Seabirds: strategic ornithological compensatory measures: review

6 Scoping and targeted reviews

For the proposed compensatory measures (Table 4) that could not readily be allocated to conservation actions, we undertook scoping reviews (see: Methods). For longline bycatch mitigation, however, where recent comprehensive work exists, we summarised the findings of these studies through a targeted review.

There is a dedicated section for each review, commencing with a list of the focal species identified in Table 4 and Table 6. This is followed by a general description of the key types of actions falling under each topic, identification of key sources, and discussion on potential conservation actions, followed by a conclusion. At the end of the section, there is a table summarising details of the identified conservation actions (Table 41).

6.1 Manage supporting habitats that relate to prey availability for seabirds

Focal and secondary species: Large gulls, Gannet, petrels, Guillemot, Razorbill, Puffin, terns

Actions identified: Habitat creation and restoration (e.g. seagrass) (CA1); Protection of spawning and nursery habitat (CA2).

This topic relates to actions aimed at improving or restoring habitats that support the prey species of seabirds. By doing so, these actions would increase prey abundance and, ultimately, enhance their availability to seabirds.

Seabird populations are sensitive to the abundance and availability of prey fish, as was outlined in the report sections focussed around prey fishery management (see Ecological feasibility: Sandeel fishery closure and Ecological feasibility: Fishery closure or enhanced management of prey fisheries (Sprat, Herring, and Mackerel)). As explained elsewhere in the report, establishing a direct link between prey abundance and positive impacts on seabird populations is challenging given the complexities within the ecosystem (illustrated in Figure 28). As such, managing prey-supporting habitats becomes even more challenging to directly correlate with population-level responses in seabird populations, which means that such measures may be difficult to develop as compensatory measures. Nevertheless, supporting habitats is crucial for seabird prey species and associated conservation actions would, in principle, lead to beneficial impacts for seabird populations.

The types and distribution of essential fish habitat supporting key fish species in Scottish Waters were recently reviewed in a Scottish Government commissioned report (Franco et al., 2022). This report reviewed many fish and shellfish species, including several which are prey species of seabirds, during at least part of their life cycle, e.g. Lesser Sandeel, Herring, gadoid species, Sprat, and Mackerel. This review builds on earlier studies which have focussed on individual species, e.g. Sandeel (Langton et al., 2021). Critical fish habitat depends on a variety of biotic (e.g. maerl beds and seagrass beds) and abiotic (e.g. substrate and water depth) factors. The types of habitats used by fish can vary across different life stages and, for migratory species, this can mean that the abundance of fish in one area is linked to conditions in a more distant area. This complexity adds difficulty when considering how this can translate in prey availability to seabirds.

We identified two high level conservation actions relating to management of supporting habitat related to prey availability in seabirds: habitat creation and restoration, and protection of spawning and nursery habitat. Each of these include a wide variety of more specific actions, e.g. habitat creation includes multiple habitat types, with one of the most widely considered being seagrass beds.

For habitat creation and restoration for inshore waters, NatureScot have produced guidance that outlines many of the points that need to be considered when developing such projects, including both ecological and practical considerations (NatureScot, 2022; 2023f). The Scottish Government, on the other hand, have produced guidance on the marine licensing considerations (Scottish Government, 2023b).

The creation and restoration of seagrass beds is one of the more developed types of marine habitat creation and restoration, which has previously been considered in the context of project-specific compensation for offshore windfarms (e.g. Hornsea Project Four). Seagrass beds have been identified as providing some of the most suitable habitat for nursery stages of several fish species in Scottish Waters (Franco et al., 2022). At the same time, seagrass beds have been associated with supporting bird populations through increased marine productivity (Unsworth and Butterworth, 2021). There is currently one such seagrass restoration project (also including oysters) underway in the Firth of Forth in Scotland, the Restoration Forth project led by WWF running between 2022-2024.

While habitat creation and restoration has promise, it is important to recognise that not all marine habitats can be recreated or restored (Tillin et al., 2022). This may limit the size of the possible benefit to seabird populations. For example, maerl beds are one important habitat type which are considered to be difficult to recover (Barbera et al., 2003). Tillin et al. (2022) provide a useful review of the principles that need to be considered to identify whether a habitat is possible to restore (there in the context of identifying what habitat is irreplaceable).

