NatureScot Research Report 1379 - Recommendations for ecosystem health monitoring approaches for cetacean Marine Protected Areas (MPAs) in Scottish Territorial Waters

Figure 1. Summary of existing NCMPAs in Scottish waters that have a cetacean species as a protected feature. Base maps © OpenStreetMap Contributors.

Summary of SAC conservation objectives

The site contributes to maintaining favourable conservation status by ensuring there is no significant risk from injury or death, distribution is maintained by avoiding significant disturbance and the condition of supporting habitats and the availability of prey are maintained.

Summary of NCMPA conservation objectives

The site seeks to conserve favourable condition by ensuring there is no significant risk from injury or death, access to resources provided by the MPA that support various life stages are conserved, distribution is maintained by avoiding significant disturbance and the structure, function, distribution and extent of any supporting features are conserved.

Once an MPA has been established, continued and consistent Site Condition Monitoring (SCM) efforts are required to provide evidence to enable assessment of the site feature(s) condition and change over time; report on whether the sites are meeting their Conservation Objectives; and support the provision of management advice at the individual site and wider MPA network scale, as summarised in the Scottish Marine Protected Areas Monitoring Strategy (Marine Scotland, 2024; hereafter the ‘Scottish MPA Monitoring Strategy’). For mobile species such as cetaceans, this has resulted in the development of a Scottish mobile species monitoring programme, to support delivery of the Scottish MPA Monitoring Strategy. This programme consists of species- or group-specific monitoring plans, including plans for the monitoring of cetaceans.

Historically, SCM activities focused on cetaceans have centred on collecting information on abundance, densities (number of individuals/km²) and/or distribution to understand population dynamics, enable detection of trends and generally underpin feature condition assessments to inform management decisions (JNCC, 2005). This type of monitoring relies on direct observation of animals, which is achieved through visual and/or passive acoustic survey approaches, abundance estimates, and demographic assessments based on photo-identification. Wider context (both within and outwith MPAs) is provided through comparison against abundance/density data collected at broader spatial and temporal scales, notably through ongoing survey efforts by environmental Non-Governmental Organisations (eNGOs) such as the Hebridean Whale and Dolphin Trust (HWDT), the Cetacean Research and Rescue Unit (CRRU) and Whale and Dolphin Conservation (WDC) across Scotland. At even larger scales, additional context is provided by activities such as the large-scale surveys undertaken at multi-year intervals under the Small Cetaceans in European Atlantic Waters and the North Sea (SCANS) survey programme (Hammond et al., 2002; 2013; 2021). 

The legal basis of current monitoring activities around Scottish MPAs is provided by various regulations:

• Under the Habitats Regulations, once every 6 years Scottish Ministers must report to the Scottish Parliament on the conservation status of protected features, including on the ability of protected sites to contribute to maintaining the feature at, or restoring the feature to, Favourable Conservation Status (FCS). In addition, these Regulations also cover the establishment and subsequent condition monitoring of Special Areas of Conservation (SACs) such as the Moray Firth SAC for bottlenose dolphin and the Inner Hebrides and the Minches SAC for harbour porpoise (Figure 1).
• Similarly, the Marine (Scotland) Act 2010 calls for regular assessments of the state of Scotland’s seas, based on Scottish Marine Regions (SMRs; Moffat et al., 2021). In addition, this Act also includes a requirement to establish and monitor Nature Conservation Marine Protected Areas, such as the North-east Lewis NCMPA for Risso’s dolphin, and the Sea of the Hebrides and Southern Trench NCMPAs for minke whale (Figure 1).
• The OSPAR Convention (specifically Recommendations 2003/3 and 2010/2; OSPAR, 2003; 2010) calls upon Contracting Parties, including the UK, to establish an ecologically coherent OSPAR Network of Marine Protected Areas. In Scotland, existing SACs and NCMPAs have been designated as part of this network. Evaluation of how well the MPA network is functioning, through an established monitoring programme, is required as part of the OSPAR Joint Assessment and Monitoring Programme (JAMP).

In addition, several other legal instruments establish the significance of monitoring the marine environment more broadly:

• Under the Water Environment and Water Services (Scotland) Act 2003, the Scottish Environmental Protection Agency (SEPA) has a duty to monitor the status of the water environment, resulting in annual reporting requirements by Scottish Ministers to the Scottish Parliament. SEPA’s monitoring responsibilities include semi-enclosed Scottish coastal waters such as the Minch and inner Moray Firth, as well as out to 3 nm from shore elsewhere, thereby encompassing all or portions of the cetacean-focused SACs and MPAs mentioned previously (Figure 1).
• The Marine Strategy Regulations 2010 (as amended) require Scottish Ministers to establish a monitoring programme to work towards achieving 'Good Environmental Status' in marine waters, and to report once every six years to the Scottish Parliament.

The requirement to undertake monitoring of Scottish MPAs’ continuing ability to function in support of the features for which they were established is therefore an established process underpinned by various pieces of legislation. In fulfilling this requirement for Scottish MPAs, the historical focus by NatureScot and others has been on directly monitoring the feature’s continued presence, density and/or abundance through repeated dedicated survey efforts, as part of SCM. In the context of Scottish cetacean MPAs, much of this feature monitoring is currently undertaken by eNGOs and academic institutions. A summary of ongoing ‘direct’ monitoring efforts associated with cetaceans in Scottish waters, many of which are undertaken within cetacean MPAs, is provided in Annex 1 (Table A1.1) of this report. Such direct monitoring approaches involve periodic dedicated surveys during which visual and/or passive acoustic observations of animals are collected, involving mobile platforms (observers on vessels, potentially towing hydrophone arrays), observations from fixed locations (shore-based sighting surveys, moored passive acoustic monitoring) or a combination of the two, depending on the specific study. These observational data are then used to underpin a wide range of assessments, including on abundance and density (either relative or absolute), on spatiotemporal heterogeneity in distribution, as well as on individual identification (photo-ID catalogues), long-term health evaluations and life histories (e.g., on growth, reproduction and survival rates). A particular example where such monitoring activities directly feed into SCM is provided by the monitoring activities undertaken by SMRU and UALFS, on behalf of NatureScot, of the Moray Firth SAC’s bottlenose dolphin population (Annex 1, Table A1.1). Similarly, the long-term observational datasets collected by eNGOs were vital in supporting the establishment of the Inner Hebrides and the Minches SAC (HWDT), and the Sea of the Hebrides (HWDT), North-east Lewis (WDC) and Southern Trench NCMPAs (CRRU; Figure 1). These ‘direct’ observations are thus fundamental to our present-day understanding of the conservation status of cetaceans in Scottish waters; their continued collection therefore provides a crucial element in the long-term management of these species as part of the Scottish MPA Monitoring Strategy.

However, by concentrating monitoring efforts solely on observing the cetaceans themselves, there is a risk that information on the underlying marine ecosystem that supports the continued presence of these species, and the various human activities occurring there that might impact them in some manner, is not adequately considered as part of status assessments. Considering a wider range of environmental and human activity parameters would provide additional information about the marine ecosystem, identify and improve understanding of drivers of population change, identify potential issues before they affect population parameters etc. Direct monitoring of cetaceans also presents a particular challenge due to inherent logistical complexities and high costs of monitoring animals that are highly mobile, difficult to observe, often occur far from land, and may only occur in Scottish waters at relatively low densities (e.g., Risso’s dolphin). As a result, obtaining sufficient observational data, particularly further offshore, in winter and/or at night may be difficult, complicating a robust assessment of how well the MPAs are performing in terms of their ability to continue to support cetacean features. 

