The UK target of a reduction in the risks to island seabird colonies from invasive predatory mammals could not be assessed because there has been no previous assessment of this risk. A total of 30 Special Protection Areas did not have invasive non-native or native mammals on offshore islands. Six had effective biosecurity measures. Twelve Special Protection Areas had rats and or feral cats present on shore islands and did not have effective biosecurity measures.

Background

UK target on bird population condition: Invasive mammals

This indicator aims to assess progress against the following target, which is set in the UK Marine Strategy Part One (HM-Government, 2012): “At the scale of the Marine Strategy Framework Directive sub-regions, the risks to island seabird colonies from non-native mammals are reduced.” However, there has been no previous assessment, so it was not possible to monitor progress towards the target.

Key pressures and impacts

The invasion of seabird colonies on offshore islands by non-native predatory mammals such as brown rats, cats, and American mink and native mammals introduced by humans like the hedgehog and fox has had severe impacts on populations of ground-nesting seabirds in the UK including petrels and puffins. Predation of eggs and young birds can cause reductions in breeding success and could lead to the desertion of whole colonies.

Measures taken to address the impacts

The UK Marine Strategy Part Three (HM Government, 2015) states that future implementation of a UK-wide programme of quarantine (also referred to as ‘biosecurity’) against invasive, non-indigenous mammals from island seabird colonies and the strategically targeted removal of mammals from some islands will increase our confidence in meeting the above target.

Further information

The risks to island seabird colonies from invasive predatory mammals

Predation of ground-nesting marine birds, their eggs and chicks by mammals can have impacts at a population scale. The main strategy adopted by seabirds to cope with mammalian predation is avoidance. They tend to nest on cliffs, offshore island or remote beaches where predators are scarce or absent (Birkhead and Furness, 1985). The introduction of mammal predators to places where they would not naturally occur without human assistance has had catastrophic impacts on bird populations around the world (see for example: Courchamp and others, 2003; Jones and others, 2008; Russell and Clout, 2005; Towns and others, 2006).

In the UK, Stanbury and others (2017) identified 9,688 distinct islands around the coast of the UK. The vast majority of these are very small, and only 506 of them are larger than 10 hectares Many of these islands have ground-nesting birds that can breed successfully in the absence of predatory mammals. Some of these islands are home to the largest seabird colonies in Europe. However, some islands do have invasive predatory mammals (see Table 1 for species list). The most widespread species on islands are the American mink (Mustela vison) and brown rat (Rattus norvegicus ), which occur on 23 % and 21 % of islands (>10 hectars), respectively (Stanbury and others, 2017). Both species are non-native to the UK. Brown rats are thought to have originated on the steppes of central Asia and spread, possibly naturally, to eastern Europe in the early eighteenth century. Brown rats were first reported arriving in England on ships around 1728 to 1729 (Non-native Species Secretariat, 2012). The American mink, escaped from fur farms following the expansion of the industry in the UK during the 1950s (Dunstone, 1993). They have since colonised almost all of mainland Britain and some of the larger Scottish islands including Skye, Lewis and Harris (see data and maps for Neovison vison in the National Biodiversity Network Atlas). American mink are adept swimmers and can easily reach seabird colonies on inshore islands, where they cause complete breeding failures, adult mortality, and eventually site abandonment. Along the west coast of Scotland, mink predation within the last 10 to 30 years has led to the redistribution and decline in numbers of common and Arctic terns, common and black-headed gulls and black guillemots (Craik 1997; 1998; Mitchell and others, 2004).

Brown rats are less adept swimmers than mink but can be accidentally introduced on to island by boats. On islands where rats have been recently introduced, the impacts on the resident seabirds is evidenced through. the extinction of puffins on Ailsa Craig and Puffin Island and of Manx Shearwaters on Canna. However, on most islands where rats are present, their impact is not as visible. This is because the presence of rats for almost 300 years in some places has led to an equilibrium between the impact of rats and the number and distribution of seabirds. This is evidenced by the fact that European and Leach’s storm-petrels are only found breeding on islands that are free of rats (Mitchell and others, 2004; Mitchell and Newton, 2004). Furthermore, seabird species have returned to breed on some islands following the eradication of rats, for example, Manx shearwaters on Lundy (Lock, 2006).

On islands where seabirds and rats co-exist, impacts are evidenced by the distribution and abundance of nesting seabirds. For example, in Orkney and Shetland, black guillemots nesting on islands with rats and stoats avoid predation by nesting in crevices high off the ground and on cliffs that are inaccessible to the rats and stoats, rather than in the boulder beaches that they use as nest sites on islands that have no rats or stoats (Ewins and Tasker, 1985). Mitchell and Ratcliffe (2007) found that throughout the UK there were significantly more puffins breeding on islands without rats, compared to islands of a similar size that do have rats.

Table 1 lists species of predatory mammals that are of a high risk to ground-nesting marine birds. In contrast to rats and mink, other species of invasive predatory mammals appear to have a much more limited distribution on islands and therefore have a more localised impact on seabirds. In addition to non-native brown rats and American mink, native species can be introduced to islands that they would not naturally get to by swimming. In such cases, these native species are considered invasive. The most widespread invasive native species on UK islands is the hedgehog (Table 1).

Table 1: Species of predatory mammals present on islands in the UK. All species are considered a high risk to ground-nesting birds (Stanbury and others, 2017).

