Northern Gannet populations facing a long road to recover study finds

The findings, published in the July issue of Biological Conservation, show bird flu was responsible for a fourfold increase in deaths of adult Gannets, for which the UK is responsible for a high proportion of the global population.

Mortality rates were found to have jumped from an annual average of 6% at Bass Rock and 11% at Grassholm in the 11 years prior to 2022, to 33% and 47% respectively during the outbreak. This led to a 26% decrease in the size of the Gannet colony at Bass Rock and a 38% decline at Grassholm in 2023, the year after the outbreak.

As it is adult breeding birds that drive the population growth in colonies, the spike in deaths will have a profound negative impact on overall population size and future sustainability. Population modelling forecasts that the colonies are unlikely to recover to the size they would have had until 2041, 19 years after the outbreak. However, the authors caution that these predictions are a likely best-case scenario and recovery could take even longer.

The study’s authors have recommended revising the species’ global conservation status – currently Least Concern on the IUCN Red List – in light of this unprecedented mortality and subsequent population recovery time linked to a single disease outbreak.

The H5N1 bird flu virus was first identified in poultry in Asia in 1996 before spreading to wild bird populations. H5N1 was first confirmed in Gannets at Bass Rock on June 4, 2022, and at Grassholm the following month. While the outbreak was already known to have killed tens of thousands of Gannets, this latest study is the first to provide robust estimates of adult survival in a seabird species, and, using these estimates, the first to predict the long-term impact and population recovery times for these two globally important seabird colonies.

Jude Lane, lead author of the study and marine conservation scientist at the RSPB, said: “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.

“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.”

Jana Jeglinski, senior author of the study and Associate Professor at the Department of EcoScience at Aarhus University in Denmark, 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.”

Recent surveys have highlighted the dire situation facing the UK’s seabirds, with the status of many breeding populations continues to deteriorate. The most recent Birds of Conservation Concern report published in 2024 placed ten (38%) of the UK’s 26 currently occurring breeding seabird species on the Red list. While Gannets remained Amber-listed, it was noted at the time that more evidence was needed to assess the impact of bird flu on the species.

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, disease such as bird flu and predation by invasive non-native mammals.