The protection of spawning and nursery habitat focusses on either removing existing pressures or avoiding potential future pressures to habitat (Aguilar and Blanco, 2019). For soft substrates, such as sand and gravel, fisheries using bottom trawling can negatively impact seafloor habitat with the extent of this varying between different gear types and sediments (Rijnsdorp et al., 2020). For Sandeel, their abundance is negatively correlated to the intensity of bottom trawling present in an area (Tien et al., 2017). For protected areas (e.g. SACs), additional regulations can be introduced to prohibit damaging gear types, as has been done recently via a bylaw prohibiting bottom towed fishing gear within the Dogger Bank SAC (MMO, 2022). Such management measures could potentially be introduced for other areas identified as being sensitive to such bottom gears.

There is an evidence base confirming the importance of supporting the habitat of seabird prey fish species and, therefore, conservation actions that could act to protect, restore, and create such habitats could ultimately lead to seabird population level responses. However, the uncertainties are very high meaning that it will rarely be possible to produce confident quantitative predictions of seabird population level responses to individual initiatives. It is therefore not clear that such measures would be suitable as compensation. However, given the potential for benefits to seabird populations, further research and investigation would be justified. An addition to improving the scientific evidence base, essential for using such measure as compensation, would be to develop a framework around which such ecosystem-based measures could be linked to seabird population level responses with sufficient confidence to justify deployment as compensation.

6.2 Reducing disease spread (including HPAI)

Focal species: All seabird species

Actions identified: Carcass collection during disease outbreaks (CA3); Managing standing water (CA4); Vaccination of wild birds (CA5); Rehabilitation of sick birds (CA6).

Birds are vulnerable to a variety of infectious diseases, with a diversity of emerging diseases increasing the future threat to wild bird populations (Bogomolni et al., 2006; Robinson et al., 2010). Botulism and HPAI, for example, have caused significant mortalities within UK seabird populations (Coulson, 2015; APHA, 2019; Klaassen and Wille, 2023; Lane et al., 2023; Pearce-Higgins et al., 2023). Depending on the disease and the context, some effective interventions exist to reduce its spread, thereby reducing population level impacts. However, in general the options are limited, particularly when dealing with seabirds breeding at remote locations.

Avian botulism is a disease leading to paralysis in birds arising from ingestion of a bacterial toxin produced by Clostridium botulinum. Outbreaks occur where there are suitable conditions for the bacteria to multiply, particularly in conditions of poor water quality (e.g. putrefying plant or animal material) (APHA, 2019). There have been sporadic outbreaks of botulism in seabirds in the UK, mostly affecting gulls (Coulson, 2015; APHA, 2019). However, there seems to have been a reduction in these occurrences following changes in landfill practices (Coulson, 2015). Best practice recommendations exist for dealing with outbreaks of botulism, with the key conservation actions identified being: the management of water bodies to reduce suitable conditions for the bacteria; collection of dead and sick birds; and rehabilitation of sick birds (WWT, 2012; APHA, 2019). There is, therefore, potential for a programme of measures to be effective in decreasing the frequency and severity of avian botulism outbreaks, and to rehabilitate sick birds. However, it is unclear to what extent such measures can be increased. If further action is both possible and effective, it may have some potential as a compensatory measure. This would require a detailed feasibility assessment.

Avian influenza is endemic to seabird populations (Granter et al., 2010; Montalvo-Corral et al., 2010; Wille et al., 2013), with recent highly pathogenic strains emerging, resulting in significant wild bird mortality (Klaassen and Wille, 2023). Since 2021, there has been an outbreak of HPAI within the UK, which has caused significant mortality among seabird populations (Lane et al., 2023; Pearce-Higgins et al., 2023). This outbreak is part of a global epidemic now impacting nearly all continents (Klaassen and Wille, 2023). Currently there are no universally accepted approaches for reducing the spread of HPAI, however there is a significant amount of ongoing research which may lead to identifying effective interventions. If these are identified and they are practical to implement in UK seabird populations, then there could be potential as a compensatory measure. Some candidate interventions have been proposed and, to a limited extent, trialled (reviewed in Pearce-Higgins et al. (2023)).

Carcass collection has been proposed with some evidence that this may reduce outbreak severity (Knief et al., 2023), though its efficacy remains unclear (Pearce-Higgins et al., 2023). NatureScot’s Scientific Advisory Committee advises that the benefits, if any, are likely to be small unless demonstrated that much of transmission occurs from carcasses and that they can be removed at scale and rapidly (NatureScot, 2023g). There is general agreement that good biosecurity protocols would be justified, however these are unlikely to significantly reduce overall mortality. Vaccination may be a future option as a vaccination is being trialled currently on California Condors with promising early results (U.S. Fish and Wildlife Service, 2023). However, vaccinating large number of wild birds would be impractical. Nonetheless, it may have potential in more limited cases, such as in cases where there are small remnant populations at sites that could be protected. Overall, reducing the risk from HPAI outbreaks in wild bird populations will be largely reliant on actions to reduce the emergence of new strains from poultry production worldwide.