For these reasons, there is currently increased interest within NatureScot to develop a more strategic, holistic Scottish monitoring mobile species programme for cetaceans and other long-lived, wide-ranging species that are difficult to monitor directly, such as basking shark (Cetorhinus maximus) and flapper skate (Dipturus intermedius). In addition to direct feature monitoring, such a monitoring programme would also encompass aspects of ecosystem health, such as prey availability and intensity of anthropogenic pressures, rather than solely focusing on feature-specific metrics. By providing a better understanding of why and how animals are using identified areas of importance over time, any cetacean monitoring plan under such a programme would provide crucial information on overall habitat quality and thereby on the condition of the MPAs. Specifically, this approach would inform to what extent these MPAs continue to fulfil their function in ensuring favourable condition of the cetacean features for which they were established. 

Since collection of such metrics will potentially involve expertise and resources outwith those traditionally involved with direct cetacean monitoring, it is important that any future ecosystem health monitoring plan for cetaceans be developed and integrated with other existing direct (regulatory) monitoring or data collection activities of cetaceans and their habitats, to share costs, avoid duplication of effort, and improve coordination.

Project aims

The main aim of this study was to identify a suite of relevant metrics to use for monitoring ecosystem health (habitat condition and anthropogenic pressures), using pressure-state relationships (linking observed feature condition [‘state’] to intensities and distributions of human activities which cause pressures on the feature or their supporting habitats) relevant to conservation and management of cetacean MPAs. The study was undertaken in several steps, summarised under the following three Work Packages (WPs):

WP1: A review of the literature to summarise current understanding of the ecology and conservation status of the four Scottish cetacean species under review in this study, including evidence gaps.

WP2: A review of potential metrics to evaluate overall utility for monitoring habitat quality and pressures, prioritised based on the following factors: specificity, ease of measurement, data availability, resource requirements, and wider ecological relevance.

WP3: Summarising WP2 outcomes into formal recommendations, including considering potential high-level resource implications of integrating proposed metrics into a holistic monitoring programme.

This work involved an evaluation of currently available data sources and consideration of issues such as complexities in data collection and analysis, relative cost, suitability and potential impact of monitoring various environmental characteristics and human activities. Ultimately, the present report provides a series of recommendations regarding monitoring metrics which, if implemented, would contribute to the development of a more holistic approach to cetacean monitoring in Scottish Territorial Waters, as part of the Scottish mobile species monitoring programme.

Work package 1: Literature review

A summary of population characteristics, critical habitat usage (a term widely used in the context of protected site conservation objectives to refer to habitat supporting breeding, feeding, and other key lifecycle behaviours of protected features), prey resource requirements and key pressures/threats has been provided for the four cetacean species under review in the present report, based on a review of the publicly available scientific and grey literature. From this exercise, it is apparent that the four species described here are quite different, in terms of abundance, distribution, residency, habitat requirements and sensitivity to particular pressures. It is also evident that various significant data gaps still remain, primarily in relation to foraging ecology, prey abundance and distribution, and the degree of spatiotemporal overlap with human activities that are known or suspected to negatively impact these species in Scottish waters. These data gaps have underpinned the subsequent selection process for novel metrics focusing on environmental factors and/or human marine activities associated with certain pressures.

Summary of abundance, critical habitat usage, prey resource requirements and key anthropogenic pressures/threats relevant for the four cetacean species considered in this report

Work package 2: Metric development and assessment

Methods

The main goal of this study was to identify a series of metrics suitable for monitoring ecosystem health (habitat condition and anthropogenic pressures) relevant to conservation and management of cetacean MPAs, in conjunction with ongoing ‘direct’ feature monitoring activities. This was achieved by bringing together a group of experts in cetacean health, ecology and management to discuss potential metrics and identify priorities.

Workshop

A full-day workshop was held at Inverness College, UHI, on January 23, 2024 (hereafter referred to as ‘the workshop’), which sought to canvass opinions across the breadth of organisations involved in cetacean research and assessment in Scotland and the wider UK as to what types of metrics would be useful in assessing habitat condition and anthropogenic pressures on the cetacean species within and outwith designated MPAs in Scottish waters (Figure 1). A total of 22 representatives of government agencies, academic institutions, and eNGOs attended the workshop, either in person or on-line. A full list of workshop participants is included in Annex 2 (Table A2.1).

To facilitate discussion, workshop attendees were organised into four subgroups, each associated with a broad Theme. Each subgroup consisted of 5-6 workshop attendees, including in-person and online attendees. The four subgroup Themes were defined as follows:

• Animal Health: the focus of this Theme was to identify metrics describing direct or indirect impacts on the health of animals, including body condition, infectious disease rates and parasite burdens.
• Ecology: the focus of this Theme was to identify metrics that related to the broader web of ecological connections involving the species of interest, mostly related to the animals’ diet but also considering wider ecological issues (e.g., competition, predation).
• Changes to Physical Environment: the focus of this Theme was to identify metrics that described changes in the animals’ physical environment, including underwater noise, loss of/damage to physical environmental features supporting the species of interest, and broader environmental trends driven by global climate change.
• Direct Impacts: the focus of this Theme was to identify metrics that explicitly described impacts resulting in death or injury of animals (e.g., entanglement in fishing gear, collisions with ships).

The Themes were defined in this way to encourage consideration of a wide range of potential metrics on the day of the workshop and to make optimal use of the breadth of knowledge and experience available among the workshop attendees. 

Following an introductory plenary session, the four subgroups were tasked to consider multiple different metrics within the wider context of their Theme. Creative, outside-the-box thinking was encouraged to capture different metrics, including ones that might not currently be collected but could be further developed with additional investment of effort and/or resources. 

Workshop participants were encouraged to consider potential metrics in relation to two broad criteria, specifically ‘Usefulness’ (i.e. how suitable is this metric in terms of its ability to inform about ecosystem health? Can the metric easily be applied to multiple regions and/or species?) and ‘Practicality’ (i.e. How difficult is it to implement data collection for this metric? Does the metric require significant amounts of effort and/or resources to monitor?). These criteria were not intended to be used in a quantitative manner by the workshop participants but sought to capture some of the multifactorial complexities surrounding the use of these proposed metrics, to enable NatureScot to decide on which metrics to select for immediate prioritisation versus further optimisation prior to being implemented.

The metric development exercise was facilitated by use of the online Google Jamboard application, which allowed subgroup participants to place proposed metrics within a virtual online space defined by two axes of Usefulness and Practicality (Figure 2). Moreover, Google Jamboard allowed participants to organise metrics according to whether they were mainly applicable to individual species, rather than applicable to all cetacean species under consideration.

As illustrated in Figure 2, the two-axis approach in Google Jamboard allowed workshop participants the opportunity to organise their proposed metrics spatially such that the ‘best’ metrics, in terms of perceived Usefulness and Practicality, should end up near the top right corner of the graph. More experimental approaches, or metrics that only informed tangentially about factors relevant to cetaceans, would score lower along one or both axes. It is worth reiterating that such metrics might still be useful under particular circumstances or could be useful in the future if developed further. The Google Jamboard notes from each subgroup, as developed during the workshop, have been included in Annex 3 (Figures A3.1-A3.8).

