This is a static version of the conservation advice for this site, generated on 20/09/2019.
Please check the latest advice for this site at https://designatedsites.naturalengland.org.uk/

Tamar Estuaries Complex SPA

Last updated: 20th March 2017

Supplementary advice

The Supplementary Advice on Conservation Objectives (SACOs) present attributes which are ecological characteristics or requirements of the classified species within a site. The listed attributes are considered to be those which best describe the site’s ecological integrity and which if safeguarded will enable achievement of the Conservation Objectives.

Conservation Objectives relating to extent and distribution of habitat and population abundance are reflected in single attributes within the Supplementary Advice. Structure and function of habitats, and supporting processes for those habitats, are reflected in multiple attributes describing integrity of these ecological characteristics.

The Conservation Objective relating to the distribution of qualifying features (individual species or assemblages) may apply to most or all of the attributes listed in the SACOs and should be considered against them. Ensuring integrity of attributes relating to supporting habitats and processes should allow birds to distribute themselves optimally within (and, sometimes, outside) the SPA boundary. This is perhaps particularly relevant for food availability; extent and distribution of supporting habitat; quality of supporting habitat; predation; and disturbance caused by human activity.

Attributes have a target which is either quantified or qualified depending on the available evidence. The target identifies as far as possible the desired state to be achieved for the attribute. In many cases, the attribute targets show if the current objective is to either ‘maintain’ or ‘restore’ the attribute. The targets given for each attribute do not represent thresholds to assess the significance of any given impact in Habitats Regulation Assessments. You will need to assess this on a case-by-case basis using the most current information available.

Where there is no evidence to determine a marine feature’s condition, a vulnerability assessment, which includes sensitivity and exposure information for features and activities in a site, has been used as a proxy for condition. Evidence used in preparing the SACO has been cited with hyperlinks included where possible. Where references have not been provided, Natural England has applied ecological knowledge and expert judgement.

Some, but not all, of these attributes can also be used for regular monitoring of the condition of the classified features. The attributes selected for monitoring the features, and the standards used to assess their condition, are listed in separate monitoring documents, which will be available from Natural England. As condition assessment information becomes available, the conservation advice package will be reviewed accordingly.

When to use

You should use this information, along with the conservation objectives and case-specific advice issued by Natural England when developing, proposing or assessing an activity, plan or project that may affect the site.

Any proposals or operations which may affect the site or its features should be designed so they do not adversely affect any of the attributes in the SACO or achievement of the conservation objectives.

Feature target

‘Maintain’ targets do not preclude the need for management, now or in the future, to avoid a significant risk of damage or deterioration to the feature. The supporting and/or explanatory notes in the SACOs set out why the target was chosen and any relevant site based supporting information. This is based on the best available information, including that gathered during monitoring of the feature’s current condition.
Feature/Subfeature nameAttributeTargetSeasonSupporting notes
Little egret (Egretta garzetta), Non-breedingConnectivity with supporting habitatsMaintain safe passage of birds moving between roosting and feeding areas.Year-round

This target has been included because the ability of the feature to safely and successfully move to and from feeding and roosting areas is critical to adult fitness and survival. This target will apply within the site boundary and where birds regularly move to and from off-site habitat where this is relevant.


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingConnectivity with supporting habitatsMaintain safe passage of birds moving between roosting and feeding areas.Year-round

This target has been included because the ability of the feature to safely and successfully move to and from feeding and roosting areas is critical to adult fitness and survival. This target will apply within the site boundary and where birds regularly move to and from off-site habitat where this is relevant.


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingDisturbance caused by human activityRestict the frequency, duration and / or intensity of disturbance affecting roosting, foraging, feeding, moulting and/or loafing birds so that they are not significantly disturbed.Non-breeding (winter and/or passage) season

The nature, scale, timing and duration of some human activities can result in bird disturbance (defined as any human-induced activity sufficient to disrupt normal behaviours and / or distribution of birds in the absence of the activity) at a level that may substantially affect their behaviour, and consequently affect the long-term viability of the population. Such disturbing effects can for example result in changes to feeding or roosting behaviour, increases in energy expenditure due to increased flight, abandonment of nest sites and desertion of supporting habitat (both within or outside the designated site boundary where appropriate). This may undermine successful nesting, rearing, feeding and/or roosting, and/or may reduce the availability of suitable habitat as birds are displaced and their distribution within the site contracts.

Disturbance associated with human activity may take a variety of forms including noise, light, sound, vibration, trampling, presence of people, animals and structures.

‘Significant’ disturbance is defined by AEWA (The Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), 2016):

“Disturbance should be judged as significant if an action (alone or in combination with other effects) impacts on (water)birds in such a way as to be likely to cause impacts on populations of a species through either

  1. changed local distribution on a continuing basis; and/or
  2. changed local abundance on a sustained basis; and/or
  3. the reduction of ability of any significant group of birds to survive, breed, or rear their young.”

