NatureScot Research Report 1360 - Site Condition Monitoring of bottlenose dolphins within the Moray Firth Special Area of Conservation 2017-2022

Year of publication: 2024

Authors: Cheney, B.J., Arso Civil, M., Hammond, P.S. and Thompson, P.M.

Cite as: Cheney, B.J., Arso Civil, M., Hammond, P.S. and Thompson, P.M. 2024. Site Condition Monitoring of bottlenose dolphins within the Moray Firth Special Area of Conservation 2017-2022. NatureScot Research Report 1360.

Keywords

abundance; bottlenose dolphin; mark-recapture; photo-identification; Special Area of Conservation

Background

The Moray Firth Special Area of Conservation (SAC) was designated in 2005 under the European Habitats Directive (92/43/EEC) for bottlenose dolphins (Tursiops truncatus). This SAC extends from the inner firths to Helmsdale on the north coast and Lossiemouth on the south coast and includes areas that are regularly used by the population of bottlenose dolphins occurring along the east coast of Scotland. As a result of this designation, NatureScot has a responsibility to report on the condition of bottlenose dolphins within the Moray Firth SAC every six years.

Since 1989, this population of bottlenose dolphins has been the focus of an intensive research programme, carried out by the University of Aberdeen in collaboration with the Sea Mammal Research Unit (SMRU) at the University of St Andrews since 1996. In 2004, NatureScot entered into a Memorandum of Agreement with the University of Aberdeen to support these photo-identification studies and use the data to report on the condition of the site. Research highlighted a range expansion outside the SAC (Wilson et al., 2004) and that the use of areas outside the SAC have been increasing (Arso Civil et al., 2019b, Cheney et al., 2013). In 2015 NatureScot entered into a Memorandum of Agreement with the University of St Andrews to conduct photo-identification studies in Tayside & adjacent waters in recognition of the requirement for data from both areas to allow monitoring of population trends.

This report presents the results for the latest site condition monitoring cycle between 2017 and 2022. Data from the University of Aberdeen research programme within the SAC and the SMRU programme outside the SAC are incorporated into a revised assessment of the condition of this bottlenose dolphin population for this site condition monitoring report.

Main findings

• In this latest monitoring cycle, mark-recapture analysis of photographs collected during photo-identification surveys indicated that the estimated number of individual dolphins using the SAC has declined by 4.9% from 122 (95% CI: 111-134) in 2017 to 94 (95% CI: 84-106) in 2022.
• Despite the decline over this 6-year period, the number of dolphins using the SAC between 2001 and 2022 shows interannual variability but numbers are stable over the long-term.
• In this latest monitoring cycle, using the same methods, the estimated number of dolphins using Tayside & adjacent waters ranged from 111 (95% CI: 85-143) in 2019 to 195 (95% CI:170-223) in 2022.
• The estimated number of dolphins using Tayside & adjacent waters between 2009 (when regular surveys began) to 2022 has also varied interannually but has increased by an estimated 4.8% per year.
• The weighted mean estimate of the number of bottlenose dolphins in the east coast bottlenose dolphin population from 2020 to 2022 was 226 (95% CI: 214-239).
• Between 2001 and 2022 there has been an increase in the number of calves born and identified each year in the SAC and Tayside & adjacent waters.
• During the period 2009 to 2022, the proportion of the population using the SAC has declined, while the proportion of the population using Tayside & adjacent waters has increased. In most years >50% of the population used both areas.
• Passive acoustic monitoring from 2017 to 2022 highlighted that despite inter-annual and seasonal variation, dolphin spend >80% of days and between 3 and 10 hours per day from April to December at one long-term monitoring sites within the SAC.
• The quality of data available for completing the Site Attribute Table is high for attributes 1.1.1, 1.1.2 and 1.1.3.

The following conclusions were reached

• The number of dolphins using the SAC continues to show interannual variability but remains stable in the long term. However, the recent reporting period has seen a decline in the number of dolphins and in the proportion of the total population using this area.
• In contrast, the number of dolphins and the proportion of the east coast population using Tayside & adjacent waters has increased.
• The population of dolphins on the east coast of Scotland is still increasing.
• Both the SAC and Tayside & adjacent waters area are used by >50% of the population in most years.
• Passive acoustic monitoring continues to show interannual variability in dolphins’ use of the SAC with a peak during summer months. However, one area was used to a similar extent during summer, autumn and winter.
• As the long-term trend in the number of dolphins using the SAC remains stable, the use of this protected area continues to be high, and the east coast population is increasing we recommend that the condition status is Favourable (maintained).

Acknowledgements

We would like to thank all the colleagues who have helped collect and analyse data during this period. We would especially like to thank the Scottish Marine Mammal Strandings team for providing a summary of their data, and Charlie Phillips and the Whale and Dolphin Conservation Wildlife Centre in Spey Bay for their photographic contributions. Grant Ellis ran many of the surveys in Tayside and adjacent waters and processed much of the data collected by SMRU. Also, thank you to NatureScot, Beatrice Offshore Windfarm Ltd., Moray East and Moray West Offshore Wind Farms, Vattenfall, Seagreen, Inch Cape Offshore Ltd, NnG Offshore Wind, Marine Scotland, The Crown Estate, Highlands and Islands Enterprise, BES, ASAB, Greenpeace Environmental Trust, Scottish Government, Whale and Dolphin Conservation, Talisman Energy (UK) Ltd., Department of Energy and Climate Change, Chevron, Natural Environment Research Council and the Universities of Aberdeen and St Andrews whose contributions have allowed us to continue these studies on an annual basis. All survey work was conducted under NatureScot Animal Scientific Licences.

1. Introduction

The Moray Firth Special Area of Conservation (SAC) includes areas that are regularly used by the population of bottlenose dolphins occurring along the east coast of Scotland. Since 1989, this population of bottlenose dolphins has been the focus of an intensive research programme, carried out by the University of Aberdeen in collaboration with the Sea Mammal Research Unit (SMRU) at the University of St Andrews since 1996. The core research programme has consisted of boat-based photo-identification studies within the Moray Firth SAC conducted by the University of Aberdeen. These studies have provided information on abundance, distribution and behaviour patterns that have supported the development and management of the SAC. Since 2009, regular surveys have also been carried out by SMRU outside the SAC with a focus on the Firth of Tay, and additional coverage of adjacent waters to the north and the Firth of Forth to the south (Figure 1). As the population has continued to expand its range outside the SAC (Wilson et al., 2004, Arso Civil et al., 2019b, Cheney et al., 2013) this combined research programme has enabled the monitoring of all three site attributes (Annex 4).

NatureScot has a responsibility to provide information to enable reporting on the condition of bottlenose dolphins within the Moray Firth SAC every six years. NatureScot entered into Memorandum of Agreements with the University of Aberdeen from 2004, and with SMRU from 2015, to support photo-identification studies and use the resulting data to fulfil their requirement to report on the condition of the site.

During the period 1990-2000 there appeared to have been a decline in the extent to which this population was using the SAC, and an apparent range expansion (Wilson et al., 2004). Data from the first reporting cycle (2002-2004) (Thompson et al., 2006) confirmed that a high proportion (75-80%) of the east coast of Scotland population still used the SAC during summer, and suggested that there may have been a slight increase in summer abundance within the SAC post-2000. On the basis of these findings, the condition status in 2006 was considered to be “Unfavourable (recovering)”.

An internal report covering 2005 to 2007 identified significant inter-annual variation in the indicators being monitored and acknowledged that it remained unclear to what extent this resulted from sampling variation or genuine biologically significant changes. In light of this uncertainty and the limited amount of data collected since the previous report, no change was made to the condition status (Thompson et al., 2009).

