Richard Collins: New evidence on seabirds seems to confirm Ashmole's Halo

A beautiful sunrise at Skellig Rock.

Ocean wanderers from all over the North Atlantic converge on Irish sea-cliffs and islands each summer. The seabird breeding colonies of the Skelligs Saltees and Blaskets are among Ireland’s greatest wildlife attractions. Visiting these avian cities is an exhilarating experience, but spare a thought for the local fish; what is it like for them?

In 1963, ornithologist Phillip Ashmole suggested that the size of a seabird breeding colony can be limited by the amount of food available in its vicinity. As bird numbers rise, he argued, the local fish stocks become exhausted and a ‘halo’ forms, inside which fish numbers decline rapidly.