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Extrapolating cetacean densities to quantitatively assess human impacts on populations in the high seas
Mannocci, L.; Roberts, J.; Miller, D.L.; Halpin, P.N. (2017). Extrapolating cetacean densities to quantitatively assess human impacts on populations in the high seas. Conserv. Biol. 31(3): 601-614.
In: Conservation Biology. Wiley: Boston, Mass.. ISSN 0888-8892; e-ISSN 1523-1739, more
Peer reviewed article  

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Author keywords
    habitat-based density models; survey coverage

Authors  Top 
  • Mannocci, L.
  • Roberts, J.
  • Miller, D.L.
  • Halpin, P.N.

    As human activities expand beyond national jurisdictions to the high seas, there is increasing need to consider anthropogenic impacts to species that inhabit these waters. The current scarcity of scientific observations of cetaceans in the high seas impedes the assessment of population-level impacts of these activities. This study is directed towards an important management need in the high seas—the development of plausible density estimates to facilitate a quantitative assessment of anthropogenic impacts on cetacean populations in these waters. Our study region extends from a well-surveyed region within the United States Exclusive Economic Zone into a large region of the western North Atlantic sparsely surveyed for cetaceans. We modeled densities of 15 cetacean taxa using available line transect survey data and habitat covariates and extrapolated predictions to sparsely surveyed regions. We formulated models carefully to reduce the extent of extrapolation beyond covariate ranges, and constrained them to model simple and generalizable relationships. To evaluate confidence in the predictions, we performed several qualitative assessments, such as mapping where predictions were made outside sampled covariate ranges, and comparing them with maps of sightings from a variety of sources that could not be integrated into our models. Our study revealed a range of confidence levels for the model results depending on the taxon and geographic area, and highlights the need for additional surveying in environmentally distinct areas. Combined with their explicit confidence levels and necessary caution, our density estimates can inform a variety of management needs in the high seas, such as the quantification of potential cetacean interactions with military training exercises, shipping, fisheries, deep-sea mining, as well as delineation of areas of special biological significance in international waters. Our approach is generally applicable to other marine taxa and geographic regions for which management will be implemented but data are sparse.

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