The 2008 to 2010 report analysed data from 1990 to 2010 and concluded that despite inter-annual variability the number of dolphins using the SAC had remained stable. Additional data suggested that there was no evidence of a decline in the population of dolphins on the east coast of Scotland, and there was a greater than 99% probability that this population was stable or increasing. However, the proportion of the east coast of Scotland bottlenose dolphin population using the SAC had declined, most probably due to an overall increase in population size. Over 50% of the population used the SAC at some point in any one year (Cheney et al., 2012) and intensive surveys in 2006 and 2007 over the entire east coast showed that >80% of well-marked dolphins in this population had been photographed in the SAC (Cheney et al., 2013). On this basis, the condition status in 2012 was considered to be “Favourable (recovered)” (Cheney et al., 2012).

The 2011 to 2013 report again found that, despite inter-annual variability, the number of dolphins using the SAC between 1990 and 2013 appeared stable. Passive acoustic monitoring from 2011 to 2013 highlighted some inter-annual and seasonal variation in the amount of time dolphins spent at sampling sites within the SAC, although at two of the sites dolphins were present on almost all days during the summer (Cheney et al., 2014b). As a result of the interim nature of this report and the limited numbers of years of data collected since the last full assessment it was recommended that no change was made to the condition status (Cheney et al., 2014b).

The last report analysed data from 2014 to 2016 (Cheney et al., 2018). This report concluded that despite interannual variability, the number of dolphins using the SAC between 2001 and 2016 appeared to be stable. Additional data from outside the SAC suggested that the dolphin population on the east coast of Scotland was still increasing. As a result, the proportion of the population using the SAC had declined, however the SAC was still being used by >50% of the population annually. The passive acoustic monitoring continued to show that dolphins’ use of the SAC displayed site specific interannual and seasonal variation, but the use of certain areas of the SAC outside the summer months remained higher than previously thought. Although the east coast of Scotland dolphin population remained small and potentially vulnerable, as a result of these conclusions, the condition status remained “Favourable (recovered)” (Cheney et al., 2018).

This report presents the results for the latest site condition monitoring cycle between 2017 and 2022 carried out by the University of Aberdeen within the Moray Firth SAC and SMRU outside the SAC in Tayside & adjacent waters. We also present data from University of Aberdeen passive acoustic monitoring studies within the SAC. These data are incorporated into a revised assessment of the condition of this bottlenose dolphin population for this full site condition monitoring report.

2. Methods

2.1 Survey protocols

Surveys in the Moray Firth SAC focused on the inner Moray Firth (light grey area, Figure 1), as a proxy for the larger SAC area. All surveys were made from an MCA certified 5.8 m Rigid Inflatable Boat (RIB), working from Cromarty Harbour. Surveys outside the SAC focussed on Tayside & adjacent waters, with extended surveys into the Firth of Forth in recent years (light grey area, Figure 1). These surveys used a variety of small (<12 m) RIBS or hard hull boats working from local harbours. Survey effort was spread through the period May to September but restricted to days with low sea state (≤ Beaufort 3) to maximise sighting probability, and good light conditions to maximise photographic quality. Survey routes were chosen to maximise sighting probability whilst also providing reasonably wide coverage of each core study area (light grey areas, Figure 1). Occasional surveys also covered other areas within the SAC, along the south coast of the Moray Firth and the Grampian coast. Surveys were made with a minimum crew of two, including an appropriately qualified skipper. All surveys were carried out under NatureScot Animal Scientific Licences granted to the University of Aberdeen (Licence #93751 for 2017-2022) and University of St Andrews (Licence # 98465 for 2017-2022).

Throughout the survey, the survey route was recorded automatically from either a handheld or the boat’s GPS, and later downloaded to a GIS. Whenever a group of dolphins was encountered, the position and time was noted, a waypoint entered on the GPS log, and an estimate made of the size of the group (Wilson et al., 1997). The boat was then carefully manoeuvred at slow speed around the dolphins to allow dorsal fin photographs to be taken with a Canon DSLR camera and a 70-200 mm lens. In doing so, every effort was made to minimise disturbance to the group, and to obtain pictures that were of sufficient quality for subsequent mark-recapture analyses. In particular, it was important to ensure that: dorsal fins were parallel to the camera; the whole fin was in the picture; the height of the fin image was >10% of the field of view; and that pictures were taken such that there was an equal probability of photographing different members of the group. The encounter was ended either when all dolphins had been photographed or when the survey vessel lost contact with the group. At this point, the end time and location were noted, and another GPS waypoint taken.

2.2 Photographic analysis

Every survey and each encounter within it were allocated unique “Trip” and “Encounter” numbers. Photographs were downloaded, and the pictures from each encounter were allocated unique names and stored in individual folders (see Annex 1).

All the pictures taken on each encounter were graded for photographic quality according to the criteria in Figure 2, adapted from Wilson et al. (1999). Subsequent analyses were restricted to the subset of high quality pictures (grade 3.1, 3.2 & 3.3) to avoid biasing mark-recapture estimates of abundance (see Wilson et al., 1999). Analyses were also restricted to the subset of animals bearing distinctive marks, i.e. those with nicks in their dorsal fin. Each of these dorsal fin pictures was initially matched against the existing catalogue (see Annex 2) by one experienced project team member. At the end of the season, each of these matches was then confirmed by a second experienced person.

Confirmed sightings of the different dolphins were then recorded in an Access database, linking that sighting with information on which side of the dolphin had been photographed, and the trip and encounter information (see Annex 1). Estimates of group size were recorded as the larger of the field estimate of the number of animals seen in each encounter and the number of animals subsequently identified from grade 3 pictures. In addition, we used all grade 3 pictures to estimate q, the proportion of animals that were well-marked. For each trip, we recorded the number of photographed individuals that were well-marked (i.e. animals with dorsal fin nicks that could be identified from either the left or right side), and the number of individuals not well-marked (i.e. no dorsal fin nicks), and recorded this information in a separate access database table (see Annex 1).

2.3 Mark-recapture analysis

2.3.1 Data

For the SAC we focused on abundance from 2001 to 2022, providing estimates from before the designation of the SAC in 2005 to the end of the current reporting period. In Tayside & adjacent waters regular dedicated photo-ID surveys began in 2009, therefore, in this report we have focused on producing abundance estimates in this area from 2009 to 2022.

To estimate annual abundance for the east coast Scotland population we used data from surveys both inside and outside the SAC. This included University of Aberdeen data from the SAC (2001-2022) and outer Moray Firth (2006-2020) (Cheney et al., 2014a), and SMRU data from Grampian (2012-2013) and Tayside & adjacent waters (2001, 2002, 2009-2022) (Arso Civil et al., 2019b). Additional data from the Moray Firth were also available from Whale and Dolphin Conservation (WDC) surveys that were made from a commercial dolphin watching vessel along the southern coast of the Moray Firth from 2001, 2002 and 2004 to 2010 (Cheney et al., 2013). These photographs were also subjected to the same rigorous quality control as those collected by the University of Aberdeen and SMRU (Figure 2).

2.3.2 Abundance of well-marked animals

Estimation of abundance was based on well-marked individuals with nicked dorsal fins that could be identified from both sides. The data for each individual are represented by a single capture history combining left and right sides for each area (SAC, Tayside & adjacent waters, and east coast population) (see Annex 1 for an example).

