Mark‐resight estimates of seasonal variation in harbor seal abundance and site fidelity

1. The impact of anthropogenic activity associated with marine renewable developments on harbour seals (Phoca vitulina) was investigated using controlled disturbance trials.2. Hauled-out seals were approached by boat until all seals had entered the water, and this was repeated approximately every 3 days (weather permitting). The time taken for seal counts to return to pre-disturbance levels was determined by monitoring haulout sites using time-lapse photography.3. Mean post-disturbance counts of hauled-out seals returned to 52% (95% confidence interval [CI] 35-69%) of pre-disturbance counts within 30 min. However, mean counts only returned to 94% (95% CI 55-132%) of pre-disturbance counts after 4 hr.4. Eight seals were tagged with Global Positioning System phone tags to provide information on haulout location and at-sea movements, allowing investigation of how disturbance may influence haulout site choice and seal distribution.5. Telemetry-tagged seals displayed a high degree of haulout site fidelity. Disturbance trials did not have a significant effect on the probability of seals moving to a different haulout site.6. When seals hauled out again within the same low-tide period after disturbance trials, the proportion of time spent hauled out was high, indicating that when seals are motivated to haul out they will do so despite past disturbance. Motivation to haul out more on disturbance trial days was not linked to a cyclic pattern of hauling out more over consecutive low-tide periods. 7. As there was no large-scale redistribution after disturbance, we suggest that monitoring effort to determine the effects of short-term increases in levels of disturbance caused by boat activity can be spatially localized. However, where disturbance is likely to be longer term or impact on important haulout sites for breeding and/or moulting, monitoring may be required over a larger geographical area.

Section: Discussionsupporting

confidence: 92%

Post‐disturbance haulout behaviour of harbour seals

Paterson

Russell

et al. 2019

“…However, surveys during the breeding season in both the Moray Firth (Cordes & Thompson, 2015) and The Wash and South East England (SCOS, 2017) show that the breeding-season distribution is similar to that of the moult. However, surveys during the breeding season in both the Moray Firth (Cordes & Thompson, 2015) and The Wash and South East England (SCOS, 2017) show that the breeding-season distribution is similar to that of the moult.…”

Section: Seasonal Timingmentioning

confidence: 99%

The status of harbour seals (Phoca vitulina) in the UK

Thompson

Duck

Morris

et al. 2019

1. Estimates of population size and trends are essential for effective conservation and management of wildlife populations. For harbour seals (Phoca vitulina), these data are required to fulfil statutory reporting obligations under national and international regulations.2. Aerial survey counts of harbour seals hauled out during their annual moult were used to estimate population sizes and trends at UK, regional (seal management unit, SMU) and local (Special Area of Conservation, SAC) scales.3. Results indicate that the current UK harbour seal population is similar to estimates from the late 1990s, but there were significant declines in some subpopulations and increases in others. 4. Fitted trends suggest that the UK harbour seal population can be divided into three geographically coherent groups: South-east populations (South-East and North-East England SMUs) have shown continuous increases punctuated by phocine distemper virus epidemics in 1988 and 2002; north-east populations (East Scotland, Moray Firth, North Coast and Orkney, and Shetland SMUs) have declined since the late 1990s; north-west populations (West Scotland, Western Isles, and South-West Scotland SMUs) have remained stable or increased. Similar geographical population substructure is evident in recent population genetics results. 5. Trends within SACs generally match SMU trends since 2002. Of the nine SACs designated for harbour seals, four declined (in East Scotland, Moray Firth, and North Coast and Orkney SMUs), four remained stable (in Shetland and West Scotland SMUs), and one increased (in South-East England SMU).6. Large changes in relative abundance have resulted from differences in regional trends. For example, in 1996-1997 the West Scotland and North Coast and Orkney SMUs each held~27% of the Great Britain population but now hold 50% and~4% respectively; in 1980, the South-East England SMU population was~50% that of the Wadden Sea population, but by 2016 it was equivalent to <20% of the Wadden Sea count.

“…There is evidence of strong fidelity to moulting and breeding sites (Bowen, Ellis, Iverson, & Boness, 2003;Cordes & Thompson, 2015;Härkönen & Harding, 2001), providing opportunities to observe and count individuals during these two important periods in the annual cycle (Thompson, Tollit, Wood, et al, 1997). There is evidence of strong fidelity to moulting and breeding sites (Bowen, Ellis, Iverson, & Boness, 2003;Cordes & Thompson, 2015;Härkönen & Harding, 2001), providing opportunities to observe and count individuals during these two important periods in the annual cycle (Thompson, Tollit, Wood, et al, 1997).…”

Section: Methodsmentioning

confidence: 99%

“…Outside this period shooting numbers were treated as missing data and estimated during model-fitting (Matthiopoulos et al, 2013). In 2009, a mark-recapture estimate for Loch Fleet (Cordes & Thompson, 2015) was scaled up to the full region using aerial survey data. In 1993, an estimate was based on onshore counts, corrected using telemetry data to estimate the proportion of animals in the water (Thompson, Tollit, Corpe, Reid, & Ross, 1997).…”

Section: Harbour Seal Datamentioning

confidence: 99%

Use of state‐space modelling to identify ecological covariates associated with trends in pinniped demography

Caillat

Cordes

Thompson

et al. 2019

1. Identifying and understanding ecological drivers that influence wildlife populations is challenging but critical for conservation. This typically requires integrating longterm data on both the population and potential drivers within statistical models that are suitable for analysing these complex relationships. State-space models offer one method for integrating such data. Once implemented within a Bayesian framework, these analyses can control for multifactorial influences on populations, allowing one to extract otherwise undetectable correlations between the environment and the underlying, inferred demography.2. In the Moray Firth, Scotland, harbour seals have been counted annually for 30 years . A Bayesian state-space model was used to explore whether patterns in vital rates were correlated to changes in prey abundance, inter-specific competition (grey seal abundance), environmental variables [the North Atlantic Oscillation (NAO) and sea-surface temperature], or level of biotoxins (saxitoxin and domoic acid) in the Moray Firth waters.3. The credible interval of the posterior distributions of three of these covariate coefficients (sandeel proxy, NAO and grey seal abundance) suggested that there was a relationship between those covariates and vital rates. Both the sandeel proxy and NAO showed a positive correlation with fecundity, whereas grey seal abundance had a negative impact on pup survival.4. This work demonstrates how an integrated state-space modelling approach can bring together diverse data sets and point to important interactions with prey, and with other predators in the system. This suggests that the wider-scale management of UK harbour seal populations with their contrasting temporal trends needs to account for variation in the marine ecosystem at appropriate spatial scales, in line with current policy concerning spatial planning in the marine environment.