Review and prioritisation of metrics

Following the subgroup sessions, the results from each subgroup were discussed in a final plenary session at the workshop. Unfortunately, limited time was available for in-depth discussion of these proposed metrics at the event itself. To enable further discussion following the workshop, the subgroup lead team first undertook an in-depth appraisal of the various proposed metrics according to a bespoke traffic light scheme, developed in consultation with NatureScot (summarised in Table 1). The scheme incorporated several elements which were based on conversations with workshop attendees and NatureScot and which were intended to capture more granular information about the perceived current or future suitability of each metric as part of a holistic cetacean monitoring plan. This secondary assessment was intended to be qualitative rather than quantitative in nature, and no threshold values (e.g., relating to costs) were defined to distinguish between categories/colours. The different elements of the traffic light scheme were not ranked and were each considered independently for every proposed metric (Table 1). Where different subgroups had independently converged on the same metric during the workshop, the assessment outcomes were combined within the most appropriate Theme to avoid duplication, while ensuring that the discussions among both subgroups were accurately captured in the accompanying notes. 

Workshop attendees were subsequently given the opportunity to review the metrics and their traffic light assessments and to suggest revisions. Importantly, during this stage all workshop attendees were also asked to independently score each proposed metric on a scale of 1-3 (where 1 = priority, 2 = high priority, 3 = immediate priority), according to their view of its ability to fulfil condition assessment of cetacean features and/or the MPA network, inform management effectiveness etc. To facilitate discussion, the various metrics suggested during the workshop were organised retrospectively under a series of broad topics:

• Cause of Death (generic)
• Entanglement/Bycatch/Commercial fishing
• Collision with Vessels
• Disturbance
• Underwater Noise
• Prey and Diet
• General Health
• Wider Ecology

Attendees were encouraged to score all the proposed metrics, although this was not a firm requirement e.g., in case of perceived lack of expertise in certain fields, or where the respondent held the view that particular metrics were less of a priority. These assessments were then aggregated by taking the average of the scores provided by workshop participants for each metric. Metrics with higher average scores (defined as >2) and low variation (standard deviation around average scores) were considered a higher priority. For ease of assessment, a basic division was implemented between metrics with standard deviations <0.5 (‘low’ SD, suggesting broad agreement among respondents) and metrics with standard deviations ≥0.5 (‘high’ SD, suggestive of divergent opinions among respondents). 

Results

Workshop outcomes

The proposed metrics developed at the workshop have been organised by Theme in a series of tables (Tables 2–5). A brief description of each metric is provided, together with a summary assessment of potentially relevant data sources, comments provided during the workshop, the post-workshop traffic light assessments, and metric rankings. Screengrabs of the Google Jamboards that were used to aggregate these metrics during the workshop have been included in Annex 3 (Figures A3.1–A3.8). 

A total of 11 out of 18 eligible workshop participants (61%, with NatureScot staff members excluded) provided feedback on metric rankings (Tables 2–5). This information was used to generate average rankings and standard deviations for each metric, to provide a general indication of which metrics were deemed to be the most immediate priority to implement, according to this cross-section of Scottish marine mammal researchers. Metrics which 1) received a high average ranking and 2) had a low standard deviation associated with this average (suggesting that most respondents were providing similar rankings) were considered the highest priority for inclusion in a future Scottish cetacean monitoring plan.

Theme 1: Animal Health: Summary of existing/potential data sources and relevant information

Theme 2: Ecology: Summary of existing/potential data sources and relevant information

Theme 3: Changes to Physical Environment: Summary of existing/potential data sources and relevant information

Theme 4: Direct Impacts: Summary of existing/potential data sources and relevant information

Evaluating metrics for prioritisation

When comparing the metrics’ average rankings and associated variability based on the responses by workshop attendees, several outcomes were apparent. First, a set of 11 proposed metrics were consistently ranked as an immediate priority by those workshop attendees who responded (average ranking of >2.5, SD <0.5; Table 6). 

A second set of 11 metrics received comparably high rankings (average ranking >2.5) from the respondents, but with greater variability around the average (a ‘high’ SD score of ≥0.5; Table 7). This suggested some divergence of opinion in terms of the perceived prioritisation of these metrics amongst those workshop participants who responded. This may have been caused by the relatively small number of participants who returned rankings for the metrics and could be particularly relevant for some of the metrics that require specialised expertise and equipment (e.g., stable isotope analysis). Given the essentially arbitrary designation of a 0.5 threshold between ‘high’ and ‘low’ SD scores, the ‘high’ SD scores ≥0.5 should therefore not be taken to mean that these metrics are less of a priority in terms of implementation, and metrics listed in Tables 6 and 7 should both be considered as immediate priorities for implementation.

The 22 metrics in Tables 6-7 largely fall within a small number of broad topics, indicating that these topics are of overriding concern among members of the Scottish cetacean research community. These results strongly suggest that any future Scottish cetacean monitoring plan should incorporate metrics such as the ones proposed here that explicitly address questions around 1) interactions with fisheries, 2) underwater noise, 3) presence/abundance/diversity of prey species, 4) causes of mortality and 5) aspects of animal health more generally. It is worth noting that many of these metrics pertain, directly or indirectly, to pressures driven by human activities which potentially are susceptible to management.

Most of the remaining metrics were ranked somewhat lower in terms of priority (average ranking 1.5 – 2.5 inclusive, typically with an SD score ≥0.5); they have been summarised in Table 8 below. Several possible reasons for these rankings were identified: 

• Some of the proposed metrics are comparatively novel or require more research to be applied more widely, e.g., using molecular methods to determine the age structure of a population (AH16), using eDNA to characterise prey fish assemblages (EC08), or measuring toxins associated with harmful algal blooms (DI19, DI20).
• Other proposed metrics refer to pressures that have not historically received much attention in a Scottish monitoring context, e.g., those relating to collisions with vessels (DI08, DI13, DI14, DI15) and disturbance (DI09, DI11, DI12).
• Some metrics might be more difficult to carry out on a large enough scale to ensure they are representative of the wider population or species (e.g., EC04, DI09).
• Finally, some proposed metrics were thought to have a narrower focus than others within the same broad topic (e.g., presence of microplastics found inside stranded animals; AH03). 

This suggests that metrics receiving a lower priority ranking might require some degree of additional methodological development or careful scoping to become fully integrated into a holistic cetacean monitoring plan. This topic will be developed in more detail below (see also Annex 4).

Finally, a small number of proposed metrics was widely considered to be a lower priority by respondents, at least for now (Table 9). This included metrics relating to interactions with other top predators (e.g., EC12, EC13). Several respondents indicated that they had ranked them in this way because they considered these metrics to be difficult to implement in a practical way, since these kinds of interactions would be largely outwith direct management control.

The workshop feedback results indicated a clear hierarchy among different topics in terms of prioritisation. Metrics that addressed known impacts leading to mortality, injury or disturbance (e.g., entanglement, underwater noise) and/or addressed questions about animal health or diet by means of well-established methods were prioritised over metrics that:

• were focused on less well-quantified impacts (e.g., collision, disturbance).
• related to impacts where the potential for active management intervention was limited (e.g., certain pollutants; predation rates, competition with other predators).
• tackled broader ecological questions (e.g., predation rates, competition with other predators).
• relied on methods that were still under development.

