AN UPDATED POPULATION ESTIMATE FOR NORTHERN GANNETS ACROSS THEIR NORTH-EAST ATLANTIC BREEDING RANGE FOLLOWING THE 2022 OUTBREAK OF HIGH PATHOGENICITY AVIAN INFLUENZA
Following a severe 2022 High Pathogenicity Avian Influenza outbreak, a comprehensive 2023/24 census reveals that the Northern gannet population across the North-East Atlantic metapopulation has declined by 17% to 345,854 apparently occupied sites, with the largest colonies suffering the most significant losses and Scotland retaining the majority of the remaining global population.
Original authors:Quinn, L., Jeglinski, J. W. E., Auhage, S., Balmer, D., Bringsvor, I. S., Burton, E., Castenschiold, J. H., Christensen-Dalsgaard, S., Danielsen, J., Dierschke, J., Ezhov, A. V., Gudmundsson, G. A., HQuinn, L., Jeglinski, J. W. E., Auhage, S., Balmer, D., Bringsvor, I. S., Burton, E., Castenschiold, J. H., Christensen-Dalsgaard, S., Danielsen, J., Dierschke, J., Ezhov, A. V., Gudmundsson, G. A., Hart, T., Jessopp, M., Jones, R., Krasnov, Y. V., Lorentsen, S.-H., Palsdottir, A. E., Provost, P., Purdie, A., Morgan, G. D., Emma, M., Olsen, B., Strom, H., Tierney, D. T., Wilson, L. J., Wanless, S.
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Imagine the Northern Gannet as a star athlete who has been on a winning streak for over a century. While many other seabirds have been struggling to stay in the game, these birds have been thriving, growing their numbers steadily throughout the 20th and 21st centuries. They were the "success story" of the ocean.
However, in 2022, a sudden and severe "flu season" hit the entire team. This wasn't just a common cold; it was High Pathogenicity Avian Influenza (HPAI), a deadly virus that swept across their entire global home. Because of this outbreak, scientists realized they needed to take a fresh headcount to see how much the team had been hurt.
The New Scoreboard The researchers went to every major nesting site across the North-East Atlantic (from Scotland and Ireland to Iceland, Norway, and even as far as Russia) to count the birds in 2023/24. Here is what they found:
The Big Drop: Between the last count in 2013/14 and this new one, the population of breeding sites dropped by 17%. Think of it like a stadium that used to hold 414,598 fans; now, only 345,858 seats are occupied.
The Heavy Hitters: The biggest losses happened at the "super-stadiums"—the massive colonies with over 10,000 birds. These giant groups lost tens of thousands of birds each, dragging the total numbers down significantly.
The Real Impact: The numbers above are likely a "conservative estimate," meaning the actual hit from the virus might be even worse than the math shows. Why? Because many colonies were actually growing right before the 2022 outbreak. If you count the growth that was lost, the drop is steeper. Also, the Canadian population wasn't counted after the virus hit, so the global picture is incomplete.
Who Holds the Most Birds? Even after the crash, the UK and Ireland remain the "home base" for these birds:
Scotland is the heavyweight champion, holding nearly 60% of all the birds in this region and almost half (46%) of the entire world's population.
Great Britain, Ireland, and the Channel Islands combined are the "powerhouse trio," holding 83% of the North-East Atlantic population and 64% of the global population.
The Takeaway This paper isn't just about updating a number on a spreadsheet. It serves as a stark reminder of how quickly a disease outbreak can shake a species that was previously thought to be safe and growing. It highlights that we need to count these birds more often, like checking a patient's vitals regularly, so we can truly understand the damage caused by events like this and help them recover.
Technical Summary: Updated Population Estimate for Northern Gannets Post-HPAI Outbreak
1. Problem Statement Northern gannets (Morus bassanus) have historically been considered a conservation success story, characterized by population growth throughout the 20th and 21st centuries, contrasting with the global decline of many seabird species. However, this trajectory was disrupted by a severe outbreak of High Pathogenicity Avian Influenza (HPAI) in 2022, which affected the species across its global distribution. This event created an urgent need to reassess the population status of the North-East Atlantic metapopulation, as previous data (last collected in 2013/14) no longer reflected the demographic reality following the disease outbreak.
2. Methodology The study conducted a comprehensive breeding census of Northern gannets across the entire North-East Atlantic metapopulation during the 2023/24 breeding season.
Geographic Scope: The survey covered all known colonies in Great Britain, Ireland, the Channel Islands, Iceland, Norway, the Faroe Islands, France, Germany, and Russia.
Metric: Population size was quantified using "apparently occupied sites" (AOS) as the primary unit of measurement.
Comparative Analysis: The 2023/24 census data were compared against the baseline data from the 2013/14 census to calculate population trends and percentage changes.
Stratification: The analysis specifically examined population changes across different colony sizes, with a focus on large colonies (>10,000 AOS).
3. Key Results
Population Decline: The North-East Atlantic metapopulation experienced a significant contraction, decreasing by 17% between the 2013/14 and 2023/24 census periods. The total number of AOS dropped from 414,598 to 345,854.
Global Impact: This regional decline represents a global decrease of at least 13%.
Drivers of Decline: The reduction was not uniform; it was disproportionately driven by the largest colonies (>10,000 AOS), which each lost tens of thousands of AOS.
Underestimation of Impact: The reported figures likely underestimate the true severity of the HPAI outbreak. This is because:
Most colonies were likely growing between the 2013/14 census and the 2022 outbreak, meaning the baseline for comparison was artificially high relative to the pre-outbreak trend.
The Canadian breeding population was last counted prior to the HPAI outbreak and was not included in this specific post-outbreak reassessment.
Geographic Distribution:
Scotland remains the critical stronghold, holding 59% of the North-East Atlantic metapopulation and 46% of the global population.
The combined region of Great Britain, Ireland, and the Channel Islands holds 83% of the North-East Atlantic metapopulation and 64% of the global population.
4. Key Contributions
First Post-Outbreak Census: This study provides the first updated breeding census for Northern gannets across the North-East Atlantic following the 2022 HPAI event.
Quantification of Disease Impact: It offers empirical evidence of the large-scale demographic consequences of a single disease outbreak on a seabird species across its entire range.
Baseline Establishment: The data establishes a critical new baseline (2023/24) for monitoring future recovery or further decline, replacing the decade-old 2013/14 data.
5. Significance The study underscores the vulnerability of even historically "successful" seabird populations to acute, high-mortality events like HPAI. The 17% decline in a single decade reverses decades of growth, signaling a potential shift in the species' conservation status. Furthermore, the research highlights a critical gap in monitoring infrastructure: the lack of regular, synchronized census efforts makes it difficult to accurately quantify the immediate and long-term demographic consequences of such catastrophic events. The authors argue for the implementation of more frequent census cycles to better inform conservation strategies and population modeling in an era of increasing disease threats.