Scottish Marine and Freshwater Science Volume 5 Number 2: A Protocol for Implementing the Interim Population Consequences of Disturbance (PCoD) Approach...
Report on developing a protocol to implement the interim Population Consequences of Disturbance (PCoD) Approach: quantifying and assessing the effects of UK offshore renewable energy developments on marine mammal populations
Illustrative Scenarios
Parameters Values Used in the Illustrative Scenarios
In order to illustrate how the interim PCoD protocol might be applied in practice, we used the protocol to simulate the effects of construction for two wind farms at hypothetical locations off the east coast of Scotland ( Figure 6) on the relevant MUs for each priority species. We arbitrarily assumed that piling at both sites occurred intermittently on 52 days in the first year and on 42 days in the second year. The pattern of piling within a year was based on data kindly supplied by Centrica. Exactly the same pattern was used for each site, but the first day of piling at one site was offset by 2 days from the first day of piling at the other site, so that on some days piling occurred simultaneously at both sites and on others it occurred at only one site. For each marine mammal species we have provided a value for the number of individuals that may be disturbed or experience PTS as the result of one day of piling at each site ( i.e. the values specified in item 4. of Box 1). These numbers are approximations of estimates provided in ES chapters for developments in areas with similar densities of animals. We assume that no mitigation measures to reduce the risks of PTS will be implemented. We recognise that developers will almost certainly take steps to mitigate these effects, although it is not clear at the moment how effective these will be. However, if regulators and their scientific advisors are satisfied that these measures will eliminate the risk of PTS, the values for the number of animals that may experience PTS can be set to 0, or some low value.
The comparatively large numbers of seals predicted to suffer PTS in these development scenarios reflect the fact that Southall et al. (2007) recommend a threshold for the onset of PTS in seals and sea lions that is 12dB lower than the one they recommend for other marine mammals.
For purely illustrative purposes, we assumed that one day of actual disturbance resulted in an additional 2 days of 'residual' disturbance for all species, based on values for harbour porpoise in Fig. 7 of Brandt et al. (2011). We also considered a number of values for the size of the sub-population(s) that might be vulnerable to the effects of disturbance associated with the two developments. These values were chosen purely for illustrative purposes and should not be considered as recommendations as to the actual size of these sub-populations.
Figure 6. Locations of the two hypothetical wind farm developments used in the simulations.
The following sections outline the decisions made on steps 1.- 7. of the interim PCoD protocol (Box 3) for each priority species :
Harbour Seal
1. Relevant Management Unit: Moray Firth
2. Estimated current population size: 1431 individuals, based on the minimum population size estimate in Anon. (2013) scaled up by 50% to allow for animals that were not hauled out at the time of the survey, as suggested by SMRU (2012: 2 "an alternative approach would be to assume that the proportion hauled out was 2/3, a value supported by telemetry data").
3. Demographic rates: Rates were adjusted so that the undisturbed population was neither increasing nor decreasing, as reported by SMRU (2012).
| Category | Value |
|---|---|
| Age at first birth | 4 |
| Pup survival | 0.6 |
| Juvenile survival | 0.822 |
| Adult survival | 0.85 |
| Fertility | 0.9 |
4. Size of the vulnerable population: We considered the following illustrative scenarios:
- All of the population is vulnerable to the effects of piling at both sites;
- 50% of the population is vulnerable to the effects of piling at one site and a different 50% is vulnerable to the effects of piling at the second site;
- 50% of the population is vulnerable to the effects of piling at both sites, the remaining 50% of the population is not affected by piling at either site.
5. Schedule of activities: as described above
6. Number of animals that may experience disturbance and PTS (assuming no mitigation measures to reduce PTS):
| Category | Inshore site | Offshore Site |
|---|---|---|
| Number of harbour seals disturbed | 200 | 100 |
| Number of harbour seals experiencing PTS | 50 | 25 |
7. Number of days of 'residual' disturbance assumed: 2
Grey Seals
1. Relevant Management Unit: Moray Firth
2. Estimated current population size: 3750 individuals, based on the estimate in Anon. (2013). We assumed that 58% of this population was female ( SCOS, 2013, p 51).
3. Demographic rates: demographic rates were adjusted so that the undisturbed population was increasing by 1% per year, the same as the overall growth rate of the British grey seal population ( SCOS, 2012).
| Category | Value |
|---|---|
| Age at first birth | 5 |
| Pup survival | 0.235 |
| Juvenile survival | 0.94 |
| Adult survival | 0.94 |
| Fertility | 0.84 |
4. Size of the vulnerable population: We considered the following illustrative scenarios:
- All of the population is vulnerable to the effects of piling at both sites;
- 50% of the population is vulnerable to the effects of piling at both sites, the remaining 50% of the population is not affected by piling at either site.
