Scottish Marine and Freshwater Science Volume 5 Number 2: A Protocol for Implementing the Interim Population Consequences of Disturbance (PCoD) Approach...

A Protocol For Applying the Interim PCoD Approach

The Interim PCoD approach has been implemented in the R statistical computing environment (R Development Core Team 2010). We have assumed that users of the PCoD approach will be familiar with creating suitable comma delimited (.csv) data files in Microsoft Excel, or a similar spreadsheet package, and with reading such files into the R environment, and with the editing and running of R program files. The R program files, together with a set of supporting documents and instructions, are available for download at The Scottish Government's website.

The approach has been designed to investigate the potential population consequences of disturbance and injury to marine mammals associated with an individual offshore renewable energy development, or the combined effects of a number of different developments. The same set of decisions will be required whether the approach is being used to assess a single development, or to assess the cumulative effects of a number of developments. The steps required to implement the approach are shown in Box 3. We recognise that there will be a need for iterative discussion between developers, regulators and advisory bodies ( e.g. SNCBs) about the values used for many of the variables and assumptions that form part of this protocol. These will include whether or not to define vulnerable sub-populations, the appropriate number of days of 'residual' disturbance, and agreed thresholds for significant population decline.

Box 3 - A Protocol for Implementing the Interim PCoD Approach

1. Identify the marine mammal MUs that may be affected by each development. If the boundaries of the development site extend over more than one MU, the effects on each MU should be modelled separately.

2. For each MU, look up the estimate for the current size of the population in Anon. (2013).

3. Look up the appropriate values for these key demographic rates in Harwood & King (in prep.):

• annual survival rate for pups or calves,
• annual survival rate for juveniles (animals that are not yet able to give birth)
• annual survival rate for adults
• average age at which females give birth for the first time, and
• fertility rate (probability of giving birth) for mature females

4. Decide on a range of values for the proportion (or proportions) of this population that is likely to be vulnerable to the effects of each development. If the area over which disturbance is expected to occur is large relative to the size of the MU, or the area around the development site is known to be important for the species, then this proportion should be set to 1.0 ( i.e. all members of the population in the MU are equally likely to be affected by the development). It is possible to specify that one sub-population is vulnerable to the effects of several different developments, but it is not possible to specify that the same development will affect more than one sub-population.

5. Prepare a schedule of information on the estimated days on which activity ( e.g. piling or turbine operation) are expected to take place for each development. We appreciate that developers will not be able to specify in advance the exact days on which construction work is likely to occur, because this will depend on many factors, including weather and the availability of suitable equipment. However, they should be able to specify whether their preference is to carry out all construction work within the shortest period possible, which would result in many days of consecutive construction work, or for the work to be conducted sporadically and thus be spread over an extended period.

6. Compile estimates of the number of animals of the species under consideration that may be disturbed and experience PTS on each day of construction work. The default is to assume that these values are constant throughout the year. However, it is possible to specify different values for summer (May - October) and winter (November - April), or for spring (March, April, May), summer (June, July, August), autumn (September, October, November) and winter (December, January, February) if these are available. For example, the number of animals may vary as a result of seasonal changes in marine mammal density or sound propagation loss.

7. Decide on an appropriate range of values for the number of days of 'residual' disturbance associated with one day of actual disturbance, which model for vulnerability to PTS will be used, and the likely effectiveness of mitigation measures to reduce the risk of animals experiencing SELs sufficient to cause PTS.

8. If the approach is being used to assess the cumulative effects of a number of developments that include tidal energy arrays, compile estimates of the number of animals in the same MU that may be involved in collisions or entanglement during each year of operation. Decide on the probability of death following such incidents.

9. Prepare appropriate data files, run the R program files and compare the results of the different scenarios.

Note: There will be a need for iterative discussion between developers, regulators and advisory bodies ( e.g. SNCBs) about many of the variable values and assumptions that will be used within this protocol.