Fin whale seasonal trends in the Pelagos Sanctuary, Mediterranean Sea. Issue 3 (24th December 2015) - Cominelli, Simone
ABSTRACT: Since 2009, a cetacean presence and distribution long‐term monitoring study has been ongoing in the Pelagos Sanctuary, a pelagic marine protected area located in the northwestern Mediterranean Sea. One of the objectives of this study is to assess trends in cetacean presence and distribution to achieve good environmental status (GES) of pelagic marine waters. We assessed the density variability of the fin whale ( Balaenoptera physalus ) in the Pelagos Sanctuary. We used data collected during summer months (Jun–Sep) from 2009 to 2013, along 2 fixed transects crossing the Pelagos Sanctuary, using ferries as platforms of opportunity. We compared 2 un‐corrected indexes: the linear encounter rate and density index, computed applying distance sampling methodology to select the most precise method. We also evaluated the effect of environmental covariates (e.g., platform height, Beaufort sea state, wind speed and direction, cloud cover and rain, longitude, latitude) on abundance and density estimation. Finally, we defined an unbiased index and used it to analyze the temporal and spatial variability of fin whale density in the Pelagos Sanctuary. Fin whale density along the 2 transects varied on a yearly basis, with a peak in 2012 and 2013. Variability also occurred on a monthly basis, with a peak during the first half of the season. A longitudinal and a depth gradient were also evident, confirming differences in species displacement in the area. These results are consistent with previous studies, and update current knowledge of species presence in the area. The protocol tested in this work can be easily applied to the other cetacean species inhabiting the Pelagos Sanctuary providing a novel and cost‐effective method to assess long‐term trends in cetacean distribution and detect incipient changes in species density. © 2015 The Authors. Journal of Wildlife Management published by The Wildlife Society.