Mammal species

Status in the UK

% of islands (>10 hectares) in the UK with confirmed or probable presence

Brown rat (aka Norway rat) Rattus norvegicus

Non-native

21%

Black rat (aka ship/roof rat) R. rattus

Non-native

2%

American mink Neovison vison

Non-native

23%

Ferret Mustela furo

Feral

4%

Stoat Mustela erminea

Native

4%

Weasel Mustela nivalis

Native

1%

European badger Meles meles

Native

1%

Hedgehog Erinaceus europaeus

Native

12%

Red Fox Vulpes vulpes

Native

2%

Cat Felis catus

Feral / free-roaming domestic pet

17%

Assessment method

Assessment of UK target

This first assessment measures the number of protected islands on which impacts from invasive mammals are already occurring and the number of predator-free islands on which the risk to seabirds from invasive mammals has been minimised by effective quarantine and other biosecurity measures. Future assessments will investigate whether the numbers of these islands have changed sufficiently to reduce the overall risk from invasive mammals and thus meet the UK target.

The presence or absence of invasive predatory mammals (see species list in Table 1) was determined at all 42 of the UK offshore Islands within the Greater North Sea and Celtic Seas that are designated as protected Special Protection Areas designated under the Birds Directive (European Commission, 2009). These Special Protection Areas contained a total of over 700 islands. All Special Protection Areas in the assessment were designated because of the national or international importance of their breeding seabird populations, and all are on islands). On those islands that do not have invasive predatory mammals, the assessment looked at whether biosecurity measures were in place and how effective they are at minimising the risk of these mammals arriving and becoming established. Brown rat and American mink are the most widespread predatory mammals on UK islands (Table 1) and are the most likely of the non-native species to arrive at an island. Mink are most likely to arrive on islands by swimming. Rats can also swim to islands close by but can also stow away on boats without being detected and can be accidentally introduced onto islands, potentially a long way from the mainland. If measures are sufficient to prevent incursion and establishment by rats and mink, then they will most probably be effective against other species.

On islands where invasive predatory mammals are currently present, this assessment focused on whether any biosecurity was in place to prevent further incursion by other species. This is important, since the invasion by new species may impact further on the resident bird communities. Sufficient biosecurity measures will also be important in ensuring the success of future eradication schemes. At each site, a risk assessment was carried out to determine if the risk from invasive predatory mammals had been minimised by effective biosecurity. The results of the risk assessment were categorised as follows:

  • ‘Yes’: the potential risk (without any biosecurity) had been a reduced to a low actual risk by having in place (or planned) ‘sufficient’ quarantine measures, invasive monitoring scheme and rapid response.
  • ‘Partially’: the potential risk had been a reduced to a lower actual risk, but not all the measures were considered ‘sufficient.’
  • ‘No’: the potential risk had NOT been reduced to a lower actual risk and measures were absent or ‘below standard.’

Defining an ‘island’

Islands were defined as being entirely distinct from the mainland at low tide, small islands that are part of bigger mainland Special Protection Areas have mostly been excluded. Exclusions include Steep Holm and Havergate Island. We have only included island Special Protection Areas designatedwholly or primarily for their breeding seabird interest features. Offshore islands that are permanently surrounded by the sea are less likely to be invaded by mammals than tidal islands that are connected to the mainland by a land-bridge at low tide. Mammals can potentially get to tidal islands during each low-tide, occurring twice daily. The biosecurity measures required to stop mammals getting onto tidal islands are so intensive that they are often not financially or logistically viable. Therefore, tidal islands were not included in this assessment. For one Special Protection Area (Ynys Feurig, Cemlyn Bay and the Skerries), only the Skerries, which are fully offshore islands, were assessed for biosecurity. A total of 723 islands were included in this assessment.

Risk assessment approach

This assessment was conducted by following the steps laid out in the flowchart in Figure 1. First, the potential risk (without biosecurity) from rats and mink was assessed as low, medium or high (L, M, and H in Figure 1) for each site. The risk was calcuated as the product of the likelihood of incursion and the potential hazard from incursion (see risk matrix in Table 2). The effectiveness of current biosecurity measures in reducing both the likelihood and the hazard were assessed to estimate the actual risk from rats and mink at each site, given the measures in place (see Figure 1 and Table 2). Each step in the assessment was scored. The majority of these scores were taken from interviews of site managers conducted by the Royal Society for the Protection of Birds as part of the Shiant Isles Seabird Recovery Project (Thomas and others, 2016). Additional information was used to supplement the results of these interviews.

Risk assessment framework for assessing whether potential risk from invasive non-native mammals has been reduced to a lower ‘actual risk’ by current biosecurity measures at each site.

Figure 1: Risk assessment framework for assessing whether potential risk from invasive non-native mammals has been reduced to a lower ‘actual risk’ by current biosecurity measures at each site.

Table 2. Risk Matrix used to assess the potential or actual risk to an island seabird population from invasion by mammal predators.

 

 

 Likelihood of invasion

 

 

L

M

H

Hazard associated with invasion

H

Medium

High

High

M

Medium

Medium

High

L

Low

Medium

Medium

Assessing potential risk

Potential risk from invasion by rats or mink was assessed only for sites that currently have no high-impact mammals. First the likelihood of incursion on the island was considered, then the hazard or potential damage they would cause following arrival. The scores for these two processes were put into the risk matrix in Table 1 to estimate the potential risk from invasion.

The potential likelihood of incursion by rats and mink was scored separately for each mammal as ‘high,’ ‘medium’ or ‘low.’ The score was dependant on the pathway of introduction, be it natural, such as swimming or human-assisted – usually accidentally by boats visiting an island. The likelihood was assessed by considering the following:

  1. Human-assisted introductions: Site managers were asked to provide information on the current levels of boat traffic to the island and the nature of the traffic – including types of vessels used and the purposes of visits. Assumptions were made that islands with resident populations would have higher risks of human-assisted pathways than those that were uninhabited. Ratcliffe and others (2009) found no rat-free islands in the UK that were inhabited by more than 100 people and considered islands with a human population less than 10 to be of low risk of invasion, islands with 11 to 50 people being medium risk and over 51 to be high risk.
  1. Natural introductions: Distances to neighbouring islands containing invasive species, and distance to the mainland determines how likely invasive species could get to the island by swimming there. Brown rats can swim for up to 1 km in open, temperate seas (Russell and others, 2008) and occasionally 2 km and possibly 4 km (Thomas and others, 2017). But Ratcliffe and others (2009) found that many UK islands are rat-free despite being less than 1 km from the mainland, possibly due to strong currents in the channels separating the islands from the mainland. Ratcliffe and others (2009) found a maximum swimming distance of 300 m fitted better with the observed distribution of rats on offshore islands in the UK. American Mink are much stronger swimmers that rats and can reach islands within 2 km of shore along the west coast of Scotland (Ratcliffe and others, 2009).

