Long-finned pilot whale
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LONG-FINNED PILOT WHALE Scientific name: Globicephala melas |
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Distribution within the Mediterranean:
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Taxonomy: PHYLUM: Chordata |
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Conservation status in the Mediterranean: Data deficient (UICN) |
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Conservation status in the world: Data deficient (UICN) |
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Mean lenght:
Between 3,6 and 7,5 meters in adults; between 1,7 and 2 meters at birth |
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Habitat:
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Diet:
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Identification characteristics:
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Can be confused with:
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Diving pattern: |
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Individual identification characteristics:
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Main threats:
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The main characteristic, which make this genus distinct from others is the bulbous forehead that may overhang the snout and which is square-shaped seen from above. The beak, if existent, barely differentiates from the head. The dorsal fin is extremely wide-based, falcate, tall, especially in the adult individuals, because it grows in length as the animals grow older. It is situated about 1/3 of the way back from the snout. The flippers are extremely long, which contrasts with the other species of the genus, the short-finned pilot whale (Globicephala macrorhynchus). The pectoral fins have strongly angled leading edges, forming an “elbow”. The tailstock is rather long and thick.
Its coloration pattern is the typical coloration pattern of the genus Globicephala. The main color is black (sometimes dark grayish-brown), which covers the whole animal except for three specific areas:
- White anchor-shaped patch on the chest, extending back and widening around the urogenital area.
- White line behind the eye extending to the dorsal part of the animal.
- White or light-gray saddle patch, situated behind the dorsal fin.
Calves are paler than adults.
Pilot whales have less teeth than other species of the Delphinidae family. This fact may be related with their diet. They have between 8 and 13 pairs of pointed and sharp teeth in each jaw.
Together with the sperm whale (Physeter macrocephalus) and the killer whale (Orcinus orca), pilot whales are extremely sexual dimorphic, being males much larger than females. Their mean length varies between 3,6 and 7,5 meters for males weighting up to 3 tonnes, and between 3,8 and 5,7 for females, which would weigh between 2 and 2,5 tonnes. Newborns are 1,7 to 2 meters long and weigh about 75 kg.
DISTRIBUTION AND MIGRATORY PATTERNS WITHIN THE MEDITERRANEAN SEA
The long-finned pilot whale has an antitropical distribution. This means that it occurs in temperate and subpolar waters of the North Atlantic ocean and the oceans of the southern hemisphere. The species was previously found in the North Pacific ocean, but appears to be absent there today. It is usually found in offshore waters, although it can also be spotted in shallow waters (Jefferson et al., 2008 & Perrin et al., 2009). The populations of the southern hemisphere are isolated from those in the northern hemisphere. The antitropical distribution contrasts with the distribution of the other species of the genus, the short-finned pilot whale (Globicephala macrorhynchus), which is distributed in tropical and subtropical waters (Perrin et al., 2009). There are some estimates that say that the world population of the species would be composed by around 1 million animals (Jefferson et al., 2008 & Perrin et al., 2009).
The species is considered to be resident in the Mediterranean Sea, although the size, structure, distribution and the dynamics of the mediterranean population are not well known (Cañadas and Sagarminaga, 2000). It is more abundant in the western basin, especially in the Alboran Sea, the Strait of Gibraltar and, to a lesser extend, in the north-western end of the Mediterranean Sea (Mangion and Gannier, 2002 & Gannier, 2005). The species has a stable population of 267 – 273 individuals in waters of the Strait of Gibraltar, which would be composed by 213 animals in summer (Verborgh, 2005 & Verborgh et al., 2009). It is rather abundant in the Alboran Sea, where several hundreds, or even a few, thousands long-finned pilot whales congregate (Cañadas and Sagarminaga, 1994; Cañadas and Sagarminaga 2000; Cañadas et al., 2002 & Cañadas et al., 2005). The proximity of both areas make researchers think that individuals spotted in the Alboran sea and in the Strait of Gibraltar could belong to the same population (Verborgh, 2005). There are only a few sightings registered in the central part of the Mediterranean Sea (Notarbartolo di Sciara, 2002; Notarbartolo di Sciara and Birkun, 2010 & Mussi et al., 2000), and the species is almost absent in the eastern basin of the Mediterranean.