(Fox and Madsen, 1997)


Site-specifics:

An over-wintering bird survey in 2014 within St John's Lake recorded a number of activities that caused disturbance including military activities, bait digging and walkers (Crowe and Waite, 2013). Since then mitigation strategies have been agreed to reduce military disturbance in the area. Recreational disturbance is the subject of a current study by Tamar Estuaries Consultative Forum (TECF), the findings of which will inform updates to this attribute in the future.


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingDisturbance caused by human activityRestrict the frequency, duration and / or intensity of disturbance affecting roosting, foraging, feeding, moulting and/or loafing birds so that they are not significantly disturbed.Non-breeding (winter and/or passage) season

The nature, scale, timing and duration of some human activities can result in bird disturbance (defined as any human-induced activity sufficient to disrupt normal behaviours and / or distribution of birds in the absence of the activity) at a level that may substantially affect their behaviour, and consequently affect the long-term viability of the population. Such disturbing effects can for example result in changes to feeding or roosting behaviour, increases in energy expenditure due to increased flight, abandonment of nest sites and desertion of supporting habitat (both within or outside the designated site boundary where appropriate). This may undermine successful nesting, rearing, feeding and/or roosting, and/or may reduce the availability of suitable habitat as birds are displaced and their distribution within the site contracts.

Disturbance associated with human activity may take a variety of forms including noise, light, sound, vibration, trampling, presence of people, animals and structures.

‘Significant’ disturbance is defined by AEWA (The Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), 2016):

“Disturbance should be judged as significant if an action (alone or in combination with other effects) impacts on (water)birds in such a way as to be likely to cause impacts on populations of a species through either

  1. changed local distribution on a continuing basis; and/or
  2. changed local abundance on a sustained basis; and/or
  3. the reduction of ability of any significant group of birds to survive, breed, or rear their young.”

(Fox and Madsen, 1997)

(Holm and Laursen, 2009)


Site-specifics:

An over-wintering bird survey in 2014 within St John's Lake recorded a number of activities that caused disturbance including military activities, bait digging and walkers (Crowe and Waite, 2013). Since then mitigation strategies have been agreed to reduce military disturbance in the area. Recreational disturbance is the subject of a current study by Tamar Estuaries Consultative Forum (TECF), the findings of which will inform updates to this attribute in the future.


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingNon-breeding population: abundanceMaintain the size of the non-breeding population at a level which is above 102, whilst avoiding deterioration from its current level as indicated by the latest mean peak count or equivalent.Non-breeding (winter and/or passage) season

This will sustain the site’s population and contribute to a viable local, national and bio-geographic population. Due to the mobility of this feature and the dynamic nature of population change, the target-value given for the population size of this feature is considered to be the minimum standard for conservation / restoration measures to achieve. This minimum-value may be revised where there is evidence to show that a population’s size has significantly increased as a result of natural factors or management measures and has been stable at or above a new level over a considerable period (generally at least 10 years). The values given here may also be updated in future to reflect any strategic objectives which may be set at a national level for this feature. Given the likely fluctuations in numbers over time, any impact-assessments should focus on the current size of the site’s population, as derived from the latest known or estimated level established using the best available data. This advice accords with the obligation to avoid deterioration of the site or significant disturbance of the species for which the site is classified, and seeks to avoid plans or projects that may affect the site giving rise to the risk of deterioration. Similarly, where there is evidence to show that a feature has historically been more abundant than the stated minimum target and its current level, the ongoing capacity of the site to accommodate the feature at such higher levels in future should also be taken into account.

Maintaining or restoring bird abundance depends on the suitability of the site. However, factors affecting suitability can also determine other demographic rates of birds using the site including survival (dependent on factors such as body condition which influences the ability to breed or make foraging and / or migration movements) and breeding productivity. Adverse human impacts on either of these rates may precede changes in population abundance (eg by changing proportions of birds of different ages) but eventually may negatively affect abundance. These rates can be measured / estimated to inform judgements of likely impacts on abundance targets. Unless otherwise stated, the population size will be that measured using standard methods such as peak mean counts or breeding surveys. This value is also provided recognising there will be inherent variability as a result of natural fluctuations and margins of error during data collection. While we will endeavour to keep these values as up to date as possible, local Natural England staff can advise whether the figures stated are the best available.


Site-specifics:

The 1996 SPA citation states that the number of little egret individuals on the site had increased dramatically, reaching 102 birds in October 1995 (more than 20% of the British population).

