Arxiu de la categoria: Marine mammals: Organisms and fauna

Cetaceans of the Mediterranean Sea

Did you know that in the Mediterranean Sea habitually lives 8 species of cetaceans, among dolphins and whales; in addition to other visitor and spontaneous species, such as the killer whale? In this post, a new version of “Cetaceans in the Catalan coast“, the first post published in this blog, I will give more information about the cetaceans that live in this small sea. 

INTRODUCTION

Cetaceans originated 50 million years ago in the ancient Tethys Sea, from terrestrial mammals. Approximately, there are 80 living species in the world, but only 8 of them live habitually in the Mediterranean and other species are present only in some seasons or sporadically.

HABITUAL CETACEANS OF THE MEDITERRANEAN SEA

STRIPED DOLPHIN 

Striped dolphin (Stenella coeruleoalba) is a cetacean with a black or bluish grey colouration in the back and white in the ventral part. There is a black line from the eye to the anal region through each side, and another one from the eye to the pectoral fin. Mediterranean striped dolphins are slightly smaller than their neighbours from the Atlantic, and achieve a maximum length of 2.2 m.

Stenella coeruleoalba delfin listado cetáceos mediterraneo
Striped dolphin (Stenella coeruleoalba) (Picture: Scott Hill National Marine Mammal Laboratory, Creative Commons).

They may live in big groups, till hundreds of individuals. Anyway, in the observations that I have done in the Mediterranean, groups included from 5 to 50 animals. They are very acrobatics and they can jump 7 meters above the sea surface.

Striped dolphins are common in both Mediterranean basins, specially in the open sea, being so many abundant in Ligurian Sea, Gulf of Lion, Alboran Sea (between Andalucía, Spain, and Morocco) and the Balearic Sea (between the Iberian Peninsula and the Balearic Islands).

This is the most abundant species in the Mediterranean (about 117,000 animals in the western basin), but they are in a vulnerable status of conservation due to the affection by morbillivirus, pollutants such as organochlorine compounds and fishing devices.

BOTTLENOSE DOLPHIN 

Bottlenose dolphins (Tursiops truncatus) maybe are the most known for the population because they are the protagonist of some movies and they are the most common cetacean in captivity.

delfin mular tursiops truncatus cetaceos mediterraneo
Bottlenose dolphin (Tursiops truncatus) (Picture: Gregory Slobirdr Smith, Creative Commons).

Their robust body is grey, clearer in the sides and white in the abdomen. Bottlenose dolphins are 4 m long.

Their groups, integrated by females and offspring or young males, range from 2 to 10 animals. They live in all the coasts of the Mediterranean Sea.

Their conservation status in the Mediterranean is vulnerable. It is though that their population is about 10,000 animals. Competence with commercial fisheries, bycatch and water pollution are among their threats.

SHORT-BEAKED COMMON DOLPHIN 

Short-beaked common dolphin (Delphinus delphis) is easily recognisable for the colouration of its body: dorsal region is dark and sides are cream-coloured or yellow, and constitute a V in the half of the body. Like striped dolphins, they are also small animals (2-2.5 m).

delfin comun delphinus delphis cetaceos mediterraneo
Short-beaked common dolphin (Delphinus delphis) (Picture: JKMelville, Creative Commons).

They live in numerous groups in open waters, from 10 to 200 animals, but sometimes groups of several thousands have been seen.

They enjoy with boats:

Despite their name, it is difficult to observe them because they are endangered in the Mediterranean. In the last 40 years, their population have been reduced by half. There are several reasons: lack of preys due to competence with fishers, bycatch, habitat degradation, sound pollution and high concentrations of pollutants.

FIN WHALE

Fin whale (Balaenoptera physalus) is the biggest whale in the Mediterranean and the second one in the world.

rorcual comun balaenoptera physalus cetaceos mediterraneo circe
Fin whale (Balaenoptera physalus) (Picture: Circe)

Fin whale’s head is V-shaped, wide and flatten. It is dark grey in the back and white in the abdomen, but asymmetric in the jaws: left side is dark grey and right side is white. Dorsal fin is short and placed in the last third of the body. In the moment of diving, caudal fin is not shown out of the water. Blow may be 8 meters height and narrow. Their maximum length is 24 m.

