Cetacean Sanctuary Research Ligurian Sea

Squid-Loving Odontocetes ProjEct (SLOPE)

Ecology, status and conservation of odontocetes in the Pelagos Sanctuary

Target species

Striped dolphin (Stenella coeruleoalba)

Risso's dolphin (Grampus griseus)

Long-finned pilot whale (Globicephala melas)

Common bottlenose dolphin (Tursiops truncatus)

Cuvier's beaked whale (Ziphius cavirostris)

Sperm whale (Physeter macrocephalus)

Drawings by Massimo Demma

Project location

The research effort of the SLOPE Project is concentrated along the western Ligurian Sea continental shelf and slope.

Tri-dimensional map of the Ligurian-Corsican-Provençal Basin (from Hachette Guides Bleus)

The Ligurian Sea continental slope, where most of the odontocetes are sighted, is characterised by an outstanding biological diversity and a high abundance of cetaceans compared to the rest of the Mediterranean.

Rationale behind this study / Research highlights

The main purpose of the Continental Slope Odontocete Project is to study the distribution, abundance, habitat use and ecology of the odontocete species inhabiting the Ligurian Sea, together with their social organization, behaviour and foraging ecology. The possible impacts of human activities are also investigated.

The activities conducted by Tethys in the context of the SLOPE project include the following:

Distribution and encounter rates (1990-ongoing)

Standard visual and acoustic surveys are conducted during summer seasons to determine distribution and encounter rates of different cetacean species into the study area. All the navigation data (position, speed, course), environmental data (sea state, weather, visibility, cloud coverage) and qualitative acoustic data (acoustic pollution and cetacean vocalizations by listening on the towed hydrophone array) are recorded. Human activities will be also monitored (counting all types of boats, ships and fishing gear in a radius of 3 nm from the ship), and the presence of other marine animals (including sea turtles, tunas, mobulas, rays, swordfish and seabirds) are reported. The position, group size and composition of the different species of cetaceans are recorded during long-lasting observation sessions. From 1990 through 2007 many sightings have been made: 2,619 of striped dolphin, 163 of Risso's dolphin, 141 of sperm whale, 36 of long-finned pilot whale, 48 of Cuvier's beaked whale, 37 of common bottlenose dolphin and 3 of short-beaked common dolphin.

Sightings made in the last 12 years (1996-2007) during summer seasons in the study area:

Striped dolphins

Risso's dolphins



Sperm whales

Other cetacean species (blue= Cuvier's beaked whale; green= long-finned pilot whale; brown= common bottlenose dolphin; pink= short-beaked common dolphin)

Acoustic surveys are carried out by means of a towed array

Acoustic survey to assess Odontocete distribution in the Ligurian Sea (1995)

Systematic acoustic monitoring can be used to obtain an index of abundance of vocalising animals. An acoustic survey to test this hypothesis was conducted in collaboration with the International Fund for Animal Welfare, in the waters of the Ligurian Sea Sanctuary. Recording sessions were performed at regular intervals at day and at night, either during navigation or drifting. Levels of odontocete clicks and whistles were scored, as well as levels of background water noise, shipping noise and self noise. Results showed that acoustic survey is significantly more efficient than visual survey in determining odontocete distribution and habitat partition. Also, the method showed to be an useful tool to assess striped dolphins behaviour, which is by far the most frequent dolphin species in the Ligurian Sea. The study indicated that the acoustic approach may provide highly relevant information to the conservation of cetaceans in the Mediterranean Sea.

Spectrogram of a pulse train: series of clicks heard as a single sound

References:

Gordon, J.C.D., Matthews, J.N., Panigada, S., Gannier, A., Borsani, J.F., and Notarbartolo-di-Sciara, G. 2000. Distribution and relative abundance of striped dolphins, and distribution of sperm whales in the Ligurian Sea cetacean sanctuary: results from a collaboration using acoustic monitoring techniques. Journal of Cetacean Research and Management, 2(1):27-36.

