**3. Case study in the Barents Sea**

The hydrodynamic data and most forcing parameters for the ABM and Oil spill model are driven by DHI's existing 3-dimensional hydrodynamic model. The model domain, encompassing the Barents Sea and the colonies in Norway, Russia and the islands of Svalbard, Franz Josef and Novaya Zemlya is shown in **Figure 4**. The modelling software package applied was DHI's 3-dimensional flexible mesh model, MIKE 3 FM [10] which includes both meteorological, tidal and oceanographic effects.

#### **3.1 Common guillemot**

Common Guillemot is a large auk species with a circumpolar distribution, breeding in dense colonies between 40°N and 75°N. Like other auk species, the wings are used for both swimming and diving. Common Guillemots are excellent divers with

*Combining Predicted Seabird Movements and Oil Drift Using Lagrangian Agent-Based Model… DOI: http://dx.doi.org/10.5772/intechopen.106956*

**Figure 4.** *Common guillemot modelled mean density September 2013. Pink dots indicate common guillemot survey sightings. The red circles/ellipses encompass the main colonies. Model domain extent in stereographic projection (Stereo\_1670\_Sc1).*

maximum diving depths of more than 200 m. It is a pelagic pursuit diver, and the primary food item in the Barents Sea is small pelagic fish such as capelin and fish larvae and fry. Common Guillemots leave the colony in late July - early August. The male follows the chick for the first two months at sea. During this period, they moult and are flightless for approximately 45–50 days.

The population of Common Guillemots in the Barents Sea has declined dramatically since the first censuses in the 1960s. In particular, the mass mortality of birds during the winter of 1986–1987 decimated the populations along the Norwegian coast and on Bjørnøya. This incident was probably caused by food limitation due to a crash in the capelin stock and very low densities of alternative food items. Since then, the populations have been growing, but the species is still listed as critically endangered on the Norwegian Red List. Colonies are found in the southern part of the Barents Sea. The Barents Sea populations are year-round residents to the southern Barents Sea area, and in addition, Common Guillemots from Norwegian colonies further south migrate into the Barents Sea during autumn.

The population of Common Guillemot of 300,000 pairs is concentrated in colonies around Bjornoya/Bear Island (83.9% of the population) and the Finnmark Coast (8.9%), with minor colonies at the Murman Coast (5.4%) and in the Norwegian Sea (1.8%). \*https://www.npolar.no/en/species/common-guillemot/

### **3.2 Oil spill**

For illustration, the oil from a hypothetical oil spill in the Barenst Sea was applied as a representative oil type with a spill rate corresponding to 700 m3 /day and a spill duration of 8 days. The spill is assumed to be a topside surface spill.

The spill was released on 1st September 2016 at (73° 34′ 40″ N, 22° 55′ 5″ E), and the simulation continued 30 days after the spill had terminated.

#### **3.3 Mortality assessment**

The sensitivity of different sea-bird species to oil pollution is described as a function of the relative amounts of time spent on the sea surface, the importance of the population within the study area and the size of the world population. The knowledge underpinning these parameters is relatively well established due to large amounts of standardised data from countrywide surveys of beached dead sea-birds, surveys of sea-bird densities at sea, counts of the number of breeding sea-birds in colonies and information on specific details of breeding and survival.

Thresholds of relevant species of sea-birds in the Barents Sea to the characteristics of oil residues (key effect features) were provided. The key effect features of oil in relation to sea-birds are film thickness, viscosity, and depth of the oil in the water column (**Table 2**). Although the effect in relation to depth in the water column can be confidently assessed from general knowledge of the diving capacity of the different species, the actual diving depth per species may fluctuate depending on season and location. It may differ in the Barents Sea from other areas. More importantly, the thresholds related to film thickness and viscosity have been established without undertaking tests on live birds [11]. Hence, they should be regarded as guidelines rather than well-defined thresholds.

The modelled distribution of Common Guillemots showed peak occurrence at the boundary between the Norwegian Coastal Current and the Atlantic water mass. The predicted (mean) distribution of suitable Common Guillemot habitat displays a well-defined concentration 150–200 km north of the Norwegian coast. Both oil and Common Guillemots displayed a high degree of spatiotemporal variation which resulted in a limited intersection between the modelled oil slick and the main concentration of the guillemots (**Figure 5**). The intersection took place in the area just south of Bjørnøya. An animation of the 38 day simulation period can be displayed here: Video: https://www.youtube.com/ watch?v=lgzBrfiQm6g.

The estimated hourly number of impacted Common Guillemots is displayed in **Figure 6**. Due to the limited intersection between the oil and guillemot particles the guillemots were only impacted during three of the 40 days in the model period (2–4 September 2016). Further, the modelled impact only took place during 15 of the 213


#### **Table 2.**

*Example of effect features of oil residues relevant for assessing impacts of oil on sea-birds in the Barents Sea. Zmin is the depth at which the species will be at risk from oil.*

*Combining Predicted Seabird Movements and Oil Drift Using Lagrangian Agent-Based Model… DOI: http://dx.doi.org/10.5772/intechopen.106956*

#### **Figure 5.**

*Overlap between modelled mean oil density (L/km2 ) and modelled mean density (n/km<sup>2</sup> ) of common guillemot during the test period. - "sources: Esri, DigitalGlobe, GeoEye, i-cubed, USDA FSA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS user community".*

#### **Figure 6.**

*Estimated hourly number of casualties of individual common guillemot during the oil spill simulation 1/9–8/102016.*

modelled hours equivalent to 7% of the trajectory time. The total number of impacted guillemots during the modelling period was 50,000. With a total number of breeding pairs of 300,000 the number of Common Guillemots in the western Barents Sea during autumn 2016 would be approximately 1 million, taking juveniles and nonbreeding immatures and adults into account. Thus, the relative impact on the population represents 5% of the population (**Figure 7**).

**Figure 7.** *Cumulative impact of simulated oil spill on common guillemot population in the Barents Sea 1/9–8/102016.*
