Unit sales of e-books published by traditional publishers fell 13% in 2015 compared to 2014, said Kempton Mooney of Nielsen during a Thursday panel aimed at examining different publishing markets.

Units fell to 204 million from 234 million in 2014. The high point of e-book sales was 2013 when units totaled 242 million units. While e-book sales fell in the year, print units rose 2.8%, to 653 million. As a result, e-books’s market share of units dipped to 24% in 2015, down from 27% in 2014. Mooney observed that some of the gain in print sales was due to the extraordinary popularity of adult coloring books last year. The e-book sales figures came from about 400 traditional publishers, Mooney said.

In another look at e-book sales, Mooney reported that the Big 5 publishers’ share of e-book sales fell to 34% in 2015, down from 38% in 2014. In 2012, the Big 5 held a 46% of e-book unit sales. The loss of share of the Big 5 was made up by self-publishers and small publishers. Self-publishers’ share of the e-book market rose to 12% last year from 8% in 2014, while small presses accounted for 30% of e-book unit sales in 2015, up from 26% in 2014.

In some other trends taken from Nielsen’s BookScan database of print sales, Mooney said sales of children’s board books posted solid gains in 2015. He attributed the increase to adults desire to read physical books to their children rather than using digital devices. He said no one title was responsible for the increase in the year and that sales were good for both new and backlist board books.

Sticking to the children’s category, Mooney pointed to a recent survey that found 51% of children under age 9 are non-white. He said publishers that aren’t publishing books that can appeal to children from diverse backgrounds are losing “huge chunks of sales.”