There are conservation actions identified for avian botulism but limited options currently available for HPAI. Further research and monitoring are required to identify whether there are effective interventions available for HPAI in wild birds. If these are identified, there may be scope for compensatory measures to allow these to be deployed at scale. However, even if options are identified, their practicality in seabird populations is likely to be constrained due to the nature of seabird colonies (e.g. steep cliffs, relatively inaccessible locations). Overall, it appears that there is limited scope for the reduction of disease spread to be developed as a compensatory measure.

6.3 Habitat Management (terrestrial breeding colonies)

Focal and secondary species: Gannet, Guillemot, Razorbill, Puffin, gulls, terns

Actions identified: Construction of coastal defence structures to reduce impact of storm events (CA7); water management to reduce flooding of burrow nesting seabirds (CA8); vegetation management to improve breeding habitat quality (CA9).

Habitat quality influences both the number of seabirds breeding at a site and their productivity. Therefore, habitat management actions can have potential to increase the breeding numbers and productivity of seabirds. Key aspects include how breeding habitat withstands extreme weather events and the presence of vegetation. To what extent these can be managed will be highly site-specific.

Seabirds breeding on coastal sites in exposed areas can experience nesting failure following summer storms, with one such event on the Isle of May leading to failure rates of 10–29% for species nesting in exposed areas (Newell et al., 2015). Such events are likely to increase in the future owing to climate change, with sea-level rises and increasing frequency and severity of storm events. Options to mitigate the impacts of these events at most seabird colonies are likely to be limited. Two potential options include coastal defence structures, such as boulders placed at cliff bases to reduce wave energy, and managing habitat to create new breeding spaces (e.g. vegetation clearance). There may also be potential for restoration or establishment of sub-sea habitats (e.g. kelp forest) that can increase wave attenuation, though it would be quite site-specific whether habitat is suitable, and the level of potential benefit in terms of reducing storm impacts is unclear (Elsmore et al., 2023).

Extreme rainfall events can lead to nesting failure through flooding in burrow nesting seabirds, including Manx Shearwater and Puffin (Thompson and Furness, 1991; Rodway et al., 1998). Climate change is increasing the frequency of extreme weather, so there is an increasing risk of flooding events. At some sites it may be possible to reduce flood risk through water management and drainage schemes; this would require site-specific investigation.

Vegetation can affect habitat quality, especially for burrow and ground nesting seabirds (Lamb, 2015). Interestingly, there is some evidence of positive feedback loops between the vegetation community and the abundance of seabirds at a site, with one study in Canada finding that when there is a greater population of Leach’s Storm Petrel there is more suitable vegetation (Duda et al., 2020). Tree Mallow (Lavatera arborea) is a native plant to the UK but can have significant negative impacts on seabird colonies, particularly on burrow-nesting Puffin (Fischer and Van Der Wal, 2007). Favourable conditions over recent decades have led to increases in Mallow (Van Der Wal et al., 2008), prompting projects aimed at its removal, such as those around the Firth of Forth. While Mallow has been largely removed from the island of Craigleith (The SOS Puffin Project), apparently leading to an increase in the number of breeding Puffin, some plants persist in inaccessible areas of the island, and a seedbank remains, necessitating ongoing management (Anderson, 2022). Further Mallow removal is planned for two further Firth of Forth islands, Fidra and Inchmickery, as part of a new project (RSPB).

Overall, there are several potential conservation actions to improve seabird breeding habitat quality. However, some of these are relatively well demonstrated (e.g. Tree Mallow removal), while others are much more speculative (e.g. flood management and wave defences). Further work would be useful to scope out, in detail, what habitat management options exist and to identify suitable sites where these could be deployed. There is likely some scope for these actions to be used as strategic compensation, so further consideration could be worthwhile.

