Cetaceans of the Strait of Gibraltar
In the Strait of Gibraltar, up to 7 species of cetaceans can be regularly sighted every year.
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It is a resident species in the area, meaning that it can be seen regularly throughout the year. The Bay of Algeciras is an important breeding and feeding site, although they can be found throughout the Strait of Gibraltar.
Length: ~ 2.5 m.
Weight: ~ 100 kg.
Physical characteristics: they display a colouring pattern on both sides of the body reminiscent of an hourglass: yellow in the front just behind the head and grey in the back. Older individuals may have a grayish spot on the dorsal fin, which is usually dark grey / black.
Social structure: common dolphins live in social groups of variable dimensions. In the Strait, there are groups of up to more than 100 individuals.
Behaviour: they like swimming in front of some whales or boats, a behaviour known as bow-riding. They are shallow divers (<200 m). In this area, they are frequently seen sailing alongside striped dolphins.
Food: they feed mainly on small fish.
Threats: one of the main threats is accidental capture in fishing nets (by-catch), as well as water pollution and climate change. In the Strait, there is a high risk of cuts and collisions with small commercial and recreational vessels, particularly those involved in illegal tuna fishing.
Conservation status: the population in the Mediterranean Sea is classified as Endangered by the IUCN (International Union for the Conservation of the Nature, Red List). Globally, the species is not threatened.
Curiosities: they are very agile, being able to reach 65 km/h.
It is a resident species in the Strait of Gibraltar, so it can be seen throughout the year. They are often seen swimming along the Strait and in the Bay of Algeciras.
Length: 2.5 m.
Weight: ~ 150 kg.
Physical characteristics: they are slightly larger than common dolphins. Its coloration stands out for the gray-blue stripes that start from the head on both sides of the body. The belly is pinkish.
Social structure: they live in social groups of variable dimensions. In the Strait, they sometimes form groups of hundreds of individuals.
Behaviour: they like to swim in front of some whales or boats, a behavior known as bow-riding. They are shallow divers (<200 m). In the Strait, they are frequently seen sailing alongside common dolphins.
Food: they feed mainly on fish and also squid.
Threats: by-catch, water pollution, climate change. In the Strait of Gibraltar, there is a high risk of cuts and collisions with small commercial and recreational vessels, particularly those involved in illegal tuna fishing.
Conservation status: the population in the Mediterranean Sea is classified as Vulnerable by the IUCN. At a global level, the concern is less.
Curiosities: it is the most abundant species in the Mediterranean Sea. They are very agile, being able to reach 65 km / h.
It is a resident species in the Strait of Gibraltar, so it can be seen throughout the year. They can also be seen in the Bay of Algeciras.
Length: 2 - 4 m.
Weight: up to 650 kg, but they are smaller in the Mediterranean.
Physical characteristics: they are of an almost uniform grayish color, with a white belly. They have a flat and rounded nose.
Social structure: they live in social groups of variable dimensions, in the Strait usually composed of about 10-15 individuals.
Behaviour: they perform bow-riding. They are shallow divers (<200 m) although they can reach higher depths. They are very active animals, usually performing big jumps, sometimes just for fun. They are territorial. In the Strait of Gibraltar they are frequently seen with pilot whales.
Food: they feed mainly on fish and also squid.
Threats: bycatch, overfishing, climate change, water pollution, destruction of their habitat. In the Strait, there is a high risk of cuts and collisions with small commercial and recreational vessels, particularly those involved in illegal tuna fishing.
Conservation status: the population in the Mediterranean is classified as Vulnerable by the IUCN. No globally, the concern is less.
Curiosities: it is the best known and studied species worldwide. Unfortunately, they can be found in aquariums around the world. They are famous for their high intelligence.
LONG-FINNED PILOT WHALE
It is a resident species in the Strait of Gibraltar, so it can be seen throughout the year. Despite of their common name, it is worth saying that they belong to the dolphin family.
Length: females ~ 5 m, males 6 m.
Weight: females ~ 1300 kg, males ~ 2300 kg.
Physical characteristics: they present sexual dimorphism, although it is difficult to distinguish between females and males with the naked eye. They are light gray at birth, but as adults they turn dark gray or black. In the ventral side of their body, they present a clear spot shaped like an inverted anchor. They have a rounded head, with the absence of the nose so characteristic of other dolphins. The dorsal fin is very wide and falcate.
Social structure: they live in matrilineal social groups, that is, made up of females and their offspring. They have strong family ties. In the Strait of Gibraltar, social groups are normally composed of an average of 14 individuals, although the number can be highly variable.
Behaviour: they tend to get together to rest floating on the surface, that is why in the Strait they are commonly known as "the sleepers". They routinely spy-hopping, a behavior that consists of taking their heads out of the water to observe their surroundings. They rarely jump out of the water. They are territorial. In the Strait, they are frequently seen with bottlenose dolphins. They feed mainly at night, reaching 800 m for it. They are very curious animals, and they frequently approach small boats.
Food: they feed mainly on squid.
Threats: diseases such as morbillivirus, water contamination, interactions with fishing and recreational boats. In the Faroe Islands they are killed annually as part of the tradition of its inhabitants.
Conservation status: the population in the Mediterranean is classified as Data Deficient by the IUCN. Globally the concern is less.
Curiosities: they have a very cohesive social structure and this seems to be related to the numerous cases of mass stranding around the world.