Social ecology of Risso’s dolphins in the Ligurian Sea (1990-ongoing)

Data on distribution and social structure of Risso's dolphin were collected from 1990 to 2007 in the Corso-Ligurian basin, within the Pelagos Sanctuary. The results of the analyses conducted on the data collected from 1990 through 1998 indicate that the depth at Risso's dolphin encounters (with sighting frequency of 0.53 sightings/100 km) ranged from 70 to 2,700 m, with a mean of 937 m. Most of the sightings occurred in a depth range of 400-1,000 m, according with other studies in north-western Mediterranean. The distribution of Risso's dolphins in respect to the water depth was in agreement with the species' main prey, mesopelagic cephalopods. About 5,000 photographs were taken for photo-identification purposes. Approximately 300 individuals have been photo-identified. Individual re-sightings ranged between 1-4 in different years, while within-season re-sightings ranged between 1-9 times. The re-sighting rate for many animals suggested a high degree of site fidelity during the summer, although the study area surely represents only part of a greater home range. The increasing rate of discovery indicates that only part of the marked individuals frequenting the study area have been photo-identified so far. Group size ranged from 1 to 70 individuals, with a mean of 12 and a mode of 5. The relatively small group size, compared with the greater Pacific aggregations that may form in response to abundant resources, may be indicative of relatively scattered or scarce food resources in this area.

References:

Airoldi S., Azzellino A., Fadda V., Gaspari S., Nani B., Zanardelli M., Notarbartolo di Sciara G., Mariani M. 2000. Social ecology of Risso's dolphins in the Ligurian Sea: preliminary results. European Research on Cetaceans 14:213-217.

Fadda V., Airoldi S. 2000. A note on the persistence of dorsal fin scars on Risso's dolphins photo-identified in the Ligurian Sea. European Research on Cetaceans 14:323.

Abundance estimate of Risso's dolphins in the western Ligurian Sea (1990-ongoing)

Risso's dolphin abundance was estimated through photographic mark-recapture. For the purposes of the mark-recapture analysis, the dataset with the most homogeneous sampling effort was chosen, i.e. 1998-2000. The analysis provided an estimate of approximately 300 individuals. These are the first estimates of Risso's dolphin abundance in any Mediterranean area, and they represent an important baseline for Risso's dolphin conservation in the Cetacean Sanctuary.

Some of the Risso's dolphins photo-identified so far in the Ligurian Sea, based on long-term natural marks on their dorsal fins.

New dolphins and re-captures positively identified during a portion of the study period

Physical habitat of cetaceans along the western Ligurian Sea continental slope (1996-ongoing)

The Corso-Ligurian basin encompasses several different habitats, ranging from a narrow continental slope, where the sea bottom abruptly declines from 200 to 2000 meters depth, to a large area of pelagic waters. In such a complex environment, physiography plays a major role in partitioning the habitat. The physical habitat of cetaceans found along the continental slope in the western Ligurian Sea was investigated matching data collected by two different sea-based surveys, respectively a dedicated vessel and a commercial whale watching platform. Sighting data were collected May through October, from 1996 through 1999, covering an area of approximately 3,000 square kilometres with an effort of about 10,000 km year-1. A total of 532 sightings have been analysed including all the species occurring in the area. A Geographic Information System was used to integrate sighting data to a set of environmental characteristics: bottom gradient, area between different isobaths, length and linearity of the isobaths within a cell unit etc. Habitat use, weighted by the effort, was analysed by means of a Multidimensional Scaling analysis that enabled to represent similarities among cells, independently from the geographical position. Significant differences in the habitat preference of some of the species were found, particularly Risso's dolphins, Cuvier's beaked whales and sperm whales were found associated to a well defined bathymetries and sea bottom gradients. Fin whale, striped dolphin and partially sperm whale distribution seems to be driven also by other factors such as temperature gradients. Research about habitat use and preference of different species is still ongoing by integrating ordinary statistical analysis with geostatistics.

