Patronage on Perth's public transport network fell by more than two million in 2013-14 - the first annual decline in more than a decade.
The Public Transport Authority has partly blamed the fall on economic factors, with evidence Perth families are spending less of their disposable income on public transport.
The Opposition said the decrease was a result of overcrowded trains, fare rises and the lack of public transport expansion in Perth's growth suburbs.
The latest figures show overall patronage fell from 149.7 million boardings in 2012-13 to 147.6 million in 2013-14.
Train travel was down across all lines, with the biggest falls on the Fremantle line (down 581,495, or 6.6 per cent) and Armadale (down 491,553, or 5.1 per cent).
Bus patronage rose slightly (by 170,666, or 0.2 per cent) but ferry numbers fell to their lowest in at least 11 years (down 29,628, or 6.4 per cent).
PTA spokesman David Hynes said the state of the economy appeared to be a factor, with strong evidence of less discretionary travel on the network.
"FamilyRider and DayRider use are down," he said. "This suggests some passengers may have less disposable income and are choosing to stay at home or are at least being more measured in their amount of leisure activity.
"Further, office vacancy rates are up, so we believe fewer people are travelling into the city on a typical work day."
Mr Hynes said the Perth City Link project had two major shutdowns, in July and August, which had an impact on patronage.
"There was also very bad weather between July and September last year," he said.
Shadow transport minister Ken Travers said public transport patronage was often price sensitive and fare increases in the past two years may have had an impact. Overcrowding had also discouraged the use of public transport.
Mr Travers said the fall in patronage was also a reflection of the Barnett Government's inability to service Perth's urban growth areas with trains.