Two of the world’s most significant northern gannet colonies may not recover from the devastation of the 2022 bird flu outbreak for nearly two decades, according to a major new study published this week. The findings have prompted calls to reclassify the species’ global conservation status.

Published in Biological Conservation, the research examined the impact of the 2022 high pathogenicity avian influenza outbreak on gannet populations at Bass Rock in Scotland and Grassholm in Wales – two colonies that together represent a substantial proportion of the global northern gannet population. 

The results indicate that mortality rates at Bass Rock jumped from an annual average of 6% in the eleven years prior to 2022 to 33% during the outbreak. At Grassholm, the figures were even more severe: from 11% to 47%. The following year, Bass Rock’s colony had shrunk by 26%. Grassholm had lost 38% of its population.

Population modelling now forecasts that neither colony is likely to recover to its pre-outbreak size until 2041, some 19 years after the virus first arrived. The authors caution that even this represents a best-case scenario.

“The bird flu outbreak in 2022 dealt an unprecedented deadly blow to UK seabirds and these findings show that key gannet colonies on Bass Rock and Grassholm will be impacted for decades to come,” said Jude Lane, lead author and marine conservation scientist at the RSPB. 

“While we can’t prevent diseases like bird flu, with long-term monitoring at key colonies and across wider populations we can better understand the impacts. With that knowledge we are in a far better position to address the many other pressures facing seabirds and halt the devastating declines of recent years.”

The reason the damage runs so deep lies in the biology of the species. Gannets are long-lived birds with low reproductive rates – a single chick raised over months of sustained effort by a devoted pair. It is adult breeding birds that drive population growth in colonies, and it was adults that the 2022 outbreak killed in disproportionate numbers. A fourfold increase in adult mortality does not only reduce the size of a colony in the short term, but removes the birds responsible for its future recovery, stunting the population’s capacity to rebuild for years to come.

H5N1 was first confirmed at Bass Rock on 4 June 2022, and at Grassholm the following month. While the scale of the kill was already known to be catastrophic, this study is the first to provide robust estimates of adult survival in a seabird species during the outbreak, and the first to model the long-term population consequences for these two globally important colonies.

Jana Jeglinski, senior author and Associate Professor at the Department of EcoScience at Aarhus University, said: “The scale of mortality we observed during the 2022 outbreak was unprecedented. Our study shows that gannet populations will not simply bounce back from the blow of a single disease outbreak but instead will take decades to recover. We must not forget that gannets, and seabirds in general, are also under increasing pressure due to bycatch, plastic pollution and climate change to name but a few. It is now, more than ever, paramount to scrutinise, quantify, and mitigate against any additional impact on the much-depleted metapopulation.”

The study’s authors have recommended revising the northern gannet’s global conservation status – currently listed as Least Concern on the IUCN Red List – in light of the mortality scale and recovery timeline now documented. The recommendation sits within a deeply troubling broader picture for UK seabirds. The most recent Birds of Conservation Concern report, published in 2024, placed ten of the UK’s 26 breeding seabird species on the Red List.

In total, 62% of UK breeding seabird species are now in decline – rising to 70% in Scotland. Threats include climate change, unsustainable fishing practices, badly sited offshore wind development, invasive non-native mammal predation and disease.

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