The potential hazard or potential damage that could be caused following the incursion of an invasive mammal onto an island seabird colony was scored as ‘high,’ ‘medium’ or ‘low’ by considering the following:

  1. The likely impact of invasion on resident seabird species – this was scored as ‘High’ for all sites included in this assessment because they are all protected for their important colonies of breeding seabirds, which would certainly be impacted if the site was invaded by a high-impact mammal species.
  2. The likelihood of establishment of a breeding population of rats and mink following an initial incursion. This is dependent on the ability to detect the invasive species and to then respond rapidly to remove any animals. Without systematic monitoring it is highly likely that rats that could arrive on an island (either by natural or human-assisted pathways) and remain undetected and then multiply quickly.

Assessing the actual risk

This part of the risk assessment considered the effectiveness of current biosecurity measures in reducing the potential risk of invasion and estimated the actual risk from invasive mammals. Current biosecurity measures were assessed against standards set in the UK Rodent Eradication Best Practice Toolkit (Thomas and others, 2017). They were scored as ‘sufficient,’ ‘below standard’ or ‘none’. At some sites, a biosecurity plan was in place, but the actual implementation of the plan had not yet taken place. In such cases, the assessment was based on the contents of the plan and on the assumption that it would be implemented.

Firstly, using data on actual biosecurity measures (for example, the quarantine) in place at each site, the potential likelihood of incursions by rats and by mink were each reassessed to determine the ‘actual likelihood of incursion’ (as low, medium or high). For example, if quarantine measures were ‘sufficient,’ the actual likelihood of incursion would be assessed as lower than the potential likelihood. There would be no reduction in actual likelihood if there were no measures in place. To meet the standard of sufficient quarantine measures, as many barriers and checks as possible need to be in place along pathways of introduction (Thomas and others, 2017). ‘Barriers’ usually involve placing traps or poison stations at strategic locations that would:

  • prevent species getting on to vessels, either directly, for example, by climbing up mooring ropes or indirectly, for example, as a stowaway in cargo
  • prevent species dispersing from land within swimming distance of the island
  • identify the presence of species on vessels in transit
  • prevent species getting off vessels
  • prevent species getting out of quarantine areas on the island

Secondly, the potential hazard from invasion was reassessed at each site given the measures in place that could reduce the likelihood of the invasive species becoming established on the island. The first of these measures include an effective surveillance scheme designed to detect the incursion of an invasive species as soon as possible after it has occurred (for example, by using non-toxic wax blocks set inside bait stations, tracking tunnels, rodent motels, and trail cameras).

Once an invasive species has been detected on an island, a rapid response is required to remove all individuals from the island before they spread far from the incursion point. Preparedness for incursion response was assessed through interviews with site managers. The biosecurity plans currently in development contain enhanced monitoring and incursion response plans to deal with possible and probable ordefinite invasive species sightings. Incursion response plans are based on setting up a grid of bait stations with rodenticide bait 250 m in all directions around the sighting or sightings augmented with snap traps and non-toxic monitoring.

The combined assessment of surveillance and rapid incursion response measures was used to determine if the actual likelihood of invasion could be scored lower than the potential likelihood. Finally, the lowest of the scores for likely impact and actual likelihood of invasion was entered as the hazard score into the risk matrix (Table 1). The actual likelihood of incursion was also entered into the risk matrix to determine an overall score for the actual risk from invasive mammals at the site.

Results

Findings from the 2012 UK Initial Assessment

This indicator was not considered as part of the 2012 Initial Assessment (HM Government, 2012).

Latest findings

Status assessment

Invasive predatory mammals were present on 12 out of the 42 Special Protection Areas assessed (see Figure 2) and absent from islands in 30 Special Protection Areas (Figure 3). Note thatthe Isles of Scilly Special Protection Area is included in both figures because high-impact invasive mammals are present on some, but not on all of its 85 islands. Of the 12 Special Protection Areas where high-impact invasive mammals were present (Figure 2), eight had rats. The other four Special Protection Areas had feral cats present. On islands in these Special Protection Areas, seabirds will be restricted to nesting in places that are inaccessible to rats and cats, such as cliffs. Hence, seabird species that don’t nest on cliffs may be scarce or absent from islands where there are rats or cats. Evidence from other islands shows that it will be a major undertaking to remove the rats and the removal of feral cats can be contentious. Biosecurity measures were carried out at only half of these sites (six) and were only partially effective at minimising the risk of other predatory mammal species arriving and becoming established (Figure 2).

Island seabird colonies within UK Special Protection Areas, where invasive predatory mammals were present and the level to which risk of further incursion has been minimised by biosecurity.Figure 2 – Island seabird colonies within UK Special Protection Areas, where invasive predatory mammals were present and the level to which risk of further incursion has been minimised by biosecurity. Isles of Scilly – refers only to Tresco, St Martin’s, Bryher, Samson, St Helen’s, Northwethel, Men-a-vaur, Tean, Merrick and Round Island. Some contain brown rats and/or feral cats.