In earlier reports the Chao et al. (1992) Mth model was used to estimate abundance within the SAC (see Cheney et al., 2018). Although this modelling framework accounts for heterogeneity in capture probabilities it does not specifically account for temporary emigration. Dolphins are known to range beyond the main surveyed areas and display variability in their movement patterns (Cheney et al., 2013). This introduces heterogeneity in capture probabilities as dolphins may be available for sampling (i.e. being photographed) in some occasions but not on others (Kendall et al., 1997). If this temporary emigration is not accounted for abundance estimates can be biased (Kendall, 1999). Robust design models can be combined with estimators that incorporate temporary emigration to produce unbiased estimates of abundance (Kendall et al., 1997, Pollock, 1982, Kendall and Nichols, 1995). Previously, this modelling framework was used to estimate abundance in Tayside & adjacent waters (Arso Civil et al., 2019b). Therefore, to apply a single analytical framework and account for temporary emigration, robust design population models were used to estimate abundance for the SAC, Tayside & adjacent waters and the east coast population. Each annual field season represented a primary sampling occasion, and two-week periods within each season (May-September) were secondary occasions, with closed population models applied to the secondary occasions. Under the robust design framework, the temporary emigration parameters γ^’’ and γ^’ represent the probability of an animal temporarily emigrating outside the sampling area between years, and the probability of remaining outside the sampling area (i.e. remaining an emigrant), respectively. These probabilities can be considered as random or Markovian, where the probability of emigrating does not or does depend on whether or not an animal was previously available, respectively. Models were also fitted with the Pledger (2000) mixture parameter, to account for added heterogeneity in capture probabilities. In these models, the population is assumed to comprise a mixture of two groups of animals each with different probabilities of capture.

To assess the fit of models to the data for each area (SAC, Tayside & adjacent waters, and east coast population) goodness of fit (GOF) tests were applied using package R2ucare (Gimenez et al., 2018) in R (R Core Team, 2023). Results indicated heterogeneity in recapture probabilities in all datasets due to trap-dependence (trap-happiness or trap-shyness; Pradel, 1993), in which some animals are more or less likely to be recaptured after initial capture. To account for this in the models, an individual time-varying covariate was introduced which allowed capture probabilities to vary depending on whether an individual was captured in the previous year or not (Huggins, 1989). A variance inflation factor ĉ (indicative of over-dispersion in the data) was estimated in R2ucare for each dataset. Model selection was based on the Akaike Information Criteria corrected for small sample size (AICc; Akaike, 1998, Burnham and Anderson, 2002) when ĉ ≤ 1 and on the quasi-AIC (QAIC) when ĉ > 1. Models were constructed in the RMark package (Laake, 2013) in R, and fitted using MARK software (White and Burnham, 1999).

2.3.3 Total abundance and trends

Estimates of abundance of well-marked animals from the robust design models were inflated by dividing by the estimated proportion of well-marked individuals (θ) to estimate total abundance. As dolphins without nicks may not be identified from both sides, θ was estimated separately for each side (right and left) on each trip. To estimate the proportion of well-marked animals each year, binomial generalized linear models (GLMs) with a logit link function were fitted with year as an explanatory variable to account for annual variation in θ. These annual estimates of θ were used to inflate the annual mark-recapture estimates of well-marked animals (Nt) for each year t (Nt total= Nt / θ), either from 2001 to 2022 (SAC) or from 2009 to 2022 (Tayside & adjacent areas and east coast population), to estimate total annual abundance of dolphins within the SAC, Tayside & adjacent waters, and east coast population. Assuming Nt total is log normally distributed, the upper and lower 95% confidence intervals were estimated by dividing and multiplying Nt total respectively, by C:

Linear regressions (GLMs with log transformed estimates) were used to investigate whether there was a trend in abundance in the SAC, Tayside & adjacent waters or the east coast population.

To allow for interannual variation in annual abundance estimates, the number of bottlenose dolphins in the east coast Scotland population was estimated using a weighted mean (Nw) from 2020 to 2022. This was calculated where weighting (wy) is the inverse coefficient of variation (CV²) for the estimate of population size each year (y), divided by the sum of the inverse CV² for all years. This weighting is then multiplied by the estimated abundance (Ny) for each year:

2.4 Births and mortality

Available data sources were used to attempt to determine if there were any changes in crude birth rates or observed mortality within the population. The number of known calf births each year within and outside the SAC (including outer Moray Firth, Grampian and Tayside & adjacent waters) from 2001 to 2022 were reviewed. Bottlenose dolphin calves were identified in their first, second or third year of life using foetal folds (vertical creases down the sides of calves from their position in the womb, which fade over time). Only calves seen in echelon position (where the calf is seen consistently surfacing alongside the mother’s dorsal fin) with known females were included to avoid possible duplication. The number of known strandings over the same time period on the east coast of Scotland was obtained from the Marine Animal Stranding database created by the Scottish Marine Animal Stranding Scheme (SMASS, 2023).

2.5 Usage of the SAC and Tayside & adjacent waters

Three methods were employed to estimate the use of the SAC by the east coast of Scotland bottlenose dolphin population. The first involved relating the number of animals estimated in the SAC to total population size and the others used different approaches to quantify the amount of time dolphins spent within the SAC.

2.5.1 Proportion of the total population

Following Cheney et al. (2014a), trends in the proportion of the total population using the SAC were investigated using parametric bootstrap procedures to account for the uncertainty around the abundance estimates. For each year, estimates of abundance for the SAC and the total population were drawn from lognormal distributions of the mean and variance of each of the abundance estimates. The annual proportion of the total population using the SAC from 2009 to 2022 was then calculated. A GLM in which the error distribution of this annual proportion was assumed to be quasi-binomial, to account for overdispersion in the data, and logit link was then fitted to the annual proportions to estimate the slope. This bootstrapping procedure was repeated 1,000 times.

This procedure was also used to investigate the proportion of the east coast population that used Tayside & adjacent waters from 2009 to 2022.

2.5.2 Encounter probability in the Sutors area

Although survey routes within the SAC varied, all surveys passed through the Sutors of Cromarty (the headlands at the mouth of the Cromarty Firth). Therefore, as in previous reports, we used a simple index of usage of the SAC based on the probability of encountering dolphins each time the survey boat passed through the Sutors area during the period May to September (Thompson et al., 2006).

2.5.3 Passive acoustic monitoring

Passive acoustic monitoring (PAM) provides a more detailed assessment of usage of the SAC. CPODs recorded changes in the presence or absence of dolphins at two sample sites within the SAC. These devices incorporate a hydrophone, processor and digital timing system. The CPOD continuously detects from 20-160 kHz, logging time, centre frequency, sound pressure level and bandwidth of each cetacean echolocation click and can log detections for periods of around 4 months. The manufacturer’s software program was used to post-process the recovered data, detect characteristic click trains, and remove noises from other sources such as boat sonar. Resulting data on the number of click trains recorded in each minute can be used to determine the presence or absence of target species in different time periods, or to identify the timing and duration of encounters with target species. CPODs were used to detect dolphin echolocation click trains.

Trends in the use of sample sites within the SAC were evaluated using available acoustic data from a series of different studies that have been conducted by the University of Aberdeen (Fernandez-Betelu et al., 2021, Graham et al., 2016, Thompson et al., 2013). Sample sites and coverage varied between years, but data were available for this reporting period from two sample sites within the SAC (Sutors and Chanonry) (Figure 1). Early failure and loss of equipment meant that coverage was not available in all months each year. Data are included only for those months in which data are available for 10 or more days (see results). To investigate annual changes in the detection of dolphins by CPODs, data from May to September were used for consistency with the summer photo-identification data. To investigate seasonal changes in use of the SAC for this reporting period all available year-round data was used.