5-year mean peaks for this species were at their highest between the period of 99/00 and 03/04. The current 5-year peak mean for this species between 09/10 and 13/14 is 77 (Holt et al., 2015).

(English Nature, 1996)


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingNon-breeding population: abundanceMaintain the size of the non-breeding population at a level which is above 194, whilst avoiding deterioration from its current level as indicated by the latest mean peak count or equivalent.Non-breeding (winter and/or passage) season

This will sustain the site’s population and contribute to a viable local, national and bio-geographic population. Due to the mobility of this feature and the dynamic nature of population change, the target-value given for the population size of this feature is considered to be the minimum standard for conservation / restoration measures to achieve. This minimum-value may be revised where there is evidence to show that a population’s size has significantly increased as a result of natural factors or management measures and has been stable at or above a new level over a considerable period (generally at least 10 years). The values given here may also be updated in future to reflect any strategic objectives which may be set at a national level for this feature. Given the likely fluctuations in numbers over time, any impact-assessments should focus on the current size of the site’s population, as derived from the latest known or estimated level established using the best available data. This advice accords with the obligation to avoid deterioration of the site or significant disturbance of the species for which the site is classified, and seeks to avoid plans or projects that may affect the site giving rise to the risk of deterioration. Similarly, where there is evidence to show that a feature has historically been more abundant than the stated minimum target and its current level, the ongoing capacity of the site to accommodate the feature at such higher levels in future should also be taken into account.

Maintaining or restoring bird abundance depends on the suitability of the site. However, factors affecting suitability can also determine other demographic rates of birds using the site including survival (dependent on factors such as body condition which influences the ability to breed or make foraging and / or migration movements) and breeding productivity. Adverse human impacts on either of these rates may precede changes in population abundance (eg by changing proportions of birds of different ages) but eventually may negatively affect abundance. These rates can be measured / estimated to inform judgements of likely impacts on abundance targets. Unless otherwise stated, the population size will be that measured using standard methods such as peak mean counts or breeding surveys. This value is also provided recognising there will be inherent variability as a result of natural fluctuations and margins of error during data collection. While we will endeavour to keep these values as up to date as possible, local Natural England staff can advise whether the figures stated are the best available.


Site-specifics:

The site SPA citation states the four-year peak mean from 1990/91 to 1993/94 of 194 avocet which at the time represented 19.4% of the British population (English Nature, 1996).

In the Tamar Estuaries Complex problems with the accuracy of Wetland Bird Survey (WeBS) peak counts have been highlighted as a result of the highly mobile nature of the species, site complexity and inability to count all sectors at the same time (Reay and Kent, 2011). It is thought that the WeBS winter peak counts that reported more than 400 (and up to 600) avocet using the site regularly during the early 2000's are over estimates.

Synchronised counts undertaken during the 2007/8 and 2011 winters recorded winter maxima of 257 and 247 respectively. This suggests the population has remained stable since peaking in the 1995/6 winter. The current maximum number recorded at one time in the site is 380, and the current 5-year mean peak 09/10 - 13/14 is 341 (Holt et al., 2015).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: air qualityMaintain concentrations and deposition of air pollutants at below the site-relevant Critical Load or Level values given for this feature of the site on the Air Pollution Information SystemYear round – to ensure the habitat remains suitable for when the feature is present

This target has been included because the structure and function of habitats which support this SPA feature may be sensitive to changes in air quality. Exceeding critical values for air pollutants may result in changes to the chemical status of its habitat substrate, accelerating or damaging plant growth, altering vegetation structure and composition and thereby affecting the quality and availability of feeding or roosting habitats.

Critical Loads and Levels are thresholds below which such harmful effects on sensitive UK habitats will not occur to a noteworthy level, according to current levels of scientific understanding. There are critical levels for ammonia (NH3), oxides of nitrogen (NOx) and sulphur dioxide (SO2), and critical loads for nutrient nitrogen deposition and acid deposition. There are currently no critical loads or levels for other pollutants such as Halogens, Heavy Metals, POPs, VOCs or Dusts. These should be considered as appropriate on a case-by-case basis. Ground level ozone is regionally important as a toxic air pollutant but flux-based critical levels for the protection of semi-natural habitats are still under development.

More information about site-relevant Critical Loads and Levels for this site is available by using the ‘search by site’ tool on the Air Pollution Information System (Centre for Ecology & Hydrology (CEH), 2014).

It is recognised that achieving this target may be subject to the development, availability and effectiveness of abatement technology and measures to tackle diffuse air pollution, within realistic timescales.