Distribution of the "occasional species" investigated by means the Discriminant Analysis

References:

Azzellino, A., D'Amico, A., McGehee, D., Portunato, N. 2004. A preliminary investigation on cetacean habitat in the Ligurian Sanctuary (Sirena '99). European Research on Cetaceans 15:244-248.

Azzellino, A., Borsani, J.F., Carron, M., D'Amico A., Demer, D., McGehee, D. In press. Preliminary development of logistic models to predict habitat use of cetacean species as function of the environmental context in the Ligurian Sea Sanctuary (Solmar - Sirena '99 and '00 campaigns). European Research on Cetaceans 16.

Azzellino, A., Carron, M., D'Amico, A., Misic, C., Podestà, M., Portunato N., Stoner R. In press. Cuvier's beaked whale (Ziphius cavirostris) habitat use and distribution in the Genoa canyon area (Sirena '02). European Research on Cetaceans 17.

Azzellino, A., Gaspari, S., Airoldi; S., Nani, B. In press. Habitat use and preferences of cetaceans along the continental slope and the adjacent pelagic waters in the western ligurian sea. Deep-Sea Research Part I.

Association patterns of Risso’s dolphins in the Ligurian Sea (1990-1998)

In this study the Simple Ratio index was used to describe the association patterns in a population of Risso's dolphins in the Northwest Mediterranean Sea. From 1990 to 1998, 128 individuals photo-identified were used for this analysis. Association indices (SR ³ 0.5) showed that about 4% of all possible pairwise interactions between dolphins were observed. Thirty four percent of the individual associations of dolphins pairs tested, were found to be significantly different (p < 0.01) from random distributions derived from a randomisation test (30,000 unrestricted permutations). The overall pattern of associations was weak with few strong associations between individuals lasting over the years. Cluster Analysis outlined the existence of four social groups. These results suggest a fission-fusion society for the considered population, and represent the first report of long term associations in Risso's dolphins.

Frequency distribution of Simple Ratio (SR) values for association of individuals identified more than twice (n=58). The percentage values corresponding to each coefficient of association is indicated on top of the bars

Cluster analysis dendrogram of 58 adult individuals shows four groups

References:

Gaspari, S., Azzellino, A., Airoldi, S., Hoelzel, A.R. 2000. Association patterns of Risso's dolphins (Grampus griseus) in the north-west Mediterranean. European Research on Cetaceans 14:138.

Radio-tracking of long-finned pilot whales in the Ligurian Sea (2001-ongoing)

This study sheds light on the feeding behaviour of long-finned pilot whales, on their amazing diving capabilities and on the magnitude and duration of the behavioural response caused by the tagging attempts. Using suction-cup attached time-depth recorder/VHF radio tags, diving data on long-finned pilot whales in the western Ligurian and Tyrrhenian Sea have been obtained. One deployment in 2001 demonstrated their exceptional diving ability, with dives as deep as 800 m. The deep bouts occurred in late afternoon. Data on behavioural response were also collected, confirming that whale tagging can provide essential information to understand the ecology and behaviour of a poorly known species, disturbance to the animals is an issue that must be carefully considered.

Individual with the tag applied and a dive profile of an adult pilot whale.

References:

Airoldi, S., Fasano, D., Gavazzi, N., Miragliuolo, A., Mussi, B., Mariani, M. In press. Diving behaviour and reactions to tagging of long-finned pilot whales in the central Mediterranean Sea. European Research on Cetaceans 17.

