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Many ecological studies rely on count data and involve manual counting of objects of interest, which is time-consuming and especially disadvantageous when time in the field or lab is limited. However, an increasing number of works uses digital imagery, which opens opportunities to automatise counting tasks. In this study, we use machine learning to automate counting objects of interest without the need to label individual objects. By leveraging already existing image-level annotations, this approach can also give value to historical data that were collected and annotated over longer time series (typical for many ecological studies), without the aim of deep learning applications. We demonstrate deep learning regression on two fundamentally different counting tasks: (i) daily growth rings from microscopic images of fish otolith (i.e., hearing stone) and (ii) hauled out seals from highly variable aerial imagery. In the otolith images, our deep learning-based regressor yields an RMSE of 3.40 day-rings and an $$R^2$$ R 2 of 0.92. Initial performance in the seal images is lower (RMSE of 23.46 seals and $$R^2$$ R 2 of 0.72), which can be attributed to a lack of images with a high number of seals in the initial training set, compared to the test set. We then show how to improve performance substantially (RMSE of 19.03 seals and $$R^2$$ R 2 of 0.77) by carefully selecting and relabelling just 100 additional training images based on initial model prediction discrepancy. The regression-based approach used here returns accurate counts ($$R^2$$ R 2 of 0.92 and 0.77 for the rings and seals, respectively), directly usable in ecological research.

To support sustainable management of apex predator populations, it is important to estimate population size and understand the drivers of population trends to anticipate the consequences of human decisions. Robust population models are needed, which must be based on realistic biological principles and validated with the best available data. A team of international experts reviewed age-structured models of North Atlantic pinniped populations, including Grey seal (Halichoerus grypus), Harp seal (Pagophilus groenlandicus), and Hooded seal (Cystophora cristata). Statistical methods used to fit such models to data were compared and contrasted. Differences in biological assumptions and model equations were driven by the data available from separate studies, including observation methodology and pre-processing. Counts of pups during the breeding season were used in all models, with additional counts of adults and juveniles available in some. The regularity and frequency of data collection, including survey counts and vital rate estimates, varied. Important differences between the models concerned the nature and causes of variation in vital rates (age-dependent survival and fecundity). Parameterisation of age at maturity was detailed and time-dependent in some models and simplified in others. Methods for estimation of model parameters were reviewed and compared. They included Bayesian and maximum likelihood (ML) approaches, implemented via bespoke coding in C, C++, TMB or JAGS. Comparative model runs suggested that as expected, ML-based implementations were rapid and computationally efficient, while Bayesian approaches, which used MCMC or sequential importance sampling, required longer for inference. For grey seal populations in the Netherlands, where preliminary ML-based TMB results were compared with the outputs of a Bayesian JAGS implementation, some differences in parameter estimates were apparent. For these seal populations, further investigations are recommended to explore differences that might result from the modelling framework and model-fitting methodology, and their importance for inference and management advice. The group recommended building on the success of this workshop via continued collaboration with ICES and NAMMCO assessment groups, as well as other experts in the marine mammal modelling community. Specifically, for Northeast Atlantic harp and hooded seal populations, the workshop represents the initial step towards a full ICES benchmark process aimed at revising and evaluating new assessment models. Publisher PDF

Climate warming in the Arctic has led to warmer and earlier springs, and as a result, many food resources for migratory animals become available earlier in the season, as well as become distributed further northwards. To optimally profit from these resources, migratory animals are expected to arrive earlier in the Arctic, as well as shift their own spatial distributions northwards. Here, we review literature to assess whether Arctic migra-tory birds and mammals already show shifts in migration timing or distribution in response to the warming climate. Distribution shifts were most prominent in marine mammals, as expected from observed northward shifts of their resources. At least for many bird species, the ability to shift distributions is likely constrained by available habitat further north. Shifts in timing have been shown in many species of terrestrial birds and ungulates, as well as for polar bears. Within species, we found strong variation in shifts in timing and distributions between populations. Ou r review thus shows that many migratory animals display shifts in migration timing and spatial distribution in reaction to a warming Arctic. Importantly, we identify large knowledge gaps especially concerning distribution shifts and timing of autumn migration, especially for marine mammals. Our understanding of how migratory animals respond to climate change appears to be mostly limited by the lack of long-term monitoring studies.

This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 746602. GA and SB have been partly funded by Gemini Wind park and the NWO (project ALWPP.2017.003). Understanding why animals move as they do when searching for resources is a central question in ecology, and a prerequisite for the development of predictive process-based models for conservation and management. Many species are central-place foragers (CPF). While several models for CPFs have been proposed, they often assume well-defined return rules to the focal point (like breeding). For some CPFs, however, the decisions to return to central sites are governed by multiple interactions between environmental and physiological factors. We present AgentSeal, a behaviour- and physiology-based, spatially explicit, agent-based model. We use harbour seals, a marine CPF, as a case study and focus on individuals outside their breeding and moulting seasons to capture general fine- and large-scale movements and drivers behind CPF. We model movement decisions based on optimal foraging strategy, cognitive and physiological processes in a realistic landscape, coupled with realistic prey distribution and tuned to a range of behavioural and physiological patterns observed at different scales and levels of organisation (pattern-orientated modelling, POM). The model can reproduce energetic, movement and other behavioural patterns such as net energy balance, at-sea and on land site fidelity, daily activity budgets and trip extents. The model reveals the crucial elements needed to model return-trips of CPFs including movement characteristics that vary as a function of local environmental conditions, cognitive mapping of foraging areas as points of attraction in subsequent foraging trips, and physiological requirements defining switches between resting and foraging. We discuss potential applications and extensions of the model, including investigations of fundamental questions in foraging ecology: how spatial distribution and aggregation of resources affect movement of marine CPFs; what are the main drivers behind their at-sea site-fidelity to foraging patches? We also discuss applied objectives such as improving our understanding of population-level consequences of anthropogenic disturbances and ultimately evolving AgentSeal into a practical management tool. Publisher PDF