This hierarchy suggests a desire within the Scottish marine mammal research community for a future Scottish cetacean monitoring plan that initially focuses on a limited number of key topics that can be reliably measured and can serve as the basis for management action to optimise conservation outcomes. If such a holistic plan were to be implemented, it should nonetheless be subject to periodic review to ensure the selection of monitoring metrics remains appropriate for each species and/or MPA and take into account the latest knowledge and methodological developments (i.e., allowing additional metrics to be incorporated in the future). Furthermore, any such review should include the possibility to enhance/expand the scope of the monitoring plan over time to incorporate the monitoring of any emerging threats identified through ongoing research.

Work package 3: Evaluation and implementation

Outcomes of the metrics evaluation process

The metrics proposed in this study (Tables 2 – 5) were developed during a one-day workshop attended by a representative cross-section of the marine mammal research community in Scotland and, to a lesser extent, the wider UK. As such, the metrics collectively are intended to address data gaps relating to 1) the quality of the cetacean habitat within and outwith MPAs and 2) the distribution and intensity of human activities that could generate negative impacts, as perceived by the marine mammal research community and in line with existing understanding of the sensitivity of cetaceans to various pressures (e.g., through the updated Feature Activity Sensitivity Tool, or FeAST; NatureScot, 2024). The list of proposed metrics presented here, while not exhaustive, therefore highlights specific areas where the Scottish marine mammal research community considers that additional monitoring efforts are required. While several proposed metrics can be implemented with comparatively limited effort, others will require additional development to enable widespread implementation. 

A multi-staged approach towards developing a comprehensive cetacean monitoring plan is therefore recommended, which would allow for rapid implementation of some metrics, while enabling further development of some of the metrics identified by workshop participants as lower than ‘immediate priority’ but deemed by regulators as worthy of further consideration. The present report should therefore be considered a step in the process of identifying a suitable series of metrics to enhance monitoring of habitat quality and human activities in and among MPAs for cetaceans in Scottish waters. 

Implementation

The workshop format facilitated agreement on identification and characterisation of potential metrics, encouraging outside-the-box, blue-sky thinking. Perhaps unsurprisingly, there was less consensus about implementation, including resource requirements. While workshop attendees were well informed about cetacean-related data collection efforts, they acknowledged their potential collective lack of awareness of other relevant monitoring programmes (of human activities, environmental factors, and other ecosystem components) that did not have a cetacean focus. Many workshop attendees noted that the absence of experts in other fields such as fisheries science, oceanography, and marine chemistry, at the workshop complicated efforts to inform about the actual implementation with regards to practicality, availability and cost of many proposed metrics. Workshop attendees made a concerted effort to identify ongoing monitoring programmes in other disciplines that could potentially provide data to underpin the metrics proposed here (Tables 2-5), but a more in-depth review was outside the scope of this study. A thorough assessment of ongoing survey and monitoring efforts across Scottish Government agencies, academic institutions and eNGOs is therefore needed to determine whether any ongoing data collection efforts, e.g., to underpin Scotland’s Marine Assessment (SMA2020; Moffat et al., 2021), could be used to enable assessment of any of the proposed metrics. 

Tables 2-5 summarise current understanding of whether data relevant to the proposed metrics are already being collected through existing monitoring schemes (see also Annex 1; Table A1.1). Some of these monitoring schemes, such as the HWDT surveys, have an explicit focus on ‘direct’ observational monitoring of cetaceans but also record a wide range of data on concurrent environmental conditions and/or human activities, which may require additional processing to become useful to NatureScot’s cetacean monitoring plans. Conversely, other ongoing monitoring activities (e.g., relating to presence and impacts of HABs) are not currently used routinely outwith the Scottish aquaculture sector but could potentially provide useful information to NatureScot, at least for specific cetacean MPAs. In addition, more in-depth analysis of existing datasets could provide significant new insights through improved integration and analysis. Finally, minor adjustment to ongoing programmes may be possible to collect additional data to support reporting on these metrics. There is a real opportunity to complement and/or make better use of data that are already being collected alongside direct monitoring efforts (Annex 1; Table A1.1), to assess species condition and ecosystem health, as well as monitor trends, changes and emerging threats. This process needs to also consider whether ongoing monitoring intensities and spatiotemporal distributions are appropriate to enable the overarching monitoring goals to be achieved. Optimising the use of these data sources and collection programmes will likely require additional investment, as many of the workshop participants expressed concern that their respective teams were already stretched to capacity and would struggle to deliver additional outputs to future monitoring plans without further support.

Any implementation of indirect ecosystem health monitoring based on the metrics proposed above as part of a holistic cetacean monitoring plan will require additional investment in terms of time and resources. The magnitude of these costs is likely to vary considerably between different metrics, as illustrated by the outcomes of the traffic light assessments (Tables 2-5). In the absence of existing guidance on what monitoring levels might be required to meet specific objectives for cetacean MPAs, an in-depth evaluation of the full costs of implementing appropriate monitoring approaches for each proposed metric is beyond the scope of this study. In the absence of comprehensive costings, the metrics proposed in this study have been categorised qualitatively in terms of resources and effort required for effective implementation. Understanding of various current monitoring operations already being undertaken by researchers in Scotland and elsewhere provides an opportunity for preliminary evaluation of resource implications for particular kinds of sampling, analysis and/or data acquisition relevant to particular metrics that were deemed to be the highest priority by workshop participants. This has been initially expressed through the traffic light assessment scheme described above (Table 1), but can be expanded upon as follows: 

• Some metrics are already being collected at appropriate scales and would require only limited alterations to data delivery and reporting processes to feed into a NatureScot cetacean monitoring plan.
• Some metrics are ‘hidden’ amongst existing datasets that are already being collected at appropriate scales and would require support for re-analysis of historic and current data to feed into a NatureScot cetacean monitoring plan.
• Some metrics are not presently assessed at appropriate scales/intensities to inform a monitoring plan due to a lack of resources, but the underlying information and expertise required to do so is available (e.g., analysis of existing tissue samples for contaminants, stable isotopes or fatty acids), suggesting that additional funding would enable the metric to be made useful for a NatureScot cetacean monitoring plan.
• Some metrics are not presently assessed at appropriate scales/intensities to inform a monitoring plan due to a lack of resources, and no mechanism for collecting the underlying data currently exists in Scotland, but the underlying science is well understood and established analytical tools are available. In these cases, new monitoring schemes may need to be developed, or existing non-cetacean monitoring schemes need to be expanded, to enable such metrics to be effectively integrated into a NatureScot cetacean monitoring plan.
• For some metrics, there is still a lack of understanding about the underlying science, a need for validation of novel methodologies and/or concerns about practical implementation which merit further research before proceeding with integrating such metrics into a NatureScot cetacean monitoring plan.

These categories are not always mutually exclusive and multiple categories may apply to a given metric. These evaluations have been summarised in Annex 4 (Table A4.1). This information may contribute to the decision-making process by NatureScot and others to implement the proposed metrics into a holistic cetacean monitoring plan. 

While many of the metrics proposed during the workshop involve techniques and analytical approaches that are already in widespread use in Scotland and elsewhere, others will likely require initial focused research (Annex 4; Table A4.1) prior to implementation as part of a cetacean monitoring plan. Crucially, this will involve cross-validation of novel techniques against existing approaches to evaluate their explanatory power, resource requirements and suitability for practical implementation. Routes through which such focused research outcomes could be achieved include commissioning specific pieces of research within the wider cetacean research community in Scotland and beyond, as well as contributing to supporting Ph.D. studentships through existing funding pathways in collaboration with Scottish academic institutions. 