3. Results

3.1 Survey details

From 2017 to 2022, between 19 and 24 photo-identification surveys were carried out each year within the Moray Firth SAC. These surveys resulted in a total of 526 encounters with dolphin groups (Table 1). Survey routes varied between years but aimed to cover as much of the inner Moray Firth SAC as possible (Figure 3). The locations of each encounter with dolphins are based on the position of the survey boat at the start of each encounter (Figure 3) (see Annex 3 for details of the GIS project).

Table 1. Summary data on the number of photo-identification surveys conducted within the Moray Firth SAC during the 2017 to 2022 reporting period.

Year	No. of surveys	Mean survey duration	No. of encounters	% of survey time with dolphins
2017	24	6:32	140	29%
2018	21	5:35	99	39%
2019	19	6:32	83	37%
2020	20	6:29	74	35%
2021	19	6:23	64	38%
2022	19	6:06	66	39%

 

From 2017 to 2022, between 19 and 28 photo-identification surveys were carried out each year in Tayside & adjacent waters. These surveys resulted in a total of 314 encounters with dolphin groups (Table 2). Survey routes varied between years, with recent expansion into the Firth of Forth (Figure 4) (see Annex 3 for details of the GIS project).

Table 2. Summary data on the number of photo-identification surveys within Tayside & adjacent waters during the 2017 to 2022 reporting period.

Year	No. of surveys	Mean survey duration	No. of encounters	% of survey time with dolphins
2017	19	5:40	54	37%
2018	21	6:57	47	27%
2019	23	5:30	56	31%
2020	22	6:36	40	27%
2021	27	6:46	42	22%
2022	28	6:48	75	21%

 

Within the SAC, median group size ranged from 6 to 10 between 2017 and 2022 but there was no significant difference in group sizes between years (Kruskal-Wallis, c² = 2.8782, df = 5, p>0.05). Around Tayside & adjacent waters, median group size ranged from 7 to 14.5 during the same period and was significantly larger than within the SAC (Kruskal-Wallis, c² = 14.427, df = 1, p<0.001). There was also a significant difference in group sizes between years in these areas outside the SAC (Kruskal-Wallis, c² = 21.232, df = 5, p<0.001) (Table 3 and Figure 5).

Table 3. Median and range of group sizes for each year and area.

Year	SAC	Tayside & adjacent waters
2017	6.5 (1-30)	10 (2-50)
2018	6 (1-40)	7 (1-30)
2019	7 (1-56)	7.5 (1-40)
2020	7 (1-40)	11 (2-50)
2021	10 (1-25)	14.5 (2-49)
2022	8 (1-47)	9 (1-71)

 

3.2 Estimate of the number of dolphins using the SAC

During the 2017 to 2022 reporting period, high quality pictures were obtained from between 40 and 52 well-marked dolphins each year. Model selection favoured models incorporating the Pledger (2000) heterogeneity mixture parameter over models without it. The most supported model had time-varying capture probabilities and a constant Markovian temporary emigration. There was a low probability of animals emigrating (γ’’= 0.06, 95%CI 0.04-0.09), and a probability of remaining an emigrant γ’ of 0.7 (95%CI 0.55-0.82). Based on this model, the mark-recapture estimates of the total number of well-marked individuals in the SAC ranged from 54 (95% confidence interval (CI): 53-60) in 2017 to 42 (95% CI: 41-50) in 2022. When inflated by the annual proportion of well-marked individuals, θ, the resulting estimate of the total number of dolphins using the SAC in the summer significantly declined from 122 (95% CI: 111-134) in 2017 to 94 (95% CI: 84-106) in 2022 (Table 4, t=-5.406, p<0.01). The annual proportional rate of change (λ) was estimated at 0.95 (95% CI: 0.93-0.97), indicating that the number of animals using the SAC has declined over this period at an estimated rate of 4.88% (95% CI: 3.14-6.59) per year.

Table 4. Results of the mark-recapture analysis for the SAC using robust design models including the number of well-marked individuals identified in grade 3 pictures (minimum number), the estimated number of well-marked individuals from the most supported model (N-hat), the GLM estimated annual proportion of well-marked individuals (θ), and the total number of dolphins estimated in the SAC (Total abundance) with 95% confidence intervals.

Year	Minimum Number	^ N	95% CI	θ	Total abundance	95% CI
2017	52	54	53-60	0.4431	122	111-134
2018	45	48	46-55	0.4126	115	103-129
2019	45	45	45-49	0.4462	102	94-110
2020	44	48	45-56	0.4460	107	94-120
2021	41	45	42-53	0.4662	97	85-110
2022	40	42	41-50	0.4477	94	84-106

 

3.3 Estimate of the number of dolphins using Tayside & adjacent waters

In Tayside & adjacent waters, high quality pictures were obtained from between 41 and 84 well-marked dolphins during the 2017 to 2022 reporting period. Model selection favoured models incorporating the Pledger (2000) heterogeneity mixture parameter, and the most supported model had time-varying capture probabilities and constant random temporary emigration. The model showed a low probability of temporarily emigrating and of remaining an emigrant (γ’’ = γ’ = 0.10, 95%CI 0.06-0.15). Based on this model, the mark-recapture estimates of well-marked individuals ranged from 55 (95% CI: 42-71) in 2019 to 96 (95% CI: 84-108) in 2022. When inflated by θ, this resulted in an estimated total of between 111 (95% CI: 85-143) and 195 (95% CI:170-223) dolphins using Tayside and adjacent waters in the summers of 2017 to 2022 (Table 5). There was no evidence for a trend in total number of dolphins over this period (t=1.45, p>0.05).

Table 5. Results of the mark-recapture analysis for Tayside & adjacent waters using robust design models including the number of well-marked individuals identified in grade 3 pictures (minimum number), the estimated number of well-marked individuals from the most supported model (N-hat), the GLM estimated annual proportion of well-marked individuals (θ), and the total number of dolphins estimated in Tayside & adjacent waters (Total abundance) with 95% confidence intervals.

Year	Minimum Number	^ N	95% CI	θ	Total abundance	95% CI
2017	56	70	57-84	0.4821	144	118-177
2018	49	65	51-83	0.5000	130	101-166
2019	41	55	42-71	0.4954	111	85-143
2020	63	84	68-104	0.5120	164	131-204
2021	63	74	63-87	0.5302	140	119-166
2022	84	96	84-108	0.4905	195	170-223

 

3.4 Trends in abundance in the SAC and Tayside & adjacent waters

Annual estimates of the number of dolphins using the SAC in the summer months from 2001 to 2022 showed variability from year to year (Figure 6) with no significant trend (t =1.162, p >0.05). Similarly, there was interannual variability in the estimated number of dolphins using Tayside & adjacent waters in the summers of 2009 to 2022. However, there was a significant increase in the estimated number of dolphins using this area (t =4.187, p =0.001). The annual proportional rate of change (λ) was estimated at 1.05 (95% CI: 1.02-1.07), indicating that the number of animals using Tayside & adjacent waters increased over this period at an estimated rate of 4.79% (95% CI: 2.52-7.12) per year.

