Status Assessment 2020 - Lesser black-backed gull
| Assessment of status | Non-Breeding Distribution | Non-Breeding Population size | Breeding Distribution | Breeding Population size | Condition i.e. breeding productivity | Previous OSPAR status assessment | Evidence of Status | |
|---|---|---|---|---|---|---|---|---|
Region | I | NA | NA | ←→2 | ←→1 | ↓235 | ● | Poor ↓1 |
| II | NA | |||||||
| III | NA | |||||||
| IV | NA | |||||||
| V | NA | |||||||
| Assessment of key pressures | Pollution | Food limitations | Climate change | Predation | Threat or impact | |
|---|---|---|---|---|---|---|
Region | I | ←→3 | ? | ←→1 | ↑5 | ←→3 |
| II | NA | |||||
| III | NA | |||||
| IV | NA | |||||
| V | NA | |||||
Explanation to table:
Distribution, Population size, Condition
Trends in status (since the assessment in the background document)
↓ decreasing trend or deterioration of the criterion assessed
↑ increasing trend or improvement in the criterion assessed
←→ no change observed in the criterion assessed
? trend unknown in the criterion assessed
Previous status assessment: if QSR 2010 then enter regions where species occurs (○) and has been recognised by OSPAR to be threatened and/or declining (● ). If a more recent status assessment is available, then enter ‘poor’/’good’
Status*(overall assessment)
red – poor
green – good
Blue cells – ? status unknown, insufficient information available,
NA - Not Applicable
*applied to assessments of status of the feature or of a criterion, as defined by the assessment values used in the QSR 2023 or by expert judgement.
Key Pressures
↓ key pressures and human activities reducing
↑ key pressures and human activities increasing
←→ no change in key pressures and human activities
? Change in pressure and human activities uncertain
Threat or impact (overall assessment)
red – significant threat or impact;
green –no evidence of a significant threat or impact
Blue cells – insufficient information available
NA – not applicable
1 – direct data driven,
2 – indirect data driven,
3 – third party assessment close-geographic match,
4 – third party assessment partial-geographic match
5 – expert judgement.
Confidence
High confidence in the status assessment because of the quantitative data used, across the entire fuscus distribution. Confidence in OSPAR region I is slightly lower due to small sample size (two monitored colonies).
Lower confidence in threat assessment because the understanding of singular as well as interactive effects of climate change, environmental pollution, competition with intermedius and the Herring gull, predation, fishing, and other threats remains poor.
Background Information
Year added to OSPAR list: 2003 (OSPAR 2003)
The original evaluation of the Lesser black-backed gull Larus fuscus fuscus against the Texel-Faial criteria referred to decline, rarity and sensitivity, with information also provided on threat.
Global/regional importance: The entire breeding population of the fuscus subspecies was at the last assessment (2009) estimated to be 18 –19 000 pairs, whereof approximately 2500 pairs bred along the Norwegian and Russian coastlines within OSPAR Region I Arctic waters. The rest of the population breeds around the Northern Baltic Sea in Sweden, Finland, Russia and Estonia. The fuscus subspecies leave the OSPAR area after breeding and spend the winter in the Middle East, eastern Mediterranean and northeast Africa, and occasionally northwest Africa.
Decline: The fuscus subspecies was considered to be strongly declining already in 2002, with a then crucial decline estimated to 90% since 1970 (ICES 2002). There were also reports of disappearance from the Murman coast of Russia.
Sensitivity: The fuscus subspecies was originally listed as sensitive due to the small breeding population being restricted to a few breeding sites. It was considered especially sensitive to oil pollution, predation and disturbances.
Anthropogenic pressures and biological factors: The likely principal threats to the fuscus subspecies were changes in the abundance of prey species, pollution such as PCBs, and competition with and predation by the Herring Gull Larus argentatus.
Last status assessment: 2009. OSPAR (2009) concluded that the subspecies continued to qualify under the OSPAR criteria due to its strong population decline, current small population size, and the limited number of breeding localities, uncontrolled threats, and inadequate conservation measures. This concern has been corroborated by the current assessment.
Geographical Range and Distribution
The Lesser black-backed gull has a complicated taxonomy with five subspecies. The subspecies fuscus breeds in the White Sea and at a few breeding sites in northern Norway, along the Baltic coasts of Sweden, Finland, and Estonia, including inland lakes in Finland and Russian Karelia.
The geographical breeding range is declining outside the OSPAR area; within the OSPAR area this is presently not known.
Outside the breeding area the subspecies is challenging to monitor as it is a long-distance migrant wintering primarily in the lakes in and around the East African Rift (Uganda, Kenya, Tanzania and Ethiopia), but also the southeastern part of the Mediterranean Sea, the Red Sea and the Arabian Sea.
Figure 1. A. Breeding distribution and B. main migratory flyways (lines) and wintering areas (end arrows) of the Lesser black-backed gull Larus fuscus fuscus. OSPAR regions I-V are denoted by Roman numerals.
Method of assessment: 2b,3b – Source: monitoring programs in Russia and Norway, but also national surveys and monitoring programs in Finland, Sweden, Estonia, as well as data for Denmark.
