a large breeding population of subantarctic fur seals and some southern right whales still migrate around the island. House mice are currently present on the island (see Invasive Species). Invasive species Pearlwort (Sagina procumbens) In 1998, a number of procumbent pearlwort (Sagina procumbens) plants were found on the island which are capable of dramatically transforming the upland plant ecosystem (as it has on the Prince Edward Islands). Eradication efforts are ongoing but are expected to require years of 'concerted effort'. House mice In April 2007, researchers published evidence that predation by introduced house mice on seabird chicks is occurring at levels that might drive the Tristan albatross and the Atlantic petrel to extinction. As of October 2018, it is estimated that as many as 2,000,000 fewer eggs and chicks are being raised due to the impact of mice on the island, threatening the extinction of several species of seabirds that breed exclusively or nearly exclusively on Gough Island. The Royal Society for the Protection of Birds awarded £62,000 by the UK government's Overseas Territories Environment Programme to fund additional research on the Gough Island mice and a feasibility study of how best to deal with them. This grant also paid for the assessment of a rat problem on Tristan da Cunha island. Trials for a method of eradicating the mice through baiting were commenced, and ultimately a £9.2 million eradication programme was planned, and set to begin in 2020, with the island expected to be mouse-free by 2022. However, the start date was delayed until 2021 due to the COVID-19 pandemic. The programme used helicopters to drop cereal pellets containing the rodenticide brodifacoum. Gough has also been identified as the third-most important island in the world (out of 107 islands) to be targeted for the removal of non-native invasive mammals to save threatened species from extinction and make major progress towards achieving global conservation targets. The proposed cull was criticised by the director of Animal Aid stating "We don’t feel we have the right to choose some animals over others ... We don’t agree with any culling for so-called conservation purposes. The conservation priority should be making sure wild spaces are protected, but allowing nature to do its thing." As of December 2021, the head of the project to cull the population of mice considers this to have been a failure, since a living mouse was spotted after the completion