Marine Spatial Planning (MSP) is a relatively new approach to ocean management and has been widely implemented worldwide. Ideally, MSP should be established as a public process that analyzes and distributes human activities across space and time to achieve ecological, economic and social goals, which historically have been accomplished exclusively in the political arena. However, in most cases MSP seems to be driven primarily by economic interests rather than by sociocultural goals. In this paper, we discuss how integrating the missing sociocultural layers into MSP can help to reduce governance rigidity, promote adaptability in decision-making, support environmental justice, and improve MSP acceptance and uptake. In particular, we focus on identifying possible points of connection between MSP and frameworks based on social-ecological system theory, including co-management and other democratic and empowering alternatives. We conclude by proposing a new definition of the MSP process that is more inclusive, and mindful of users’ rights and sociocultural objectives. If we bridge the gap between the dominant economic rhetoric and a de facto sociocultural-ecological system approach, we are likely to improve the chances of the MSP process succeeding on both the human and nature fronts. Central place foragers often segregate in space, even without signs of direct agonistic interactions. Using parsimonious individual-based simulations, we show that for species with spatial cognitive abilities, individual-level memory of resource availability can be sufficient to cause spatial segregation in the foraging ranges of colonial animals. The shapes of the foraging distributions are governed by commuting costs, the emerging distribution of depleted resources, and the fidelity of foragers to their colonies. When colony fidelity is weak and foragers can easily switch to colonies located closer to favorable foraging grounds, this leads to space partitioning with equidistant borders between neighboring colonies. In contrast, when colony fidelity is strong—for example, because larger colonies provide safety in numbers or individuals are unable to leave—it can create a regional imbalance between resource requirements and resource availability. This leads to nontrivial space-use patterns that propagate through the landscape. Interestingly, while better spatial memory creates more defined boundaries between neighboring colonies, it can lower the average intake rate of the population, suggesting a potential trade-off between an individual’s attempt for increased intake and population growth rates. space partitioning, public information, animal movement, species distribution, animal tracking, central place foraging

Dit syntheserapport richt zich op de ecologische situatie kort na de aanleg van suppletie (T1) waarvoor in juni 2019 een zandspiering en in september 2019 een benthosbemonstering is uitgevoerd. De voor- en na-situatie worden met elkaar vergeleken om inzicht te krijgen in de impact van de pilotsuppletie. De veldgegevens zijn aangevuld met literatuurgegevens en data van vogels en zeehonden uit andere studies. Met als doel het beantwoorden van de onderzoeksvragen: Is de verspreiding van benthische habitats en benthische soortensamenstelling in de T1-bemonstering vergelijkbaar met het patroon dat is gevonden tijdens de T0-bemonsteringen; en is de suppletie van invloed geweest? Wat is de samenstelling van de bodemvisgemeenschap in de buitendelta van het Amelander Zeegat ten opzichte van de T0 en is de suppletie hierop van invloed geweest? Zijn er vogelsoorten waarvoor de buitendelta van het Amelander Zeegat een belangrijk rust- en of foerageergebied vormt en zo ja, is er een relatie tussen de verspreiding over en het gebruik door vogels van de buitendelta en specifieke onderdelen van de buitendelta en is de suppletie hierop van invloed geweest? Vormen de buitendelta’s belangrijke foerageergebieden voor de grijze zeehond, de gewone zeehond en de bruinvis en zo ja, is er dan een relatie tussen het gebruik als foerageergebied en specifieke onderdelen van de buitendelta en is de suppletie hierop van invloed geweest?