Although the structure of the population is not well known, researchers believe that individuals found in the Mediterranean Sea belong to a single population (Reeves and Notarbartolo di Sciara, 2006). There are no evidences of genetic flow between individuals of the Mediterranean Sea and animals of the Atlantic Ocean through the Strait of Gibraltar. Studies conducted in this area and other places of the Mediterranean Sea strongly suggest that the populations of those areas are resident, showing a high fidelity to their areas of residence (Mussi et al., 2000; Verborgh, 2005; De Stephanis, 2008; De Stephanis et al., 2008a & Verborgh et al., 2009).
The total number of individuals of the Mediterranean population are not known, although some (non-published) data suggest that the population of the Alboran Sea could be formed by 1.500 to 1.900 individuals, being the greatest population of the Mediterranean Sea.
HABITAT AND FEEDING
Long-finned pilot whale usually inhabits areas close to the continental slope, especially those with steep slopes or with high topographic relief (Perrin et al., 2009). In the Mediterranean, the species has been mainly studied in the Strait of Gibraltar and the Alboran Sea, where the different studies agree with other studies carried out outside the Mediterranean Sea. In this sense, the mediterranean population of the species inhabits waters between 300 and 1.550 meters deep, with intermediate slopes, preferring waters deeper than 600 meters. It has also been seen in waters deeper than 2.000 meters (Notarbartolo di Sciara et al., 1993; Baird et al., 2002; Cañadas et al., 2002; Gannier, 2005 & De Stephanis 2008b).
Although long-finned pilot whales show a seasonal and geographical variability (Santos et al., 2014), they mainly feed on neritic or oceanic squids. They show a clear predilection for the species Todarodes sagitattus and Loligo pelaei, selecting them before other species when they are available (Desportes and Mouritsen, 1993 & Gannon et al., 1997). To a lesser extend, they also feed on other squids, such as some species belonging to the family Omasttraphidae, the genus Gonatus or the species Histioteuthis reversa or Chiroteuthis veranyi. Beside squids, fishes such as the Atlantic mackerel (Scomber scombrus), the Atlantic herring (Clupea harengus), the blue whiting (Micromesistius poutassou) or the greater argentine (Argentina silus) are a secondary source of food for the long-finned pilot whale, or even become dominant when squids are not available (Desportes and Mouritsen, 1993 & Gannon et al., 1997). The population of the Alboran Sea primarily feeds on different squid species, especially on Todarodes sagitattus (Cañadas and Sgarminaga, 2000). Although the prey species live in rather deep waters, between 100 and 1.000 meters deep, their daily vertical migration would allow the long-finned pilot whale to feed in shallower waters, mainly between 100 and 500 meters deep (Desportes and Mouritsen, 1993 & De Stephanis et al., 2008c).
Diet may vary depending on the size, the age or reproductive state. Thus smaller animals feed on smaller prey and lactating females and larger males, show a bigger proportion of fishes in their diet (Desportes and Mouritsen, 1993).
REPRODUCTION AND LIFE HISTORY
The long-finned pilot whale show many characteristics shared by several species of large cetaceans concerning its life history, such as a long life span, delayed maturity, different rates of maturation for males and females and the production of a single calf every time they give birth.
Whereas males can live up to 35 to 45 years, although some slightly older individuals have been found, females can reach the age of 60 years (Bloch et al., 1993; Jefferson et al., 2008 & Perrin et al., 2009). Gestation lasts for 15 to 16 months and calving interval for three years. Newborns measure 1,7 to 1,8 meters in length and they show a fast postnatal growing rate, which considerably slows down during the juvenile stages (Bloch et al., 1993; Perrin and Reilly, 1984 & Perrin et al., 2009). Weaning starts at the age of 6 months, although it can begin earlier, and lactation lasts for 3 years (Desportes and Mouritsen, 1993; Perrin and Reilly, 1984 & Perrin et al., 2009). The fact that milk has been found in the stomachs of males up to 7 years old and females up to 12 years old, makes researchers think that the lactation period would be much longer than 3 years. This elongated lactation period would respond to social reasons rather than nutritional ones (Tyack 1986; Desportes and Mouritsen, 1993 & Perrin et al., 2009). Males reach sexual maturity at the age of 12 and females at the age of 8. Mating usually occurs between spring and summer, although it also has been observed between july and september in the Alboran Sea (Cañadas and Sagarminaga, 2000 & Jefferson et al., 2008).
