North West Mediterranean Sea, Slope and Canyon System IMMA

Area Size

145 297 km2

Qualifying Species and Criteria

Fin whale – Balaenoptera physalus

Criterion A; B (ii); C (i, ii)

Sperm whale – Physeter macrocephalus

Criterion A; C (i, ii)

Risso’s dolphin – Grampus griseus

Criterion C (i, ii)

Marine Mammal Diversity 

Criterion D (ii)

Stenella coeruleoalba, Globicephala melas, Delphinus delphis, Ziphius cavirostris, Tursiops truncatus

Summary

The North West Mediterranean has a set of geomorphological and oceanographic characteristics, including canyon systems and upwellings, which promote levels of productivity of extraordinary biological and ecological significance for the region. The Pelagos Sanctuary area, within the Provençal-Corsican-Ligurian Basin – complemented by an extension to the West encompassing the offshore portion of the Gulf of Lion to the Balearic sub-basin – contains habitat supporting a diversity of cetacean species regularly found in the Mediterranean Sea. In particular, this area contains important habitat for Vulnerable Mediterranean fin whales (Balaenoptera physalus), Endangered sperm whales (Physeter macrocephalus), and Risso’s dolphins (Grampus griseus).

Description of Qualifying Criteria

Criterion A – Species or Population Vulnerability

The IUCN Red List classifies the Mediterranean subpopulation of sperm whale as Endangered and infers that their numbers are declining from significant anthropogenic threats. Although no past or present abundance estimate is available for the entire range of the subpopulation, some data are available for limited areas within the region. The estimated overall abundance of sperm whales in the Ionian Sea is considered to be 62 animals (95% CI = 24–165), and zero animals in the Strait of Sicily. By contrast, results from a survey of a large portion of the western basin (from Gibraltar to Sicily and bounded on the north by a line from the Balearics east to Sardinia) in summer 2003 indicate a sperm whale detection rate roughly eight times that in the Ionian Sea. This is in agreement with the North Western Mediterranean Sea, and is described to be an important habitat for sperm whale. Genetic data from a sample of sperm whales across the Mediterranean have not provided evidence for within-region population structure. It is assumed that sperm whales form a single subpopulation within the Mediterranean, as they are thought to roam widely across the basin.

In 2012 the fin whale was assessed and Vulnerable [C2a(ii)] by the IUCN Red List of Threatened Species. No population estimate exists for the entire region of the Mediterranean Sea for the species. For the North Western Mediterranean Sea, recent estimates made by aerial survey are 1032 individuals (95% CI: 462-2526) in winter and 2500 (95% CI: 14720-4310) in summer. Fin whales have been described as particularly abundant during the summer months in the Corso-Ligurian-Basin, which is considered their major feeding ground in the Mediterranean Sea. A sharp decrease in fin whale abundance has been observed in the Pelagos Sanctuary over the last decade, with estimates of 900 individuals reported from the western Ligurian Sea in 1992, declining to significantly lower numbers (N=147; CV=27.04%; 95% CI=86–250) in 2009. This may be due to whales relocating elsewhere within the Mediterranean and the decrease in prime fin whale habitat must be addressed with precaution, and a population decline in the Mediterranean cannot be discounted at this time. Fin whales in the Mediterranean are a subpopulation based on the IUCN definition. Genetic data from a sample of fin whales from the Mediterranean have not provided evidence for within-region subpopulation structure.

Criterion B: Distribution and Abundance

Sub-criterion Bii: Aggregations

Fin whales occur throughout the Mediterranean, from the Balearic Islands to the Levantine Sea, although they are in large part found in the area between the Gulf of Lion and western Ligurian Sea. Fin whales have been described as particularly abundant during the summer months in the Corso-Ligurian-Basin, which is considered their major feeding ground in the Mediterranean Sea. A density of 0.014 ind./km² has been calculated for the North Western Mediterranean Sea in summer. Systematic surveys over the last 30 years from several research groups in the area have provided evidence of large aggregations of fin whales. Between 500 and 1000 individuals are described as present in the Pelagos Sanctuary area only. Photo-identification data point to seasonal residence and to a persistent site fidelity over the years.

Criterion C: Key Life Cycle Activities

Sub-criterion Ci: Reproductive Areas

Information on the localized existence of calving grounds in the Mediterranean for fin whales. The wide geographical distribution of the overall record of neonate fin whales in the Basin (and the strandings of neonates) argue against any precise calving location for fin whales in the Mediterranean Sea; however, the high percentage of calves reported for the North Western Mediterranean area indicates this region of importance to fin whale reproduction. Evidence from biopsy sampling analyses (n = 150) in that north-western portion of the Mediterranean Sea further support the hypothesis of a reproductive area there, with at least a third of sampled individuals being pregnant females and two thirds of males with a status of active stallion.

