Patterns of space use in sympatric marine colonial predators reveals scales of spatial partitioning

E.L.J. and D.J.F.R. were funded under Scottish Government grant MMSS001/01. D.J.F.R. was funded by the UK Department of Energy and Climate Change (DECC) as part of their Offshore Energy Strategic Environmental Assessment programme. S.S. was part-funded by the EU MYFISH project.Species distribution maps can provide important information to focus conservation efforts and enable spatial management of human activities. Two sympatric marine predators, grey seals Halichoerus grypus and harbour seals Phoca vitulina have overlapping ranges on land and at sea but contrasting population dynamics around Britain: whilst grey seals have generally increased, harbour seals have shown significant regional declines. We analysed two decades of at-sea movement data and terrestrial count data from these species to produce high resolution, broad-scale maps of distribution and associated uncertainty to inform conservation and management. Our results showed that grey seals use offshore areas connected to their haul-out sites by prominent corridors and harbour seals primarily stay within 50km of the coastline. Both species show fine-scale offshore spatial segregation off the east coast of Britain and broad-scale partitioning off western Scotland. These results illustrate that for broad-scale marine spatial planning, the conservation needs of harbour seals (primarily inshore, the exception being selected offshore usage areas) are different from those of grey seals (up to 100km offshore and corridors connecting these areas to haul-out sites). More generally, our results illustrate the importance of detailed knowledge of marine predator distributions to inform marine spatial planning; for instance, spatial prioritisation is not necessarily the most effective spatial planning strategy even when conserving species with similar taxonomy.Peer reviewe

Sympatric seals, satellite tracking and protected areas : habitat-based distribution estimates for conservation and management

Analysis was funded by the UK Government Department for Business, Energy and Industrial Strategy (BEIS; OESEA-16-76/OESEA-17-78) with support from the Natural Environment Research Council (NERC; INSITE Phase II NE/T010614/1 EcoSTAR), EU INTERREG (MarPAMM), and the Scottish Government (MMSS/002/15). DJFR’s contribution was funded by NERC National Capability Funding (NE/R015007/1). WJG was supported by INSITE Phase I (MAPS). Telemetry tags and their deployment were funded in the UK by BEIS (and previous incarnations), NERC, Marine Scotland, Scottish Government, NatureScot, SMRU, SMRU Instrumentation Group, Marine Current Turbines, Ørsted, the Met Office, the Zoological Society of London (ZSL), the Crown Estate, Highlands & Islands Enterprise, Moray Firth Renewables Limited (MORL), Beatrice Offshore Windfarm Limited (BOWL), SITA Trust, BBC Wildlife Fund and the Hampshire & Isle of Wight Wildlife Trust. Tags and their deployment in Ireland were funded by Inland Fisheries Ireland, the Department of Communications, Marine and Natural Resources, the Higher Education Authority of Ireland, the National Geographic Society, the Department of Agriculture, Food and the Marine, and the National Parks and Wildlife Service. UK aerial surveys conducted by SMRU were funded by NERC (NE/R015007/1), NatureScot, the Department for Agriculture, Environment and Rural Affairs (Northern Ireland), Marine Current Turbines, Marine Scotland, Natural England, and Scottish Power. Aerial surveys in Ireland were funded by the Department for Tourism, Culture, Arts, Gaeltacht, Sport and Media.Marine predator populations are crucial to the structure and functioning of ecosystems. Like many predator taxa, pinnipeds face an increasingly complex array of natural and anthropogenic threats. Understanding the relationship between at-sea processes and trends in abundance at land-based monitoring sites requires robust estimates of at-sea distribution, often on multi-region scales. Such an understanding is critical for effective conservation management, but estimates are often limited in spatial extent by spatial coverage of animal-borne tracking data. Grey (Halichoerus grypus) and harbour seals (Phoca vitulina) are sympatric predators in North Atlantic shelf seas. The United Kingdom (UK) and Ireland represents an important population centre for both species, and Special Areas of Conservation (SACs) are designated for their monitoring and protection. Here we use an extensive high-resolution GPS tracking dataset, unprecedented in both size (114 grey and 239 harbour seals) and spatial coverage, to model habitat preference and generate at-sea distribution estimates for the entire UK and Ireland populations of both species. We found regional differences in environmental drivers of distribution for both species which likely relate to regional variation in diet and population trends. Moreover, we provide SAC-specific estimates of at-sea distribution for use in marine spatial planning, demonstrating that hotspots of at-sea density in UK and Ireland-wide maps cannot always be apportioned to the nearest SAC. We show that for grey seals, colonial capital breeders, there is a mismatch between SACs (where impacts are likely to be detected) and areas where impacts are most likely to occur (at sea). We highlight an urgent need for further research to elucidate the links between at-sea distribution during the foraging season and population trends observed in SACs. More generally, we highlight that the potential for such a disconnect needs to be considered when designating and managing protected sites, particularly for species that aggregate to breed and exhibit partial migration (e.g. grey seals), or spatial variation in migration strategies. We demonstrate the use of strategic tracking efforts to predict distribution across multiple regions, but caution that such efforts should be mindful of the potential for differences in species-environment relationships despite similar accessible habitats.Publisher PDFPeer reviewe