They are usually seen alone or in small groups (normally mother and calf) in open waters. In the Mediterranean, they are most frequently sighted between Balearic Islands and Ionian Sea, being specially abundant in the Gulf of Lion.

According to IUCN, it is a vulnerable species in the Mediterranean, but it is endangered worldwide. The Mediterranean population includes 5,000 adults. They are victims of strikes with ships, high DDT concentrations, acoustic pollution due to seismic surveys and bycatch.

Have you seen this fin whale rescue from Fuerteventura?

SPERM WHALE

Sperm whales (Physeter macrocephalus)  are the biggest toothed whales and one of the biggest cetaceans in the Mediterranean.

cachalote-physeter-macrocephalus-cetaceos-mediterraneo
Sperm whale (Physeter macrocephalus) (Picture: Gabriel Barathieu, Creative Commons).

Sperm whales have a rounded or triangular hump instead of a dorsal fin, which is followed by six exaggerated “knuckles”. An important clue for its identification is the blow: it is a bushy blow directed low, left and forwards. Head, which is square, represent 1/3 of the total length of the body. It is dark or grey, with the lower part of the mouth white. To dive, they show the caudal fin out of the water. They may be 20 long.

Their groups are composed by females and their offspring, other groups of young males and adult males are solitary. The number of animals per group ranges from 10 to 15, but smaller groups also exist. They are usually seen in oceanic waters of all the Mediterranean.

It is an endangered species in the Mediterranean due to they are accidentally captured in fishing nets, by strikes with vessels and the annoyance provoked by marine traffic. It is estimated that live some thousands in the Mediterranean.

Have you seen this video of a sperm whales that “adopt” a deformed cetacean?

RISSO’S DOLPHIN 

Risso’s dolphin (Grampus griseus) is grey when is born, but becomes paler with age for the presence of scars that do not disappear. They might measure 4 m.

calderon gris grampus griseus cetaceos mediterráneo
Risso’s dolphin (Grampus griseus) (Picture: Rob, Creative Commons).

Generally, they live in groups of 3-50, despite sometimes groups of some thousands have been spotted. In the Mediterranean, it is widely distributed in open waters, being more abundant in the western basin, where they prefer continental slope and submarine canyons.

Their status of conservation is unknown, but bycatch and acoustic and chemical pollution affect them.

LONG-FINNED PILOT WHALE

Long-finned pilot whale (Globicephala melas) is the biggest dolphin species in the Mediterranean, since it may achieve 6 m. Black in general, this pilot whale has a anchor-shaped ventral patch. Its flippers measure one fifth of the length.

globicephala melas calderón común cetáceos mediterráneo
Long-finned pilot whale (Globicephala melas) (Picture: Wikiwand).

Their groups range from 10 to 60 animals, but also several thousands. Groups include several generations of females with their calves. In the Mediterranean, it is abundant in the western basin, specially in the Strait of Gibraltar and Alboran Sea.

There is deficient data to evaluate its status of conservation. Anyway, it is known that are threatened by bycatch, strikes and acoustic and chemical pollution.

CUVIER’S BEAKED WHALE

Cuvier’s beaked whales (Ziphius cavirostris) are dark grey or brown, paler in the head. Their head is bulky, and the beak is not much marked. They may be 7 m long.

zifio cuvier ziphius cavirostris cetaceos mediterraneo
Cuvier’s beaked whale (Ziphius cavirostirs) (Picture: WDC).

They usually live in groups of 2-7 individuals or alone, in deep oceanic waters.

It is difficult to observe them due to the little activity in surface, reason that can explain why there are not enough information to evaluate their conservation status. It is known that are specially sensible to acoustic pollution, both military activities or seismic surveys. Moreover, the ingestion of plastic and bycatch also affect them.