3.5 Trends in abundance in the east coast population

Data from 2001 to 2022 were used in the same robust design framework to estimate the number of dolphins within the east coast bottlenose dolphin population. However, as data from outside the SAC were not collected consistently until 2009, the earlier population abundance estimates are unlikely to accurately reflect the actual size of the population. Therefore, we have only included the results from 2009 to 2022 (Figure 7). Models including the Pledger (2000) mixture parameter were once again more supported than those not including it. The most supported model had time-varying capture probabilities and time varying Markovian emigration. Temporary emigration parameters were not estimated for all years, but in general, the probability of temporarily emigrating was low, similar to the SAC and Tayside and adjacent waters results. Between 2009 and 2022, the most supported model estimated that the bottlenose dolphin population on the east coast of Scotland had significantly increased (t=3.119, p<0.01), with an annual rate of change of λ=1.02 (95% CI: 1.01-1.03). This indicates that the population increased over this period at an estimated rate of 2.07% (95% CI: 0.76-3.40) per year (Figure 7). In 2022 the number of dolphins in this population was estimated as 245 (95%CI: 224-268) (Table 6). A three year, rather than five year, weighted mean estimate was also calculated as this reflected more recent abundance data and was consistent with an increasing population. The weighted mean estimate of the number of bottlenose dolphins on the east coast of Scotland from 2020 to 2022 was 226 (CV=0.028) with lognormal 95% confidence interval of 214 to 239.

Table 6. Results of the mark-recapture analysis for the east coast Scotland population using robust design models including the number of well-marked individuals identified in grade 3 pictures (minimum number), the estimated number of well-marked individuals from the most supported model (N-hat), the GLM estimated annual proportion of well-marked individuals (θ), and the total number of dolphins estimated in the population (Total abundance) with 95% confidence intervals.

Year	Minimum Number	^ N	95% CI	θ	Total abundance	95% CI
2017	102	108	108-115	0.4569	236	217-257
2018	86	89	86-96	0.4411	203	186-221
2019	82	87	82-94	0.4597	190	172-209
2020	93	101	93-110	0.4706	214	194-237
2021	101	108	101-117	0.4982	218	199-238
2022	108	116	108-125	0.4720	245	224-268

 

3.6 Births and mortality

In total, 297 calves were identified on the east coast of Scotland between 2001 and 2022 (Figure 8). The number of newborn calves ranged from 3 to 22 in each year. Effort outside the SAC varied in each year before 2009, which complicates interpretation of these trends. In addition, calves are not always detected in their year of birth and therefore data from 2022 are preliminary. However, linear regression analyses suggests births have been increasing over this period both in the SAC (t=2.992, F = 8.953, df = 20, p<0.01) and outside (t=7.134, F = 50.89, df = 20, p<0.0001).

The Scottish Marine Animal Stranding Scheme (SMASS, 2023) recorded 98 dead stranded bottlenose dolphins on the east coast of Scotland between 2001 and 2022 (Figure 9). The number of stranded individuals ranged from 1 to 16 each year. The unusually high number of strandings in 2021 is a result of a mass stranding event (MSE) of between 40 and 100 bottlenose dolphins observed in the inner Moray Firth between the 13^th and 15^th August, of which 15 were later found dead. Of the individuals photographed, both alive and dead, none were a match to the east coast catalogues. A number of these dolphins had nicks at the tip of their dorsal fins which could be an indication that they were offshore animals (Oudejans et al., 2015).

The observed variability in other years could be a result of changes in mortality, search effort or simple stochasticity due to the small number of animals. Even excluding the MSE it is unknown if all these stranded animals belong to the east coast of Scotland population. Many of these strandings are of young animals and/or in an advanced state of decomposition. As a result, only four dolphins stranded between 2001 and 2022 were matched to our east coast of Scotland bottlenose dolphin catalogue (Figure 9).

3.7 Usage of the SAC and Tayside & adjacent waters

3.7.1 Proportion of the total population using the SAC

The proportion of the east coast bottlenose dolphin population that used the SAC was investigated using annual estimates of abundance in the SAC and total population size. The parametric bootstrap took uncertainty around these estimates into account and provided evidence that the proportion of the population using the SAC has declined between 2009 and 2022, with 93% of bootstrap replicate GLMs showing significant negative slope coefficients (mean = −0.055, SE = 0.0003). However, 67% of bootstrap replicates showed that >50% of the population used the SAC in a year during this time-series (Figure 10).

3.7.2 Proportion of the total population using Tayside & adjacent areas

The proportion of the east coast bottlenose dolphin population that used Tayside & adjacent areas was also investigated using the same parametric bootstrap method. This provided evidence that the proportion of the population using Tayside & adjacent areas has increased, with all bootstrap replicate GLMs showing positive slope coefficients (mean = 0.07, SE = 0.0006), although only 42% were significant. In addition, 85% of bootstrap replicates showed that >50% of the population used Tayside & adjacent waters in any year during this time-series (Figure 11).

3.7.3 Use of each area by individual dolphins

Of the 431 dolphins identified across the east coast of Scotland between 2009 and 2022, 131 dolphins (30%) were photographed in both the SAC and Tayside & adjacent waters, with between zero and 26 dolphins seen in both areas in a single year. In addition, 96 (22%) of the dolphins identified in Tayside & adjacent waters during this period have never been photographed in the SAC.

3.7.4 Encounter probability in the SAC

Effort in different parts of the SAC varied among surveys and years, but the Sutors area was visited during every survey. The probability of encountering groups of dolphins within this area averaged 0.74 from 2017 to 2022 (Table 7), slightly lower than that reported previously (0.79; Cheney et al., 2012, Cheney et al., 2018, Cheney et al., 2014b).

Table 7. Estimates of the usage of the SAC based on the probability of encountering groups of dolphins within the Sutors area.

Year	Total number of trips	Proportion of trips encountering dolphins in the Sutors area
2017	24	0.71
2018	21	0.57
2019	19	0.68
2020	20	0.75
2021	19	0.58
2022	19	0.79
Total	112	0.74

 

3.7.5 Long range movement out of the SAC

Research in the early 1990s suggested that this bottlenose dolphin population’s core range was within the inner Moray Firth, with 90% of the population using this area year round (Wilson et al., 1997, Wilson et al., 1999). Since the mid 90s the population expanded its range southwards along the east coast of Scotland (Wilson et al., 2004, Arso Civil et al., 2019b) and since at least 2007 into northeast England (Thompson et al., 2011). Subsequently, other long-range movements were observed between the east and west coast of Scotland and into Ireland, but photo-identification showed that those individuals were not part of the known east coast Scotland population (Robinson et al., 2012). Therefore, to our knowledge no dolphins from this population have previously been photographed outwith the northeast coast of the UK.

During this reporting period we discovered a previously unknown long-range movement of dolphins from this population. A total of 35 individuals that were seen regularly in the SAC were not photographed in this area in 2019. In 2019 with opportunistic sightings and photographs from citizen scientists we identified 5 of these dolphins in images from the east and west coast of Ireland (estimated group size = 15), and 8 (estimated group size = 20) in the Netherlands. In 2020, 6 of these dolphins returned and were photographed in the SAC. However, to date, a number of these individuals remain in these other areas: including 4 dolphins photographed around Denmark; 3 on the west coast of Ireland; 1 female with a new calf around the Isle of Man; 2 on the south coast of England; and five with a new calf on the west coast of Scotland. Two of these individuals (1 in Denmark, 1 on the Scottish west coast) died and stranded in 2023.