Island seabird colonies within UK Special Protection Areas (SPA)

Figure 3. Island seabird colonies within UK Special Protection Areas, where invasive predatory mammals were absent. Isles of Scilly – refers only to Annet (successful response to rat incursion in 2004) and St Agnes and Gugh, where rats were eradicated in 2013/14. Firth of Forth Islands include Isle of May, Bass Rock, Inchmickery, Craigleith, Lamb and Fidra.

At the Special Protection Areas that had no invasive predatory mammals, the risk of invasion was minimised by effective biosecurity at six sites and was partially reduced at a further ten sites (Figures 3 and 4). At the remaining 14 Special Protection Areas, biosecurity was either not carried out or was below the standard required to reduce the risk of invasive mammals arriving.

The number of UK Special Protection Areas, where invasive predatory mammals were absent (as listed in Figure 3) and where biosecurity measures have minimised the risk (yes, partially, or no) from predatory mammals arriving and becoming established.

Figure 4. The number of UK Special Protection Areas, where invasive predatory mammals were absent (as listed in Figure 3) and where biosecurity measures have minimised the risk (yes, partially, or no) from predatory mammals arriving and becoming established.

Trend assessment

The trends are unknown. The indicator was not considered as part of the UK Initial Assessment (HM Government, 2012).

Further information

Table 3 shows the results of the step-by-step process to assess risk from invasive brown rats and American mink on the 30 island Special Protect Areas where both species are currently absent. The column headings in Table 3 correspond to the steps outlined in the risk assessment process in Figure 1. Potential risk (without current biosecurity) and actual risk (with current biosecurity) were estimated using the risk matrix in Table 2. The majority of the scores in Table 2 were taken from interviews of site managers conducted by the Royal Society for the Protection of Birds as part of the Shiant Isles Seabird Recovery Project (Thomas and others, 2016). The results of the risk assessment in Table 3 are summarised in Figures 2 and 3 and below in Tables 4 and 5.

Table 3a.– Risk assessment of non-native rats and American mink and the effectiveness of biosecurity measures at island seabird colonies within UK Special Protection Areas where they are not currently present.

MSFD Sub-region

Country

Special Protection Area name

Approximate size of islands (hectars)

Key islands within SPA

Total number of islands within SPA

Celtic Seas

England

Isles of Scilly

170

Annet, Gugh, St Agnes

 

Celtic Seas

Northern Ireland

Carlingford Lough

8

Green Island

2

Celtic Seas

Northern Ireland

Copeland Islands

156

Copeland, Lighthouse

7

Celtic Seas

Northern Ireland

Larne Lough

0.75

Swan, Blue Circle

2

Celtic Seas

Scotland

Ailsa Craig

90

Ailsa Craig

1

Celtic Seas

Scotland

Canna and Sanday

1327

Canna, Sanday

30

Celtic Seas

Scotland

Flannan Isles

54

Mor, Tighe

27

Celtic Seas

Scotland

Glas Eileanan

1.43

Glas Eileanan

2

Celtic Seas

Scotland

Mingulay and Berneray

1135

Mingulay, Berneray, Pabbay

21

Celtic Seas

Scotland

North Rona and Sula Sgeir

128

Rona, Sule Sgeir

20

Celtic Seas

Scotland

Priest Island

120

Priest

1

Celtic Seas

Scotland

St Kilda

860

Hirta, Dun, Soay, Boreray

76

Celtic Seas

Scotland

Sule Skerry & Sule Stack

8

Sule Skerry, Sule Stack

2

Celtic Seas

Scotland

The Monach Isles

364

Monach, Siolaigh

16

Celtic Seas

Scotland

The Shiant Isles

177

Rough, House (jointed), Mary

7

Celtic Seas

Scotland

Treshnish Isles

107

Lunga, Fladda

16

Celtic Seas

Wales

Glannau Aberdaron & Ynys Enlli / Aberdaron Coast & Bardsey Island

183

Bardsey

3

Celtic Seas

Wales

Grassholm

9

Grassholm

1

Celtic Seas

Wales

Skokholm and Skomer

399

Skokholm, Skomer and Middleholm

7

Celtic Seas

Wales

Ynys Feurig, Cemlyn Bay and The Skerries

12

The Skerries only (other islands are tidal)

4 (including YF, excluding Anglesey)

Celtic Seas

Wales

Ynys Seiriol / Puffin Island

23

Puffin

1

Greater North Sea

England

Coquet Island

8

Coquet

1

Greater North Sea

England

Farne Islands

35

Inner Farne & Wideopens Knoxes, Brownsman & Stable

13

Greater North Sea

Scotland

Auskerry

84

Auskerry

1

Greater North Sea

Scotland

Calf of Eday

217

Calf of Eday

1

Greater North Sea

Scotland

Copinsay

78

Copinsay, Horse of Copinsay

3

Greater North Sea

Scotland

Firth of Forth

75

Isle of May, Craigleith, Bass Rock, Fidra, Inchmickery, Lamb

10

Greater North Sea

Scotland

Mousa

171

Mousa

7

Greater North Sea

Scotland

Noss

344

Noss

14

Greater North Sea

Scotland

Ramna Stacks & Gruney

12

Gruney

15

Table 3b.– Risk assessment of non-native rats and American mink and the effectiveness of biosecurity measures at island seabird colonies within UK Special Protection Areas where they are not currently present, assessment continues in Table 3c.