Any future cetacean monitoring plan will need to be able to interpret outcomes in the light of continuing environmental shifts due to climate change. While long-term impacts of climate change on cetaceans have not been explicitly assessed in this study, the various monitoring metrics described above may underpin such an evaluation to a greater or lesser extent. In-depth evaluation of climate change impacts on cetaceans in Scottish waters will rely on availability of environmental data such as sea surface temperature (SST), wave height, ocean circulation patterns, primary productivity etc. (exemplified by metrics EC10, PE03, PE06 and DI21, among others), in combination with metrics on cetacean health, food availability and population-level parameters. Several of these types of data were identified as potentially desirable metrics during the workshop (Tables 2-5). 

More generally, such data are fundamental in underpinning predictive species distribution models (SDM) or ecosystem models (e.g., EcoPath with EcoSim), which allow for fine-scale analysis of habitat suitability for cetaceans and their prey. These modelling approaches can be beneficial in situations where baseline data are sparse or non-existent, or where monitoring is logistically difficult, to predict where conditions might be suitable for a given species to occur, as was in fact done in preparation for implementing various cetacean-focused MPAs in Scotland and elsewhere in the UK (e.g., Heinänen and Skov, 2015). Various versions of such models already exist in academia and/or among regulators and could be further improved upon through the provision of more accurate data (e.g., Hill et al., 2021). More accurate evaluation of biomass, energy content etc. of those prey species targeted by cetaceans (e.g., by metrics EC01-EC08), could significantly improve the accuracy of such models, thereby enabling better understanding of local marine ecosystems and cetaceans’ roles within them. These modelling exercises are crucial tools to undertake assessment of different scenarios (e.g., climate change scenarios C1-C8; IPCC, 2023), exploring sensitivity of observations to certain aspects of monitoring, and undertake power analyses. It is important to ensure that modelling outcomes are subject to critical review and are integrated into a comprehensive monitoring and status assessment framework that allows regular ground-truthing on the basis of actual observations.

Case studies

The present section contains several Case Studies, to demonstrate how the various proposed metrics might be used to align with relevant conservation objectives for different cetacean species associated with MPAs. It is important to note that these case studies, as presented here, are intended as generic examples only and should not be viewed as recommendations for detailed implementation of components of a holistic cetacean monitoring programme.

Case Study 1: A site-specific case study: Harbour porpoises in the Inner Hebrides and the Minches SAC

As described in the Conservation Objectives for the Inner Hebrides and the Minches SAC (NatureScot, 2020a), harbour porpoises in western Scottish waters, including within the Inner Hebrides and the Minches SAC, are considered sensitive to removal of non-target and target species (i.e., bycatch of porpoises in fishing gear and [over-]fishing of their prey species), contaminants (through impacts on water quality and bioaccumulation through foraging, which may negatively impact health and reproductive rate of porpoises with potential long-term population-level consequences), underwater noise (from various marine industries and activities), and death or injury by collision with various types of vessels, as well as potentially with tidal turbines.

Furthermore, the Conservation Objectives for the SAC (NatureScot, 2020a) emphasize the importance of ensuring that:

• Harbour porpoise within the Inner Hebrides and the Minches SAC are not at significant risk from injury or killing.
• The distribution of harbour porpoise throughout the site is maintained by avoiding significant disturbance.
• The condition of supporting habitats and the availability of prey for harbour porpoise are maintained.

Based on the results from the present report, several potential metrics could be implemented to address the points raised in the Conservation and Management Advice documentation for this SAC: 

• Respondents highlighted the importance of accurately assessing cause of cetacean deaths, with particular focus on bycatch and entanglement related to fishing gears. Porpoise bycatch in commercial fisheries is presently thought to be an uncommon occurrence off western Scotland, mainly due to the limited use of gillnets in this area (although bycatch has been reported elsewhere, e.g., off Shetland; Leaper and Calderan, 2019). Continued focus on fishing activities remains warranted to ensure that future changes in fleet distributions, adoption of technological changes to fishing activities etc. do not inadvertently lead to an increase in bycatch risk to this species. Evaluating evidence of bycatch among stranded animals can be strengthened through additional training of the SMASS volunteer pool. Although no current harbour porpoise photo-ID catalogue exists, photographs of live animals collected through ongoing surveys can potentially be scrutinised for evidence of scarring resulting from an entanglement, although this is unlikely to be as effective as for some of the larger cetacean species. Given current information on gillnet fishing activities, evidence of bycatch among porpoises seen alive or found dead in or around the Inner Hebrides and the Minches SAC may also inform about connectivity between this site and other parts of Scottish waters.
   
• Similarly, evaluating underwater noise was a clearly identified top priority among respondents. Underwater noise monitoring of the local marine soundscape will inform on ambient noise levels generated by various marine activities such as shipping, aquaculture and fisheries. To some extent this monitoring is already ongoing under the current SPAN monitoring network (four SPAN monitoring stations are located within the Inner Hebrides and the Minches SAC, with several others in adjacent areas). Additional focused PAM survey efforts occur periodically using various types of stationary or towed PAM equipment (e.g., HWDT undertaking towed PAM surveys in concert with visual survey trips). Dedicated analysis of these data, in collaboration with Marine Directorate and other partners, will be needed to provide focused assessment of spatiotemporal changes in marine soundscapes within the SAC and characterise potential impacts of such changes at the individual and population level.
   
• Metrics related to prey availability were considered of high importance by respondents. The bulk of information that is presently available is derived from sampling of stomach contents of necropsied porpoises by SMASS. This work could be expanded upon by increasing the number of animals sampled, particularly from the west coast of Scotland, as well as by further investment in Scottish capacity to undertake metagenomics, fatty acid and stable isotope analysis of existing tissue samples to inform on longer-term dietary trends.
  
  Questions about prey availability for porpoises are not adequately addressed by existing fisheries stock assessment programmes. Moreover, porpoise diets also include species that are not routinely targeted by fisheries (e.g., gobies and other small benthic species, which are especially important for recently weaned juvenile porpoises). To evaluate prey availability across the SAC, additional survey efforts for fish will be required involving the commercial fishery sector, as well as dedicated effort for non-commercial species. With prey switched across age groups, such efforts should ideally be undertaken across different seasons. There are also opportunities to engage with local community conservation groups (e.g., the Coastal Communities Network) who may be able to contribute to survey efforts in particular areas and on relevant prey species that are otherwise poorly sampled (e.g., gobies). 
   
• Numerous metrics relating to general health were identified as an immediate priority by respondents, including contaminant screening and concerns about collision. Particular contaminant levels in porpoises are already being assessed on a regular basis by SMASS through necropsy of stranded animals, and this information could be used to evaluate the current condition of the SAC in terms of contaminants (noting that animals may also consume prey outside this area). In addition, regular assessment of contaminants in porpoise prey would represent an expansion of existing monitoring activities. 
  Harmful algal blooms (HABs) are presently being monitored locally in inshore waters by the aquaculture industry and these data could potentially provide a useful metric to evaluate both the immediate risk to porpoises through biotoxins and long-term environmental changes due to climate change. However, in order to integrate this data stream into a cetacean monitoring programme, further work is needed to better understand the effects of HAB-related toxins on cetaceans in Scottish waters. 
  
