This document summarizes a study that used particle modeling to examine why two bird species, Common Guillemot and Razorbill, aggregate at the Brown Ridge in the North Sea. Researchers modeled the birds as floating particles subject to hydrodynamics to see if ocean currents could explain their distribution. The forward modeling matched the bird distributions through September, but the backward modeling showed the birds likely use active flight rather than currents to reach the Brown Ridge. Specifically, some Common Guillemots may follow currents from the English Channel and coast, but Razorbills likely rely solely on active flight. Overall, both species require active movement to gather and remain at the Brown Ridge, so hydrodynamics alone do not explain their aggregation there.

1. 3 November 2014
Using Particle Modeling for Ecological Questions Case Study Birds Dispersion in the North Sea Transportmodelling of Common Guillemot and Razorbill in the North Sea
Steve Geelhoed (IMARES)
Marc Weeber ; Mathieu Chatelain (Deltares)

2. Setup
1.Introduction
2.Background information
3.Modelling
4.Results
5.Surveys
6.Conclusion

3. Introduction
•Project “Aanvullende Beschermde Gebieden”
•Potential NATURA 2000 areas
•Brown Ridge is currently not protected. However, aggregation of bird species at the Brown Ridge
•What could be the reason?
•Good feeding grounds (more fish available)
•Effect of hydrodynamics

4. Background information
Common Guillemot
Razorbill
Location
Common Guillemot
Razorbill
Seaborne
June
September
Brown Ridge
November-February
January-March

5. Background information
Common Guillemot
Razorbill

6. Background information
August-September
December-January

7. Modelling
Research question:
- Can the effect of the hydrodynamics
explain why these bird species aggregate
at the Brown Ridge?
Approach:
- Model the bird species as floating
particles in the North Sea.
- Assume that flying has no effect on their
distribution
11 november 2014
Forward:
Where do particles go to after
release from the central North
Sea?
Backward:
Where do particles that end up at
the Brown Ridge come from?

8. Modelling
Hydrodynamics: 2003 – 2004 (average wind / high peaks) 2005 – 2006 (average wind / low peaks ) 2006 – 2007 (high wind) Wind: Yes / No Release period:
Forward
Backward
15 Jul
15 Dec
1 Aug
15 Jan
15 Aug
15 Feb
1 Sep
15 Mar

9. Results
Forward 15 Aug 2005

10. Results
Forward
-Hydrodynamics:
-First days remain in place due to tide.
-Eventually moves out of the North model boundary along the Danish coast.
-Wind:
-Particles move out of the North model boundary more quickly with wind influence.
-The amount of particles that get stuck along the Dutch and Danish coast increases with wind influence.
-Release period:
-The amount of time that the particles remain in the model is overall longest when released on 15 July. Probably due to lower wind velocities.
-Period:
-The periods 2005-2006 and 2006-2007 look alike (end at North model boundary)
-The period 2003-2004 deviates as in two release periods some particles end up along the English coast.

11. Results
Backward 15 Dec 2003

12. Results
Backward
-Hydrodynamics:
-Particles are originating from the English Channel and the English South East coast.
-Wind:
-With wind particles can also be originating from the English North East coast.
-With wind it is less likely that particles are originating from outside the model boundary of the English Channel.
-Release period:
-Period of release and place of origination doesn’t has a consistent effect in the different periods
-Period:
-In the periods 2003-2004 and 2005-2006 particles can originate from the English North East coast.
-In the period 2005-2006 there are no particles orginating from the English Channel.

13. Results

14. Surveys: distribution Common Guillemot

15. Surveys: distribution Razorbill

16. Conclusion
Forward:
•The forward simulation corresponds with the distribution of Common Guillemot and Razorbill up to September (moulting). Backward:
•For Common Guillemot it is likely that part of the individuals that end up at the Brown Ridge make use of the currents (English Channel, English East Coast). Most distribute by active transport.
•For Razorbill it is unlikely that they make use of the currents to end up at the Brown Ridge. Active transport by flying.

17. Conclusion
Overall:
•Both Common Guillemot as Razorbill need active movement to end up at the Brown Ridge within the modelled time span.
•Both species need active movement to maintain at the Brown Ridge. Concluding : Hydrodynamics are not (solely) responsible for high aggregation at the Brown Ridge. Common Guillemot and Razorbill specifically move towards the Brown Ridge.

18. Thank you
Thank you for your attention.
Questions?