Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark-recapture experiment

E.H. Ries, L.R. Hiby, P.J.H. Reijnders

    Research output: Contribution to journalArticleAcademicpeer-review

    34 Citations (Scopus)

    Abstract

    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.
    Original languageEnglish
    Pages (from-to)332-339
    JournalJournal of Applied Ecology
    Volume35
    Issue number2
    DOIs
    Publication statusPublished - 1998

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    population size
    harbor
    aerial survey
    experiment
    radio
    activity pattern
    breeding season
    Wadden Sea
    virus
    sand
    air

    Cite this

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    title = "Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark-recapture experiment",
    abstract = "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.",
    author = "E.H. Ries and L.R. Hiby and P.J.H. Reijnders",
    year = "1998",
    doi = "10.1046/j.1365-2664.1998.00305.x",
    language = "English",
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    Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark-recapture experiment. / Ries, E.H.; Hiby, L.R.; Reijnders, P.J.H.

    In: Journal of Applied Ecology, Vol. 35, No. 2, 1998, p. 332-339.

    Research output: Contribution to journalArticleAcademicpeer-review

    TY - JOUR

    T1 - Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark-recapture experiment

    AU - Ries, E.H.

    AU - Hiby, L.R.

    AU - Reijnders, P.J.H.

    PY - 1998

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    N2 - 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.

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