KILLER WHALES IN THE MEDITERRANEAN?

Killer whales (Orcinus orca) are one of the most fascinating cetaceans. They live in polar and tropical waters, from the coast to open sea.

orca orcinus orca cetáceos mediterraneo
Killer whale (Orcinus orca) (Picture: Jose J. Díaz)

In the Mediterranean, however, they are only considered residents in the Strait of Gibraltar, with a size population of 32 whales. Their presence in the Strait, it is believed that is linked to the presence of bluefin tuna, their food.

Did you know that they use different dialects to communicate each other? Did you know that homosexual behaviours have been described in this species? Albino killer whales have been reported.

Their status of conservation is unknown, but direct death by fishers, reduction of their preys, annoyances and habitat degradation are among the causes of their reduction.

REFERENCES

  • CRAM: Cetacis
  • Day, T (2008). Guía para observar ballenas, delfines y marsopas en su hábitat. Ed. Blume
  • Gobierno de Canarias: Curso de Observación de Cetáceos
  • IUCN (2012). Marine Mammals and Sea Turtles of the Mediterranean and Black Seas. Gland, Switzerland and Malaga, Spain: IUCN
  • Kinze, CC (2002). Mamíferos marinos del Atlántico y del Mediterráneo. Ed. Omega
  • Lleonart, J (2012). Els mamífers marins i els seus noms. Terminàlia, 5, 7-25
  • Notarbartolo di Sciara G. (compilers and editors) (2006). The status and distribution of cetaceans in the Black Sea and Mediterranean Sea. IUCN Centre for Mediterranean Cooperation, Malaga, Spain.
  • Cover picture: Scuba Diver Life

Difusió-anglès

Anuncis

Brief evolution of cetaceans

Cetaceans have always called attention to people, either for their spectacular lives, their intelligence or their imposing size. But, do you know which the origin of dolphins and whales is? Do you know how they have evolved? Here, you can discover the answers! 

TERRESTRIAL ORIGIN 

Cetaceans originated in the ancient Tethys ocean, 50 million years ago, from terrestrial mammals that were adapting to the aquatic environment. They have evolved so that they are the dominant group of marine mammals for their species and habitats diversity and their wide distribution in the planet.

Distribució dels continents fa 50 milions d'anys, moment en que varen originar-se els cetacis. A la regió actual del mar Mediterrani és on es trobava el mar de Tethys (Foto: Cuaderno de Cultura Científica)
Continent distribution 50 million years ago, moment in which cetaceans originated. In the nowadays region of the Mediterranean sea is where Tethys ocean were found (Picture: Cuaderno de Cultura Científica).

FROM EARTH TO SEA: THE EVOLUTION OF FIRST CETACEANS

Archaeocetes are the group of primitive cetaceans that lived during the Eocene (34-55 million years ago, mya), which were developing the features to live in the aquatic environment. Among archaeocetes, we find the organism that originated the two nowadays groups of cetaceans, the toothed whales and the baleen whales. We may find 5 families in this group: the Pakicetidae, Protocetidae, Ambulocetidae, Remingtonocetidae and Basilosauridae.

THE PAKICETIDAE

The Pakicetidae lived 50 mya in India and Pakistan, which had an appearance similar to wolf. They presented the nostrils close to the forehead and the eyes in a dorsal position, like crocodiles. The main feature to be classified as cetaceans is the structure of ears because they are adapted to an underwater hearing. In addition, they have dense bones to walk under the water. Pakicetidae were mainly terrestrial or freshwater animals. The most known animal is Pakicetus.

Pakicetus és un dels cetacis més primitius, el qual començava a adaptar-se al medi aquàtic (Foto: Encyclopaedia Britannica).
Pakicetus is one of the more primitive cetaceans, which begin to adapt into the aquatic environment (Picture: Encyclopaedia Britannica).

