Assessment

Assessment of the environmental status of seabird populations

The assessment of the environmental status of seabirds in Portugal is based on indicators developed under the OSPAR Convention, in conjunction with the criteria set out in the Marine Strategy Framework Directive (MSFD; Directive 2008/56/EC).

Mainland

On the Mainland, some populations maintain abundance levels consistent with Good Environmental Status, reflecting stable trends over the last few decades. This is the case for breeding populations of Yellow-legged Gulls, whose abundance has remained relatively stable despite interannual fluctuations, and for other breeding species such as the Cory's Shearwater, the Band-rumped Storm-petrel and the Little Tern. However, some species show less favourable trends (Table 1). Variability in productivity is particularly evident in species dependent on small pelagic fish, such as the Cory's Shearwater, suggesting a possible link to fluctuations in food availability. In the case of the European Shag, the combination of a decline in relative abundance with reduced productivity constitutes a more robust sign of changes in environmental status.

In the case of non-breeding populations that use the continental shelf, trends are generally more difficult to interpret due to high interannual variability and the influence of large-scale oceanographic factors (Table 2). Nevertheless, indicator B1 points to contrasting situations between species. Some show values consistent with a favourable environmental status, such as the Common Scoter Melanitta nigra, the Great Shearwater Ardenna gravis, the Great Cormorant Phalacrocorax carbo and the Sandwich Tern Thalasseus sandvicensis. In contrast, other species show less favourable trends in relative abundance, namely the Manx Shearwater Puffinus puffinus, the Balearic Shearwater Puffinus mauretanicus, the Northern Gannet Morus bassanus, the Great Skua Catharacta skua, the Razorbill Alca torda and the Atlantic Puffin Fratercula arctica, possibly reflecting changes in seasonal distribution or prey availability.

Overall, on the Mainland, the prevailing pattern is one of heterogeneity across species, with some populations stable and others in a less favourable situation.

Azores

The Azores are home to some of the most important breeding populations of seabirds in the North-East Atlantic, giving the region a heightened international responsibility. Species such as the Cory’s Shearwater, the Band-rumped Storm-petrel and the Roseate Tern play a central role in the regional assessment.

With regard to the abundance of breeding populations, several species show values consistent with Good Environmental Status. This is the case for the Band-rumped Storm-petrel, the Monteiro's Storm-petrel, the Yellow-legged Gull and the Common Tern, whose recent trends do not show significant reductions compared to the reference values. In contrast, other species do not meet the thresholds defined for Good Environmental Status. The Barolo Shearwater, the Roseate Tern and the Cory's Shearwater show relative abundance values below the reference levels, suggesting demographic changes that warrant close monitoring. In the case of these species, the decline in abundance may reflect a combination of factors, including variability in food availability, pressures on the open sea and constraints within the colonies.

With regard to productivity, it was only possible to assess three species, with the Band-rumped Storm-petrel showing figures consistent with a stable population trend. The Cory’s Shearwater and the Monteiro's Storm-petrel, however, do not meet the defined thresholds, which is a significant indicator, given that persistent declines in breeding success may foreshadow future declines in abundance.

Overall, the Azores present a largely stable picture, but with signs of vulnerability in some key species, reinforcing the importance of maintaining robust time series and continuous monitoring.

Madeira

In Madeira, it was only possible to assess the environmental status for a smaller number of species, reflecting the limited size of the breeding populations and the availability of consistent time series. In total, only five species provided sufficient data for the application of the indicators.

With regard to the abundance indicator, the majority of the species assessed show values consistent with Good Environmental Status. The exceptions are the Yellow-legged Gull and the Black-headed Gull Larus ridibundus, for which relative abundance values fall below the defined thresholds.

Cory’s Shearwater shows favourable results for both the abundance and productivity indicators, suggesting an overall stable demographic situation in the region. In contrast, the endemic species, the Desertas Petrel and the Zino's Petrel, do not meet the thresholds defined for the productivity indicator. Given the small size of their populations and their restricted distribution, these results are of particular relevance for regional conservation, highlighting the vulnerability of these species to changes in environmental conditions and cumulative pressures.

National assessment

A joint analysis of the three regions reveals a varied picture of the environmental status of seabirds in Portugal (Table 3). On the Mainland, there is significant heterogeneity between species, with contrasting situations in both breeding and non-breeding populations, reflecting the high oceanographic variability and the diversity of pressures on the continental shelf. In the Azores, although several species maintain levels consistent with Good Environmental Status, signs of vulnerability are emerging in key species, particularly when considering the productivity indicator. In Madeira, where only four of the 10 breeding species could be assessed, the situation is generally stable for most of the species analysed, but there is particular concern regarding endemic species, for which productivity below the defined thresholds highlights their ecological sensitivity.

Overall, the results reveal a largely stable situation at national level, but one marked by regional contrasts and specific warning signs that justify enhanced monitoring, particularly for species with restricted distribution or those heavily dependent on variable marine resources.