Begin januari 2019 heeft het containerschip MSC ZOE door een storm meer dan 300 containers verloren ten noorden van de Waddeneilanden. De verloren containers waren beladen met een variatie aan goederen, waaronder ook plastic onderdelen en plastic pellets (basismateriaal voor de plasticindustrie). Om een eerste indruk te krijgen van mogelijk overlast die zeehonden kunnen hebben ondervonden van de verloren lading, is de doodsoorzaak en het verteringsstelsel van vijftien dood aangespoelde zeehonden onderzocht. Ook is er gekeken naar de geregistreerde strandingen van dode dieren in Noord-Nederland, door Ecomare, EHBZ en RTZ. Het aantal gemelde strandingen van dode gewone en grijze zeehonden is toegenomen in 2019, het jaar na het incident met de MSC ZOE. De strandingsgegevens worden niet nationaal beheerd waardoor er fouten, zoals duplicaten en inconsequente leeftijdscategorieën zijn toegewezen. Daarnaast is in deze strandingsgegevens geen correctie voor de groei van de zeehondenpopulatie toegepast. Twee van de vijftien zeehonden zijn waarschijnlijk omgekomen doordat deze in aanraking gekomen zijn met een voorwerp in het water. Of het een voorwerp betreft dat afkomstig is geweest van de MSC ZOE, was niet te achterhalen. Daarnaast kan, door het ontbreken van een monitoringsprogramma, niet achterhaald worden of de sterfte van zeehonden verhoogd is ten opzichte van voor het incident. In het verteringsstelsel van de zeehonden zijn geen plastics aangetroffen die direct of via hun dieet zijn binnengekomen. Van de vissoorten, waarvan resten gevonden zijn in de magen en darmen, is in literatuur te vinden dat daar plastics kunnen worden aangetroffen. Op basis van deze gegevens is geen indicatie gevonden dat zeehonden overlast hebben ondervonden van de verloren lading van de MSC ZOE. Daarbij moeten drie kanttekeningen gemaakt worden: 1) Vijftien zeehonden is een te laag aantal om harde conclusies aan te verbinden. 2) Een nationaal gecontroleerd en gemanaged registratiesysteem voor dode zeehonden ontbreekt, en het is voor deze maar ook voor volgende projecten raadzaam om hierin te investeren. 3) Door het ontbreken van een monitoringsprogramma voor het achterhalen van de doodsoorzaak van overleden zeehonden en het bekijken van de hoeveelheid plastics, is niet te zeggen of de bevindingen afwijken van normaal.

Common seals in the Wadden Sea areas of the Netherlands, Lower Saxony, Schleswig-Holstein and Denmark are monitored through trilaterally coordinated aerial surveys. The flights are scheduled during the seal whelping and moulting seasons (i.e. June/early July and August, respectively), when the highest numbers of hauling out seals can be registered.

In 2012 the coordinated aerial surveys for the harbour seal counts of the entire Wadden Sea were performed as in previous years (started in 1975). The counts are synchronised between the three Wadden Sea countries: Denmark, Germany and the Netherlands in order to obtain a single estimate for the number of harbour seals in the entire Wadden Sea, and the number of pups born. Seals are counted when hauling out on sandbanks and counts are carried out when low tide occurs during midday.

In the Netherlands, dedicated aerial surveys have been carried out since 2002. From 2006 onwards, aerial surveys of grey seals have been synchronized and coordinated trilaterally within the Wadden Sea. However, this only applies to Germany and the Netherlands as no breeding population of grey seals is present in the Danish part of the Wadden Sea. During summer harbour seal counts, 40 grey seals were observed in Denmark. Like in former years, two surveys are carried out during the moult (March-April). These are supplemented by several aerial or boat counts during the pupping season (November-January). On Helgoland (Germany), surveys are carried out from land.

In the German and Dutch Wadden Sea several aerial and boat counts are conducted during the pupping season (November-January) whilst on Helgoland (Germany), surveys are carried out from land. Two dedicated grey seal aerial surveys are carried out during the moult (March-April). In the Danish Wadden Sea grey seals are only counted during the summer counts for harbour seals.

Since the beginning of the trilateral cooperation of the seal experts in 1991, grey seal numbers have grown significantly and grey seals are considered an important part of the biodiversity of the Wadden Sea. From 2006 onwards, aerial surveys of grey seals have been synchronized and coordinated trilaterally within the Wadden Sea. Despite the apparent growth in numbers in Denmark to a maximum of 57 animals counted in summer, despite the observation of pups, still, no births have been documented there. The pups could have come from the German colonies Dedicated grey seals surveys are only carried out in Germany and the Netherlands. Two aerial surveys are conducted during the moult (March-April) and several aerial or boat counts are conducted during the pupping season (November-January). In Helgoland (Germany), surveys are carried out from land.

In 2010 the coordinated aerial surveys for the harbour seal counts of the Wadden Sea were performed as usual. The counts are synchronised between the three Wadden Sea countries: Denmark, Germany and the Netherlands in order to obtain a single estimate for the size of the entire Wadden Sea population, and the number of pups born. As seals are counted when hauling out on sandbanks, counts are carried out when low tide occurs during midday.

In 2011 the coordinated aerial surveys for the harbour seal counts of the Wadden Sea were performed as usual. The counts are synchronised between the three Wadden Sea countries: Denmark, Germany and the Netherlands in order to obtain a single estimate for the size of the entire Wadden Sea population, and the number of pups born. As seals are counted when hauling out on sandbanks, counts are carried out when low-tide occurs during midday.

