[MARMAM] New publication on trends in cetacean density

Rebecca Jewell rj67 at st-andrews.ac.uk
Thu May 10 07:24:59 PDT 2012

Dear colleagues,

We are pleased to announce that a new publication on detecting trends in cetacean density is now available with open access in Marine Ecology Progress Series at http://www.int-res.com/abstracts/meps/v453/.

Jewell R, Thomas L, Harris CM, Kaschner K, Wiff R, Hammond PS, Quick NJ. 2012. Global analysis of cetacean line-transect surveys: detecting trends in cetacean density. Marine Ecology Progress Series 453:227-240
doi: 10.3354/meps09636

Abstract: Measuring the effect of anthropogenic change on cetacean populations is hampered by our lack of understanding about population status and a lack of power in the available data to detect trends in abundance. Often long-term data from repeated surveys are lacking, and alternative approaches to trend detection must be considered. We utilised an existing database of line-transect survey records to determine whether temporal trends could be detected when survey effort from around the world was combined. We extracted density estimates for 25 species and fitted generalised additive models (GAMs) to investigate whether taxonomic, spatial or methodological differences among systematic line-transect surveys affect estimates of density and whether we can identify temporal trends in the data once these factors are accounted for. The selected GAM consisted of 2 parts: an intercept term that was a complex interaction of taxonomic, spatial
and methodological factors and a smooth temporal term with trends varying by family and ocean basin. We discuss the trends found and assess the suitability of published density estimates for detecting temporal trends using retrospective power analysis. In conclusion, increasing sample
size through combining survey effort across a global scale does not necessarily result in sufficient power to detect trends because of the extent of variability across surveys, species and oceans. Instead, results from repeated dedicated surveys designed specifically for the species and geographical region of interest should be used to inform conservation and management.


Rebecca Jewell, Research Student
Sea Mammal Research Unit
Scottish Oceans Institute
University of St Andrews
St Andrews
KY16 8LB

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