3.7.6 Passive acoustic monitoring in the SAC

Results from 2017 to 2022 showed annual variation in the median number of hours per day dolphins spent at the two SAC sample sites (Table 8), which was also seen in previous years (2008-2022, Figure 12). At Sutors the median number of hours dolphins were detected each year were significantly different during the reporting period (Kruskal-Wallis Test, c²= 12.993, df = 5, p<0.05); but dolphins were still detected on an average of 95% of days and 7 hours per day. However, this was slightly less than during the previous reporting period (2011 to 2016) where dolphins were detected on 99% of days and 8 hours per day. At Chanonry, there was also a significant difference (c²= 54.439, df = 5, p<0.0001) in the number of hours dolphins were detected in each year, although dolphins were still detected on average for 94% of days and for a median of 4.5 hours per day. This was very slightly lower than the previous reporting period where dolphins were detected for a median of 96% of days and for 5 hours per day. The median number of hours dolphins were detected each year tended to be higher in the Sutors than at Chanonry (Figure 12), and except for 2019 and 2021 this pattern was similar for the proportion of days dolphins were detected (Table 8). Between 2008 and 2022 there was a moderate positive linear correlation between the median number of hours per day dolphins were detected at Sutors and the SAC abundance estimates (Pearson’s Product-Moment Correlation t = 2.434, R = 0.56, df = 13, p<0.05), but not at Chanonry (t = 0.853, df = 13, R = 0.23, p>0.05).

There were also seasonal changes in the detection of dolphins at the Sutors and Chanonry areas from 2017 to 2022 (Table 9 and Figure 13). These data indicate that, similar to previous years, there was a peak in dolphin occurrence during the summer photo-identification survey period. At Sutors dolphins were present for a median of 3 to 10 hours and over 82% of days and at Chanonry dolphins were present for a median of 2 to 7 hours and on between 77% and 100% of days over the summer. Nevertheless, dolphins were also present in these areas for a significant number of days and amount of time per day, at other times of the year (Table 9 and Figure 13). For example, at Sutors, dolphins were detected on average between 4 and 7 hours per day during April and between October and December (inter-quartile ranges = 2 to 11), similar to summer medians of 4 to 10 hours per day (inter-quartile ranges = 1 to 10). In addition, in the same “non-summer” months, dolphins were detected on >83% of days the CPODs were deployed (Figure 13a and Table 9). At Chanonry, dolphins were detected on between 64% and 94% of days in the same “non-summer” months, for a median of 1 to 4 hours per day (Figure 13b and Table 9).

Table 8. The percentage of days and median number of hours per day that dolphins were detected on CPODs at the Sutors and Chanonry sites during the summer (May to September) from 2017 to 2022 (* CPOD data were unavailable in some months in some years, see Table 9).

Sutors

Year	No. days sampled*	% days dolphins detected	Median hrs/day detected	Inter-quartile range
2017	152	99.3	7	5 – 10
2018	151	98.7	8	5 – 11
2019	153	86.3	6	2 – 10
2020	152	93.4	7	3 – 10
2021	151	94.0	8	3 – 12
2022	153	96.1	6	3 – 10

 

Chanonry

Year	No. days sampled*	% days dolphins detected	Median hrs/day detected	Inter-quartile range
2017	59	88.1	4	1 - 5.5
2018	151	95.4	7	4 – 9
2019	141	92.9	4	3 – 6
2020	152	95.4	6	3 – 9
2021	133	96.2	5	3 – 8
2022	153	87.6	4	3 – 7

 

Table 9. The percentage of days and median number of hours per day that dolphins were detected on CPODs at the Sutors and Chanonry sites each month from 2017 to 2022. (* CPOD data were unavailable in these months in some years).

Sutors

2017 to 2022	No. Years sampled	No. days sampled	% days dolphins detected	Median hrs/day detected	Inter-quartile range
January*	5	144	62.5	1	0 – 4
February*	4	112	46.4	0	0 – 2
March*	4	105	63.8	1	0 – 3
April*	4	104	95.2	4	2 – 7
May	6	185	98.4	8	5 – 11
June	6	180	99.4	9	6 – 12
July	6	186	99.5	10	8 – 13
August	6	185	92.4	5	3 – 8
September	6	176	83.0	3	1 – 5
October*	5	142	96.5	5	3 - 9.75
November*	5	114	96.5	7	4 – 10
December*	4	124	83.1	4	1 – 7

 

Chanonry

2017 to 2022	No. Years sampled	No. days sampled	% days dolphins detected	Median hrs/day detected	Inter-quartile range
January*	5	136	73.5	2	0 – 4
February*	4	106	32.1	0	0 – 1
March*	5	117	36.8	0	0 – 1
April*	4	85	94.1	4	2 – 6
May*	5	154	96.1	6	4 – 8
June*	5	150	98.7	6	4 – 8
July*	5	155	100	7	5 – 10
August	6	184	92.4	4	2 – 7
September	6	146	77.4	2	1 – 4
October*	5	154	66.2	2	0 – 3
November*	5	150	64.7	1.5	0 – 4
December*	5	155	67.1	1	0 – 4

 

4. Discussion

There are three attributes and associated targets for the bottlenose dolphin feature of the Moray Firth SAC, as outlined in the Site Attribute Table (Annex 4). The University of Aberdeen photo-identification monitoring programme in the SAC focuses on providing data to monitor the first and second of these attributes (the number of individual dolphins using the SAC and frequency of occurrence of dolphins within the SAC). Ongoing photo-identification studies in Tayside & adjacent waters by the University of St Andrews Sea Mammal Research Unit provides monitoring of this area outside the SAC. Combining these photo-identification data from across the east coast of Scotland and additional data from other collaborative projects enables monitoring of the third site attribute (dolphin population trends). Data on the proportion of the population using the SAC, variation in sightings rates in the Sutors area, and data from passive acoustic monitoring studies within the SAC provide extra information to assess the second attribute.

Similar to previous reports, due to the large size of the SAC, efforts to assess the first site attribute and monitor changes in the number of dolphins using the SAC (Attribute 1.1.1, the number of individual dolphins using the SAC) have been based on photo-identification surveys within a core study area in the inner Moray Firth (Cheney et al., 2018, Cheney et al., 2014b, Cheney et al., 2012). This ensures consistency, the increased sighting probability in this area provides more precise abundance estimates, and previous studies have shown that this area provides a good proxy for use of the SAC (Bailey and Thompson, 2009, Wilson et al., 1999, Durban et al., 2005, Thompson et al., 2011). To assess this first site attribute, we have estimated abundance from 2001 to 2022 using a robust design model framework, providing estimates from before the designation of the SAC in 2005 to the end of the current reporting period. Using data collected in the current reporting period, we estimated that the number of dolphins using the SAC in the summer has significantly declined from 122 (95% CI: 111-134) in 2017 to 94 (95% CI: 84-106) in 2022, approximately 4.9% per year. This could be due to the increase in the number of dolphins using Tayside & adjacent waters, where the number of dolphins using this area increased by 4.8% per year, along with the newly observed long-range movement of individuals regularly seen in the SAC to previously unknown areas. These potential explanations highlight different conservation and management implications. However, using the longer time series of 22 years of data, results indicated that there has been considerable inter-annual variability in the number of dolphins using the SAC, but no evidence of a trend.

The second site attribute is the frequency of occurrence of dolphins within the SAC (Attribute 1.1.2). For this assessment we used the same robust design model framework to estimate abundance for the east coast of Scotland bottlenose dolphin population, and compared this to estimates of the number of individuals using the SAC. Results indicate that between 2009 and 2022 there was a decrease in the proportion of the total population using the SAC (mean slope = −0.055). This appears to be, at least in part, driven by an increase in overall population size (Figure 7). Despite this decrease, results suggest that in most years the SAC is still used by over half of this bottlenose dolphin population, but that it is less important to the population as a whole in 2022 than it was in 2009. In addition, we used a simple estimator that provided information on variation in the probability of sighting dolphins in the Sutors area (an area visited on every survey). Data from 2017 to 2022 confirm that dolphins continue to be encountered within this area at a high rate (on an average of 74% of visits to the area). However, this was slightly lower than in previous reporting periods (Cheney et al., 2012, Cheney et al., 2014b, Cheney et al., 2018).