 

Likelihood of invasion

Potential hazard from invasion

Biosecurity assessment

Actual likelihood of incursion given biosecurity

Special Protection Area name

by rats

by ferrets and mink

likely impact

likelihood of invasion/ difficulty of removal

Potential risk from invasive mammals

Current quarantine measures

by rats

by ferrets and mink

Isles of Scilly

High

Low

High

Medium

High

Sufficient

Medium

Low

Carlingford Lough

High

High

High

High

High

None

High

High

Copeland Islands

Low

Medium

High

Medium

High

None

Low

Medium

Larne Lough

Medium

High

High

Medium

High

None

Medium

High

Ailsa Craig

Low

Low

High

Medium

Medium

None

Low

Low

Canna and Sanday

High

Medium

High

High

High

Below standard

Medium

Low

Flannan Isles

Low

Low

High

Medium

Medium

None

Low

Low

Glas Eileanan

Medium

High

High

Medium

High

Below standard

Low

Medium

Mingulay and Berneray

Low

Medium

High

High

High

None

Low

Medium

North Rona and Sula Sgeir

Low

Low

High

High

Medium

Below standard

Low

Low

Priest Island

Medium

High

High

Medium

Medium

Sufficient

Low

Low

St Kilda

Medium

Medium

High

High

High

Sufficient

Low

Low

Sule Skerry & Sule Stack

Low

Low

High

High

Medium

None

Low

Low

The Monach Isles

Medium

Low

Medium

High

Medium

None

Medium

Low

The Shiant Isles

Medium

Medium

High

High

Medium

Sufficient

Low

Low

Treshnish Isles

Low

Medium

High

High

High

None

Low

Medium

Glannau Aberdaron & Ynys Enlli / Aberdaron Coast & Bardsey Island

Medium

Low

High

Medium

Medium

Below standard

Low

Low

Grassholm

Low

Low

Medium

Low

Low

Sufficient

Low

Low

Skokholm and Skomer

High

High

High

High

High

Below standard

Medium

Medium

Ynys Feurig, Cemlyn Bay and The Skerries

High

High

High

Medium

High

Below standard

Medium

Medium

Ynys Seiriol / Puffin Island

Low

High

Medium

High

High

Below standard

Low

Medium

Coquet Island

High

High

High

Medium

High

Sufficient

Low

Low

Farne Islands

High

High

High

High

High

Sufficient

Low

Low

Auskerry

Low

Low

High

Medium

Medium

None

Low

Low

Calf of Eday

High

High

Medium

High

High

None

High

High

Copinsay

High

High

High

Medium

High

Sufficient

Low

Low

Firth of Forth

High

High

High

Medium

High

Below standard

Medium

Medium

Mousa

Medium

Medium

High

Medium

Medium

Sufficient

Low

Medium

Noss

High

High

High

Medium

High

None

High

High

Ramna Stacks & Gruney

Low

Low

High

Medium

Medium

None

Low

Low

Table 3c.– Risk assessment of non-native rats and American mink and the effectiveness of biosecurity measures at island seabird colonies within UK Special Protection Areas where they are not currently present, continued from Table 3b.

 

Biosecurity assessment

Actual hazard from mammal invasion

Actual Risk from invasive  mammals

Has risk been minimised by effective biosecurity

Special Protection Area name

current surveillance measures

current preparedness for rapid response

Actual likelihood of invasion given the surveillance and response measures

likely impact of invasion on resident seabird species

Isles of Scilly

Sufficient

Sufficient

Low

High

Low

Yes

Carlingford Lough

None

None

High

High

High

No

Copeland Islands

None

None

High

High

Medium

No

Larne Lough

Below standard

None

Medium

High

High

No

Ailsa Craig

Below standard

None

Medium

High

Medium

partially

Canna and Sanday

Sufficient

Below standard

Medium

High

Medium

partially

Flannan Isles

Below standard

None

Medium

High

Medium

No

Glas Eileanan

None

Below standard

Low

High

Medium

partially

Mingulay and Berneray

None

None

High

High

High

No

North Rona and Sula Sgeir

Below standard

None

High

High

Medium

No

Priest Island

Sufficient

Sufficient

Low

High

Low

Yes

St Kilda

Below standard

Sufficient

Medium

High

Medium

partially

Sule Skerry & Sule Stack

None

None

High

High

Medium

No

The Monach Isles

None

None

Medium

Medium

Medium

No

The Shiant Isles

Sufficient

Sufficient

Low

High

Low

Yes

Treshnish Isles

Below standard

None

High

High

High

No

Glannau Aberdaron & Ynys Enlli / Aberdaron Coast & Bardsey Island

Below standard

Below standard

Medium

High

Low

partially

Grassholm

Sufficient

Below standard

Low

Medium

Low

partially

Skokholm and Skomer

Below standard

Below standard

Medium

High

Medium

partially

Ynys Feurig, Cemlyn Bay and The Skerries

Below standard

Below standard

Medium

High

Medium

partially

Ynys Seiriol / Puffin Island

None

None

Medium

Medium

Medium

No

Coquet Island

Sufficient

Sufficient

Low

High

Low

Yes

Farne Islands

Sufficient

Sufficient

Low

High

Low

Yes

Auskerry

None

None

Medium

High

Medium

No

Calf of Eday

None

None

High

Medium

High

No

Copinsay

Sufficient

Sufficient

Low

High

Low

Yes

Firth of Forth

Below standard

None

Medium

High

Medium

partially

Mousa

Below standard

None

Medium

High

Medium

partially

Noss

Below standard

None

Medium

High

High

No

Ramna Stacks & Gruney

None

None

Medium

High

Medium

No

Table 4. Celtic Seas: summary assessment of the effectiveness of biosecurity measures at reducing risk from invasive predatory mammals at island seabird colonies within UK Special Protection Areas where they are not currently present. Notes: 1Isles of Scilly – refers only to Annet (successful response to rat incursion in 2004) and St Agnes and Gugh, where rats were eradicated in 2013 to 14; 2Ailsa Craig – rat eradication in 1991; 3Canna & Sanday - rat eradication in 2005; 4The Shiant Isles – rat eradication in 2015 to 16; 5Puffin Island - rat eradication in 1992.

