title: Risso's Dolphin, Grampus griseus, in the Western Ligurian Sea: Trends in Population Size and Habitat Use.
abstract: This paper provides a summary of 25 years of research on Risso's dolphins (Grampus griseus) in the western Ligurian Sea. Seasonal variations in abundance, distribution and habitat use were observed. Photographic mark-recapture methods provided a population size estimate for the period from 1998 to 2012, of about 100 individuals (95% CI of 60-220 individuals). The same methods detected a decline in population size from an average of about 120-150 from 2000 to 2005, to an average of 70-100 during 2010 to 2014. Species occurrence appeared to be significantly decreasing in coastal and continental slope areas, while it seemed to be stable in the most pelagic area. In addition, a dramatic change was observed in the local primary production, which was analysed based on time series of sea surface temperature and chlorophyll data from 1990 to 2014. Based on fisheries landings, there may have been a general decrease in fishery productivity, both in the western Ligurian Sea and in adjacent regions. Environmental variability, depletion of resources by fisheries and possibly interspecies competition may all have contributed to cause changes in Risso's dolphin habitat use and occurrence in the western Ligurian Sea.
authors: Politecnico di Milano, University of Technology, Milano, Italy; Tethys Research Institute, Milano, Italy. Electronic address: arianna.azzellino@polimi.it.
authors: A
authors: A
authors: Azzellino
authors: Tethys Research Institute, Milano, Italy.
authors: S
authors: S
authors: Airoldi
authors: National Research Council (CNR), Institute of Marine Sciences (ISMAR), Ancona, Italy.
authors: S
authors: S
authors: Gaspari
authors: Politecnico di Milano, University of Technology, Milano, Italy; Tethys Research Institute, Milano, Italy.
authors: C
authors: C
authors: Lanfredi
authors: CIMA Research Foundation, Savona, Italy.
authors: A
authors: A
authors: Moulins
authors: Museum of Natural History of Milan, Milano, Italy.
authors: M
authors: M
authors: Podestà
authors: CIMA Research Foundation, Savona, Italy.
authors: M
authors: M
authors: Rosso
authors: CIMA Research Foundation, Savona, Italy; University of Genoa, Genoa, Italy.
authors: P
authors: P
authors: Tepsich
mesh_terms: D000818:Animals; D004289:Dolphins / Q000502:physiology*; D017753:Ecosystem; D008522:Mediterranean Sea; D011157:Population Dynamics; D013997:Time Factors
keywords: Abundance; Distribution; Grampus griseus; Ligurian Sea; Niche partitioning; Population structure; Risso's dolphin; Trend