A recent study, published in the journal British Birds, suggests that major oil pollution in the 1940s had a major impact on breeding seabirds around Skomer, Pembrokeshire.
Tim Birkhead from Sheffield University used photographs of the island’s cliffs taken in 1934 to estimate there were 100,000 Guillemots before World War II. By the 1960s there were fewer than 5,000. Professor Birkhead used the annual number of shipwrecks off western Britain as an index of oil pollution, to which auks such as Guillemots are very susceptible.
Not surprisingly, there was a big increase in shipwrecks in the early 1940s (350 in 1940-41 alone). These would have released oil as they sank, and many would do so for a decade or more.
Since the mid 1980s, guillemot numbers on Skomer have increased at around 5% per annum, but at almost 24,000 individuals (in 2015), this is still a just a quarter of the pre-war numbers observed from photos taken some eighty years ago.
Tim’s study highlights the value of ongoing, long-term studies of the islands seabird populations and also the need to carefully archive the data collected.
For more on this story, read this article by Tim Birkhead.