While the proportion of the east coast population using the SAC has declined, the proportion using Tayside & adjacent waters has increased. Although there is interannual variability during this reporting period, the estimated number of dolphins using Tayside & adjacent waters has increased from 144 (95% CI: 118-177) in 2017 to 195 (95% CI:170-223) in 2022. Group sizes were also significantly larger in this area than within the SAC. In addition, although 50% of the population use both these areas in most years, the estimated number of dolphins using the SAC has been lower than in Tayside & adjacent waters since 2013, and in 2022 less than half the number of dolphins were estimated to use the SAC. The higher estimates in Tayside & adjacent waters could in part be due to the increased effort when surveys extended into the Firth of Forth from 2020 onwards, and the additional number of surveys in 2021 and 2022. Despite this the results suggest that Tayside & adjacent waters may currently be more important to the population than the SAC. This also adds weight to a continuing range expansion in this population first identified by Wilson et al. (2004). Photo-ID shows that although there is movement between these areas, with 30% of dolphins observed in both areas between 2009 and 2022, 22% of dolphins identified during the same period have never been photographed in the SAC.

The passive acoustic monitoring data from two sample sites within the SAC between 2017 and 2022 showed dolphins were detected in all months at both sites, with inter-annual variability in patterns of occurrence which has been observed in previous years (Cheney et al., 2018). There was a slight decrease in the number of days dolphins were detected and amount of time spent each day around both sites compared to the previous reporting period (2011 to 2016). However, dolphins were still detected on >87% of days and for >4 hours per day during the summer months. During this reporting period dolphins were detected for fewer hours per day every year at Chanonry compared to the Sutors, and in most years on fewer days each summer. There remains a seasonal pattern of occurrence with a peak in dolphin detections during the summer months, but at both sites dolphins were detected for >50% of days in all but 1 month at Sutors and 2 months at Chanonry. In addition, at Sutors there were similarly high number of days dolphins are detected throughout April to December (>80%). Unfortunately, PAM data are not available in this report for Tayside & adjacent waters. Therefore, although abundance estimates show that more dolphins have been using this area recently than the SAC we have no data on whether dolphins spend a similar amount of time in this area as they do in the SAC.

The third site attribute relates to overall trends in the east coast of Scotland dolphin population (Attribute 1.1.3). Monitoring to address this attribute requires photo-identification data to be collected from both within and outside the SAC. We reported population size from 2009 to 2022 when data were consistently collected both within the SAC and from Tayside & adjacent waters. Results indicate the east coast bottlenose dolphin population is increasing. This is potentially the result of increasing reproduction, and calf and juvenile survival. Between 2001 and 2022 there was an increase in the number of new calves identified in both the SAC and Tayside & adjacent waters and recent analyses also showed increasing trends in fecundity within the SAC (Cheney et al., 2019). In addition, no unusual observations in the frequency of strandings within the population were recorded and previous survival analyses found that there was likely an increase in juveniles within the population (Arso Civil et al., 2019a), and increase in early calf survival within the SAC (Cheney et al., 2019).

In May 2005, the original site condition monitoring assessment concluded that the condition of the population was “Unfavourable (no change)”. Subsequent analysis of monitoring data indicated that there was a higher probability that targets 1.1.1 and 1.1.2 were being met, and this was reflected in a revision of the condition status to “Unfavourable (recovering)” (Thompson et al., 2006). The internal report for 2005 to 2007 highlighted that there was significant inter-annual variation in the indicators being monitored, and it remained unclear to what extent this resulted from sampling variation or genuine biologically significant changes. Therefore, the condition status was not changed (Thompson et al., 2009). Subsequent reports suggested that despite inter-annual variability the number of dolphins using the SAC was stable; that the east coast dolphin population was increasing; and, although the proportion of the dolphin population that used the SAC had declined, that this was likely due to an overall increase in population size (Cheney et al., 2012, Cheney et al., 2014b, Cheney et al., 2018). As such, since the 2008 to 2010 site condition monitoring report (Cheney et al., 2012) all attributes for the bottlenose dolphin feature of the Moray Firth SAC have been met, and the condition status was revised and remained “Favourable (recovered)” (Cheney et al., 2012, Cheney et al., 2014b, Cheney et al., 2018).

Results from current reporting period show that the number of dolphins using the SAC has declined and suggests that there has been a slight decline in the proportion of the population using the SAC over the last six years. This could be due to further range expansion to the south along the east coast of Scotland and to other areas. Regardless of the reason, it is important that monitoring continues to assess whether this decline continues into the next reporting period. However, this report also found that the number of dolphins using the SAC was stable over the longer term and that over half the population use this area. In addition, passive acoustic monitoring demonstrated that, despite inter-annual and seasonal variation, dolphins were detected at one sample site in the SAC on almost all days from April to December. In addition, the east coast bottlenose dolphin population is still increasing. We therefore recommend that the condition status of the Moray Firth SAC is Favourable (maintained).

To support future site condition assessments, continued monitoring of both the Moray Firth SAC and coastal waters along the east coast of Scotland, particularly Tayside & adjacent waters, is crucial to detect changes in this protected area and the east coast population. Complementing this focussed data collection by integrating available citizen science sightings of known bottlenose dolphins will increase understanding of use of areas outside the Coastal East Scotland management unit. There are also opportunities to explore the recent decline within the SAC and investigate whether this is due to changing conditions in this area or improvements in other areas. Explicitly by focussing research on ecosystem quality, including stressors and drivers of population change. Surveillance of key habitat features (e.g. prey) and pressures (e.g. vessel activity) could indicate how these are driving changes in dolphins’ habitat use. Specifically, as vessel traffic within the SAC is expected to increase to support offshore energy developments, we highlight the potential for exploiting AIS data and broadband PAM to evaluate any impacts of this change in key dolphin hotspots. Also, we recommend exploring links between trends in key prey species (e.g. Marine Scotland’s time series of salmon abundance) and observed trends within bottlenose dolphin population parameters such as abundance, survival, and reproduction. Ultimately the development of an integrated population model which takes account of age and/or size structure would provide greater insights into how this dolphin population’s demographic parameters are responding to these changes in their habitat.

5. Conclusions

Estimates of the number of dolphins using the Moray Firth SAC continue to show inter-annual variability, and the number of dolphins using the SAC between 2001 and 2022 appears to be stable in the long term. However, during the current reporting period the number of dolphins using the SAC has declined. The proportion of the population using the SAC has also declined, although in most years over half of the population still use this area. This is likely due to an increase in population abundance, an increase in the number of dolphins using Tayside & adjacent waters, and the recent long-range movement of some individuals outside the SAC. The increase in the proportion of the population using Tayside & adjacent waters suggests that this area is becoming more important to this population.

Passive acoustic monitoring continues to show inter-annual variation in the amount of time dolphins spend at sample sites within the SAC, with a summer peak in occurrence. However, data show that certain areas of the SAC are used to a similar extent during summer, autumn and winter.