  Risk to porpoises from collision with vessels, in terms of its effects on survival and health, is currently poorly understood in Scottish waters, although this kind of interaction has been previously reported here and elsewhere (e.g., Camphuysen and Siemensma, 2011; Deaville et al., 2018; SMASS, 2020). A wide variety of vessel types operate in western Scotland including fishing vessels, cargo vessels, wildlife tour boats, passenger ferries, cruise ships and private yachts of varying sizes. The Inner Hebrides and the Minches SAC contains various areas where vessel traffic densities are known to be high, including ferry routes, designated shipping lanes for cargo vessels, areas near busy harbours, and narrow straits where geography concentrates vessel traffic, such as the Sound of Mull. This area has experienced a significant increase in vessel traffic in recent years (463% between 2013-2017; Robbins et al., 2022), potentially resulting in elevated collision risks as well as increased levels of disturbance and underwater noise. While porpoises are generally shy and avoid closely approaching vessels, available information suggests that collisions with vessels can and do occur, and further focus (e.g., via SMASS) is needed to get a clearer picture. Further work could be undertaken to improve understanding of vessel distributions, densities, and speeds, building on existing work (e.g., Heriot-Watt University’s Scottish Vessel Project, AIS data collection by HWDT and others) to better determine the areas where collision risk to porpoises in this SAC might be elevated. Similarly, disturbance and displacement of porpoises through various activities (shipping, marine tourism, aquaculture etc.) is poorly monitored in this SAC at present. Further work could be undertaken to amalgamate existing data on vessel traffic levels to highlight potential key areas where disturbance is likely. 

Regular future assessment of the metrics proposed in this study would contribute towards a more complete assessment of the status of the Inner Hebrides and the Minches SAC in respect of its ability to continue to support harbour porpoises in the area.

Case Study 2: A species-specific case study: A focus on metrics that are applicable to minke whales in Scottish waters (including Southern Trench and Sea of the Hebrides NCMPAs)

Baleen whale entanglement is a growing global problem and is a significant welfare and conservation issue. Minke whales are particularly susceptible to mortality if they become entangled due to their small size (compared to other baleen whales) as they are typically unable to break out of, or tow away, the fishing gear (Song et al., 2010); globally, minke whale entanglements were estimated to lead to a fatality in 70% of cases (Lien, 1994). In Scottish waters, entanglement is the single largest cause of death for minke whales (Northridge et al., 2010; MacLennan et al., 2021) which are now considered at risk of localised depletion on the west coast (Leaper et al., 2022). Around a fifth of live animals seen in Scottish waters also show evidence of deformation, scars and wounds consistent with entanglement (Northridge et al., 2010; MacLennan et al., 2021). Minke whale entanglement in Scottish waters is primarily linked to the commercial creel fishery for Norway lobster (Nephrops norvegicus), brown crabs (Cancer pagurus) and other benthic crustaceans (MacLennan et al., 2021). Accordingly, minke whales across Scotland, including within the Southern Trench and Sea of the Hebrides NCMPAs, have been assessed as sensitive to entanglement and incidental bycatch (NatureScot, 2020b, 2020c).

Entanglement has been documented throughout Scottish seas and therefore any monitoring and management of this pressure will be most effective when considered at this scale. Implementing measures in areas that have the highest densities of minke whales and creels would be most effective however management at a site level would be a particular concern for the entanglement of marine mammals and basking sharks, where displacing creel fishing effort around the MPA boundary could increase the likelihood of entanglement in these areas. This needs to be linked to any monitoring programme that will be developed. However, it is worth highlighting that entanglement is already identified as the biggest threat to minke whales, including as a feature for the Sea of the Hebrides MPA. Current conservation and management advice for this site states that the “development and adoption of existing best practice to reduce or limit the risk of entanglement of basking sharks and minke whales in creel ropes and long lines is recommended” (NatureScot, 2020b); the metrics outlined below for monitoring should be considered as part of a best practise approach to achieve this outcome. It is, however, important to note that in this situation, where the significance of entanglement risk to minke whales is already well understood, monitoring needs to be part of proactive management to address the issue by implementing mitigation measures (e.g., through changes in how fisheries are managed) and evaluate their success over time.

• Metrics relating to bycatch and entanglement generally had high average scores and low standard deviations (see Tables 6-7), indicating consensus among the expert group that metrics relating to bycatch/entanglement are a high priority requiring immediate action. Discussions at the workshop also highlighted bycatch and entanglement as a significant cause for concern that needs to be prioritised now. Out of all the metrics proposed, there were only two that were scored the highest rating by all respondents, resulting in an average score of 3 and standard deviation of 0.0. Both metrics relate to bycatch/entanglement and are discussed below. The bycatch/entanglement metrics fell into several categories: monitoring a) the distribution and density of fishing effort, b) the number of confirmed entanglement cases and c) the number of live animals showing evidence of experiencing an entanglement event. 
   
• When considering distribution of fishing effort, respondents were unanimous in their scoring of the metric relating to the density/distribution of static fishing gear (number of units/km²) as a metric that should be prioritised immediately. Information on distribution in space and time of commercial fishing activity (based on vessel movement) and gathering information on static gear usage/distribution through surveys of fishers (questionnaires) to provide more detailed information also scored high. The risk of an entanglement occurring is linked to the amount of rope in the water column, and these metrics are important to identify areas where there is a high likelihood of interactions between fishing gear and minke whales (i.e. Northridge et al., 2010; MacLennan et al., 2021). It is in these areas where mitigation will have the greatest impact. Long-term monitoring of spatiotemporal trends and changes in fishing effort is also important to monitor success of mitigation measures in reducing entanglement (e.g., the proposed introduction of weighted lines in certain creel fisheries; Calderan, 2022) as well as to identify where additional management measures need to be implemented. For example, restrictions on other types of fishing as being proposed for the Scottish Government fisheries management measures consultation expected later this year (2024), could result in an increase in creel effort within/around important areas for minke whales such as the designated Sea of the Hebrides or Southern Trench NCMPAs, and therefore increase the risk of entanglement. Monitoring will be needed to verify whether such an unintended shift actually occurs and, if so, ensure that appropriate additional management measures can be implemented. Data on the density and distribution of static gear are already available for some areas, such as the Scottish west coast, but additional effort is needed to analyse these existing data and expand data collection into other areas. 
   
• Respondents were also unanimous in their scoring of the metric relating to the number of confirmed bycatch/entanglement cases per unit time. They all scored it a rating of 3 as a metric that should also be prioritised immediately. Data on confirmed cases are available and routinely collected from the assessment of stranded animals conducted by SMASS and should be recorded through the Bycatch Monitoring Scheme. The assessment of external evidence of bycatch in stranded animals that are not collected for necropsy also scored highly. SMASS collect some data on this through their volunteer strandings network, but they highlighted that additional protocols could be developed, and training provided on how to recognise signs of bycatch and entanglement in cases when a necropsy cannot take place. This could be based on protocols that have already been developed elsewhere, such as the Cornwall Wildlife Trust Marine Strandings Network Bycatch Evidence Evaluation Protocol (Crosby et al., 2022). However, it is worth noting that many entangled animals are likely never found, are not reported if found, or are too decomposed to assess with certainty whether scars resulted from entanglement (Neilson et al., 2009). The Scottish Entanglement Alliance estimated less than 5% of entanglement cases encountered by creel fishers were reported to SMASS (MacLennan et al., 2021). Therefore, additional data sources, such as questionnaires of fishers, are important to more accurately assess the number of entanglement cases in Scottish waters. Many bycatch/entanglement cases are also not brought to SMASS for necropsy. Therefore, it is recommended that NatureScot, together with SMASS and other relevant stakeholders, explore pathways and processes for bycatch and entanglement cases to be reported and recovered for necropsy. These cases would provide important data to more accurately assess the scale and extent of bycatch and entanglement of cetaceans in Scottish seas. Allowing bycatch/entanglement cases to be provided for necropsy would also provide valuable data on the at-sea population rather than stranded animals, which feeds into many of the other metrics highlighted in this report (i.e. infection rates, diet, reproductive status and welfare assessments). 
   