Population/Abundance
Trends in the number of breeding pairs (Figure 2) demonstrate a stable trend in the Lesser black-backed gull Larus fuscus fuscus in OSPAR region I since the last assessment. The seeming population drop in the Baltic Sea 1996-2000 and subsequent recovery 2000-2004 is driven by uncertainty in the Swedish surveys between 1996-2004. The trend is in reality most likely flatter during the first half of the study period (1990-2005). Whereas the trends are robust, the actual estimates are more uncertain (Figure 2 and Table 1). The number of breeding pairs in the Baltic Sea is considerably higher than in OSPAR region I.
Method of assessment: 3a – Source: national surveys and monitoring programs in Finland, Sweden, Estonia, Russia and Norway
| OSPAR Region | 2008 | 2020 | ||
|---|---|---|---|---|
| No. pairs | Relative abundance | No. pairs | Relative abundance | |
| I | 2 400 | 2,6 | 2 400 | 2,6 |
| Baltic Sea | 9 000 | 0,55 | 7 500 | 0,47 |
| Total | 11 400 | 0,66 | 9 900 | 0,58 |
Figure 2. Trends in the number of breeding pairs of the Lesser black-backed gull Larus fuscus fuscus during the period 1990-2020.
Condition
Overall, breeding success in the Lesser black-backed gull Larus fuscus fuscus is exceptionally low, in OSPAR region I as well as in the Baltic, although it varies strongly between colonies and among years. Breeding success is in general too low to maintain a stable population size, although data from the last 20 years indicate that the population in OSPAR region I might on average just reach the minimum 0,45 chicks per breeding pair per year required to maintain a stable population size (Hario & Nuutinen 2011), given adequate adult survival rates.
Method of assessment: 2b – Source: current literature, expert judgements, and indirect data.
Threats and Impacts
Threats appear to be continuing or increasing in OSPAR region I. Climate change and environmental pollution remain serious threats. The threat from predators in the breeding colonies appear to increase. The Lesser black-backed gull Larus fuscus fuscus is potentially still suffering from changes in prey abundance and composition. There is also competition from the larger subspecies intermediusand the Herring gull Larus argentatus. Other local threats are culling around fur farms and misidentification during hunting (among immatures, fuscus are mistaken for Herring gulls). The general population decline across the entire distribution suggests that the decline might be the result of several anthropogenic stressors and increased predation pressure.
Measures that address key pressures from human activities or conserve the species/habitat
Russia and Norway have introduced national legislation, as well as the HELCOM countries Denmark, Estonia, Finland and Sweden. The subspecies is on the national Red list in all the above-mentioned countries except Norway which is not recognizing subspecies. Russia and Norway, in addition to the mentioned HELCOM countries, have taken measures to protect at least some of the key areas. Similarly, there are some MPAs, although none provide the highest level of protection. Russia and Norway have monitoring programmes in place, and Norway have undertaken some awareness raising activities. In addition, Norway has an ongoing bycatch monitoring project and have implemented actions from the Nordic Action Plan for Seabirds.
The Lesser black-backed gull Larus fuscus fuscus is a long-distance migrant and there are currently a few monitoring and conservation efforts on the wintering grounds, although yet none along the migratory trajectory.
Conclusion (including management considerations)
The present status assessment confirms the vulnerable status by a small population size, but demonstrates no trend in the population size of the Lesser black-backed gull Larus fuscus fuscus in OSPAR region I since the last assessment. In the Baltic, there is a decided decline in numbers. The majority of the population is however located in the Baltic Sea. Outside the OSPAR area, the breeding range is likely in the process of shifting slightly northwards.
Threats are continuing or increasing in OSPAR region I. Climate change and environmental pollution remain serious threats, while the threat from increased predation on eggs and offspring seem to increase. Studies from the Baltic indicate that chick mortality due to organochlorine pollution has abated somewhat. Apart from the stable population development in OSPAR region I, the population decline of the Lesser black-backed gull Larus fuscus fuscus across almost its entire range is consistent with the general seabird declines. This suggests that the decline cannot be attributed to single causes but might be a result of a combination of several anthropogenic stressors, pathogens, predation, competition and food limitation.
The Lesser black-backed gull Larus fuscus fuscus, is therefore still justified for inclusion in the OSPAR List of Declining Species.
There are still no specific conservation measures targeted at protecting the fuscus subspecies and the threats remain uncontrolled.
Knowledge Gaps
The assessment was based on counts of nests or individuals during the breeding season at two monitored breeding colonies within OSPAR region I. Our understanding of the population development would benefit from inclusion of breeding success, and juvenile and adult survival into the present monitoring programs, and from monitoring also at the wintering grounds outside the OSPAR area.
The assessment of threats suffers from a lack of understanding of the joint impact of the stressors potentially responsible for the continuation of the population decline.
Method used
Main source of information:
3. Assessment derived from a mix of OSPAR data assessment and assessments from third parties
Assessment is based upon:
a) complete survey or a statistically robust estimate: this status assessment was greatly improved compared to the background document (OSPAR 2009), by the inclusion of survey data from the national monitoring programs in Finland, Sweden, Estonia, Russia and Norway, as well as data for Denmark.
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Sheet reference:
BDC2020/Lesser_black-backed_gull, Larus fuscus fuscus