It is not considered a resident species in the Strait of Gibraltar. It is usually seen in this area on a regular basis during the summer months, although they have been seen occasionally in the rest of the seasons. It is the largest of the dolphin family.
Length: females ~ 6-7 m, males ~ 7-8 m.
Weight: females ~ 3800 kg, males ~ 5500 kg.
Physical characteristics: they present sexual dimorphism. Males are easily distinguished from females by their large dorsal fin, which is triangular in shape and up to 1.80 m tall. Females have a smaller, curved dorsal fin. The coloration of killer whales is very particular, with a great contrast between their white belly and their black back. They have a so-called white eye-patch on both sides of the head and a grayish spot called a saddle on the back just behind the dorsal fin. Their pectoral fins are very large and rounded.
Social structure: they live in matrilineal social groups. In the Strait of Gibraltar, up to 5 families (known as pods) have been described, ranging from approximately 6 to 15 individuals. The last estimate of abundance was made in 2015, and it is 50 individuals, of which at least 43 are adults.
Behaviour: they perform very elaborate group hunting techniques. In the Strait, there are families that are frequently seen interacting with tuna fishing boats with longlines and others that do not interact. They perform jumps out of the water and spyhopping. Sometimes they approach small boats.
Food: they feed on a wide variety of prey, from small fish to sharks and even other marine mammals such as seals, dolphins or large whales. The population of the Strait of Gibraltar is piscivorous, and its main food is bluefin tuna ( Thunnus thynnus ).
Threats: overfishing, water pollution, interactions with fishing and pleasure boats, climate change and other anthropic activities.
Conservation status: the population in the Mediterranean is classified as Critically Endangered by the IUCN. Globally it is classified as Data Defficient.
Curiosities: today, there are several specimens in captivity. Despite their reputation as killers, there is no data on attacks on people in the wild. They are extremely intelligent animals.
It is not a resident species in the Strait of Gibraltar. They are usually seen in this area on a regular basis during the spring and autumn months, although they have been sighted occasionally in all seasons. The Strait has been recognised as a migration corridor for this species.
Length: newborns 4 m, females ~ 10 m, males ~ 16 m, maximum 20 m.
Weight: up to 80 tons.
Physical characteristics: they present sexual dimorphism, the males being notably larger than the females. In the Mediterranean Sea, they do not usually exceed 12-13 m in length. They have a very robust greyish-brown body. The head represents one third of the body and contains a unique organ in this species, the spermaceti, which consists of a viscous fatty substance that serves for echolocation and helps them to submerge, changing their density with the temperature of the water. They have large flukes and small pectoral fins. Sperm whales have teeth only in the lower jaw. Their body is asymmetrical: the blowhole, the hole through which they breathe, is located on the left side of their head, making their inclined breath unmistakable on the surface.
Social structure: sperm whales live in groups made up of females and younger individuals, and mature males take a solitary life. In the Strait, the individuals that are usually seen are adult and sub-adult males, and they are rarely seen in groups.
Behaviour: they dive for up to 1 hour in search of food and surface to rest for around 12 min. They make dives around 400 - 1200 m deep. When submerging, they exhibit their large tail. Sperm whales use echolocation clicks to find and stun their weights. They perform what is known as "marguerite formation", which consists of the formation of a circle by several individuals, placed with their heads inwards, to protect a young or a sick individual located in the center of it.
Food: They feed mainly on giant squid in the deep sea.
Threats: collision with large vessels, ingestion of large amounts of plastic, entanglement with ghost fishing nets, military sonar.
Conservation status: the population in the Mediterranean Sea is classified as Endangered by the IUCN. Globally it is classified as Vulnerable.
Curiosities: it is the largest of the odontocetes (cetaceans with teeth). They have the largest brain and the longest intestine in the entire animal kingdom. To sleep, they "stand" in an upright position in the water column.
It is not a resident species in the Strait of Gibraltar. They are usually seen in this area on a regular basis during the winter and summer months, although they have been sighted occasionally in other seasons. The Strait is a migration corridor for this species.
Length: up to 27 m.
Weight: more than 100 tons.
Physical characteristics: they present sexual dimorphism, being the females larger than the males, something unusual in mammals. They have an elongated body, very hydrodynamic, being able to reach speeds of more than 30 km/h. Fin whales have a small dorsal fin located at the rear of the back and are characterised by their asymmetric coloration: the lower jaw is dark on the left side, while on the right side it is white. They present V-shaped coloring pattern that is unique for each individual on both sides of the head (being more recognisable on the right side) called a chevron. Like all mysticetes, it has two spiracles.
Social structure: they can form groups of a few individuals, but in the Strait it is frequently to see solitary individuals or an adult with a young.
Behaviour: they usually dive for <16 min and surface to breathe a few times. To feed, it turns on the right side of its body. They use the Strait as a passageway to the Atlantic. It usually makes shallow dives (<200 m) although they can reach 470 m. Sometimes they jump exhibiting their entire body out of the water, a behaviour known as breaching.
Food: they feed on small fish, crustaceans (mainly krill) and squid, which they obtain by filtering huge amounts of water with their baleens.
Threats: collision with large vessels, overfishing, degradation of their habitat.
Conservation status: it is listed as Vulnerable worldwide and in the Mediterranean Sea by the IUCN.
Curiosities: it is the second largest animal in the world after the blue whale (Balaenoptera musculus). Some individuals live for more than 100 years. It is the only mysticete (cetaceans with not teeth) that frequently visits these waters and the Mediterranean Sea in general.
Illustrationss: © Akris Painting
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