Only two scenarios were considered for grey seals because they generally have a wider foraging distribution than harbour seals.
5. Schedule of activities: as described above
6. Number of animals that may experience disturbance and PTS (assuming no mitigation measures to reduce PTS):
| Category | Inshore site | Offshore Site |
|---|---|---|
| Number of grey seals disturbed | 500 | 250 |
| Number of grey seals experiencing PTS | 50 | 50 |
7. Number of days of 'residual' disturbance assumed: 2
Bottlenose Dolphin
1. Relevant Management Unit: Coastal East Scotland
2. Estimated current population size: 195 individuals, based on the estimate of Cheney et al. (2013) used by Anon. (2013).
3. Demographic rates: We adjusted the demographic rates so that the undisturbed population was neither increasing nor decreasing.
| Category | Value |
|---|---|
| Age at first birth | 9 |
| Calf survival | 0.8 |
| Juvenile survival | 0.94 |
| Adult survival | 0.94 |
| Fertility | 0.25 |
4. Size of the vulnerable population: We considered the following illustrative scenarios:
- All of the population is vulnerable to the effects of piling at both sites;
- 50% of the population is vulnerable to the effects of piling at both sites, the remaining 50% of the population is not affected by piling at either site.
5. Schedule of activities: as described above
6. Number of animals that may experience disturbance and PTS (assuming no mitigation measures to reduce PTS):
| Category | Inshore site | Offshore Site |
|---|---|---|
| Number of bottlenose dolphins disturbed | 6 | 6 |
| Number of bottlenose dolphins experiencing PTS | 1 | 1 |
7. Number of days of 'residual' disturbance assumed: 2
Harbour Porpoise
1. Relevant Management Unit: North Sea
2. Estimated current population size: 227,298 individuals, based on the estimate in Anon. (2013). This estimate has a wide confidence interval, but this is captured in the uncertainty that the interim approach incorporates into the estimates of the number of animals that may experience PTS and disturbance (see Appendix 2).
3. Demographic rates: We adjusted the demographic rates suggested by Winship & Hammond (2006) so that the undisturbed population was neither increasing nor decreasing, as suggested by the trend analysis in Paxton et al. (2012).
| Category | Value |
|---|---|
| Age at first birth | 5 |
| Calf survival | 0.6 |
| Juvenile survival | 0.85 |
| Adult survival | 0.925 |
| Fertility | 0.48 |
4. Size of the vulnerable population: We considered the following illustrative scenarios:
- All of the population is vulnerable to the effects of piling at both sites;
- 10% of the population is vulnerable to the effects of piling at both sites, the remaining 90% of the population is not affected by piling at either site. These percentages were chosen because of the large extent of the MU relative to the area of the two development sites.
5. Schedule of activities: as described above
6. Number of animals that may experience disturbance and PTS (assuming no mitigation measures to reduce PTS):
| Category | Inshore site | Offshore Site |
|---|---|---|
| Number of harbour porpoises disturbed | 200 | 500 |
| Number of harbour porpoises experiencing PTS | 2 | 5 |
7. Number of days of 'residual' disturbance assumed: 2
Minke Whale
1. Relevant Management Unit: European waters.
2. Estimated current population size: 23,163 individuals, based on the estimate in Anon. (2013).
3. Demographic rates: We adjusted the demographic rates so that the undisturbed population was decreasing slightly, as suggested by the trend analysis in Paxton et al. (2013).
| Category | Value |
|---|---|
| Age at first birth | 9 |
| Calf survival | 0.7 |
| Juvenile survival | 0.76 |
| Adult survival | 0.96 |
| Fertility | 0.86 |
4. Size of the vulnerable population: We considered the following illustrative scenarios:
- All of the population is vulnerable to the effects of piling at both sites;
- 10% of the population is vulnerable to the effects of piling at both sites, the remaining 90% of the population is not affected by piling at either site. These percentages were chosen because of the large extent of the MU relative to the area of the two development sites.
5. Schedule of activities: as described above
6. Number of animals that may experience disturbance and PTS (assuming no mitigation measures to reduce PTS):
| Category | Inshore site | Offshore Site |
|---|---|---|
| Number of minke whales disturbed | 100 | 100 |
| Number of minke whales experiencing PTS | 10 | 10 |
7. Number of days of 'residual' disturbance assumed: 2
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