RTE Radio 1 head Tom McGuire said that it was "poignant" to see the late Marian Finucane's surge in listenership for her Sunday show in the months before her death.
The latest JNLR figures revealed that the legendary broadcaster gained 19,000 more listeners for her weekend programme, bringing her up to 309,000.
Her Saturday morning show had a slight drop of 2,000 down to 341,000 but was still the most listened to show at the weekend.
"It was particularly poignant for us to see the great performance of Marian reflected in her programme's increase. Her Sunday show went to over 300,000 and that's a really brilliant performance," he said.
"She went out on a high and was so crucial to our schedule. About 12 or 13 years ago we didn't have this listenership on a Saturday or a Sunday morning.
"Before that, you might feature a gardening or a comedy show, but this was a new creation and she did build up the audience.
"This is a really big challenge for us now."
He said that Finucane, who died suddenly at her home in Kildare on January 2, was irreplaceable and RTE will be completely revamping her slot on the weekend schedule.
"It will be a couple of months before we confirm anything. We have been having conversations about it but we need to be respectful following Marian's death," he said.
"We won't be replacing her; we will be launching a new programme in the middle of March."
He added he was "happy enough" with RTE Radio 1's performance in the latest JNLR survey, which is compiled every three months and shows gains for all its shows.
Miriam O'Callaghan made huge gains in the latest survey, her Sunday programme jumping 29,000 listeners to 265,000.
Morning Ireland retained its position as the most listened to programme, standing now at 441,000.
Ryan Tubridy increased his audience by 2,000 to 336,000, while Sean O'Rourke jumped 6,000 to reach 321,000.