For the sperm whale 23 years of data have been gathered for analysis on the presence of neonates. 24 biopsies have been made from which genetic analyses were conducted to sex animals their judge their reproductive status through hormones. It appears that only recently, since the mid-2000s, encounters with social units and neonates have increased: for the decade 2005-2015 the percentage of neonates is 1.79% of all individuals, mainly in spring and summer. Biopsies revealed that at least one female was pregnant, and in august 2016, offshore Toulon, the birth of a sperm whale had been observed. The area where the newborns are mainly seen is smaller as the entire area where other sperm whales are encountered.

Risso’s dolphins are resident all year round and across multiple years. Regular sightings of newborns are made and calves presence is reported during long term studies, mostly in summer each year. The canyons of the north-western Mediterranean Sea are mostly the sectors where groups with newborns are mostly observed.

Sub-criterion Cii: Feeding Areas

Fin whales concentrate in the Corsican-Ligurian-Provencal Basin in summer to feed on krill, although whales can be observed there year-round. Potential fin whale feeding habitat in the Western Mediterranean Sea undergoes considerable seasonal variation, ranging from a highly-diffused condition in winter and spring to extreme summer concentration in the Ligurian Sea and Gulf of Lion area. However, observations of fin whales engaging in feeding, frequent on many feeding grounds in the world, are very rare in the Ligurian-Corsican-Provençal Basin. This is likely related to the vertical distribution and movement pattern of the whales’ main prey in the area. Krill in the Mediterranean are known to spend the daylight hours at depths often in excess of 1000 m, and to migrate to about 30-50 m from the surface only during the night. Fin whales have been described to perform in the Ligurian Sea the deepest dives known for the species, exceeding 470 m, and their behaviour was attributed to deep feeding activity. Feeding was also inferred from swimming behaviour and frequently observed defecation events.

For sperm whales, it is known that they are feeding on mesopelagic squid from several acoustic studies. Sperm whales feed around canyons, slopes, and seamounts, as these geomorphological features are known to be where aggregation of squid occur, and sperm whales have been seen to gather around such features.  Sperm whales are present in the area for several months, even year-round, in these favourable habitats. This is further supported by several acoustic studies and also stomach content of stranded animals that were found full of prey remnants.

Risso’s dolphins feed almost exclusively on neritic and oceanic cephalopods. It has been reported that the species in the western Mediterranean feeds mainly on oceanic cephalopods, particularly pelagic octopods being abundant along with Ommastrephidae, Histioteuthis and Onychoteuthis families. The evidence of long-term presence of the species associated with the slope and canyon system, and the evidence of behaviour of feeding in the groups encountered, confirm that the area is used for foraging by the species. Further research indicates that feeding Risso’s dolphin groups were mostly encountered inside canyons (92% of the sightings of feeding animals over the slope) rather than outside canyons.

Criterion D: Special Attributes  

Sub-criterion Dii: Diversity

The North Western Mediterranean Sea is one of the most productive areas in the Mediterranean Sea, attracting many Mediterranean species of cetaceans in high numbers; all seven common and also other rare cetacean species can be observed in the area. This high level of diversity lead to the creation of a cetacean Sanctuary (called Pelagos Sanctuary for Mediterranean Marine Mammals) encompassing its western portion. However, the eastern part is of high importance for cetaceans as well. In the last 30 years, the western part of the area has been studied, and published scientific papers support the knowledge of a high diversity area.

Supporting Information

Airoldi, S., Azzellino, A., David, L., Dhermain, F., Di-Meglio, N., Jimenez, V., Jourdan, J., Labach, H., Lanfredi, C., Remonato, E., Rosso, M., Roul, M., Scuderi, A. 2015. Absolute abundance of Risso’s dolphin (Grampus griseus) in the north western part of the Pelagos Sanctuary. Pelagos Sanctuary Convention No. 03/2014, 59 pages. Istituto Tethys /EcoOcean Institut/GECEM/Fondazione CIMA/GIS3M.

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Azzellino A., S. Airoldi, S. Gaspari, C. Lanfredi, A. Moulins, M. Podestà, M. Rosso and P. Tepsich. 2016. Risso’s Dolphin, Grampus Griseus, in the Western Ligurian Sea: Trends in Population Size and Habitat Use.

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