Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark–recapture experiment
Article first published online: 5 JAN 2002
British Ecological Society
Journal of Applied Ecology
Volume 35, Issue 2, pages 332–339, April 1998
How to Cite
Ries, E. H., Hiby, L. R. and Reijnders, P. J.H. (1998), Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark–recapture experiment. Journal of Applied Ecology, 35: 332–339. doi: 10.1046/j.1365-2664.1998.00305.x
- Issue published online: 5 JAN 2002
- Article first published online: 5 JAN 2002
- Cited By
- correction factor;
- Phoca vitulina;
1. The harbour seal population Phoca vitulina in the entire Wadden Sea was severely depleted due to a virus-epizootic during 1988. A comprehensive study on the population biology and activity patterns was subsequently initiated to design a management and conservation plan. The main objective of this study was to estimate harbour seal abundance in the different regions of the Wadden Sea.
2. We investigated the potential of a mark–recapture experiment using VHF radio-tags in combination with repeated aerial surveys to estimate the number of harbour seals in the Dutch part of the Wadden Sea. The number of harbour seals hauled-out and the presence of any radio-tagged seals was monitored during seven aerial surveys of all known haul-out sites in the Dutch Wadden Sea over the 1994 breeding season.
3. A maximum likelihood (ML) estimator was developed to infer the rate of tag-loss and the size of the local prepupping population.
4. The ML estimate of the number of harbour seals in the Dutch Wadden Sea was 1536 (95% confidence limits were 1225 and 2200). The corresponding maximum proportion of seals hauled-out was 68%.
5. The use of VHF radio-tags which can be monitored from the air provides a way of correcting aerial survey counts for the proportion of harbour seals hauled-out during the surveys. Since haul-out behaviour may be influenced by local conditions, such as exposure time of sand banks, we recommend this technique be repeated in other areas of the Wadden Sea rather than using the estimates from the current study in other areas.