Site-specifics:

Within the Tamar Estuaries Complex SPA the maximum nitrogen deposition, acidity, NH3, NOx, and SO2 values, based on a 3-year mean, do not exceed the site relevant critical load values associated with any of the avocet or little egrets' supporting habitat (Centre for Ecology and Hydrology (CEH), 2014).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: air qualityMaintain concentrations and deposition of air pollutants at below the site-relevant Critical Load or Level values given for this feature of the site on the Air Pollution Information SystemYear round – to ensure the habitat remains suitable for when the feature is present

This target has been included because the structure and function of habitats which support this SPA feature may be sensitive to changes in air quality. Exceeding critical values for air pollutants may result in changes to the chemical status of its habitat substrate, accelerating or damaging plant growth, altering vegetation structure and composition and thereby affecting the quality and availability of feeding or roosting habitats.

Critical Loads and Levels are thresholds below which such harmful effects on sensitive UK habitats will not occur to a noteworthy level, according to current levels of scientific understanding. There are critical levels for ammonia (NH3), oxides of nitrogen (NOx) and sulphur dioxide (SO2), and critical loads for nutrient nitrogen deposition and acid deposition. There are currently no critical loads or levels for other pollutants such as Halogens, Heavy Metals, POPs, VOCs or Dusts. These should be considered as appropriate on a case-by-case basis. Ground level ozone is regionally important as a toxic air pollutant but flux-based critical levels for the protection of semi-natural habitats are still under development.

More information about site-relevant Critical Loads and Levels for this site is available by using the ‘search by site’ tool on the Air Pollution Information System (Centre for Ecology & Hydrology (CEH), 2014).

It is recognised that achieving this target may be subject to the development, availability and effectiveness of abatement technology and measures to tackle diffuse air pollution, within realistic timescales.


Site-specifics:

Within the Tamar Estuaries Complex SPA the maximum nitrogen deposition, acidity, NH3, NOx, and SO2 values, based on a 3-year mean, do not exceed the site relevant critical load values associated with any of the avocet or little egrets' supporting habitat (Centre for Ecology and Hydrology (CEH), 2014).

Overwintering avocet are sensitive to impacts from nutrient nitrogen, NH3 and NOx on their supporting habitat (littoral sediment and saltmarsh), values should therefore not be allowed to exceed the critical load (Centre for Ecology and Hydrology (CEH), 2014).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: conservation measuresMaintain the structure, function and supporting processes associated with the feature and its supporting habitat through management or other measures (whether within and/or outside the site boundary as appropriate) and ensure these measures are not being undermined or compromised.Year round – to ensure the habitat remains suitable for when the feature is present

This target has been included because active and ongoing conservation management is often needed to protect, maintain or restore this feature at this site. Other measures may also be required, and in some cases, these measures may apply to areas outside of the designated site boundary in order to achieve this target. Further details about the necessary conservation measures for this site can be provided by Natural England. This information will typically be found within, where applicable, supporting documents such as Natura 2000 Site Improvement Plan, Site Management Strategies or Plans, the Views about Management Statement for the underpinning SSSI and / or management agreements.


Site-specifics:

Management measures and plans relevant to the Tamar Complex SPA include:

- Tamar Estuaries Management Plan 2013 – 2018 . This management plan covers the Plymouth European Marine Site (EMS) which includes the Plymouth Sound and Estuaries SAC & Tamar Estuaries Complex SPA (Tamar Estuaries Consultative Forum, 2012).
- Site Improvement Plan: Plymouth Sound and Tamar Estuary. This provides a high level overview of the issues (both current and predicted) affecting the condition of the Natura 2000 features on the site(s) and outlines the priority measures required to improve the condition of the features (Natural England, 2014).
- IFCA byelaws are in place.
- Views about management statements are also available for St John’s Lake Site of Special Scientific Interest (SSSI), the Tamar – Tavy Estuary SSSI and the Lynher Estuary SSSI (English Nature, 2005), (English Nature, 2005), (English Nature, 2004).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: conservation measuresMaintain the structure, function and supporting processes associated with the feature and its supporting habitat through management or other measures (whether within and/or outside the site boundary as appropriate) and ensure these measures are not being undermined or compromised.Year round – to ensure the habitat remains suitable for when the feature is present

This target has been included because active and ongoing conservation management is often needed to protect, maintain or restore this feature at this site. Other measures may also be required, and in some cases, these measures may apply to areas outside of the designated site boundary in order to achieve this target. Further details about the necessary conservation measures for this site can be provided by Natural England. This information will typically be found within, where applicable, supporting documents such as Natura 2000 Site Improvement Plan, Site Management Strategies or Plans, the Views about Management Statement for the underpinning SSSI and / or management agreements.