In summary, the quality of data available in this current report for completing the Site Attribute Table is high for attribute 1.1.1, 1.1.2 and 1.1.3. As a result of the findings of this report showing the long-term trend in the number of dolphins using the SAC is stable, the use of this protected area remains high and the east coast population is increasing, we recommend that the condition status of the Moray Firth SAC is Favourable (maintained).

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Annex 1 - Example raw data tables

This Appendix contains five tables of the raw data used in this project to produce estimates of the number of dolphins using the Moray Firth SAC, Tayside & adjacent waters, and the total population. Full tables are provided in electronic format. Only the first few rows of each table are displayed to illustrate the format of each file. In all cases, “-99” is an identifier for no data.

Surveys – containing basic information on the date and timing of surveys, with a unique “trip number” that links these data to those from any encounters with groups of dolphins during that survey.

Trip No	Date	University	Time start	Time end	No of encounters	No of pictures	No of Q3 picture
1630	05-May-17	UoA	06:01	12:30	7	359	83
1631	09-May-17	UoA	08:23	15:11	8	1232	427
1632	10-Sep-17	SMRU	12:30	16:22	3	501	84
1633	17-May-17	SMRU	08:22	14:52	2	157	49
1634	18-May-17	UoA	08:14	16:21	11	1623	531
1635	25-May-17	UoA	08:23	13:28	6	653	268
1636	25-May-17	SMRU	10:43	15:11	6	815	277
1637	02-Jun-17	UoA	09:47	16:19	4	905	286
1638	02-Jun-17	SMRU	11:28	16:24	5	654	251
1639	14-Jun-17	SMRU	10:10	17:16	8	247	46
1640	14-Jun-17	UoA	08:37	17:05	11	1194	409
1641	20-Jun-17	SMRU	08:24	15:36	2	598	81
1642	20-Jun-17	UoA	09:53	16:27	6	471	148
1643	26-Jun-17	UoA	07:47	15:06	10	1529	491
1644	04-Jul-17	SMRU	09:15	13:58	3	372	137

 

Encounters – containing information on the location of the start of the encounter, estimates of group size, and a unique “encounter number” that links these data with any photographs and sightings of individually recognisable dolphins.

Encounter	Frame	Side	Conf ID
3795	AU17-1630-007	L	1025
3795	AU17-1630-017	R	1113
3795	AU17-1630-022	R	1187
3795	AU17-1630-024	R	1113
3795	AU17-1630-035	R	1187
3795	AU17-1630-037	R	1025
3795	AU17-1630-038	R	580
3795	AU17-1630-042	R	1187
3795	AU17-1630-046	L	580
3795	AU17-1630-050	L	580
3795	AU17-1630-052	L	580
3795	AU17-1630-055	L	1187
3795	AU17-1630-056	L	580
3795	AU17-1630-058	L	1187
3795	AU17-1630-064	R	580

 

Pictures – containing information on all confirmed Grade 3 pictures with ID numbers the dolphin.

Year	Trip	L Marked	L Total	θ	R Marked	R Total	θ
2017	1630	6	11	0.54545	5	9	0.55556
2017	1631	15	30	0.5	21	43	0.48837
2017	1632	10	16	0.625	7	19	0.36842
2017	1633	3	6	0.5	2	6	0.33333
2017	1634	21	41	0.5122	19	40	0.475
2017	1635	11	25	0.44	9	17	0.52941
2017	1636	3	6	0.5	14	31	0.45161
2017	1637	10	27	0.37037	10	25	0.4
2017	1638	18	34	0.52941	13	29	0.44828
2017	1639	8	12	0.66667	5	10	0.5
2017	1640	19	41	0.46341	18	44	0.40909
2017	1641	5	7	0.71429	14	26	0.53846
2017	1642	8	11	0.72727	11	20	0.55
2017	1643	22	52	0.42308	18	49	0.36735
2017	1644	8	20	0.4	7	25	0.28

 

Annex 2 - Photo-identification catalogue

Example page of the east coast Scotland photo-identification catalogue including all the well-marked dolphins recorded during the reporting period.

Annex 3 - GIS project

The GIS Project “NatureScot2022.mpk” contains GPS derived tracks of all surveys conducted by the University of Aberdeen and University of St Andrews as well as locations of all encounters with bottlenose dolphins during these surveys between May and September 2017 to 2022.

The ArcMap Project includes a map of Great Britain with the UKSACs with layers for each University (e.g. UoA and SMRU). Each of these layers contains all the individual survey trip trails/tracks conducted in 2017 to 2022 (e.g. 2017). In addition, there are separate layers with the combined survey tracks for all the trips per year as lines (e.g. UoA_2017_Trip_Lines or SMRU_2017_Trip_Lines). There are layers containing all the bottlenose dolphin encounters in 2017 to 2022 (e.g. UoA_2017_BND_Encounters or SMRU_2017_BND_Encounters).

For the University of Aberdeen each survey track is also provided as a .dbf and shapefile labelled with trip number and the date of the trip is included in the attribute table. For the University of St Andrews, the survey tracks for each year are combined in an excel spreadsheet and shapefile labelled with the year, and the trip numbers and dates are included in the attribute table. Bottlenose dolphin encounters are grouped by University and by year and provided as an excel spreadsheet and shapefile for each year and in the attribute table there is information on each individual encounter. This information includes the trip and encounter number, date, latitude and longitude of the start of each encounter, and the best estimate of the number of dolphins in the encounter.

Site attribute table

Site	Reporting Category	Interest Feature	Interest level	Attribute	Target	Prescription	Result of Monitoring	Target met? (Y/N)
Moray Firth	1 Mammals	1.1 Bottlenose dolphin (Tursiops truncatus)	SAC	1.1.1 Number of individual dolphins using the SAC	1.1.1 A stable or increasing number of dolphins using the SAC.	Apply photo-identification and mark-recapture extrapolation techniques to annual observations.	Between 2001 and 2022, annual estimates of the number of dolphins using the SAC showed interannual variability ranging from 66 (95% CI: 57-76) to 136 (95% CI: 119-156). During the reporting period there was a significant decline in the number of dolphins using the SAC from 122 (95% CI: 111-134) in 2017 to 94 (95% CI: 84-106) in 2022. However, there was no evidence of any linear trend in the number of dolphins using the SAC over the longer term (2001-2022).	Y
-	-	-	-	1.1.2 Frequency of occurrence of dolphins within the SAC	1.1.2 Maintain or increase the level of use of the SAC.	Determine the probability of occurrence of dolphin groups at sample sites within the SAC.	The proportion of the population using the SAC has declined, but this is likely a result of the increase in the size of the east coast population, with over 50% of the population using the SAC in most years. Visual and passive acoustic monitoring data indicate site specific inter-annual and seasonal variation in the amount of time dolphins spend at sample sites within the SAC. The data show broadly similar patterns of use from 2008 to 2022 where dolphins occur at sites within the SAC on most days and for multiple hours per day between May to September, and for a similar extent in some autumn and winter months. However, PAM data suggests the use of the SAC may have slightly declined in this reporting period.	Y
-	-	-	-	1.1.3 Dolphin population trends	1.1.3 Maintain a stable or increasing bottlenose dolphin population.	Evaluate trends in population size using all available data. Evaluate other anecdotal data sources which may suggest changes in birth or mortality rates within the population.	A robust design mark-recapture model of photo-identification data collected from the SAC and Tayside & adjacent waters again suggests that the bottlenose dolphin population on the east coast of Scotland is increasing. There was a significant increase in the number of calves born in both the SAC and Tayside & adjacent waters. There were no unusual observations recorded in terms of the frequency of strandings within the population.	Y