• The proportion of live animals showing evidence of entanglement (attached gear, scarring) also scored highly. Assessing the number of live animals showing evidence of entanglement is import because as highlighted in the NatureScot Feature Activity Sensitivity Tool (FeAST) the sublethal effects of surviving an entanglement may include changes to behaviour and increased energetic costs leading to reductions in feeding, growth or reproductive rates. This has important implications for the long-term fitness and welfare of an individual as well as potential longer-term population-level consequences of high entanglement rates. In some cases, it may be possible to determine the gear type (and thus the fishery) involved in the entanglement.

A lot of the required data are already being routinely collected through existing long-term monitoring programmes (i.e. SMASS and HWDT) and the Scottish Entanglement Alliance partners have the collective expertise to provide the relevant information to address many of the metrics discussed above (i.e. MacLennan et al., 2021) but this requires funding to continue and, where needed, expand into other parts of Scotland. 

In addition to entanglement, other pressures should also be considered when developing a minke whale-focused monitoring approach. Underwater noise has expanded considerably over time in Scottish waters and poses a risk to minke whales through disturbance, masking of important auditory cues, and various degrees of injury. Noise impacts are driven by activities such as commercial shipping, coastal and offshore construction, seismic survey activity, cable laying, unexploded ordinance detonation, military exercises and numerous others. Assessment of spatiotemporal variability in soundscapes, including characterisation of ambient anthropogenic noise levels, will be key in understanding the role of anthropogenic noise in driving minke whale distribution, including within the Southern Trench and Sea of the Hebrides NCMPAs. 

Some pressures for minke whales, e.g., collision risk, are much less well understood in terms of scope and severity in a Scottish context. This was also reflected in the metric scoring, with those metrics relating to collision risk all scoring comparatively low (Table 8). Recent analysis indicates the waters off western Scotland have experienced the greatest increase in vessel density across the northeast Atlantic region, with a 302% increase in vessel density between 2013 and 2017 (Robbins et al., 2022). Such findings will have implications not just for collision risk, but also underwater noise and other related metrics identified as part of this study. An assessment of collision risk for Scottish waters would allow an evaluation of its potential importance. The focus of a collision component of any future minke whale monitoring plan should be on supporting the collection of baseline data and corresponding analysis to assess the scale and extent of the collision risk to minke whales in Scottish waters. Some initial data collection and collation of existing data sets is already underway through the Scottish Vessel Project but requires funding to be able to continue and expand to assess collision risk. 

Pressures such as entanglement, noise and collision risk must be regularly assessed to identify when additional management measures are required to ensure the conservation objectives of the sites are met and that the species remain in favourable condition.

Case Study 3: Scotland-wide evaluation of health and population parameters across cetacean species

Several metrics described in this report are applicable across multiple species and cover the whole of Scotland. This information is relevant for population-level management across Scottish waters and beyond, e.g., as undertaken under Scotland’s Marine Assessment 2020 and the OSPAR intermediate assessment, rather than the management of cetaceans within individual MPAs. Nonetheless, these parameters can provide important contextual information on how well cetacean populations are doing in Scottish waters, which can have a bearing on management of MPAs.

Due to the ongoing efforts by SMASS to undertake regular post-mortem analysis of stranded cetaceans, a significant dataset is now available, extending back decades, on many aspects of cetacean health and physiology that can provide important context for management of cetacean MPAs. This dataset includes information on:

• Cause of death (NB: determination of cause of death will not be possible for all carcasses reported, typically due to advanced autolysis). SMASS produces regular reports to the Scottish Government summarising assessments of cause of death for stranded cetaceans, allowing multi-year trends to be identified within and across species.
• Body condition (one of the most important metrics available to evaluate animal health and integrate cumulative impacts to get an index of reproductive fitness, with population-level implications).
• Life history traits (pregnancy and birth rates, age structure etc.) are of crucial importance in determining long-term persistence of cetacean populations. These are also crucial parameters in population impact modelling.
• Parasite and pathogen loads can provide information on general health condition of individual as well as indicate potential risks for outbreaks of infectious diseases among this or other marine mammal populations.
• Contaminant levels (e.g., heavy metals, persistent organic pollutants, HAB-derived biotoxins), sampled across a variety of tissues, providing information on numerous health-related impacts, as well as insights into individuals and populations’ resilience to enable coping with these.
• Dietary data from analysis of hard parts within the digestive tract, combined with metagenomics, fatty acid and stable isotope analysis (see Case Study 1, above, for an application of this approach in the context of a specific SAC).

The SMASS programme already collects and maintains a wide range of datasets that could be combined innovatively to deliver new insights in cetacean ecology in the context of MPAs. Examples of such potential SMASS-based research projects, with wider implications for cetacean management across Scottish waters, could include the following:

• Using a combination of hard parts analysis, metagenomics and stable isotope analysis to understand spatiotemporal variation in prey preferences and foraging strategies, dietary breadth and overall trophic position of the cetacean in question.
• Using a combination of techniques to validate novel age determination methods based around molecular clocks (DNA methylation approaches).
• Exploring the prevalence and composition of nanoplastic pollution in various cetacean tissues and linking this information to other metrics such as body condition, general health, pollutant burden, parasite loads and reproductive history.

It should be noted that the SMASS dataset is largely based on strandings data and thus will exhibit the known biases inherent in such data (around representativeness in terms of which animals, from what species and in what state of health, are likely to strand, and where strandings are most likely to be discovered and reported).

Similarly, the various photo-ID monitoring programmes run by different organisations (notably SMRU/Aberdeen, HWDT, WDC, CRRU for different species; see Annex 1, Table A1.1) represent long-term datasets on health and life histories of live animals and may encompass entire local populations (notably for bottlenose dolphins off eastern Scotland). Such data allow long-term assessment of:

• Life-history parameters such as pregnancy and birth rates.
• Growth rates and body condition (collected using photogrammetry).
• Observations of site usage, thereby improving understanding of which parts of the MPA are of particular relevance to animals over time, potentially also allowing understanding of individual preferences.
• Observations of interactions with anthropogenic pressures, e.g., evidence of past/current entanglement events and spatio-temporal overlap with particular noise emissions.

These kinds of long-term monitoring programmes are a vital means to obtain information on causes of death, health status and numerous other metrics that are relevant to management of cetacean MPAs. Specifically, this information is essential to evaluate whether cetacean populations are likely to deviate from a ‘Favourable Condition’ assessment on the basis of population-level impacts on health, reproductive status and survival. This information could form part of a multiyear assessment of overall health status for focal species in relation to specific MPAs. 