Site-specifics:

Management measures and plans relevant to the Tamar Complex SPA include:

- Tamar Estuaries Management Plan 2013 – 2018 . This management plan covers the Plymouth European Marine Site (EMS) which includes the Plymouth Sound and Estuaries SAC & Tamar Estuaries Complex SPA (Tamar Estuaries Consultative Forum, 2012).
- Site Improvement Plan: Plymouth Sound and Tamar Estuary. This provides a high level overview of the issues (both current and predicted) affecting the condition of the Natura 2000 features on the site(s) and outlines the priority measures required to improve the condition of the features (Natural England, 2014).
- IFCA byelaws are in place.
- Views about management statements are also available for St John’s Lake Site of Special Scientific Interest (SSSI), the Tamar – Tavy Estuary SSSI and the Lynher Estuary SSSI (English Nature, 2005), (English Nature, 2005), (English Nature, 2004).

The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: extent and distribution of supporting habitat for the non-breeding seasonMaintain the extent, distribution and availability of suitable habitat (either within or outside the site boundary) which supports the feature for all necessary stages of the non-breeding/wintering period (moulting, roosting, loafing, feeding) at the extent shown in the supporting notes.Year round – to ensure the habitat remains suitable for when the feature is present

This target may apply to supporting habitat which also lies outside the site boundary. Inappropriate management and direct or indirect impacts which may affect the extent and distribution of habitats may adversely affect the population and alter the distribution of birds.


Site-specifics:

The types of habitat which support little egret within or outside of the site boundary are:

- Atlantic salt meadows (Glauco-puccinellietalia maritimae) (Extent: 226 ha) (Environment Agency (EA), 2011), (Downie and Gilliland, 1997)
- Coastal reedbeds (Extent: unknown]
- Freshwater and coastal grazing marsh (Extent: 9 ha) (Dargie, 1993)
- Intertidal mixed sediments (Extent: 14 ha) (Curtis, 2010), (Curtis, 2010)
- Intertidal mud (Extent: 824 ha) (Curtis, 2010), (Curtis, 2010), (Natural England, 2010), (English Nature, 2003), (Environment Agency (EA), 2011), (Posford Duvivier Environment, 1997).
- Intertidal sand and muddy sand (Extent: 382 ha) (Curtis, 2010), (Curtis, 2010).
- Intertidal seagrass beds (Extent: 40) (Joint Nature Conservation Committee (JNCC), 2014)
- Intertidal coarse sediment (Extent: unknown)
- Intertidal rock (Extent: unknown)

Little egret is found in all areas of the site with highest numbers recorded in St John's Lake, Tavy Estuary and just north of the Tamar bridge.

This target also applies to important areas of supporting habitat which lie outside the site boundary, such as known roosting sites. An example of an important roosting site located outside the site boundary is Drake's Island. Areas of Drake's Island are considered supporting habitat as little egret associated with the Tamar Estuaries Complex SPA are known to roost here, with a peak of 79 individuals recorded in September 2010 (Devon Birdwatching and Preservation Society (DBWPS), 2010). Birds will not be roosting on habitat regularly flooded by the tide but they will be found in intertidal habitats above the Mean High Water Mark (which may not have been mapped).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: extent and distribution of supporting habitat for the non-breeding seasonMaintain the extent, distribution and availability of suitable habitat (either within or outside the site boundary) which supports the feature for all necessary stages of the non-breeding/wintering period (moulting, roosting, loafing, feeding) at the extent shown in the supporting notes.Year round – to ensure the habitat remains suitable for when the feature is present

This target may apply to supporting habitat which also lies outside the site boundary. Inappropriate management and direct or indirect impacts which may affect the extent and distribution of habitats may adversely affect the population and alter the distribution of birds.


Site-specifics:

The types of habitat which support avocet within or outside of the site boundary are:

- Atlantic salt meadows (Glauco-puccinellietalia maritimae) (Extent: 226 ha) (Environment Agency (EA), 2011), (Downie and Gilliland, 1997)
- Freshwater and coastal grazing marsh (Extent: 9 ha) (Dargie, 1993)
- Intertidal mixed sediments (Extent: 14 ha) (Curtis, 2010), (Curtis, 2010)
- Intertidal mud (Extent: 824 ha) (Curtis, 2010), (Curtis, 2010), (Natural England, 2010), (English Nature, 2003), (Environment Agency (EA), 2011), (Posford Duvivier Environment, 1997)
- Intertidal sand and muddy sand (Extent: 382 ha) (Curtis, 2010), (Joint Nature Conservation Committee (JNCC), 2014)
- Intertidal coarse sediment (Extent: unknown)
- Intertidal rock (Extent: unknown)
- Water column

Within the Tamar Estuaries Complex avocet roost on saltmarsh and areas of upper shore muddy habitats. Intertidal mud and mixed sediment habitats are used for feeding. The most important roosting sites are in Kingsmill Lake and off Hole's Hole (Reay and Kent, 2011).