Ecology of sperm whales in the western Ligurian Sea (1990-ongoing)

The Mediterranean sperm whale population is poorly known. In order to assess presence, distribution and relative sighting frequency of this species 78 different individuals were photo-identified during 141 different sightings and. Position, group size, acoustic recordings, individual size, tissue and faecal samples were collected. Distribution data between 1990 to 2000 have been analysed with a Geographic Information System. The analysis of the above data enabled to determine distribution patterns and definite depth range of the species. Forty sperm whales were photo-identified giving preliminary information about site fidelity and habitat use of this species in the study area. Acoustic data were collected by means of a towed hydrophone array. The analysis showed a higher occurrence of feeding activity on the continental slope. The faecal samples contained some beaks of Histioteuthys bonellii, a common prey item for sperm whales worldwide. Genetic analyses of skin samples of 5 individuals revealed that they were all males.

Three of the 40 individual sperm whales photo-identified so far in the Ligurian Sea, based on long-term natural marks on their flukes and the study area subdivided into three homogeneous zones, considering both the effort and the bathymetry, with the sperm whale sightings.

References:

Patti P., Azzellino A., Airoldi S. In press. Sperm whale distribution and habitat use in the western Ligurian Sea: first insight. European Research on Cetaceans 17.

Azzellino, A., Fasano, D., Airoldi, S., Patti, P. In press. Sperm whale (Physeter macrocephalus) distribution in the western Ligurian Sea: does a correlation exist with sea surface temperature? European Research on Cetaceans 19.

Behaviour and habitat use of striped dolphins in the western Ligurian Sea (1997-ongoing)

The behaviour and group composition of striped dolphins living in the western Ligurian Sea were systematically recorded. They proved to be quite unselective with respect to specific habitat features. However, a differential habitat use was found for striped dolphin as function of the monthly period and the group size. A study has been carried out (and it is still ongoing) to correlate specific oceanographic features (monthly sea surface temperatures and chlorophyll profiles) to the relative abundance and the behavioural categories of the species. Multivariate statistical analyses (Correspondence Analysis, Multidimensional Scaling and Principal Component Analysis) have been applied in order to identify behavioural categories and correlations between behaviour and different oceanographic zones. Patterns in behavioural categories "distribution" have been observed and evidence of habitat features selection are expected by correlating remote sensing data (SST and ocean colour) to the animal spatial distribution.

Some pie charts represent of the relative frequencies of specific events within the cluster categories
and hierarchical Cluster Analysis of the BEHA-set

References:

Jahoda M., Azzellino A., Airoldi S., Francia C. 2005. Definition of behavioural categories in striped dolphins (Stenella coeruleoalba) in the Ligurian Sea Sanctuary in the presence of boats. European Research on Cetaceans, 19.

Biological consequences of global warming: the sea surface temperature affect cetacean distribution in the western ligurian sea. (1997-ongoing)

Aim of this study is to assess if sea surface temperature affects cetacean distribution in the Western Ligurian Sea. Relationships with temperature were already investigated for: striped dolphin (Stenella coeruleoalba), fin whale (Balaenoptera physalus) and sperm whale (Physeter macrocephalus). Remotely sensed Sea Surface Temperature (SST) data were studied. A series of 20 monthly images (i.e. June to September monthly images from 1996 to 2000) was considered. Concurrently, distribution data collected during shipboard summer surveys, and covering an area of about 20,000 km2 in the Western Ligurian sea, were analysed. The relationship between the three species presence and SST was investigated by using a grid of 3x3 nautical miles cell units. For every cell the SST mean, SD, CV and the deviation from the monthly average were calculated. Binary logistic regression functions allowed to assess significant (P<0.05) relationships with temperature in these species. These logistic models, were able to predict 60-78% of the species presence(1)/absence(0) cells, and suggest the need for further investigations spanning longer time periods to assess how the global climate change has been changing and will change in the future cetacean distribution in The Western Ligurian Sea.

References:

Azzellino, A., Airoldi, S., Lanfredi, C., Gaspari, S. 2007. Biological consequences of global warming: does sea surface temperature affect cetacean distribution in the Western Ligurian sea? In Abstracts of 21st Annual Conference of the European Cetacean Society.