THE AMBULOCETIDAE 

The next archaeocetes were the Ambulocetidae, also from India and Pakistan, present in the middle-Eocene (41-50 mya). They were similar to crocodiles in some features, with short fins and a powerful body and tail. They had a big head, with the eyes in a dorsal and laterally position. Their lower limbs were adapted to swim and they swam by ventrally rippling the body, like the nowadays whales.

Ambulocetus natans (Foto: Paleo World).
Ambulocetus natans (Picture: Paleo World).

THE REMINGTONOCETIDAE

The Remingtonocetidae were found in India and Pakistan, about 43-46 mya. Despite the archaeocetes had big snouts, in this group were specially big. It is thought that their size was between Pakicetidae and Ambulocetidae. The nostrils were placed close to the forehead, they had small eyes and the inner ear were more adapted to underwater life.

Remingtonocetus (Foto: Nobu Tamura, Creative Commons).
Remingtonocetus (Picture: Nobu Tamura, Creative Commons).

THE PROTOCETIDAE

The Protocetidae lived in the middle-Eocene and were found in India, Pakistan, Africa, Europe and North America. Probably, they lived in warm seas close to tropics. They had a long snout, big eyes and the position of nostrils allowed them to breathing without leaving the head of the water, like present cetaceans. There are so many genus, but the one that give the name to the group is Protocetus. 

Protocetus (Foto: Nobu Tamura, Creative Commons).
Protocetus (Picture: Nobu Tamura, Creative Commons).

THE BASILOSAURIDAE

The last group are the Basilosauridae, which existed during the middle and last Eocene. Species could be between 4 and 18 m long. It’s a paraphyletic group, it is that all the descendents of the common ancestor are not included in the group. Their hind limbs were very reduced and their appearance were similar to the current cetaceans. The group includes, among other genera, Basilosaurus and Saghacetus .

Basilosaurus (Foto: Nobu Tamura, Creative Commons).
Basilosaurus (Picture: Nobu Tamura, Creative Commons).

REFEREES

  • Berger WH. 2007. Cenozoic cooling, Antarctic nutrient pump, and the evolution of whales. Deep Sea Res. II 54, pp. 2399-2421.
  • Berta A, Sumich J & Kovacs KM. 2011. Marine mammals. Evolutionary Biology. 2ª edició. Califòrnia: Academic Press
  • Fordyce RE. 2009. Cetacean Evolution. Dins Perrin W, Würsig B & Thewissen JGM (ed). Encyclopedia of Marine Mammals. 2ª edició. Canadà: Academic Press. pp. 201-207
  • Fordyce RE. 2003. Cetacea evolution and Eocene-Oligocene oceans revisited. Dins Prothero DR, Ivany LC & Nesbitt E (ed). Secondary Adaptation of Tetrapods to Life in Water. New York: Columbia University Press. pp. 154-170
  • Gray NM, Kainec K, Madar S, Tomko L & Wolfe S. 2006. Sink or swim? Bone density as a mechanism for bouyancy control in early cetaceans. Anat. Rec.: Adv. Integr. Anat. Evol. Biol. 290. pp. 638-653
  • Gingerich PD, Smith BH i Simons EL. 1990. Hind limbs of Eocene Basilosaurus: Evidence of feet in whales. Science 249. pp. 154-157
  • Gringerich PD. 2005. Cetacea. Dins Rose KD & Archibald JD (ed). Placental Mammals: Origin, Timing, and Relationships of the Major Extant Clades. Baltimore: Johns Hopkings University Press. pp. 234-252
  • Jaramillo Legorreta AM, Rojas Bracho L & Gerrodette T. 1999. A new abundance estimate for vaquitas: first step for recovery. Mar. Mamm. Sci 15 (4): 957-973
  • Lindberg DR & Pyenson ND. 2007. Things that go bump in the night: Evolutionary  between cephalopods and cetaceans in the Tertiary. Lethaia 40. pp. 335-343
  • Miralles L, Lens S, Rodríguez-Folgar A, Carrillo M, Martín V, et al. (2013) Interspecific Introgression in Cetaceans: DNA Markers Reveal Post-F1 Status of a Pilot Whale. PLoS ONE 8(8): e69511. doi: 10.1371/journal.pone.0069511
  • Thewissen JGM. 2009. Cetacean Evolution. Dins Perrin W, Würsig B & Thewissen JGM (ed). Encyclopedia of Marine Mammals. 2ª edició. Canadà: Academic Press. pp. 46-48
  • Uhen MD. 2009. Basilosaurids. Dins Perrin W, Würsig B & Thewissen JGM (ed). Encyclopedia of Marine Mammals. 2ª edició. Canadà: Academic Press. pp. 91-94
  • Uhen MD i Gingerich PD. 2001. New genus of dorudontine archaeocete (Cetacea) from the middle-to-late Eocene of South Carolina. Mar. Mamm. Sci. 17 (1). pp. 1-34
  • Williams EM. 1998. Synopsis of the earliest cetaceans: Pakicetidae, Ambulocetidae, Remingtonocetidae and Protocetidae. Dins Thewissen JGM (ed). The Emergence of Whales, Evolutionary Patterns in the Origin of Cetacea. New York: Plenum Press. pp. 1-28