Feeding behaviour in the site is more widespread; the most regularly used areas are north of the Tamar bridge and in the Lynher near Warren Point and Tredown Quay. Avocets have been recorded in all sectors of the site. This target may apply to supporting habitat which also lies outside the site boundary. Birds will not be roosting on habitat regularly flooded by the tide but they will be found in intertidal habitats above the Mean High Water Mark (which may not have been mapped).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: food availabilityMaintain the distribution, abundance and availability of key food and prey items (eg. fish, frogs, beetles, dragonfly larvae, crickets) at preferred sizes (eg. fish of <6 cm).Year-round

The availability of an abundant food supply is critically important for successful breeding, adult fitness and survival and the overall sustainability of the population. As a result, inappropriate management and direct or indirect impacts which may affect the distribution, abundance and availability of prey may adversely affect the population and alter the distribution of birds. Main food sources can be found within: the intertidal and saltmarsh.

(Cramp and Simmons, 1977), (Kushlan and Hancock, 2005)


Site-specifics:

In the Tamar Estuaries Complex SPA intertidal mudflat and sandflat infauna was assessed in 2010 as part of condition monitoring for the component SSSIs, and was found to be in favourable condition (Curtis, 2010), (Curtis, 2010). In 2013 saltmarsh was surveyed within the site, and was in favourable condition (Seebold, 2013). So whilst the amount of food present was not directly measured it is assumed that it is also favourable. Assessment included number and range of invertebrates which are a food source for the little egret.


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: food availabilityMaintain the distribution, abundance and availability of key food and prey items (eg. Gammarus, Corophium, flies, beetles, Nereis, Hydrobia, Cardium, gobies) at preferred sizes (eg. fish or worms between 4-15 mm long).Year-round

The availability of an abundant food supply is critically important for successful breeding, adult fitness and survival and the overall sustainability of the population. As a result, inappropriate management and direct or indirect impacts which may affect the distribution, abundance and availability of prey may adversely affect the population and alter the distribution of birds. Main food sources can be found within: the intertidal and lagoons.

(Cramp and Simmons, 1983), (Hill et al., 1989), (Reay, 1991), (Moreira, 1995), (del Hoyo et al., 1996)


Site-specifics:

In the Tamar Estuaries Complex SPA intertidal mudflat and sandflat infauna was assessed in 2010 as part of condition monitoring for the component SSSIs, and was found to be in favourable condition (Curtis, 2010), (Curtis, 2010). Assessment included number and range of invertebrates which are the primary food source for avocet.


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: hydrology/flow within intertidalMaintain the availability of fresh water on mudflats within feeding and resting areas.Year round – to ensure the habitat remains suitable for when the feature is present

Changes in source, depth, duration, frequency, magnitude and timing of water supply or flow can have important implications for this feature. Such changes may affect the quality and suitability of habitats used by birds for drinking, preening, feeding or roosting. Unless these have already been undertaken, further site-specific investigations may be required to fully inform conservation measures for this feature and / or the likelihood of impacts on this attribute.

(Ravenscroft and Beardall, 2003)


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: landformMaintain the density of channel networks within intertidal feeding areas.Year round – to ensure the habitat remains suitable for when the feature is present

The physical topography and landform of a site will strongly influence the quality and extent of supporting habitats used by this feature for feeding and / or roosting as appropriate. This will also influence the interactions with underlying supporting processes on which the supporting habitat may rely. Any changes or modifications to site topography may adversely affect the ability of the supporting habitats to support and sustain this feature.

(Lourenço et al., 2005)


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: landscapeMaintain the area of open and unobstructed terrain around roosting and feeding sites.Year round – to ensure the habitat remains suitable for when the feature is present

This feature is known to favour large areas of open terrain, largely free of obstructions, in and around its roosting and feeding areas. Often there is a need to maintain an unobstructed line of sight within feeding or roosting habitat to detect approaching predators, or to ensure visibility of displaying behaviour. An open landscape may also be required to facilitate movement of birds between the SPA and any off-site supporting habitat.


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: water depthMaintain the availability and area of standing water of 3-5 cm deep.Year round – to ensure the habitat remains suitable for when the feature is present

This attribute ensures that important habitats used by the feature are not impacted, regardless of whether the bird is present at that time. This feature is known to require extensive areas of water in which to feed. Birds are visual predators, with some having the ability to dive or to feed from the surface. As they will rely on detecting their prey within the water to hunt, the depth of water at critical times of year may be paramount for successful feeding and therefore their fitness and survival. Deep water surrounding nesting sites may also be important to deterring predators.

