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
Executive Summary
This report describes a protocol for implementing an interim version of the Population Consequences of Disturbance ( PCoD) approach for assessing and quantifying the potential consequences for marine mammal populations of any disturbance and/or injury that may result from offshore energy developments. It has been designed to use the kinds of information that are likely to be provided by developers in their Environmental Statements and Habitats Regulations Assessments. We emphasise the interim nature of this approach, which was developed to deal with the current situation, where there are limited data on the way in which changes in behaviour and hearing sensitivity may affect the ability of individual marine mammals to survive and to reproduce. The research that is needed to improve our knowledge and understanding of these processes has been identified by Harwood & King (2012) and some of this work is currently underway. Results from this research, and any other relevant developments (such as reports from the Habitats and Birds Directives - Marine Evidence Group convened by Defra) should be incorporated into the approach as they become available.
The interim PCoD approach is a formal, mathematical version of the Population Consequences of Acoustic Disturbance ( PCAD) conceptual model developed by the US National Research Council (2005). It uses the opinions of international experts, solicited through a formal elicitation process, to quantify the transfer functions that describe the relationships between the different compartments of the PCAD model (see Figures 1 and 2).
The assessments of the likely changes in abundance of any marine mammal population provided by this approach rely heavily on expert opinions and a number of strong assumptions. They should therefore be interpreted as illustrations of the consequences of those opinions, not as predictions of future population size. There is clearly a pressing need to collect more empirical data on the potential consequences of disturbance and hearing damage for marine mammal populations in order to refine and replace these opinion-based values. However, in the absence of those empirical data, the interim approach described here provides a rigorous, auditable and quantitative methodology, supported by the best available evidence, and can be used to inform the consenting and decision-making processes for offshore energy projects. In particular, it provides the only currently available tool for assessing the cumulative effects of a single development over the course of construction on a range of marine mammal populations, and for assessing the cumulative impacts of multiple developments that use different technologies.
We explain how this interim approach has been implemented and show how it could be used to examine the potential cumulative effects of the construction of two hypothetical wind farms and the operation of a hypothetical tidal energy array off the Aberdeenshire coast on relevant Management Units for five priority species: harbour seal, grey seal, bottlenose dolphin, harbour porpoise and minke whale. We also examine the sensitivity of these potential effects to some of the assumptions used in the approach. We stress that the results presented in these examples are purely illustrative and should not be interpreted in any way as providing predictions of the potential effects of any actual proposed offshore renewable energy development on marine mammal populations.
Glossary of acronyms and terms used in the Interim PCOD protocol.
| Acronym / Term | Definition |
|---|---|
| IAMMWG | Inter-Agency Marine Mammal Working Group |
| JNCC | Joint Nature Conservation Committee |
| MU | Management Unit: see below for definition |
| NE | Natural England |
| NERC | Natural Environment Research Council |
| NRC | National Research Council of the United States National Academy of Sciences |
| NRW | Natural Resources Wales |
| ONR | US Office of Naval Research |
| PCAD | Population Consequences of Acoustic Disturbance |
| PCOD | Population Consequences of Disturbance |
| PTS | Permanent Threshold Shift: a non-recoverable elevation of the hearing threshold that occurs under conditions that cause a 40dB temporary shift in the threshold ( TTS) for hearing at a particular frequency |
| SEL | Sound Exposure Level |
| SMRU | Sea Mammal Research Unit |
| SNCB | Statutory Nature Conservation Body |
| SNH | Scottish Natural Heritage |
| TTS | Temporary Threshold Shift: a recoverable elevation of the hearing threshold at a particular frequency |
| Acute effect | The indirect effect of a change in behaviour or physiology on vital rates via individual health |
| Body condition | A measure of an individual's energy stores. In marine mammals, usually blubber thickness or total body lipid |
| Carrying capacity | The maximum number of individuals of a species that can be supported in the long term by the resources available in a given area. A population that is at carrying capacity is neither increasing nor decreasing. Most equations describing the operation of density dependence in a population require an estimate of the carrying capacity for the population being modelled. |
| Chronic effect | The direct effect of a change in behaviour or physiology on vital rates |
| Demographic rates | The average survival and fertility rates experienced by all members of a population in a particular year |
| Demographic stochasticity | Variation among individuals in their realised vital rates as a result of random processes |
| Density dependence | The process whereby demographic rates change in response to changes in population density, resulting in an increase in the population growth rate when density decreases and a decrease in that growth rate when density increases |
| Delphi process | An established process whereby experts are asked to reconsider their opinions in the light of what other experts have said in answer to the same set of questions |
| Disturbance - high level | The total number of days on which significant disturbance events occur that is required before disturbance results in the maximum reduction in vital rates suggested by the results of the expert elicitation process |
| Disturbance - Moderate | A level of disturbance sufficient to cause a reduction in vital rate, but less than that required to cause the maximum reduction in these rates |
| Environmental Impact Assessment ( EIA) | The process of evaluating the likely environmental impacts of a proposed project or development, prior to decision-making, taking into account inter-related socio-economic, cultural and human-health impacts, both beneficial and adverse |
| Environmental Statement ( ES) | The report produced as part of the EIA process by, or on behalf of, a developer, which must be submitted with the application for consent or authorisation. The ES describes the project, gathers and presents relevant environmental information, predicts and describes the environmental effects of the project; and defines ways of avoiding, reducing or compensating for the adverse effects |
| Environmental variation | Variation in demographic rates among years as a result of changes in environmental conditions |
| Expert elicitation | A formal technique for combining the opinions of many experts. Used in situations where there is a relative lack of data but an urgent need for conservation decisions |
| Fertility | The probability that an individual adult female will give birth to a viable offspring in any particular year |
| Fitness | A relative term reflecting the potential contribution of the genotype of an individual to future generations. The fittest individuals leave the greatest number of descendants relative to the number of descendants left by other individuals in the population |
| Habitats Regulations Assessment ( HRA) | The process of evaluating the likely effects of a proposed project or development, prior to decision-making, on European sites ( SACs and SPAs) or Ramsar sites and their designated features |
| Health | All internal factors that may affect individual fitness and homeostasis, such as condition, and nutritional, metabolic, and immunological status |
| Management Unit ( MU) | The animals of a particular species in a geographical area to which management of human activities is also applied (Anon. 2013) |
| Population size | The number of animals of a species estimated to occur in a particular Management Unit, as defined by the IAMMWG (Anon. 2013) |
| 'Residual' disturbance | The persistence of the effects of a significant disturbance event beyond the day on which it actually occurs. The number of days of residual disturbance associated with 1 day of significant disturbance is set by the user of the protocol |
| 'Significant' behavioural response | A change in an individual's behaviour pattern that may affect its ability to survive, breed, reproduce or raise young, or that is likely to result in that individual being displaced from an area for a longer period than normal |
| 'Significant' disturbance event | An event that may causes a ' significant' behavioural or physiological response that is likely to impair an individual's ability to survive, breed, reproduce, or raise young, |
| 'Significant' physiological response | A change in an individual's physiology ( e.g. in hearing ability , hormone levels or immune status) that may affect its ability to survive, breed, reproduce or raise young |
| Uncertainty | Incomplete information about a particular subject. In this report, we are only concerned with those components of uncertainty that can be quantified |
| Vital Rates | The probability that an individual will survive from one year to the next, the probability that an individual adult female will give birth in one year |
| Vulnerable sub-population | Those members of the population within a Management Unit that are likely to be at risk of exhibiting significant disturbance events associated with a particular development |
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