Country

Special Protection Area (SPA) name 

Risk from invasive mammals

Has the risk been minimised by biosecurity

Potential (without current biosecurity)

Actual (with current biosecurity)

England

Isles of Scilly1

High

Low

Yes

Northern Ireland

Carlingford Lough

High

High

No

Northern Ireland

Copeland Islands

High

Medium

No

Northern Ireland

Larne Lough

High

High

No

Scotland

Ailsa Craig2

Medium

Medium

Partially

Scotland

Canna and Sanday3

High

Medium

Partially

Scotland

Flannan Isles

Medium

Medium

No

Scotland

Glas Eileanan

High

Medium

Partially

Scotland

Mingulay and Berneray

High

High

No

Scotland

North Rona and Sula Sgeir

Medium

Medium

No

Scotland

Priest Island

Medium

Low

Yes

Scotland

St Kilda

High

Medium

Partially

Scotland

Sule Skerry & Sule Stack

Medium

Medium

No

Scotland

The Monach Isles

Medium

Medium

No

Scotland

The Shiant Isles4

Medium

Low

Yes

Scotland

Treshnish Isles

High

High

No

Wales

Bardsey Island/Ynys Enlli (part of (Glannau Aberdaron & Ynys Enlli / Aberdaron Coast & Bardsey Island SPA)

Medium

Low

Partially

Wales

Grassholm

Low

Low

Partially

Wales

Skokholm and Skomer

High

Medium

Partially

Wales

The Skerries (part of Ynys Feurig, Cemlyn Bay and The Skerries SPA)

High

Medium

Partially

Wales

Ynys Seiriol / Puffin Island5

High

Medium

No

Table 5. Greater North Sea: summary assessment of the effectiveness of biosecurity measures at reducing risk from invasive predatory mammals at island seabird colonies within UK Special Protection Areas where they are not currently present. Notes: 6Firth of Forth Islands – includes Isle of May, Bass Rock, Inchmickery, Craigleith, Lamb and Fidra. All are rat-free.

Country

Special Protection Area (SPA) name 

Risk from invasive mammals

Has risk been minimised by biosecurity

Potential (without current biosecurity)

Actual (with current biosecurity)

England

Coquet Island

High

Low

Yes

England

Farne Islands

High

Low

Yes

Scotland

Auskerry

Medium

Medium

No

Scotland

Calf of Eday

High

High

No

Scotland

Copinsay

High

Low

Yes

Scotland

Firth of Forth6

High

Medium

Partially

Scotland

Mousa

Medium

Medium

Partially

Scotland

Noss

High

High

No

Scotland

Ramna Stacks & Gruney

Medium

Medium

No

Rats have been eradicated from some of the islands included in Tables 3, 4 and 5 – a review of these eradication programmes is provided in Stanbury and others (2017) and Ratcliffe and others, (2009). These included a long-running eradication programme on the Isles of Scilly. In 2013, the islands of St Agnes and Gugh were declared rat-free (but work is ongoing to prevent re-incursions of rats at other islands in the archipelago. Most recently, in 2015 work began to eradicate black rats from the Shiants Islands in the Western Isles. So far evidence suggests the eradication on the Shiants may have been successful. There have also been schemes to eradicate and control the spread of American mink – on Lewis and Harris in the Western Isles (and in and around the sea lochs of Argyll and Lochaber) (Craik, 1997; 1998).

Table 6 shows the results of the step-by-step process to assess the biosecurity in place on the 12 Special Protection Areas where high-impact invasive mammals are currently present (listed below in Table 7 and shown in Figure 2). The results of the assessment are summarised in Table 7 below. A full risk assessment (as shown in Table 3) was not carried out since the risk has already been realised on these islands which are already impacted by invasive mammals. The assessment of biosecurity on these sites is still important, since the invasion by new species, may impact further on the resident bird communities.

Table 6a. Risk assessment of non-native rats and American mink and the effectiveness of biosecurity measures at island seabird colonies within UK Special Protection Areas: site information.

MSFD Sub-region

Country

Special Protection Area (SPA) name 

Approx size (ha) of islands

Key islands within SPA

Total number of islands within SPA

High impact mammals present

Celtic Seas

England

Isles of Scilly

817

Tresco, St Martin’s, Bryher, Samson, St Helen’s, Northwethel, Men-a-vaur, Tean, Merrick, Round.

 

brown rat, feral cats

Celtic Seas

Northern Ireland

Rathlin Island

1439

Rathlin

5

Brown rat, ferret, possibly pet cats

Celtic Seas

Scotland

Handa

330

Handa

7

Brown rat

Celtic Seas

Scotland

Rum

10727

Rum

16

Brown rat, feral goat, neutered pet cats (restricted to inhabited zone)

Greater North Sea

Scotland

Hoy

9500

Hoy

3

Brown rat, hedgehog, feral cat, Stoat

Greater North Sea

Scotland

Rousay

4697

Rousay

1

Brown rats, feral cat

Greater North Sea

Scotland

Pentland Firth Islands

129

Swona, Muckle Skerry

3

Possibly Brown rat

Greater North Sea

Scotland

Fair Isle

798

Fair Isle

176

Cats

Greater North Sea

Scotland

Fetlar

4652

Fetlar

61

Cat, hedgehog

Greater North Sea

Scotland

Foula

1305

Foula

62

hedgehog, feral cat

Greater North Sea

Scotland

Papa Stour

569

Papa Stour

2

feral cat assumed present.

Greater North Sea

Scotland

Papa Westray (North Hill and Holm)

884

Papa Westray, Holm of Papa

2

rodents, cats (domestic, possibly feral),

Table 6b. Risk assessment of non-native rats and American mink and the effectiveness of biosecurity measures at island seabird colonies within UK Special Protection Areas.