Surveys of gray seals (Halichoerus grypus) during the molt period, when they are abundant on land, can be used to monitor changes in population size, but accurate interpretation of results requires an understanding of the molt process and how it may vary between years. This study investigates variability in onset (start date) and duration of visible molt by gray seals in the Wadden Sea, and the influence of environmental conditions on the onset. Molt was monitored in nine captive seals and observed molt phases were applied to wild seals over seven annual molt periods between 2004 and 2010, monitored using aerial photography. The onset of visible molt varied significantly between years, for example it differed 28 d between 2008 and 2009. Model selection by AIC retained one environmental variable that correlated with molt onset; however, its effect was inconsistent within the molt season and did not explain some of the apparent observed annual variation. Hence, the main causes of interannual variability in the onset of molt remain unclear and warrant further study. Researchers should account for annual variability in the onset of molt when interpreting survey results based on molt counts.

In dit syntheserapport wordt een overzicht gegeven van de resultaten van de T0-metingen (2017 en 2018) aan benthos en zandspiering in het Amelander zeegat en de daarin gelegen suppletielocatie.

Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels, and may again act as a top-down regulatory force on marine ecosystems. Also the harbour seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960’s, and the current number ∼38,000 is close to the historic population size. Here we estimate the impact of the harbour seal predation on the fish community in the Wadden Sea and nearby coastal waters.Fish remains in faecal samples and published estimates on the seal’s daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey.Harbour seals from the Dutch Wadden Sea fed predominantly on demersal fish, e.g. flatfish species (flounder, sole, plaice, dab), but also sandeel, cod and whiting. Total fish biomass in the Wadden Sea was insufficient to sustain the estimated prey consumption of the entire seal population year-round. This probably explains why seals also acquire prey further offshore in the adjacent North Sea, only spending 13% of their diving time in the Wadden Sea. Still, seal predation was estimated to cause an average annual mortality of 43% and 60% on fish in the Wadden Sea and adjacent coastal zone, respectively. There were however large sources of uncertainty in the estimate, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species.Our estimate suggested a considerable top-down control by harbour seals on demersal fish. However predation by seals may also alleviate density-dependent competition between the remaining fish, increasing fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could potentially become an important component in the functioning of shallow coastal systems.

