Skomer is also home to 350,000 breeding pairs of Manx shearwaters and thousands of guillemots and razorbills.
The job advert said: “In spring, the focus is on our breeding seabirds – so that’ll mean puffin counts and assisting with boat counts of seabird species.
“In summer, the focus moves to chick productivity, whilst in autumn the focus of our work is on grey seal monitoring and some of our other species, including Skomer voles, reptiles, cetaceans and moths.”
The volunteers will work on the island for about three months at a time between the end of March through to the end of September, while the seabird monitoring officer will work from 23 May to 23 June.
Volunteer duties could also include boat counts of seabird species and checking on chick productivity or grey seal monitoring, depending on the time of year.
They will also help with the day-to-day running of the island and welcoming its 25,000 visitors a year, the WTSWW said.
The Marine Conservation Society said the waters around Skomer and the Marloes peninsula constitute Wales’ only marine conservation zone.