(Cadbury et al., 1989)


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: water depthMaintain the availability of standing water at optimal depths, typically <0.2 m deep.Year round – to ensure the habitat remains suitable for when the feature is present

This feature is known to require extensive areas of water in which to feed. Birds are visual predators, with some having the ability to dive or to feed from the surface. As they will rely on detecting their prey within the water to hunt, the depth of water at critical times of year may be paramount for successful feeding and therefore their fitness and survival. Deep water surrounding nesting sites may also be important to deterring predators.

(Cramp and Simmons, 1977), (Kushlan and Hancock, 2005)


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: water quality - contaminantsRestrict aqueous contaminants to levels equating to High Status according to the Water Framework Directive, avoiding deterioration from existing levels.Year-round

Contaminants may have a range of biological effects on different species within the supporting habitat, depending on the nature of the contaminant (Joint Nature Conservation Committee (JNCC), 2004), (UK Technical Advisory Group on the Water Framework Directive (UKTAG), 2008), (Environment Agency, 2014). This in turn can adversely affect the availability of bird breeding, rearing, feeding and roosting habitats, and potentially bird survival.


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: water quality - contaminantsRestrict aqueous contaminants to levels equating to High Status according to the Water Framework Directive, avoiding deterioration from existing levels.Year-round

Contaminants may have a range of biological effects on different species within the supporting habitat, depending on the nature of the contaminant (Joint Nature Conservation Committee (JNCC), 2004), (UK Technical Advisory Group on the Water Framework Directive (UKTAG), 2008), (Environment Agency, 2014). This in turn can adversely affect the availability of bird breeding, rearing, feeding and roosting habitats, and potentially bird survival.


Site-specifics:


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: water quality - dissolved oxygenMaintain the dissolved oxygen (DO) concentration to levels equating to High Ecological Status, avoiding deterioration from existing levels.Year-round

Dissolved Oxygen (DO) levels affect the condition and health of supporting habitats. Excessive nutrients and/or high turbidity can lead to a drop in DO, especially in warmer months. Low DO can have sub-lethal and lethal impacts on fish and infauna and epifauna communities (Best et al., 2007) and hence can adversely affect the availability and suitability of bird breeding, rearing, feeding and roosting habitats. However, there is a significant amount of natural variation that should be considered.


Site-specifics:

The Tamar Estuaries Complex SPA, lies completely within the Plymouth Tamar WFD waterbody. Monitoring of this waterbody has consistantly recorded dissolved oxygen levels equating to High Ecological Status between 2009 and 2014 (Environment Agency Marine Monitoring Service, 2014).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: water quality - dissolved oxygenMaintain the dissolved oxygen (DO) concentration to levels equating to High Ecological Status, avoiding deterioration from existing levels.Year-round

Dissolved Oxygen (DO) levels affect the condition and health of supporting habitats. Excessive nutrients and/or high turbidity can lead to a drop in DO, especially in warmer months. Low DO can have sub-lethal and lethal impacts on fish and infauna and epifauna communities (Best et al., 2007) and hence can adversely affect the availability and suitability of bird breeding, rearing, feeding and roosting habitats. However, there is a significant amount of natural variation that should be considered.


Site-specifics:

The Tamar Estuaries Complex SPA, lies completely within the Plymouth Tamar WFD waterbody. Monitoring of this waterbody has consistantly recorded dissolved oxygen levels equating to High Ecological Status between 2009 and 2014 (Environment Agency Marine Monitoring Service, 2014).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: water quality - nutrientsMaintain water quality and specifically mean winter dissolved inorganic nitrogen (DIN) at a concentration equating to High Ecological Status (specifically mean winter DIN is < 12 µM for coastal waters), avoiding deterioration from existing levels.Year-round

High concentrations of nutrients in the water column can cause phytoplankton and opportunistic macroalgae blooms, leading to reduced dissolved oxygen availability. This can impact sensitive fish, epifauna and infauna communities (Devlin et al., 2007), (Best, 2014) and hence adversely affect the availability and suitability of bird breeding, rearing, feeding and roosting habitats. The aim is to seek no further deterioration or improve water quality.


Site-specifics:

The mean winter dissolved inorganic nutrient levels for site have been assessed at to be at background levels, with biological indicators of eutrophication (opportunistic macroalgal cover and phytoplankton communities) consistent with undisturbed conditions (e.g. opportunistic macroalgal cover is < 5% with no entrainment) (Environment Agency Marine Monitoring Service, 2014).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: water quality - nutrientsMaintain water quality and specifically mean winter dissolved inorganic nitrogen (DIN) at a concentration equating to High Ecological Status (specifically mean winter DIN is < 12 µM for coastal waters), avoiding deterioration from existing levels.Year-round

High concentrations of nutrients in the water column can cause phytoplankton and opportunistic macroalgae blooms, leading to reduced dissolved oxygen availability. This can impact sensitive fish, epifauna and infauna communities (Devlin et al., 2007), (Best, 2014) and hence adversely affect the availability and suitability of bird breeding, rearing, feeding and roosting habitats. The aim is to seek no further deterioration or improve water quality.