Though it seems unlikely that marine mammals, including seals suffer at a large scale from direct mortality caused by the construction or operation of windfarms at sea, they are likely to be affected by disturbance and habitat alterations.In 2014, Luchterduinen windfarm was constructed in the Dutch coastal zone south west of IJmuiden and the permit (WV/2009-1229) requested monitoring with respect to both harbour and grey seals. Two main questions were formulated:1. How do seals use the coastal zone? The aim was to gain insight in harbour and grey seal movement routes along the Dutch North Sea coastal zone (between the Wadden Sea and the Delta region).2. What is the impact of Luchterduinen on seals? (with a focus on the impact of piling).This rapport discusses the results of the harbour seal studies. The initial monitoring (T0-T1; 2013-2015) based on a series of studies on the movements and habitat use of harbour seals deployed in spring (March), was timed in relation to the construction (2014) and operation of the windfarm. These studies were evaluated after T1 (in 2016). It was concluded that by limiting the study to spring deployments, the harbour seals’ habitat use during a large part of the year was missing. Since harbour seals moult in summer, the trackers attached to the fur typically fell off in June –July. In this study (T2-T3) therefore, a deliberate choice was made to study the behaviour of the seals in the post moult, from September onwards. A total of 18 seals were tracked from September onwards: in 2016 (T2) 6 from the Wadden Sea area and 6 from the Delta and again 6 from the Wadden Sea area in 2017(T3).With longer track durations of 20 to 187 days (mean 106 ± 46 days) in this last study information has been collected covering seven calendar months, six of which had not been studied before in this region. However there was large variation in behaviour, possibly but not solely as a result of the male bias in the sample (11 males, 7 females). Though the maximum and mean distance travelled by the seals was slightly less in autumn, the waters in the study area (i.e. the area off the west coast of the Netherlands enclosed by 51.95°N to 52.94°N, and from the coast offshore to 3.73°E) were used much more extensively by the seals tracked in autumn. In total the seals tracked during T2-T3 spent 27.3% of their time in the defined study area, while during spring deployments for T0-T1, this was only 1.5%. Out of the 18 seals tracked in autumn, 11 were observed in the study area. Interestingly these were animals tagged in the Wadden Sea region. During this time of the year animals are mostly feeding, which probably explains their higher presence in the study area. In contrast, during spring, mostly seals from the Delta crossed the study area en route to their breeding sites in the Wadden Sea. This probably explains the limited amount of time spent in the coastal zone. During the complete Luchterduinen study (T0-T3) comprising of 44 animals in spring and 18 in autumn, only one animal entered the Luchterduinen wind farm area. Its visits were short; which suggests it only crossed the area. Animals tracked during T2-T3 were observed more often in the vicinity of the wind farm, compared to the animals tagged during T0-T1.Based on these studies we concluded that harbour seals use the coastal zone west of North and South Holland to migrate to breeding areas in spring/summer, and use it to feed in autumn and winter. Recently, the recovery of the harbour seals in the Wadden Sea has come to a halt. However, pup production in the Wadden Sea is still increasing, and over two thousand pups are born in the Dutch Wadden Sea each year. Since the population size no longer grows, this suggest that an equal number of individuals die each year. Possibly the population has reached a ‘natural’ carrying capacity. However, human use at sea could also play a role in influencing the survival of individuals and the size of the population. Like other North Sea countries, the Dutch government has shown a clear intention to intensify the use of the marine areas in the near future, for windfarms but also sand mining, traffic and aquaculture. Quite likely this will affect the way the seals use the marine area. Further studies are needed to better understand how habitat changes play a role in the survival of individual animals. Hoewel het onwaarschijnlijk is dat zeezoogdieren en dus zeehonden op grote schaal direct dodelijke gevolgen ondervinden van de bouw of ingebruikname van windparken op zee, is het hoogstwaarschijnlijk zo dat ze worden beïnvloed door de verstoring en veranderingen in hun habitat.Luchterduinen windpark werd in de Nederlandse kustzone ten zuidwesten van IJmuiden gebouwd in 2014 en de vergunning (WV/2009-1229) vereiste de monitoring van grijze en gewone zeehonden. Twee belangrijke vragen werden gesteld:1.Hoe gebruiken zeehonden de kustzone? Het doel was om inzicht te krijgen in de routes van de gewone en de grijze zeehond gedurende hun aanwezigheid in de Nederlandse kustzone (tussen de Waddenzee en het Deltagebied).2.Wat is de impact van Luchterduinen op de zeehonden? (met een focus op de hei-werkzaamheden)Dit rapport bespreekt de resultaten van de studies naar de gewone zeehond. De eerste monitoring (T0-T1; 2013-2015), gebaseerd op een reeks studies van beweging en habitat gebruik van gewone zeehonden gezenderd in het voorjaar (maart), was getimed in relatie tot de constructie (2014) en ingebruikname van het park. Deze studies werden na de T1 geëvalueerd (2016). Er werd geconcludeerd dat, door de studie te beperken tot het zenderen in het voorjaar, inzicht in het habitatgebruik van de gewone zeehonden voor een belangrijk deel van het jaar ontbrak. Aangezien de dieren in de zomer verharen, verloren ze de op de vacht geplakte zenders gewoonlijk in juni-juli. In de huidige studie (T2-T3) werd daarom een bewuste keuze gemaakt om het gedrag van de gewone zeehonden na de verharing te bestuderen, vanaf september. In totaal werden 18 zeehonden in het najaar gezenderd: in 2016 (T2) 6 in het waddengebied en 6 in het Deltagebied en het jaar erna, in 2017(T3) 6 in het waddengebied.Gemiddeld was de tijd dat de dieren gevolgd werden langer dan in de eerdere studies namelijk 20 tot 187 dagen (gem. 106 ± 46 dagen). In deze studie werd bovendien informatie verzameld over een periode van zeven maanden waarvan één maand overlap vertoonde met de eerder studiesEr was een grote variatie in gedrag tussen de dieren, mogelijk speelde o.a. de scheve geslachtsverhouding van de gezenderde zeehonden hierbij een rol; er werden 11 mannetjes en 7 vrouwtjes gezenderd. Hoewel de gemiddelde en de maximale afstand die de dieren zwommen in de herfst iets lager was, gebruikten de zeehonden in deze periode het studiegebied (ten westen van de westkust van Nederland begrensd door 51.95°N en 52.94°N, en van de kust af tot 3.73°E) veel intensiever. De zeehonden gezenderd in het najaar tijdens T2-T3 besteedden 27.3% van hun tijd in dit gebied, terwijl de dieren gezenderd in het voorjaar voor T0-T1 maar 1.5% van hun tijd hier doorbrachten. Van de 18 zeehonden gezenderd in de herfst werden er 11 in het gebied gezien. Interessant is wel, dat al deze dieren in het waddengebied waren gezenderd. In deze periode van het jaar zijn de dieren vooral aan het foerageren, wat mogelijk deze verspreiding verklaart. In tegenstelling daarmee, waren het vooral de in de Delta gezenderde dieren die in de lente het gebied doorkruisten op weg naar het waddengebied waar ze zich voortplanten. Dit verklaart mogelijk de beperkte tijd dat de dieren in het studiegebied gezien werden. Tijdens de gehele Luchterduinen-studie (T0-T3) met 44 dieren gezenderd in de lente en 18 in de herfst werd er maar één dier in het park zelf gezien. Gezien de korte verblijfsperiode in het park is het waarschijnlijk dat het dier het gebied alleen doorkruist heeft. Tijdens T2-T3 werden er meer dieren in de buurt van het windpark dan tijdens T0-T1.Gebaseerd op deze studies concluderen we dat gewone zeehonden het gebied ten westen van de Noord- en Zuid-Hollandse kust in de lente en zomer vooral gebruiken om te migreren naar de voortplantingsgebieden, en in de herfst en winter om te foerageren. De laatste jaren zijn de getelde aantallen gewone zeehonden in de Waddenzee min of meer gelijk gebleven, terwijl het aantal pups nog steeds groeit. Er worden tegenwoordig jaarlijks meer dan 2000 pups geboren. Aangezien er geen groei is suggereert dit dat er even zoveel dieren jaarlijks sterven. Mogelijk heeft de populatie de “natuurlijke” draagkracht bereikt. Echter menselijk gebruik van de zee zou ook een rol kunnen spelen en de overleving van individuen en de populatiegrootte kunnen beïnvloeden. Net als andere Noordzeelanden heeft de Nederlandse regering een duidelijke intentie getoond om in de nabije toekomst het gebruik van de zee te willen intensiveren voor windparken, en daarnaast ook voor zandwinning, vaarbewegingen en aquacultuur. Het is aannemelijk dat dit de manier waarop de zeehonden de zee gebruiken zal beïnvloeden. Verdere studies zijn nodig om te begrijpen hoe verandering van het habitat van de zeehonden een rol kan spelen op de overleving van individuele dieren.

