Beleaguered radio station Newstalk needs to "pull it together" after the resignation last week of Claire Byrne from its breakfast programme, according to advertising agencies which are monitoring the frequent departures from the station with increasing concern.

Byrne's departure follows the resignation of Eamon Keane from Newstalk's lunchtime programme in May and a recent demand by Byrne's co-host, Ivan Yates, that he start work a little later every morning.

Byrne is to co-present an afternoon show on RTE television, Daily Extra, with weatherman Daithí Ó Sé.

"Lunchtime and the morning slot are the drivers in radio, and Newstalk have to make sure they have their very best talent in those times," said Mark Hopkins, managing director of advertising agency Hopkins Communications. "It is time to pull it together, and as soon as possible too. If they don't keep up their market share it will result in a very tricky situation for the station. The next while is going to be crucial in financial and advertising terms and there is the opinion now that it is time for new blood."

According to Shane McGonigle, managing director of Leo Burnett, Newstalk needs "someone with a bit of weight to their name now and advertisers are watching closely. Eamon [Keane] had quite a dedicated listenership and a certain appeal for advertisers so his departure was a bit of a shock. He was very well versed and quite professional and had a good approach, and now that Byrne is gone it is more crucial than ever that a big change happens.

"They have a problem now which they need to fix, and there is no doubt that new names will have to be brought in. Claire brought a bit of personality and a bit of notoriety to the show and that is what they are going to have to find again.

"They are very important slots in terms of time and audience that need to be permanently filled in order to get the revenue in to keep the station going," said McGonigle.

Speaking about her departure, Byrne said it was "an extremely difficult decision. I agonised for months on what to do. However, when this opportunity came along, I knew it was the right thing for me to do and was the right next step. I have been out of TV four years now but I understand how it works and I know where I'm going with this."

Sources in the station say management is now looking for a permanent replacement for both Byrne and Keane.

"Juggling the presenters around isn't really an option, so they are faced with a massive dilemma, especially given the fact it is so important for advertisers and revenue," one source said.