Phenological sensitivity to climate across taxa and trophic levels

Differences in phenological responses to climate change among species can desynchronise ecological interactions and thereby threaten ecosystem function. To assess these threats, we must quantify the relative impact of climate change on species at different trophic levels. Here, we apply a Climate Sensitivity Profile approach to 10,003 terrestrial and aquatic phenological data sets, spatially matched to temperature and precipitation data, to quantify variation in climate sensitivity. The direction, magnitude and timing of climate sensitivity varied markedly among organisms within taxonomic and trophic groups. Despite this variability, we detected systematic variation in the direction and magnitude of phenological climate sensitivity. Secondary consumers showed consistently lower climate sensitivity than other groups. We used mid-century climate change projections to estimate that the timing of phenological events could change more for primary consumers than for species in other trophic levels (6.2 versus 2.5–2.9 days earlier on average), with substantial taxonomic variation (1.1–14.8 days earlier on average)

An approximate Bayesian method applied to estimating the trajectories of four British grey seal (Halichoerus grypus) populations from pup counts.

1. For British grey seals, as with many pinniped species, population monitoring is implemented by aerial surveys of pups at breeding colonies. Scaling pup counts up to population estimates requires assumptions about population structure; this is straightforward when populations are growing exponentially, but not when growth slows, since it is unclear whether density dependence affects pup survival or fecundity. 2. We present an approximate Bayesian method for fitting pup trajectories, estimating adult population size and investigating alternative biological models. The method is equivalent to fitting a density dependent Leslie matrix model, within a Bayesian framework, but with the forms of the density dependent effects as outputs rather than assumptions. 3. This approach requires fewer assumptions than the state space models currently used, and produces similar estimates. The simplifications made the models easier to fit, reducing their computational intensity and allowing regional differences in demographic parameters to be considered. 4. The approach is not restricted to situations where only a single component of the population is observable, but, particularly in those cases, provides a practical method for extracting information from limited datasets. 5. We discuss the potential and limitations of the method and suggest that this approach provides a useful tool for at least the preliminary analysis of similar datasets.Publisher PDFPeer reviewe