6.4 Bycatch mitigation in longline fisheries

Focal species: Gannet, Fulmar

Actions identified: Mitigation of bycatch in longline fisheries (CA10)

In Scottish Waters, there is a floated-demersal longline fishery (also referred to as ‘piedra bola’) which primarily targets European Hake (Merluccius merluccius). This is a unique type of longline fishery gear composed of longlines with a series of baited hooks interspersed with weights and floats that act to hold the hooks up above the seabed. Analyses of bycatch rates in UK Waters have identified concerning levels of bycatch of seabirds in this fishery, particularly of Fulmar and, to a lesser extent, Gannet (Northridge et al., 2020; Northridge et al., 2023). This followed on from earlier work mapping fishing activity, its overlap with seabird distributions, and species-specific bycatch risk that suggested longline fisheries could be of concern, i.e. a vulnerability assessment (Bradbury et al., 2017).

The incidental bycatch of seabirds by fisheries has been identified as one of the top three threats to seabird species globally, and the threat with the greatest average level of impact (Dias et al., 2019). Longline fisheries, in particular, have a high risk of seabird bycatch (Anderson et al., 2011), a phenomenon that has been extensively studied in albatross and petrel species in the southern hemisphere but has received less attention in the North-East Atlantic. Seabirds are attracted to fishing vessels for offal, bait, discards, and also for the catch itself, depending on the fishery and the seabird species.

Bycatch rates have been estimated based on a UK fishery observer programme ^[4], which deploys observers onto UK registered vessels operating out of UK ports, predominantly in the north-west of Scotland. Estimates of bycatch rates have high levels of uncertainty due to relatively low observer coverage and a non-systematic sampling approach (sampling has been undertaken on a ‘sporadic and opportunistic basis’), with coverage of ca. 0.5% (Kingston et al., 2023), which falls well below the recommended minimum of >20% (Babcock et al., 2003). In any given year, there are ca. 500 trips made by UK registered longline vessels, but between 2010–2021 only 23 trips were observed (including 201 hauls) (Kingston et al., 2023). Kingston et al. (2023) produced the most up-to-date bycatch estimates, including year-specific estimates. For Fulmar, estimates were of >1000 individuals for most years, with levels increasing in recent years due to higher fishery activity. For Gannet, estimates were around 50 individuals/year but increased >100 individuals/year in recent years. In addition, there are small numbers of Great Skua (ca. 10 individuals/year) and Great Shearwater (ca. 15-25 individuals/year). It should be noted that non-UK registered vessels also operate in UK waters and are not included within these bycatch estimates, so total bycatch mortality is likely to be significantly higher.

It should also be noted that there are likely to be sub-lethal impacts for surviving birds (e.g. physical injury and stress). Bycatch monitoring exclusively records mortality, and not live-caught birds that are released. The level of live bycatch is unclear; if bycatch primarily occurs during setting, which is likely, then most birds would be dead due to drowning. However, some birds will likely be bycaught live as gear is recovered and/or during deployment if the gear does not fully sink with birds remaining at the surface. Therefore, benefits from bycatch mitigation may be greater than anticipated solely from bycatch morality estimates.

Estimates of the population level impacts of these revised bycatch rates have not been produced, however, based on bycatch levels previously assessed (Northridge et al., 2020), which were somewhat higher than the revised estimates, population viability analyses were undertaken (Miles et al., 2020). This indicated that Fulmar populations would be somewhat larger in the absence of bycatch mortality (whole UK ca. 7% after 25 years), while for Gannet numbers were lower, but still potentially significant (up to 1% after 25 years)^[5]. Bycatch impacts will not be spread evenly, with the fishery concentrated along the shelf edge to the west and north of Scotland, and around the Shetland Isles. Therefore, we can anticipate that Gannet and Fulmar populations breeding in these areas are likely to be experiencing the highest bycatch rates so would benefit from bycatch mitigation.

Bycatch is one of the most tractable threats to seabird populations with multiple bycatch mitigation methods developed with success in decreasing bycatch rates substantially (Anderson et al., 2011; Løkkeborg, 2011; Melvin et al., 2014). Reducing bycatch rates can also be economically advantageous to the fisheries by reducing costs from lost bait, gear damage, and time lost extracting bycaught birds (Kühn, 2016; Avery et al., 2017). Trials of various bycatch mitigation measures have successfully decreased rates of bycatch, specifically in Fulmar (Løkkeborg and Robertson, 2002; Fangel et al., 2016; Kühn, 2016). A key issue for the fishery operating in Scotland is that the sink-rate of the gear (i.e. how quickly the hooks move into deeper water where less accessible to seabirds) is relatively low due to the configuration of weights and floats used with the gear (Rouxel et al., 2022) which, if increased, could substantially decrease the time when gear is accessible to birds and also improve the efficacy of other mitigation measures (bird-scaring lines/streamer lines). Options for mitigating bycatch in this fishery are further explored by Kingston et al. (2023).

