Scottish seabird conservation action plan: vulnerability report

Annex 1: Assessing Sensitivity

Sensitivity criteria used by Rogerson et al. (2021) to score Tolerance, Recovery and Confidence.

Scoring Tolerance

Rogerson et al. (2021) assigned tolerance scores using the criteria in Table A1.1:

Table A1. 1: Criteria for assessing the tolerance potential of species

None: A severe decline (>50%) in the estimated size of the local population as a result of increased mortality, reduced reproductive success, displacement or any other mechanism

Low: A significant decline (>10 and ≤50%) in the estimated size of the local population as a result of increased mortality, reduced reproductive success, displacement or any other mechanism.

Medium: A moderate decline (loss of up to 10%) in the estimated size of the local population as a result of increased mortality, reduced reproductive success, displacement or any other mechanism.

High: No population decline is expected. Effects affecting key functional and physiological attributes of the species (e.g. food intake rate, energy expenditure rate) may occur but are buffered from feeding through to changed rates of reproduction or mortality and hence population size by virtue of species’ flexibility to respond to the pressure e.g. by redistribution, dietary shifts, increased foraging effort, etc.

If there was insufficient data within the assessment to determine a tolerance score as described above, but it was considered through expert opinion that there remained scope for potential impacts (of unknown magnitude) upon the species, a score of ‘sensitive’ was assigned. ‘Not assessed’ was assigned where there was no evidence available to allow an assessment of sensitivity.

Scoring Recovery

Scoring of recovery is determined by life history parameters indicative of the recovery potential of species (Table 2) and are detailed in Rogerson et al (2021).

Table A1. 2: Criteria for assessing the recovery potential of species

Life history parameters: Definition

Low recovery potential: Full recovery expected within 10-25 years.

Medium recovery potential: Full recovery expected within 2-10 years.

High recovery potential: Full recovery expected within 2 years.

Life history parameters: Lifespan

Low recovery potential: Long- lived (10 years +)

Medium recovery potential: Moderate lifespans (5-10 years)

High recovery potential: Short-lived (up to 5 years)

Life history parameters: Age at first maturity

Low recovery potential: Deferred maturity (first breeds when more than 3 years old)

Medium recovery potential: First breeds when 2-3 years old

High recovery potential: First breeds at one year of age

Life history parameters: Adult mortality rate

Low recovery potential: Low natural mortality (<15%)

Medium recovery potential: Moderate natural mortality rate (15-25%)

High recovery potential: High natural annual mortality (>25%)

Life history parameters: Fecundity / reproductive success

Low recovery potential: Low reproductive output (<2 chicks per pair per annum)

Medium recovery potential: Moderate reproductive output (2-5 chicks per pair per annum)

High recovery potential: High reproductive output (>5 chicks per pair per annum)

The framework for this was originally developed for a wider spectrum of bird species and consequently, all of the 22 seabird species covered by the Scottish Seabird Vulnerability Report fall into the low recovery category, hence, by default, the recovery score is low.

Confidence In Tolerance, Recovery & Sensitivity Scores

For each of the tolerance and recovery scores, confidence in the assessment was also scored, following a scoring system considering three confidence components (Table A1.3). For each of the components (quality of evidence, applicability of evidence and degree of concordance) a score was given and they were added up. The resulting confidence score falls between 3 and 15 points, and the degree of confidence is defined as:

• High confidence: total score >12;
• Medium confidence: total score 6 – 12; and
• Low confidence: total scores <6.

Table A1. 3: Definitions of confidence categories for assessments of tolerance, recovery and sensitivity

Confidence: High (Score = 5)

Quality of information sources: Based on Peer Reviewed papers (observational or experimental) or grey literature reports by established agencies on the feature

Applicability of evidence: Assessment based on the same pressures arising from similar activities, acting on the same type of feature in comparable areas (i.e. Ireland, UK)

Degree of concordance: Evidence agrees on the direction and magnitude of impact

Confidence: Medium (Score = 3)

Quality of information sources: Based on some peer reviewed papers but relies heavily on grey literature or expert judgement on feature or similar features

Applicability of evidence: Assessment based on similar pressures on the feature in other areas

Degree of concordance: Evidence agrees on direction but not magnitude of impact

Confidence: Low (Score = 1)

Quality of information sources: Based on expert judgement, which is not clearly documented