Gray seals were first observed breeding in the Dutch Wadden Sea in 1985, after centuries of absence. The breeding colony there is now the largest on the European continent. We describe the changes in gray seal numbers and their geographical expansion, and estimate how these processes were influenced by immigration from other colonies. Counts of hauled out animals were carried out between 1985 and 2013, monitoring three different periods of the seals’ annual cycle. Using priors determined for the UK population, a Bayesian demographic model was fitted to pup numbers to estimate the population parameters driving the growth. This included immigration of subadults into the breeding population, which contributed to an average growth rate in the pup counts of 19%/yr, much higher than expected in a closed population. This immigration may account for approximately 35% of the total annual growth. In addition, at least 200 gray seals from the UK visit the area temporarily. Recovery of the population in the Netherlands occurred more than 50 yr after gray seals were protected in the UK. These time scales should be taken into account when studying long living marine mammals, e.g., in impact and conservation studies.

1. If animals moved randomly in space, the use of different habitats would be proportional to their availability. Hence, deviations from proportionality between use and availability are considered the tell-tale sign of preference. This principle forms the basis for most habitat selection and species distribution models fitted to use-availability or count data (e.g. MaxEnt and Resource Selection Functions). 2. Yet, once an essential habitat type is sufficiently abundant to meet an individual's needs, increased availability of this habitat type may lead to a decrease in the use/availability ratio. Accordingly, habitat selection functions may estimate negative coefficients when habitats are superabundant, incorrectly suggesting an apparent avoidance. Furthermore, not accounting for the effects of availability on habitat use may lead to poor predictions, particularly when applied to habitats that differ considerably from those for which data have been collected. 3. Using simulations, we show that habitat use varies non-linearly with habitat availability, even when individuals follow simple movement rules to acquire food and avoid risk. The results show that the impact of availability strongly depends on the type of habitat (e.g. whether it is essential or substitutable) and how it interacts with the distribution and availability of other habitats. 4. We demonstrate the utility of a variety of existing and new methods that enable the influence of habitat availability to be explicitly estimated. Models that allow for non-linear effects (using b-spline smoothers) and interactions between environmental covariates defining habitats and measures of their availability were best able to capture simulated patterns of habitat use across a range of environments. 5. An appealing aspect of some of the methods we discuss is that the relative influence of availability is not defined a priori, but directly estimated by the model. This feature is likely to improve model prediction, hint at the mechanism of habitat selection, and may signpost habitats that are critical for the organism's fitness.

The annual reproductive cycle of most seal species is characterized by a tight synchrony of births. Typically, timing of birth shows little inter-annual variation. Here, however we show that harbour seals Phoca vitulina from the Wadden Sea (southeast North Sea) have shortened their yearly cycle, moving parturition to earlier dates since the early 1970s. Between 1974 and 2009, the birth date of harbour seals shifted on average by −0.71 d yr −1 , three and a half weeks (25 days) earlier, in the Dutch part of the Wadden Sea. Pup counts available for other parts of the Wadden Sea were analysed, showing a similar shift. To elucidate potential mechanism(s) for this shift in pupping phenology, possible changes in population demography, changes in maternal life-history traits and variations in environmental conditions were examined. It was deduced that the most likely mechanism was a shortening of embryonic diapause. We hypothesize that this could have been facilitated by an improved forage base, e.g. increase of small fishes, attributable to overfishing of large predator fishes and size-selective fisheries.

Phocine distemper virus (PDV) has caused two mass mortalities of European harbour seals (Phoca vitulina) in recent decades. Levels of mortality varied considerably among European populations in both the 1988 and 2002 epidemics, with higher mortality in continental European populations in comparison to UK populations. High levels of genetic differentiation at neutral makers among seal populations allow for the possibility that there could be potential genetic differences at functional loci that may account for some of the variation in mortality. Recent genome sequencing of carnivore species and development of genomic tools have now made it possible to explore the possible contribution of variation in candidate genes from harbour seals in relation to the differential mortality patterns. We assessed variation in eight genes (CD46, IFNG, IL4, IL8, IL10, RARa, SLAM and TLR2) encoding key proteins involved in host cellular interactions with Morbilliviruses and the relationship of variants to disease status. This work constitutes the first genetic association study for Morbillivirus disease susceptibility in a non-model organism, and for a natural mortality event. We found no variation in harbour seals from across Europe in the protein coding domains of the viral receptors SLAM and CD46, but SNPs were present in SLAM intron 2. SNPs were also present in IL8 p2 and RARa exon 1. There was no significant association of SLAM or RARa polymorphisms with disease status implying no role of these genes in determining resistance to PDV induced mortality, that could be detected with the available samples and the small number of polymorphisms indentified. However there was significant differentiation of allele frequencies among populations. PDV and other morbilliviruses are important models for wildlife epidemiology, host switches and viral evolution. Despite a negative result in this case, full sequencing of pinniped and other 'non-model' carnivore genomes will help in refining understanding the role of host genetics in disease susceptibility for these viruses.