We conclude that there is evidence that bycatch rates are substantial and likely to lead to population level impacts in Fulmar and, to a lesser extent, in Gannet. Bycatch mitigation methods are available and could likely decrease bycatch rates substantially. While other issues would need to be considered when deciding whether to pursue this as a strategic compensatory measure (explored further in: Practical feasibility: Bycatch mitigation), it is clear that this is an ecologically feasible conservation action that could potentially operate as compensation for Fulmar and Gannet.

6.5 Large gull management

Focal species: Large gulls (Great Black-backed Gull, Lesser Black-backed Gull, Herring Gull)

Conservation actions identified: Reduce level of licensed control (CA11); SPA designation of non-traditional colonies (CA12); Establishing artificial colonies (CA13); Translocation of eggs/chicks from non-traditional to traditional or artificial colonies (CA14).

Large gulls, including Great Black-backed Gull, Lesser Black-backed Gull, and Herring Gull are generalist species foraging on both marine and terrestrial habitats. They are also opportunistic, making use of both natural and anthropogenic food sources. Amongst the three species, Great Black-backed Gull are the least generalist being associated principally with coastal and marine habitats (see Species accounts). This flexibility in ecology and their adaptation to live alongside humans can lead to conflicts (Ross-Smith et al., 2014; Smith, 2020; Rock, 2022). As predators there is also potential for conservation conflicts between conserving other species and gull conservation (Donehower et al., 2007; Scopel and Diamond, 2017; Langlois Lopez et al., 2023), which is considered elsewhere in this report (see Ecological feasibility: Avian predator management and Practical feasibility: Avian predator management). While the three species are protected, exemptions are made with licences being issued for the control of these species (either of adults or eggs/chicks). There have been substantial changes in the licensing regime for gull control in recent years, however it is likely that control still has substantial population level impacts. Changes in the approach to control could therefore realise population level benefits for these species.

Traditionally, the three gull species primarily nested at coastal sites and some riparian areas. Over recent decades, however, they have increasingly nested in non-traditional sites, particularly in urban and industrial areas (Ross-Smith et al., 2014; Burnell, 2021; Rock, 2022). Previous national seabird censuses have not fully covered non-traditional nesting sites, so we lack data on how the relative abundance of traditional and non-traditional nesting sites have changed over time. Nonetheless, there has been an observed increase in the proportion of the population nesting in non-traditional sites. The most recent seabird census provided population counts for traditional (termed ‘natural’) and non-traditional (termed ‘urban’) sites for Herring Gull and Lesser Black-backed Gull (Burnell et al., 2023). For both species, most individuals now nest on non-traditional sites. However, in Scotland, the proportion of gulls nesting on non-traditional sites is proportionally lower than in England, largely owing to less available urban areas. Nevertheless, the nesting density on non-traditional sites is higher in Scotland. Counts for non-traditional sites were not provided for Great Black-backed Gull, which are still largely restricted to traditional sites. However, it was noted that some individuals do nest on non-traditional sites, and this occurrence is likely to increase over time (Rock, 2022).

Several SPA designations in Scotland include large gulls as feature species (Table 14), however currently no non-traditional sites used by gulls have SPA protection. There is precedent for the protection of non-traditional nesting sites through SPA designation, with Imperial Dock Lock, Leith SPA designated for breeding Common Tern (Sterna hirundo) (NatureScot, 2023e). The site designation describes this as “… [a] man-made structure at the mouth of the Imperial Dock in the heart of the Port of Leith and lies within the City of Edinburgh Local Authority area…”. For SPA qualifying species there are a variety of criteria that sites need satisfied to be considered for SPA designation (JNCC, 2023), these include any area used regularly by 1%, or more, of the Great Britain species population, with several secondary criteria including an assessment of the ‘naturalness’ of a site. Consideration could be given to designating key non-traditional nesting sites that meet SPA designation criteria. This would afford additional protection to the birds connected with these sites. Overall, designating new SPAs would likely enhance the coherence of the national site network, so has potential as strategic compensation. As mobile species, birds from key non-traditional sites would then be subject to HRA regulations; though apportioning effects of a potential plan or project between SPA and non-SPA colonies for gulls is complex given the mix of traditional and non-traditional colonies (Quinn, 2019).

