the service, including price, comfort, and driving, at close to 100 per cent.
Committee chairman Lyall Thurston said the regional council acknowledged the issues.
"Until we get the infrastructure and the proper electric bus fleet and make the whole experience more favourable for people we acknowledge that we're going to have a challenge.
"What were truing to do is free up the congestion."
He said the regional and city councils were working collaboratively to find solutions.
Public transport advocate Heidi Hughes of Greater Tauranga said dropping bus usage rates were no surprise given the unreliability of the network.
"My husband often takes the bus and two days ago it was 20 minutes late. He ended up taking the car the next day."
She said the issues were the result of years of inadequate investment in bus infrastructure and the network.
"Tauranga City has not kept up with some other main centres in terms of investment."
She said councils had a window of opportunity to make the most of the current Government's commitment to increasing transport funding.
Tauranga was in a strong position to argue for a bigger piece of the public transport funding pie given its port and potential for economic growth, Hughes said.
In a letter tabled at today's public transport meeting, Transport Minister Phil Twyford said he would welcome the council's feedback on improving Tauranga's bus services, as well as developing the rail network to the Port of Tauranga.
Bus patronage - year to date comparison
Tauranga Bayhopper: down 6 per cent
Tauranga Schoolhopper: down 9.7 per cent
Rotorua: down 9.9 per cent
Eastern Bay main centres: up 8.9 per cent.
Source: Bay of Plenty Regional Council