Charting Progress 2. Chapter 3. Healthy and Biologically Diverse Seas:Seals

3.5.1 Key pointsi. IntroductionTwo species of seal live and breed in the UK.About 36% of the world’s population of greyseals reside in the UK; almost 90% of these arein Scotland. About 4% of the world’s populationor 30% of the European subspecies of harbour(also known as common) seal are found in theUK with 80% of these in Scotland. Althoughboth species can be seen all round the UKcoast, they are considerably more abundant insome areas than others. Changes in local sealpopulation size and distribution may be relatedto changes in the marine environment. Underthe Conservation of Seals Act 1970, the NaturalEnvironment Research Council has a statutoryobligation to provide the UK Governmentwith ‘…scientific advice on matters relatedto the management of seal populations’. Amajor component of this advice is up-to-dateinformation on the size and distribution of UKseal populations. Both grey and harbour sealswere given protection under the Conservationof Seals Act 1970 and under the EU HabitatsDirective. In Scotland, the Conservation of SealsAct has been replaced by the Marine (Scotland)Act 2010, which has extended seal protectionmeasures.Five species of Arctic seal occasionally visit theUK coast.ii. How has the assessment beenundertaken?UK seal populations are monitored by differentorganisations using a variety of techniques. Greyseal populations are assessed through estimationof pup production at traditional breedingcolonies. Pup production is monitored annuallyat colonies that contribute an estimated 85% ofpups born in the UK. Most colonies are surveyedusing aerial photography, others through groundcounting. The great majority of colonies in Walesand south-west England are not included as theyare extremely difficult to survey and cannot besurveyed frequently because grey seals breed incaves or on beaches at the foot of remote cliffs.Harbour seal populations are also monitoredmostly by aerial survey, although at a differenttime of their annual cycle since they do notaggregate when breeding. In south-east Englandand parts of Scotland they are monitoredannually. In the remainder of Scotland they aremonitored at about four to five year intervals. InNorthern Ireland, counts are monthly. Grey sealpup production has been monitored since theearly 1960s; harbour seals have been monitoredsince the late 1980s. Both grey and harbourseals are probably more numerous now thanin the historical past, when they were locallyhunted and/or harvested.iii. Current and likely future status of sealpopulationsIn the UK, grey seals are considerably morenumerous than harbour seals. After decadesof increase, total grey seal pup productionappears to be levelling off in the UK and is nowincreasing at only a small number of colonies.Harbour seal numbers have declined dramaticallyin Shetland, Orkney and the east coast ofScotland since 2001, by over 50%. There hasbeen a smaller decline in the Outer Hebrides butnumbers on the west coast of Scotland haveremained relatively stable. The causes of thesedeclines are not yet known. Two outbreaksof phocine distemper virus (PDV) affected theharbour seal population in eastern England with50% dying in 1988 and 22% dying in 2002.In marked contrast to European harbour sealpopulations which showed an immediate andrapid recovery, recovery in the eastern England508 Healthy and Biologically Diverse Seaspopulation after the 1988 outbreak was delayedfor three years and has yet to begin followingthe 2002 outbreak. PDV outbreaks are likelyto recur in the future but it is not possible topredict the proportion of the population thatmight be affected, which populations are mostvulnerable (besides eastern England) or preciselywhen outbreaks will occur.iv. What is driving change?The previous increase in grey seal pupproduction is at least in part due to the increasedavailability of breeding sites following theabandonment of human settlements on remoteislands, including the automation of lighthouses.The current reduction in the rate of increaseis thought to be due to density dependentfactors affecting the population as a whole. It isnot yet clear whether factors affecting survivalare more important than factors affectingfecundity. Causes of the declines in harbour sealpopulations in north and east Scotland remainunclear. Contributing factors could be eithernatural or anthropogenic or both and include:competition with grey seals, predation by killerwhales, unregulated shooting and declines inimportant prey species (e.g. sandeels).It is difficult to predict future trends in UKseal populations with certainty. Grey seal pupproduction appears to be stabilising, so thegrey seal population is likely to stabilise overthe next decade or so. It is far harder to predictwhat harbour seal populations in north and eastScotland will do, given recent declines and thelack of any obvious cause(s). In east England,PDV outbreaks are likely to recur in the future.The observed recent declines in north and eastScotland populations are not related to theoutbreak of PDV in 2002 as none of the harbourseals sampled in areas of decline had beenexposed to PDV.v. What are the uncertainties?While there are uncertainties in estimatingthe size of the total grey seal population fromthe annual estimates of pup production, theprocedures used to estimate pup productionare considered to be robust. Through the1970s, 1980s and early 1990s, seal researchwas focussed heavily on grey seals, withharbour seals only coming to attention in1988, after the first PDV outbreak. With therecently documented declines, harbour sealsare becoming increasingly important. Most ofthe pressure assessment is based on expertjudgement but it is difficult to assess the effectsof different pressures on seal populations. Thisapplies to both species.vi. Forward lookThe Scottish Government and Scottish NaturalHeritage have funded a number of projectsinvestigating the declines in harbour seals innorth and east Scotland. Increasing renewableenergy production may impact marine mammalpopulations, requiring additional information incertain areas. Harbour seal monitoring frequencyin Scotland is infrequent compared with greyseal monitoring