A variant on designating existing non-traditional colonies would be to establish artificial colonies near existing non-traditional colonies to divert breeding gulls away from sites where they are not wanted (e.g. urban rooftops). Artificial colonies could be established e.g. on the edge of cities by protecting areas of open land from predation through predator exclusion fencing (Dalrymple, 2023). This would be a novel approach and would require substantial preparatory work to establish the practical feasibility. Such sites could then eventually be designated as SPAs once they meet designation criteria. This approach would fit well with a broader ‘landscape approach’ to the management of gulls in urban areas (see Belant (1997)).

Historically, large gulls were included on NatureScot’s general licence (NatureScot, 2023c), which permitted authorised persons to undertake various otherwise illegal control methods (e.g. nest removal and culling of adults). Since April 2020 large gulls were removed from NatureScot’s general licence, with a new licensing regime introduced with it now necessary for authorised persons to apply for individual licenses if they wish to use control methods, these must either be on grounds of preventing serious damage (‘to prevent serious damage to livestock and foodstuffs for livestock’) (NatureScot, 2023b) or for public health and safety and air safety (NatureScot, 2023a). Together with these licensing changes, there has been increased emphasis on considering alternative methods to reduce issues with gulls with guidance issued by NatureScot (NatureScot, 2023d) and associated guidance issued by many Scottish councils (e.g. Aberdeen City and West Dunbarton). It is not yet known how this has impacted the level of lethal control, but it is likely that this has reduced the number of lethal control of adult gulls. Some level of illegal control may also occur, although to what extent is unknown. While the licensing regime has already been substantially changed in recent years, there is still potential to refine this further, e.g. by requiring greater consideration of preventative and alternative non-lethal methods before being granted licenses. This would need to be scoped out and a feasibility study undertaken to establish what specific actions could be undertaken and to understand what level of benefit, in terms of reducing population level impacts on large gulls from licensed control, would arise. Without more detailed assessment it is not clear how viable this may be as a compensatory measure.

An alternative to destroying eggs and chicks of gulls (under licence, as above) would be to translocate these to either traditional colonies or artificial colonies. This could act to boost traditional colonies or increase the rate at which artificial colonies establish. Translocation can be an effective seabird conservation tool, though it is resource intensive and there are only a few recorded cases of its use in the conservation of gull species (Spatz et al., 2023b). While it likely would be possible, its feasibility would need to be investigated for the relevant gull species to ascertain whether it could be scaled up to achieve conservation gains required to be suitable as a strategic compensatory measure.

Overall, there is a need for an integrative approach to gull conservation across populations using both traditional and non-traditional nesting sites. This must also consider ways of mitigating and, where possible, avoiding the various potential conflicts between gulls and humans. Further action could be developed to reduce conflict, e.g. by addressing waste management in towns and using a landscape approach (e.g. building design to reduce nesting suitability) (Belant, 1997; Smith, 2020). There is a negative perception of gulls which is greatest in Scotland and northern England in the UK (Baker et al., 2020), though the same study indicated that gulls are tolerated more than most other perceived ‘pest’ species. Public perception of gulls could likely be improved through engaging with local communities which would lead to greater tolerance with potential to reduce demand for control methods (Quinn, 2019). Any work around urban nesting gull populations would require working alongside local councils, particularly in those areas where gull conflict is perceived. A wider review of gull ecology, with due consideration to how this is adapting over time, would inform an integrative and adaptive approach. Studies to better understand the metapopulation dynamics of gulls and how traditional and non-traditional populations are linked (e.g. rates of emigration between these) would be beneficial. More tagging of gulls from both traditional and non-traditional nesting populations would also be useful to inform on the connectivity between traditional and non-traditional nesting gulls and different habitats (Ross-Smith et al., 2014; Quinn, 2019).

We have identified several options that could afford more protection to large gulls, particularly those not originating from traditional nesting sites. Some of these conservation actions may have potential to be developed into strategic compensatory measures. However, we advise that there is a need for a wider review of our approaches for conserving gull populations and how traditional and non-traditional nesting sites are considered.

6.6 Conservation actions identified from scoping and targeted reviews

Table 41. Conservation actions identified in the scoping reviews, with a preliminary assessment for each against several criteria. Note these findings are preliminary only as these are based on a high-level assessment. The assessment is in the context of using such actions as compensatory measures. Note that the assessment against the criteria included may differ in other contexts (e.g. for broader seabird conservation purposes). Potential is also assessed in the short- to medium-term only, some actions may have potential in the longer term but would require significant research and development.

This table can be viewed in Excel format.