[MARMAM] New paper on the abundance monitoring of mobile coastal dolphins

Milaja Nykänen milaja.ny at gmail.com
Mon Jul 20 23:17:34 PDT 2020

Dear colleagues,

On behalf of my co-authors, I'd like to draw your attention to a recently
published paper on the abundance monitoring of a mobile population of
coastal bottlenose dolphins.

Nykänen M, Oudejans MG, Rogan E, Durban J, Ingram SN. 2020. Challenges in
monitoring mobile populations: Applying Bayesian multi-site mark–recapture
abundance estimation to the monitoring of a highly mobile coastal
population of bottlenose dolphins. Aquatic Conservation: Marine and
Freshwater Ecosystems DOI: 10.1002/aqc.3355

The article is available on early view at:

1. Monitoring the abundance of mobile and wide-ranging cetacean populations
for conservation management is challenging, especially when the management
is focused on static protected areas. Where abundance estimates are
derived from mark–recapture data, such as photo-identification of naturally
marked individuals, unpredictable movements of animals in and out of the
survey area can reduce ‘capture’ probabilities and affect the precision and
accuracy of
resulting estimates.
2. A Bayesian hierarchical log–linear model was applied to
photo-identification data collected in summer 2014 to derive a multi-site
abundance estimate for a population of bottlenose dolphins, Tursiops
truncatus, ranging widely throughout the coastal waters of western Ireland.
In addition, the effects of varying levels of sampling effort on the
minimum detectable decrease in population size were examined.
3. The abundance (median) of dolphins was estimated as 189 (coefficient
of variation (standard deviation/mean), 0.11; 95% highest-posterior density
interval, 162-232). Over 50% of the well-marked dolphins encountered
throughout the study were sighted in more than one distinct coastal area,
thus displaying high mobility. In addition, it was found that it would
require biennial surveys to detect a 25% decline in abundance within the
six-year reporting period of the EU’s
Habitats Directive.
4. Given that the Special Area of Conservation designated for these
dolphins consists of two separate areas covering a substantial portion of
the west coast of Ireland, the multisite approach is appropriate for
monitoring this population. It produces a more precise estimate and is well
suited for sparse recapture data collected opportunistically at multiple
sites, when the lack of resources prevents large-scale surveys or when
concentrating surveys on smaller localized areas fails to capture the broad
range and unpredictable occurrence of the animals. The Bayesian multi-site
approach could be applied to the management of other wide-ranging marine or
terrestrial taxa.

For a pdf copy, please contact: milaja.ny at gmail.com.

All the best,
Milaja Nykänen

Dr Milaja Nykänen
Post-doctoral researcher

University of Eastern Finland

Saimaa ringed seal research

Department of Environmental and Biological Sciences

PO Box 111

FI-80101 Joensuu
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