 

Risk of further incursion

Biosecurity Assessment

Special Protection Area (SPA) name

rats

mink/stoats/ferrets

Current biosecurity measures

Current surveillance measures

Current preparedness for rapid response

Has risk of further incursion been minimised by effective biosecurity?

Isles of Scilly

rats

mink/stoats/ferrets

Current biosecurity measures

Current surveillance measures

Current preparedness for rapid response

Has risk of further incursion been minimised by effective  biosecurity

Rathlin Island

High

Low

Below standard

Below standard

Below standard

partially

Handa

 

High

None

None

None

No

Rum

 

High

Below standard

Below standard

Below standard

partially

Hoy

 

Low

None

None

None

No

Rousay

 

Low

None

Below standard

Below standard

partially

Pentland Firth Islands

 

High

None

None

Below standard

No

Fair Isle

High

Medium

None

None

None

No

Fetlar

High

Low

None

None

None

No

Foula

High

High

None

None

Below standard

No

Papa Stour

Medium

High

None

None

None

No

Papa Westray (North Hill and Holm)

High

High

None

None

None

No

Table 7.Island seabird colonies within UK Special Protection Areas that have invasive predatory mammals. Isles of Scilly – refers only to Tresco, St Martin’s, Bryher, Samson, St Helen’s, Northwethel, Men-a-vaur, Tean, Merrick and Round Island. Some contain brown rats or feral cats.

MSFD sub-region

Country

Special Protection Area (SPA) name 

Predatory mammals present

Has risk of further incursion been minimised by effective biosecurity

Celtic Seas

England

Isles of Scilly*

Brown rat, feral cat

Partially

Celtic Seas

Northern Ireland

Rathlin Island

Brown rat, ferret, possibly pet cats

No

Celtic Seas

Scotland

Handa

Brown rat

Partially

Celtic Seas

Scotland

Rum

Brown rat, feral goat, neutered pet cats (restricted to inhabited zone)

No

Greater North Sea

Scotland

Hoy

Brown rat, hedgehog, feral cat, stoat

Partially

Greater North Sea

Scotland

Rousay

Brown rat, feral cat

Partially

Greater North Sea

Scotland

Pentland Firth Islands

Possibly brown rat

No

Greater North Sea

Scotland

Fair Isle

Feral cat

No

Greater North Sea

Scotland

Fetlar

Feral cat, hedgehog

Partially

Greater North Sea

Scotland

Foula

hedgehog, feral cat

No

Greater North Sea

Scotland

Papa Stour

feral cat assumed present.

No

Greater North Sea

Scotland

Papa Westray (North Hill and Holm)

Possibly brown rats, cats (domestic, possibly feral),

No

Conclusions

The UK target of a reduction in the risks to island seabird colonies from non-native mammals could not be assessed because there has been no previous assessment of this risk. This assessment also included invasive native species of predatory mammals as well as non-natives. It focussed on all the 42 Special Protection Areas that were designated to protect the UK’s most important seabird colonies on offshore islands. These sites receive the highest level of statutory protection. Despite this, invasive predatory mammals (brown rats, domestic and feral cats, and hedgehog) were present at 12 Special Protection Areas  The full extent of the impact of these mammals at these sites is currently unknown. There is a medium to high risk of other invasive mammal species arriving at these sites and becoming established because biosecurity measures are either absent or ineffective.

High-impact invasive mammals were absent from 30 Special Protection Areas and absent from some Special Protection Areas on islands in the Isles of Scilly. The risk from high-risk mammals has been minimised by effective biosecurity at only six of these sites (including Isles of Scilly Special Protection Areas) Risk has been partially minimised by current biosecurity at a further ten sites. However, these existing measures need enhancing to meet the standards set in the UK Rodent Eradication Best Practice Toolkit (Thomas and others, 2017).

This assessment was conducted with moderate confidence: confidence in data availability was high, but the methods used in this risk assessment are new.

Future assessments of this indicator must improve on the current assessment to meet the UK target of reducing risks to island seabird colonies from invasive predatory mammals. This assessment supports the conclusions of the UK Marine Strategy Part Three (HM Government, 2015). A UK-wide programme of biosecurity at island seabird colonies will help to achieve this target in the future.

Further information

Most of the Special Protection Areas that require improvements in biosecurity are in Scotland. This is because the majority of seabird island Special Protection Areas are in Scotland – 30 out of 42. Of these Scottish Special Protection Areas ten already have high-risk mammals on them, and biosecurity is currently insufficient to minimise the risk of further invasion by predatory mammals. Management options at these sites could include both mammal eradication and improvements in biosecurity. The risk of invasion at the other 19 Special Protection Areas in Scotland, is currently minimised by effective biosecurity at only three and partially minimised at six sites. Improvements in biosecurity are therefore required at up to 16 Special Protection Areas in Scotland to increase the probability of maintaining them free of invasive predatory mammals.

In Northern Ireland, current biosecurity was assessed as ineffective on all five Special Protection Areas and Rathlin island Special Protection Area already has rats and ferrets. Improvements in biosecurity at Northern Ireland Special Protection Area would contribute to meeting the UK target in the future.

In England, improvements in biosecurity would only be required on some islands in the Isles of Scilly Special Protection Area that have rats or feral cats on them. Elsewhere, current biosecurity was assessed as effective on rat-free islands in Special Protection Areas of the Isles of Scilly, Coquet Island and the Farne Islands.

In Wales, no predatory mammals were present on any of the five seabird island Special Protection Areas that were assessed. Improvements in biosecurity would be required on all sites to minimise risk, but current measures were considered partially effective at four sites.

Knowledge gaps

This assessment clearly identifies where biosecurity needs to be improved to meet the UK target in the future. However, it is not clear how the risk will be reduced on the 12 Special Protection Areas where invasive predatory mammals are already present (Figure 2). A better understanding of the extent of the impacts on seabirds and other ground-nesting birds in these Special Protection Areas will identify the measures needed to reduce these impacts.

