Postponed – Using seismic data to study fin whales in offshore waters off southwest Portugal.

Speaker: Andreia Pereira (Instituto Dom Luis,Faculty of Sciences, University of Lisbon, Portugal)

Abstract

Instruments used for seismic monitoring have been recording baleen whales along with the target data. These long-term datasets, some in offshore waters, provide valuable information for the study of large cetaceans that would otherwise be difficult to obtain due to economic and logistic reasons. Fin whales are classified as ‘Endangered’ and therefore knowledge of stock structure, population size and spatial and temporal distribution patterns is essential for good management strategies. In Portugal, sightings of fin whales off mainland waters are rare and are insufficient to assess any kind of trend. Therefore, acoustic data, even collected from opportunistic sources such as seismic surveys, are useful for monitoring this species. An array of 24 ocean bottom seismometers (OBS) was deployed between August 2007 and July 2008 in offshore waters southwest of Portugal to study potential tsunami sources. Calls of fin whales were also recorded during this deployment. The aim of this study was to develop a spectrogram cross correlation automatic detection routine to: 1) analyse the occurrence of 20 Hz calls; 2) characterize the main two calls produced by fin whales (20 Hz and back-beats); and 3) assess movement patterns. The occurrence of the 20 Hz call was seasonal, with a peak in the winter months (Dec-Feb). The two main calls could be clearly distinguished by the median frequency, frequency bandwidth and inter-call interval and they seem to show seasonal differences. Movement patterns were assessed considering the presence of a seamount in the study area, the Gorringe Bank, which has been proposed for a new marine protected area, and the proximity with the entrance to the Mediterranean Sea. These results provide baseline knowledge about this endangered species in offshore waters off Portugal and contribute to our understanding of fin whale occurrence and seasonal movements in relation to areas of conservation interest.