Site-specifics:

The mean winter dissolved inorganic nutrient levels for site have been assessed at to be at background levels, with biological indicators of eutrophication (opportunistic macroalgal cover and phytoplankton communities) consistent with undisturbed conditions (e.g. opportunistic macroalgal cover is < 5% with no entrainment) (Environment Agency Marine Monitoring Service, 2014).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Avocet (Recurvirostra avosetta), Non-breedingSupporting habitat: water quality - turbidityMaintain natural levels of turbidity (e.g. concentrations of suspended sediment, plankton and other material) across the habitat.Year-round

Water turbidity is a result of material suspended in the water, including sediment, plankton, pollution or other matter from land sources. Turbidity levels can rise and fall rapidly as a result of biological (eg plankton blooms), physical (eg storm events) or human (eg development) factors. Prolonged changes in turbidity may influence the amount of light reaching supporting habitats, affecting the primary production and nutrient levels of the habitat’s associated communities. Changes in turbidity may also have a range of biological effects on different species within the habitat, eg affecting their abilities to feed or breathe.

A prolonged increase in turbidity is indicative of an increase in suspended particulates. This has a number of implications for the aquatic / marine environment, such as affecting fish health, clogging the filtering organs of suspension feeding animals and affecting sedimentation rates. This in turn can adversely affect the availability and suitability of bird breeding, rearing, feeding and roosting habitats.


Site-specifics:

The estuary turbidity maxima for the Tamar normally occurs in the low salinity upper reaches. It is characterised by fine sediment in suspension (50 to 100μm) particle diameter).

Suspended sediment concentrations from the lower Tamar estuary showed a background concentration of 0.02 kg m−3 throughout most of the spring–neap cycle. On spring tides the depth-averaged concentration increased to 0.25–0.40 kg m−3 (Tattersall et al., 2003). The turbidity maxima is normally associated with the fresh/saltwater interface, but occasionally occurs further upstream.

During summer, the peak turbidity maxima is normally encountered close to Gunnislake weir (0 to 10km). However, in winter it moves down estuary between 15 to 25 km from the weir. At 25km from the weir, the turbidity maxima is located between Saltash Bridge (24 km) and Weston Mill Lake (26 km). The movement of the turbidity maxima appears to be associated with changes in river flow (Debut, 2007).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

Little egret (Egretta garzetta), Non-breedingSupporting habitat: water quality - turbidityMaintain natural levels of turbidity (e.g. concentrations of suspended sediment, plankton and other material) across the habitat.Year-round

Water turbidity is a result of material suspended in the water, including sediment, plankton, pollution or other matter from land sources. Turbidity levels can rise and fall rapidly as a result of biological (eg plankton blooms), physical (eg storm events) or human (eg development) factors. Prolonged changes in turbidity may influence the amount of light reaching supporting habitats, affecting the primary production and nutrient levels of the habitat’s associated communities. Changes in turbidity may also have a range of biological effects on different species within the habitat, eg affecting their abilities to feed or breathe.

A prolonged increase in turbidity is indicative of an increase in suspended particulates. This has a number of implications for the aquatic / marine environment, such as affecting fish health, clogging the filtering organs of suspension feeding animals and affecting sedimentation rates. This in turn can adversely affect the availability and suitability of bird breeding, rearing, feeding and roosting habitats.


Site-specifics:

The estuary turbidity maxima for the Tamar normally occurs in the low salinity upper reaches. It is characterised by fine sediment in suspension (50 to 100μm) particle diameter).

Suspended sediment concentrations from the lower Tamar estuary showed a background concentration of 0.02 kg m−3 throughout most of the spring–neap cycle. On spring tides the depth-averaged concentration increased to 0.25–0.40 kg m−3 (Tattersall et al., 2003). The turbidity maxima is normally associated with the fresh/saltwater interface, but occasionally occurs further upstream.

During summer, the peak turbidity maxima is normally encountered close to Gunnislake weir (0 to 10km). However, in winter it moves down estuary between 15 to 25 km from the weir. At 25km from the weir, the turbidity maxima is located between Saltash Bridge (24 km) and Weston Mill Lake (26 km). The movement of the turbidity maxima appears to be associated with changes in river flow (Debut, 2007).


The target has been set using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring / have occurred on the site.

See further guidance on how to undertake an HRA for a plan or project on a European site.

These tables bring together the findings of the best available scientific evidence which may be updated or supplemented in further publications from Natural England and other sources. You may decide to use other additional sources of information.

These tables do not give advice about SSSI features or other legally protected species which may also be present within the European site.