Applicability of evidence: Assessment based on proxies for pressures e.g. natural disturbance events

Degree of concordance:Evidence does not agree on concordance or magnitude

Key:

M=Medium, L=Low, S=Sensitive, NA= Not Assessed Br=Breeding season only, Nbr=Non-breeding season only

1. Water clarity changes

2. Nitrogen & phosphorus enrichment

3. Under-water noise

4. Temperature changes - local

5. Water flow (tidal current) changes – local

6. Physical removal (extraction of sub-stratum)

7. Habitat loss from coastal infra-structure

8. Mortality or sub-lethal impacts of synthetic compounds (e.g. pesticides, antifoulants)

9. Mortality or sub-lethal impacts of non-synthetic compounds (e.g. heavy metals)

Table A1. 5: Pressures for which one or more seabird species show a ’medium’ sensitivity that were not taken forward to Step 2 (exposure analysis).

Pressure: Water clarity changes

Sensitivity: Common tern have a medium sensitivity to water clarity changes. Common tern have a high reliance on visually locating food from the air. Increased turbidity can reduce the ability of common tern to successfully catch prey.

Reason for not considering pressure further: In Scotland, common tern may experience this pressure to a small extent in highly localised situations and over a short time period.

Pressure: Nitrogen & phosphorus enrichment

Sensitivity: Terns, razorbill and common guillemot have a medium sensitivity to the effects of nitrogen and phosphorous enrichment. Indirect impacts of nitrogen and phosphorous enrichment resulting in algal blooms have been recorded as causing mass mortality of seabirds. Cormorants are negatively affected by fertilizer use most likely associated with run-off from inland and estuarine locations.

Reason for not considering pressure further: In Scotland, terns, razorbill and common guillemot may experience this pressure to some extent when enrichment results in algal blooms. Nitrogen and phosphorous enrichment is mostly associated with run-off from inland and estuarine locations.

Pressure: Underwater noise

Sensitivity: Common guillemot have a medium sensitivity to underwater noise. Underwater noise may directly affect guillemot, being submerged for comparably long periods when diving in search for prey on the seabed. Guillemots have been found to show consistent reactions to underwater sound during controlled trials.

Reason for not considering pressure further: In Scotland, common guillemot may experience this pressure to a small extent. Limited evidence suggests a potential negative effect from underwater noise but the impact is expected to be temporary.

Pressure: Water flow (tidal current) changes – local

Sensitivity: Lesser black-backed gull and little gull have a medium sensitivity. Increases in water flow could increase energy expenditure of resting birds or birds diving for prey. It could also influence the availability of prey close to the water surface and species composition could be altered. These impacts could give rise to reduced body condition and therefore direct impacts. Lesser black-backed gulls are known to drift passively with the tidal current for several hours to rest.

Water flow is reported to have a strong influence on little gull foraging.

Reason for not considering pressure further: In Scotland, lesser black-backed gull and little gull may experience this pressure to a small extent in localised situations.

Pressure: Mortality or sub-lethal impacts of synthetic compounds (e.g. pesticides, antifoulants)

Sensitivity: Kittiwake, common tern and Arctic tern have a medium sensitivity to impacts of synthetic compounds. Synthetic compounds can have impacts on seabird physiology such as hormone levels, breeding probability, hatching dates and even on genetics and behaviour. Evidence of impacts from synthetic contaminants on reproduction has been found in terns and impacts to time spent on eggs has been found in Kittiwake.

Reason for not considering pressure further: Legacy contaminants are expected to be in decline and recent studies have found declines in pollutant concentrations in colonies in the German Baltic Sea.

Pressure: Mortality or sub-lethal impacts of non-synthetic compounds (e.g. heavy metals)

Sensitivity: Cormorant and black guillemot have a medium sensitivity to impacts of non-synthetic compounds.

Sub-lethal levels of heavy metal concentrations can lead to chronic diseases in seabirds and can have adverse effects on growth, development, reproduction, metabolism and behaviour. Bioaccumulation of mercury is known to occur in cormorants and black guillemot from their prey.

Reason for not considering pressure further: For cormorants, levels of non-synthetic compounds are very low and appear to not have any significant influence on the birds. Trends in mercury contamination have been seen to fall since 1993 and therefore this pressure is expected to be limited.