Summary of recommendations

The present study has identified various indirect monitoring metrics that would collectively provide far greater understanding of ecosystem health (habitat condition and anthropogenic pressures) associated with Scottish cetacean-focused MPAs than is presently the case. Based on analysis of the workshop data, several metrics have been identified as immediate priority for inclusion into a future holistic Scottish mobile species monitoring programme, and where appropriate also be reflected in the various monitoring plans for cetacean species and specific sites that are currently under development. Based on the analysis of the workshop data collected under this study, the following broad recommendations can therefore be made:

Recommendation 1: Prioritisation of metrics to address urgent needs

The outcomes of this review process have indicated the importance of prioritisation of metrics that can be implemented immediately with (relatively!) limited levels of effort or investment. The following types of metrics should be considered an immediate priority for implementation, as they 1) represent approaches that address urgent impacts on cetaceans or fill major knowledge gaps concerning their biology, 2) are well understood methodologically, and 3) relevant monitoring programmes may already exist or could be implemented with comparatively limited additional effort/resources:

• Information on distribution and intensity of commercial fishing effort, particularly static fishing gears such as creels.
• Improved assessment of bycatch/entanglement recording through improved training of stranding volunteers and collation of observations of historic bycatch/entanglement within the live population from existing photo-ID programmes.
• Improved passive acoustic monitoring, notably regarding the abundance, distribution and intensity of anthropogenic noise sources related to marine activities such as shipping, energy development (incl. renewables), fisheries, aquaculture, marine tourism etc. This includes focused (re-)analysis of existing PAM data archives.
• Characterisation of cetacean diet, including relative importance of different prey species vs. energetic requirements of individuals. This can then be linked to cetacean prey abundance, distribution, and quality through in-depth sampling of strandings cases, improved commercial fisheries surveys and community-based monitoring approaches (e.g., local ROV surveys).

• Increased focus on basic metrics of cetacean population health, including cause of death, body condition and birth rates.

  Implementing these metrics should be underpinned by a collaborative approach to ensure that external stakeholders (such as those invited to the workshop underpinning the present report) can contribute to optimising the process of sourcing, providing and analysing existing data.

Recommendation 2: A staged approach to monitoring plan implementation

A multi-stage process is proposed where the monitoring plan implements those metrics that are most appropriate and ready to be implemented. In this way, the monitoring plan could begin by focusing on the topics of immediate priority as identified in this report. 

At the same time, the plan would incorporate further development of other metrics which were not ranked as an immediate priority in the present report (Table 8), but which could provide extremely valuable information about the condition of cetaceans and the MPAs designated on their behalf (Figure 1). For example, expanding monitoring of vessel traffic intensity would result in much needed information on collision risks for cetaceans both inside and outside MPAs. This could take the form of direct support for focused research into these metrics, to prioritise them for the next stage of implementation. 

Recommendation 3: Regular review of monitoring plan implementation 

The monitoring plan needs to be adaptive in the face of the emergence of new threats, and link closely with the wider research community to ensure that managers are made aware of new information that comes to light. There is therefore a need for periodic review of the plan, potentially once every 1-2 years, to ensure that the selection of monitoring metrics remains appropriate for each species and/or MPA site. Establishment of an external Steering Group, consisting of cetacean experts from the scientific and eNGO communities, is recommended to contribute to such a review. The review process should summarise the outputs of the monitoring plan’s implementation and identify where further work is necessary. The review should also include a focus on identifying needs for monitoring metric development, for example in the face of new and emerging threats to cetaceans, or in the case of powerful new monitoring techniques and approaches becoming available. Finally, the review process should include an opportunity to allocate additional resources to implement recommendations from the Steering Group, including in relation to metric development.

Recommendation 4: Making best use of existing data

As mentioned previously, considerable amounts of data relevant to many of the metrics proposed here are already being collected by various organisations around Scotland. This ongoing data collection effort provides opportunities to integrate monitoring of these metrics into a comprehensive monitoring plan at comparatively limited costs (Annex 4, Table A4.1). Close engagement with the relevant organisations involved in collecting and curating these datasets (Annex 1, Table A1.1) is therefore recommended as an integral component of developing an ecosystem health-based mobile species monitoring programme, ensuring that utility of existing datasets is optimised.

Recommendation 5: Engage with non-cetacean marine monitoring activities to enhance collaboration and integration

The workshop involved a cross-section of experts involved in cetacean research and management in Scottish waters. It is clear, however, that multidisciplinary engagement with a wide range of other experts with in-depth knowledge about particular industries (e.g., fisheries, aquaculture or marine tourism) and different research areas (e.g., oceanography, biogeochemistry, climate change science and metabarcoding) is needed to optimise the implementation of the metrics provided here. This type of engagement should be initiated at the earliest possible opportunity to ensure that all metrics proposed in this report are comprehensively vetted in terms of practicality, methodological rigour, and resource implications. For example, considerable gains could be made through greater engagement with the fishery sector to determine how to increase the number of bycaught cetaceans that are made available for assessment by SMASS. Similarly, the use of advanced eDNA metabarcoding approaches may provide important insights in the makeup of cetacean communities and the wild fish communities upon which they feed (e.g., Boyse et al., 2024), but a realistic consideration of capabilities, sampling designs, analytical approaches etc. will be required to successfully implement this metric as part of a future cetacean monitoring programme. 

A thorough review of ongoing non-cetacean marine survey and monitoring efforts across the various Scottish government agencies, academic institutions, eNGOs etc. is needed in the first instance to ensure relevant monitoring activities are captured, particularly for metrics identified as immediate priority, to facilitate their implementation. Compulsory data sharing by the marine renewables and oil and gas industries (e.g., collected for their Environmental Impact Assessments), and integration of such relevant data into monitoring assessments, is also recommended.

Recommendation 6: Ensure support for ongoing cetacean monitoring activities

While monitoring of ecosystem health (habitat condition and anthropogenic pressures) will be vital in underpinning future cetacean management in Scotland, knowledge of population abundance and distribution also remains crucially important. As highlighted in Annex 1 (Table A1.1), numerous monitoring activities focused on direct (visual/passive acoustic) observations of cetaceans are presently ongoing in Scotland, much of it funded and undertaken by eNGOs and academic institutions. Some of these efforts contribute directly to SCM, whereas others provide wider context against which to evaluate observations within MPAs. Many existing datasets could achieve more for MPA monitoring with the provision of additional resources. Therefore, continued, sustained and, where possible, expanded resourcing of these direct monitoring efforts is essential for long-term successful management of cetacean MPAs in Scotland.

Implementing these recommendations will result in significant benefit to a holistic monitoring plan for cetaceans, as part of an overarching Scottish mobile species monitoring programme, while also providing considerable useful outcomes for other Scottish policy initiatives. For example, both Scotland’s Fisheries Management Strategy 2020-2030 (Scottish Government 2022) and the Priority Marine Features programme (PMFs; Tyler-Walters et al., 2016) would benefit from improved focus on the status of important species such as Atlantic herring, particularly on the west coast of Scotland where knowledge of local pelagic fish stocks is presently limited. Similarly, Scotland’s Marine Assessment (SMA2020; Moffat et al., 2021) is based on significant multidisciplinary monitoring effort, and additional monitoring of the metrics proposed here could contribute to these larger-scale assessments. Finally, such an approach would also contribute to improved management of marine environments more broadly, in line with current best practice (e.g., as recommended by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES; 2019). Implementing a holistic monitoring plan for cetaceans therefore offers an opportunity for improving integration across different marine monitoring programmes in Scotland to benefit a wider range of government priorities, and the present set of recommendations is intended to contribute to this process.