L’etude porte sur le developpement de l’intelligence emotionnelle (IE) trait chez les adolescents a hauts potentiels. L’IE est evaluee au moyen du Trait Emotional Intelligence Questionnaire (version francaise). Les competences sociales et academiques sont evaluees au moyen de l’inventaire d’adaptation socioaffective d’Achenbach. L’echantillon est compose de 90 jeunes âges de 11 a 18 ans issus d’une population consultante. Les resultats obtenus sont analyses en fonction de differentes variables (presence ou absence de difficultes sociales ou scolaires, sexe, âge…) et compares a ceux d’un echantillon controle. Au niveau de l’IE, les resultats ne mettent pas en evidence de competences plus developpees chez les jeunes a hauts potentiels. Par ailleurs, le niveau d’IE trait est en lien avec le niveau de competences sociales. Plus le niveau d’IE trait est eleve, plus les competences sociales sont developpees. On observe egalement un lien entre la reussite academique et le developpement de l’IE trait. Les jeunes qui reussissent bien obtiennent de meilleurs resultats au test d’IE, et ce tant pour les jeunes a hauts potentiels que dans l’echantillon controle.

The European Union requires member states to achieve or maintain good environmental status for their marine territorial waters and explicitly mentions potentially adverse effects of underwater sound. In this study, we focused on producing maps of underwater sound from various natural and anthropogenic origins in the Dutch North Sea. The source properties and sound propagation are simulated by mathematical methods. These maps could be used to assess and predict large-scale effects on behavior and distribution of underwater marine life and therefore become a valuable tool in assessing and managing the impact of underwater sound on marine life.

Anthropogenic sound in the marine environment can have negative consequences for marine fauna. Since most sound sources are intermittent or continuous, estimating how many individuals are exposed over time remains challenging, as this depends on the animals' mobility. Here we explored how animal movement influences how many, and how often, animals are impacted by sound. In a dedicated study, we estimated how different movement strategies affect the number of individual harbour porpoises Phocoena phocoena receiving temporary or permanent hearing loss due to underwater detonations of recovered explosives (mostly WWII aerial bombs). Geo-statistical distribution models were fitted to data from 4 marine mammal aerial surveys and used to simulate the distribution and movement of porpoises. Based on derived dose-response thresholds for temporary (TTS) or permanent threshold shifts (PTS), we estimated the number of animals affected in a single year. When individuals were free-roaming, an estimated 1200 and 24 000 unique individuals would suffer PTS and TTS, respectively. This equates to respectively 0.50 and 10% of the estimated North Sea population. In contrast, when porpoises remained in a local area, fewer animals would receive PTS and TTS (1100 [0.47%] and 15 000 [6.5%], respectively), but more individuals would be subjected to repeated exposures. Because most anthropogenic sound-producing activities operate continuously or intermittently, snapshot distribution estimates alone tend to underestimate the number of individuals exposed, particularly for mobile species. Hence, an understanding of animal movement is needed to estimate the impact of underwater sound or other human disturbance.

European harbour seal (Phoca vitulina) populations decreased substantially during the phocine distemper virus (PDV) outbreaks of 1988 and 2002. Different hypotheses have stated that various seals and terrestrial carnivore species might be the source of infection. To further analyse these hypotheses, grey (Halichoerus grypus) and ringed (Phoca hispida) seals, polar bears (Ursus maritimus) and minks (Mustela lutreola) were sampled from the North Sea and East Greenland coasts between 1988 and 2004 and investigated by RT-PCR using a panmorbillivirus primer pair. However, all samples were negative for morbillivirus nucleic acid.

The present study was designed to identify 15 beta-hemolytic streptococci isolated during a period between 1988 and 2005 from nine harbour seals and six grey seals from various origins of the North Sea. All isolates were identified as Streptococcus equi subsp. zooepidemicus. The bacteria were additionally investigated for relatedness by restriction fragment length polymorphism analysis of PCR amplified 16S-23S rDNA intergenic spacer region and gene szp and by macrorestriction analysis of chromosomal DNA of the strains by pulsed field gel electrophoresis. The molecular analysis yielded identical or closely related patterns within the strains of the present study and with the S. equi subsp. zooepidemicus strains isolated from harbour seals of German North Sea which were investigated previously [Akineden, O., Hassan, A.A., Alber, J., El-Sayed, A., Estoepangestie, A.T.S., Lammler, C., Weiss, R., Siebert, U., 2005. Phenotypic and genotypic properties of S. equi subsp. zooepidemicus isolated from harbor seals (Phoca vitulina) from the German North Sea during the phocine distemper outbreak in 2002. Vet. Microbiol. 110, 147-152]. This indicates that this single or closely related bacterial clone existed during both phocine distemper virus epidemics in 1988 and 2002 and that a direct transmission of the strains has occurred between two seal species and between seal populations of far distant regions possibly with grey seals as a vector.