Further information

It will not be easy to fully understand the impacts on seabirds at Special Protection Area where invasive predatory mammals, particularly rats, are already present (Figure 1). If rats have been present for many years, a stable state of coexistence may have been established, so that impacts are not that visible. Following the invasion by rats, the seabirds nesting on the islands will have moved to areas that are inaccessible to rats, while some species, such as European storm-petrels, may have deserted the islands completely. There is unlikely to be any visible evidence of rat predation such as predated eggs or chicks on these islands, yet the impacts of rats persist.

Rats are absent from four Special Protection Area where feral cats are present: Foula, Fetlar, Fair Isle, and Papa Stour. Predation by cats is usually more obvious than the impacts of rats including through the presence of predated bird carcasses. However, the extent of impacts by cats on these four Special Protection Area is currently unknown.

References

Birkhead TR, Furness, RW (1985) ‘Regulation of seabird populations’ in: Behavioural ecology: ecological consequences of adaptive behaviour (editors: Sibley, RM, Smith, RH), pages 145-167. Blackwell, London.

Courchamp F, Chapuis J-L, Pascal M (2003) ‘Mammal invaders on islands: impact control and control impact’ Biological Reviews, 78:347-383 (viewed on 24 October 2018)

Craik, JCA (1998) ‘Recent mink-related declines of gulls and terns in west Scotland and the beneficial effects of mink control’ Argyll Bird Report, 14: 98-110 (viewed on 24 October 2018)

Dunstone, N (1993) 'The Mink' T & AD Poyser, London.

European Commission (2009) ‘Directive 2009/147/EC of the European Parliament and of the Council of 30 November 2009 on the conservation of wild birds’ Official Journal of the European Union L 20, 26.1.2010, pages 7–25 (viewed 24 October 2018)

Ewins PJ, Tasker ML (1985) ‘The breeding distribution of Black Guillemots Cepphus grylle in Orkney and Shetland’ Bird Study 32:186-193 (viewed on 24 October 2018)

HM Government (2012) ‘Marine Strategy Part One: UK Initial Assessment and Good Environmental Status’ (viewed on 5 July 2018)

 

HM Government (2015) ‘Marine Strategy Part Three: UK Programme of Measures’ December 2015. (viewed on 5 July 2018)

Jones HP, Tershy BR, Zavaleta ES, Croll DA, Keitt BS, Finkelstein ME, Howald GR (2008) ‘Severity of the effects of invasive rats on seabirds: a global review’ Conservation Biology 22: 16-26 (viewed on 24 October 2018)

Lock J (2006) ‘Eradication of brown rats Rattus norvegicus and black rats Rattus rattus to restore seabird populations on Lundy Island, Devon, England’ Conservation Evidence 3: -111-113 (viewed on 24 October 2018)

Mitchell PI (2004) ‘Leach’s Petrel Oceanodroma leucorhoa’ Pages 101-114 in: Mitchell PI, Newton SF, Ratcliffe N, Dunn TE (2004) ‘Seabird Populations of Britain and Ireland’ T & AD Poyser, London (viewed on 24 October 2018)

Mitchell PI, Newton SF (2004) ‘European storm-petrel Hydrobates pelagicus’ Pages 81-100 in: Mitchell PI, Newton SF, Ratcliffe N, Dunn TE (2004) ‘Seabird Populations of Britain and Ireland’ T & AD Poyser, London (viewed on 24 October 2018)

Mitchell PI, Ratcliffe, N (2007) ‘Abundance & distribution of seabirds on UK islands – the impact of invasive mammals’ in Proceedings of the conference on Tackling the problem of invasive alien mammals on seabird colonies – Strategic approaches and practical experience. Edinburgh 2007. The National Trust for Scotland, Royal Zoological Society of Scotland and Central Science Laboratory.

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Ratcliffe N, Mitchell I, Varnham K, Verboven N, Higson P, (2009) ‘How to prioritize rat management for the benefit of petrels: a case study of the UK, Channel Islands and Isle of Man’ International Journal of Avian Science, 151: 699-708 (viewed on 24 October 2018)

Russell JC, Clout MN (2005) ‘Rodent incursions on New Zealand islands’ in Parkes, J., Statham, M. & Edwards, G. (editors) Proceedings of the 13th Australasian Vertebrate Pest Conference Lincoln, New Zealand 2-6 May, 2005. Landcare Research pages 324–330 (viewed on 24 October 2018)

Stanbury A, Thomas S, Aegerter J, Brown A, Bullock D, Eaton M, Lock L, Luxmoore R, Roy S, Whitaker S, Oppel S (2017) ‘Prioritising islands in the United Kingdom and crown dependencies for the eradication of invasive alien vertebrates and rodent biosecurity’ European Journal of Wildlife Research, 63:31 (viewed on 24 October 2018)

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Acknowledgements

Assessment Metadata

Please contact marinestrategy@defra.gov.uk for metadata information

Recommended reference for this indicator assessment

Ian Mitchell1, Sophie Thomas6, Laura Bambini6, Karen Varnham, K.6, Phillips, R.1, Gemma Singleton1, Andrew Douse,2 Simon Foster,2 Melanie Kershaw,3 Neil McCulloch4, Matty Murphy5, & Jane Hawkridge1 2018. Invasive mammal presence on island seabird colonies. UK Marine Online Assessment Tool, available at: https://moat.cefas.co.uk/biodiversity-food-webs-and-marine-protected-areas/birds/invasive-mammals/

1Joint Nature Conservation Committee

2Scottish Natural Heritage

3Natural England

4Department of Environment, Agriculture & Rural Affairs, Northern Ireland

5Natural Resources Wales

6Royal Society for the Protection of Birds