What’s damaging new fronds on the tree fern?

Hello all. Got a tree fern around Christmas and didn’t put enough frost protection in the crown during the winter so it has struggled slightly to establish itself. Was very excited to see a number of new fronds emerging this week. Woke up to find this damage on one of the new fronds that hasn’t unfurled yet – any idea what’s causing this? The existing fronds have similar damage to various degrees and I had put it down to abrasion sustained against the old fronds stumps so I have trimmed them shorter. But this one looks like animal damage? I’ve seen the odd snail/slugs in the crown; do they nibble? Although this doesn’t look like a nibble either. Thanks all!