It said these were causing boarding delays as punctuality fell from 90% a year ago to 88% over the past nine months.
More passengers paying far lower fares meant profits, after tax, fell 8% to €95 million in the third quarter, worse than the City had expected, and shares fell 1.9% to €14.49.
"Pricing will continue to be challenging; and we will respond to adverse market conditions with strong traffic growth and lower unit costs, Chief Executive Michael O'Leary said".
A weaker pound means that fares paid by United Kingdom customers translate into lower income for Dublin-based Ryanair - which is Europe's largest airline by passenger numbers.
Ryanair, a vocal proponent of the United Kingdom remaining in the European Union, also said there remains "significant uncertainty" about what a so-called "hard" Brexit would entail.
Ryanair has reported third quarter profits fell eight per cent to €95 million.
The company recorded an increase in revenue of €15m to €1,345bn during the period.
Ryanair chief executive Michael O'Leary also said the collapse in sterling following the European Union referendum "exacerbated" the hit from falling fares. "These falling yields were exacerbated by the sharp decline in sterling following the Brexit vote", Mr O'Leary added.
Traffic grew 16% to 29 million customers and Ryanair maintained its full year profit guidance of between 1.3 billion euro (£1.12 billion) to 1.35 billion euro (£1.16 billion), but said this is dependent on the absence of any "unforeseen security events" taking place, adding the outlook for 2017 is "cautious".
Ryanair reiterated that it expects to grow more slowly in the United Kingdom than it once planned following the country's June 23 vote to quit the European Union.
"Our headline case is that we don't expect to grow as quickly in the United Kingdom as we would otherwise have done on the fault of Brexit - because there (are) too many uncertainties there", said Chief Financial Officer Neil Sorahan at a press conference in central London. Ryanair managed to cut unit costs by 6%, excluding fuel, and unit costs overall fell by 12%.
"We expect to continue to grow strongly in continental Europe in 2017, with more new bases and routes still to be added".
Ryanair wants the United Kingdom to remain in the EU's open skies system, which allows any member-state registered airline to fly anywhere within the bloc, but has suggested that this may not be possible.