ECOLOGY, BEHAVIOUR AND IDENTIFICATION
The social structure of the long-finned pilot whale is based on small matrilinieal groups including 2 to 4 generations. In these groups male and female offspring travel with their mothers for their whole lives. This social organization is called natal group philopatry (Ottensmeyer and Whitehead, 2003; De Stephanis, 2008 & De Stephanis et al., 2008a). These “basic social units”, or pods, show a different degree of stability in the different areas, being rather ephemeral in waters of Nova Scotia, but more stable in other zones such as the Faroe Islands, the Strait of Gibraltar or the Mediterranean Sea. Different pods joint together in order to form bigger groups called clans, which are usually composed by 20 to 90 individuals. Clans vary in size in the different regions. In Nova Scotia they are composed by 80 to 100 individuals and they are bigger in the Strait of Gibraltar, where they can reach the 150 animals (Amos et al., 1990; Ottensmeyer and Whitehead, 2003; De Stephanis, 2008 & De Stephanis et al., 2008a). In other regions of the Mediterranean Sea, such as the Alboran Sea, groups are usually composed by 7 to 20 individuals, sometimes forming bigger aggregations of 300 to 350 animals (Cañadas and Sagarminaga, 1994 & Cañadas and Sagarminaga, 2000).
Although there are strong familiar bonds between mothers and their offspring in matrilineal pods, reproduction occurs between individuals of different pods. In the Alboran Sea, males of one pod show higher levels of association with females of other pods, rather than with females of the same pod (Cañadas and Sagarminaga, 2000). Thus, different authors suggest that males do not mate within their own pod, but with females of other groups. In this sense, long-finned pilot whales of the Strait of Gibraltar are believed to form a single clan, whose individuals mate with animals of other clans, possibly clans of the Alboran Sea (De Stephanis, 2008 & De Stephanis et al., 2008a).
Long-finned pilot whales are commonly found floating motionless on the surface, allowing vessels to approach them. Sometimes they can be seen feeding or traveling in a linear formation in which individuals are placed side by side. Young individuals may approach and bow-ride slow-moving vessels, whereas adults tend to be shyer. Another common behaviour is spyhopping in which animals stick their heads up out of the water to spy and look around (Carwardine, 2004 & Shirihai and Jarret, 2006). Long-finned pilot whales usually perform several short dives before starting a long dive, that lasts for a few minutes. Day-time dives are shallower (between 1 and 16 meters), whereas night-time dives are deeper and would probably be related to feeding behaviour (Baird et al., 2002 & Perrin et al., 2009).
At sea, it is almost impossible to distinguish the long-finned pilot whale from the other species of the genus, the short-finned pilot whale (Globicephala macrorhynchus), but their distributions only overlap in a few specific areas. Other similar species are the killer whale (Orcinus orca) or the false killer whale (Pseudorca crassidens), although long-finned pilot whales can easily be distinguished from them by the characteristic shape of their dorsal fins. Other traits that help in their identification are the bulbous head, the almost entirely black coloration of the body, and the shape and the position of the dorsal fin. Furthermore, long-finned pilot whales have a very characteristic diving pattern. First the melon emerges out of the water and the animal blows. Afterwards, the body start arching while the animal moves forward, until the tailstock is almost entirely out of the water. They rarely raise their fluke out of the water before starting a dive (Jefferson et al., 2008 & Shirihai and Jarret, 2006).
INDIVIDUAL IDENTIFICATION CHARACTERISTICS
As other cetacean species, the long-finned pilot whale show specific characteristics that allow researchers to identify the different individuals of a group. These marks can be used in research studies that use the photo-identification as main procedure to identify the individuals. Thus it is important that these marks are stable over time, which means that they should not disappear as the animal gets older. Long-finned pilot whales have three different kinds of marks which meet these requirements (Auger-Méthé and Whitehead, 2007):
Notches on the dorsal fin: Like most species of the family Delphinidae, long-finned pilot whale individuals can be distinguished by the shape of their dorsal fin as well as by the shape, position, size and number of notches on the posterior margin of the dorsal fin. This is the main trait used by most research groups around the world. Despite of this, only around 33 % of the individuals of a specific population can be identified using this natural mark.
Saddle patch: It is a white or light-colored patch located behind the dorsal fin. Its shape and coloration are stable over time and unique for each individual and allow researchers to differentiate the animals. This mark would be genetically inherited in a different way for both sexes and it is intricate enough to decrease the chance of duplication. It is not visible in young individuals. Combining the use of the saddle patch to the characteristic explained above in photo-identification studies, the percentage of identifiable individuals would double from 33 % to 67 % (Auger-Méthé and Whitehead, 2007).