Azzellino, A., Airoldi, S., Lanfredi, C., Gaspari, S. Biological consequences of global warming: does sea surface temperature affect cetacean distribution in the Western Ligurian sea? In press on the Journal of the Marine Biological Association of the United Kingdom.

Social kin associations and genetic structuring of striped dolphin populations in the Mediterranean Sea (1997-2007)

Social kin associations and genetic structuring of striped dolphin populations in the Mediterranean was investigated. Hierarchical patterns of genetic subdivision were investigated, and kinship within and between social groups of striped dolphins within the Tyrrhenian Sea was assessed. A total of 165 samples were analysed at 8 microsatellite DNA loci, including out group samples from the Adriatic, Scotland and Spain for population-level comparisons. It was found population genetic structure within the Mediterranean basin, including small but significant differentiation between the Adriatic and Tyrrhenian Seas, and between putative "inshore" and "offshore" populations in the Tyrrhenian Sea. Assessment of kinship within and among 12 association groups showed higher average kinship for females within than between groups, and smaller groups showed higher average kinship. Comparisons of relatedness for both sexes showed a significant difference between males and females, with females more likely to associate with adult kin. Together these data emphasize the importance of the social cohesion of kin in small groups to the structuring of striped dolphin populations in this environment.

Map of the origin of the samples and in the square the core area of the study

References:

Gaspari S., Airoldi S., Hoelzel A.R. 2004. Molecular ecology of striped dolphins (Stenella coeruleoalba) in the Mediterranean Sea. European Research on Cetaceans 15:309-310.

Gaspari S., Hoelzel A.R., Azzellino A. In press. Patterns of population subdivision, genetic variability and groups kin structure of Mediterranean striped dolphins (Stenella coeruleoalba). European Research on Cetaceans 16.

Gaspari, S., Airoldi, S., Hoelzel, A.R. In press. Patterns of population structure of Risso's dolphin (Grampus griseus). European Research on Cetaceans 19.

Gaspari, S., Azzellino A., Airoldi, S., Hoelzel, A.R. 2007. Social kin associations and genetic structuring of striped dolphin populations (Stenella coeruleoalba) in the Mediterranean Sea. Molecular Ecology 16, 2922-2933.

Patterns of population structure in Risso's dolphins (1997 ongoing)

The Risso's dolphin has a worldwide distribution, but little is known about their phylogeography. This study considered the genetic difference between Mediterranean and Eastern North Atlantic population. The two populations clearly indicate differentiation and relatively low diversity of a population sampled in UK waters (primarily from the Western Isles, Scotland). It is evident the reduced variability of the UK population in comparison to the Mediterranean population. The signal for differentiation between the Mediterranean and the Eastern North Atlantic Risso's dolphins is strong for the mtDNA data. Samples obtained in the Mediterranean were mostly collected in the Ligurian Sea during the summer months. Considering the high genetic variability found in Risso's dophin, it is conceivable that the animals sampled in the Ligurian Sea during the summer belong to different populations that my migrate in the Ligurian sea for feeding. During the summer, the Ligurian Sea is particularly rich in food, and it is know that some species of cetaceans migrate to the area for feeding, such as fin whales (Notarbartolo di Sciara et al. 2003). While further study is necessary, these results indicate that the UK Risso's dolphin population should be identified as a separate management unit when considering conservation strategies.

The Minimum-spanning network (MSN) of 16 haplotypes of Risso's dolphins show the frequency of haplotypes (the size of the circles reflects the frequency). Haplotypes in black represent the UK population while haplotypes in white represent the Mediterranean Sea.

References:

Gaspari, S., Airoldi, S., Hoelzel, A.R. In press. Patterns of population structure of Risso's dolphin (Grampus griseus). European Research on Cetaceans 19.

Risso's dolphins (Grampus griseus) in UK waters are differentiated from a population in the Mediterranean Sea and genetically less diverse. Stefania Gaspari, Sabina Airoldi, & A. Rus Hoelzel. 2007. Conservation Genetics vol 8(3) 727-732.