The European Union requires member states to achieve or maintain good environmental status for their marine territorial waters and explicitly mentions potentially adverse effects of underwater sound. In this study, we focused on producing maps of underwater sound from various natural and anthropogenic origins in the Dutch North Sea. The source properties and sound propagation are simulated by mathematical methods. These maps could be used to assess and predict large-scale effects on behavior and distribution of underwater marine life and therefore become a valuable tool in assessing and managing the impact of underwater sound on marine life.

Terrestrial and marine wildlife populations have been severely reduced by hunting, fishing and habitat destruction, especially in the last centuries. Although management regulations have led to the recovery of some populations, the underlying processes are not always well understood. This study uses a 40-year time series of counts of harbour seals (Phoca vitulina) in the Wadden Sea to study these processes, and demonstrates the influence of historical regional differences in management regimes on the recovery of this population. While the Wadden Sea is considered one ecologically coupled zone, with a distinct harbour seal population, the area is divided into four geo-political regions i.e. the Netherlands, Lower Saxony including Hamburg, Schleswig-Holstein and Denmark. Gradually, seal hunting was banned between 1962 and 1977 in the different regions. Counts of moulting harbour seals and pup counts, obtained during aerial surveys between 1974 and 2014, show a population growth from approximately 4500 to 39,000 individuals. Population growth models were developed to assess if population growth differed between regions, taking into account two Phocine Distemper Virus (PDV) epizootics, in 1988 and 2002 which seriously affected the population. After a slow start prior to the first epizootic, the overall population grew exponentially at rates close to assumed maximum rates of increase in a harbour seal population. Recently, growth slowed down, potentially indicative of approaching carrying capacity. Regional differences in growth rates were demonstrated, with the highest recovery in Netherlands after the first PDV epizootic (i.e. 17.9%), suggesting that growth was fuelled by migration from the other regions, where growth remained at or below the intrinsic growth rate (13%). The seals' distribution changed, and although the proportion of seals counted in the German regions declined, they remained by far the most important pupping region, with approximately 70% of all pups being born there. It is hypothesised that differences in hunting regime, preceding the protection in the 1960's and 1970's, created unbalance in the distribution of breeding females throughout the Wadden Sea, which prevailed for decades. Breeding site fidelity promoted the growth in pup numbers at less affected breeding sites, while recolonisation of new breeding areas would be suppressed by the philopatry displayed by the animals born there. This study shows that for long-lived species, variable management regimes in this case hunting regulations, across a species' range can drive population dynamics for several generations.

Estimating the spatial position of organisms is essential to quantify interactions between the organism and the characteristics of its surroundings, for example, predator-prey interactions, habitat selection, and social associations. Because marine mammals spend most of their time under water and may appear at the surface only briefly, determining their exact geographic location can be challenging. Here, we developed a photogrammetric method to accurately estimate the spatial position of marine mammals or birds at the sea surface. Digital recordings containing landscape features with known geographic coordinates can be used to estimate the distance and bearing of each sighting relative to the observation point. The method can correct for frame rotation, estimates pixel size based on the reference points, and can be applied to scenarios with and without a visible horizon. A set of R functions was written to process the images and obtain accurate geographic coordinates for each sighting. The method is applied to estimate the spatiotemporal fine-scale distribution of harbour porpoises in a tidal inlet. Video recordings of harbour porpoises were made from land, using a standard digital single-lens reflex (DSLR) camera, positioned at a height of 9.59m above mean sea level. Porpoises were detected up to a distance of 3136m (mean 596m), with a mean location error of 12m. The method presented here allows for multiple detections of different individuals within a single video frame and for tracking movements of individuals based on repeated sightings. In comparison with traditional methods, this method only requires a digital camera to provide accurate location estimates. It especially has great potential in regions with ample data on local (a)biotic conditions, to help resolve functional mechanisms underlying habitat selection and other behaviors in marine mammals in coastal areas.

Serum clinical chemistry parameters were examined in lactating southern elephant seal Mirounga leonina mothers and their pups from the declining Macquarie Island population. There were significant changes in serum values from 2 to 21 days postpartum in both nursing mothers (increase: inorganic phosphate; decrease: creatinine, potassium, chloride, cholesterol, total protein, albumin, globulin, aspartate aminotransferase, creatine kinase) and suckling pups (increase: inorganic phosphate, globulin, cholesterol; decrease: albumin, alkaline phosphatase, gammaglutamyl transferase; increase followed by decrease: triglycerides, iron). We found no evidence that changes were due to chronic stress effects caused by repeated chemical immobilisations (mothers) or physical restraint (pups): at late lactation, clinical chemistry values were similar for mother-pup pairs of a control group (not handled previously), moderate treatment group (previously handled twice) and high treatment group (previously handled three to four times). We were not able to detect differences in clinical chemistry values between mother-pup pairs distributed over two areas differing in the frequency of human visits. The clinical chemistry values presented here can serve as reference ranges to allow future comparison with other southern elephant seal populations to investigate factors, e.g. food limitation, suspected to be involved in population declines.