White scars: They are irregularly shaped scars, which formation is associated with other mark types, such as notches. They are stable over time, thus could be used in photo-identification studies, although they are not prevalent in the population.
CONSERVATION STATUS AND MAIN THREATS
Long-finned pilot whales are mainly distributed in temperate and subpolar waters of the North Atlantic Ocean and all the oceans of the southern hemisphere. World’s population is estimated around 1 million individuals, but this estimates are rather old and the trends in abundance are unknown. For all these reasons, the International Union for the Conservation of Nature (IUCN) listed the species under the status of data deficient. Due to the lack of knowledge about the long-finned pilot whale’s populations living in the Mediterranean sea and its abundance, the IUCN also listed the species under the status of data deficient in this region. The main threats for the species are:
- Mass strandings: Pilot whales are one of the cetaceans most frequently involved in mass strandings. Different theories have been developed in order to explain such events, but all agree, that the strong social bonds between the individuals of the species is a determinant factor (Geraci and Lounsbury, 2005). Some authors suggest that the magnetic fields could be responsible for some mass strandings, other authors believe that mass strandings occur because cetaceans get trapped in shallow water areas, whereas other researchers think that such events could be caused by abrupt environmental changes such as hurricanes, earthquakes or the production of very high sonic pressures, usually related to military sonars or underwater explosions (Geraci and Lounsbury, 2005). There is no evidence of a mass stranding event of long-finned pilot whales in the Mediterranean Sea.
- Direct catch: Direct catch of this species only takes place in the Faroe Islands, where around 850 individuals are killed every year. The inhabitants of these Islands consider this slaughter as a tradition that started during the Middle Age. According to the International Whaling Commission and the North Atlantic Marine Mammal Commission (NAMMCO), this slaughter would not be a threat to the long-finned pilot whales population of the area, which is estimated to be composed by around 100.000 individuals.
- Interaction with humans: Although the exact effects of human activity on the species are not well known, there are many factors that could be seen as a threat in the future. Some of them are the collision with vessels, the interaction with fisheries, the underwater noise production and the whale watching, which could considerably disturb the animals (Reeves and Notarbartolo di Sciara, 2006 & De Stephanis, 2008).
Bycatch seems to be an important issue of concern in other areas of the planet, such as California, where pilot whales get trapped in drift-nets, or Hawaii, where they get caught by longline fisheries (Perrin et al., 2009). - Pollution: The Mediterranean Sea is one of the most polluted seas in the world, due to the intensive agricultural and industrial activities developed in the countries surrounding it in the last centuries (Aguilar, 2000). Long-finned pilot whale populations of both sides of the Atlantic Ocean show high levels of organochlorine pollutants such as DDTs and PCBs in their tissues. Concentrations of heavy metals such as cadmium or mercury are higher than normal in individuals of the Faroe Islands (Caurant et al., 1993 & Perrin et al., 2009). Although pilot whales may tolerate high levels of pollutants, these compounds have been proved to cause several health problems, such as hormone concentration disorders, reproductive disorders in other species of cetaceans. They also affect growth and the immune system of cetaceans (Aguilar, 2000; Borrell and Aguilar, 2006 & Reijnders, 1998).
- Morbilivirus: An epizootic outbreak caused by a morbillivirus affected the population of the Strait of Gibraltar during the years 2006 and 2007. A total of 27 long-finned pilot whale individuals were found dead between october 2006 and april 2007 in an area extending from the Strait of Gibraltar to the shores of the Balearic Islands. This could be the first epizootic outbreak caused by a morbillivirus for this species (Fernández et al., 2008).
There are many international conventions protecting the long-finned pilot whale, such as the appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) or the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic Area (ACCOBAMS). Some populations of the species are included in the the appendix II of the Convention on Migratory Species (CMS). In the Mediterranean Sea, there is a very important area for the cetacean species located in the Ligurian Sea. In fact it is the only Marine Protected Area especially created in order to protect the different species of cetaceans in the Mediterranean and promote their conservation.
Although the designation of Areas of Special Interest in the Alboran Sea and the Gulf of Vera has been repeatedly claimed in the last years (Cañadas et al., 2005), it has not been until 2013, that the Spanish government declared new marine Community Interest Areas, belonging to the Natura 2000 network, in the Frame of the Indemares project. The expansion of the area surrounding the Alboran Island, and the northern part of the Alboran sea, which are very important to the distribution of the long-finned pilot whale, have been included in the designation.
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