Difusió-anglès

Cetaceans with dialects: the killer whale and the sperm whale

Last week, the press was full of news about a recent article that highlight that sperm whales in the Eastern Pacific have distinct dialects. For this reason, the post of this week will explain what a dialect is (in cetaceans), which cetaceans have dialects in addition to sperm whales and which is the explanation to this. 

INTRODUCTION

The first question to be answered is “What is a dialect?”. This question is not simple because sometimes this concept is confused with another one: geographic variation. While dialects are song differences between neighbouring populations of potentially interbreeding individuals, geographic variations refer to differences in song over long distances and between populations which normally do not come together. In the case of dialects, the explanation of their presence is social learning, while in geographic variations the reason can be found in their genes. The function of dialects is to be an acoustical signature that help maintain cohesion and integrity of groups and as an inbreeding avoidance mechanism.

CETACEANS WITH DIALECTS

To date, dialects have been described in two cetacean species: killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). These two species have several features in common:

  • They live in matrilineal groups, that are highly stable groups of individuals linked by maternal descent that protect themselves against predators and other dangers.
  • They live in multilevel societies, that consist of hierarchically nested social levels. From the upper to the lowest level, there are three levels: vocal clans, social units and individuals. This kind of societies are also present in human and other primates and in African elephants.

KILLER WHALE DIALECTS

Dialects have been found in resident killer whales from the northeastern Pacific, Norway and Kamchatka. In this species, these dialects consists on repertories of several call types that are different among pods. Each pod have distinctive features in the call repertories and, therefore, each pod has a particular dialect. Pods that share part of the repertories constitute acoustic clans. So, each clan is acoustically different. Pods from different clans can overlap and interact and new pods can be formed by fission of other pods, which turn out in divergence of dialects.

Killer whales are one of the cetacean species with dialects (Picture: Oceanwide Science Institute).
Killer whales (Orcinus orca) are one of the cetacean species with dialects (Picture: Oceanwide Science Institute).

SPERM WHALE DIALECTS 

Sperm whales have repertories that varied in the proportional usage of different coda types and classes. Sperm whale codas are stereotyped sequences of 3-40 broad-band clicks usually lasting less than 3 seconds in total, which functions are to help maintain group cohesion, reinforce bonds, aid negotiations and collective decision-making. These groups with distinct dialects also interact. To give a particular example, in the South Pacific and the Caribbean, there are six sympatric acoustic clans based on coda sharing, which simultaneously differ in movement and habitat use patterns and in feeding success.

Dialects have been described in sperm whales (Physeter macrocephalus) (Picture: CBC News).
Dialects have been described in sperm whales (Physeter macrocephalus) (Picture: CBC News).

ORIGIN OF DIALECTS IN CETACEANS

A recently published article in the magazine Nature suggests a mechanism that may explain the origin of multilevel societies in sperm whales. As we have seen, it is in these societies where dialects are present in cetaceans. So, here we will explain the origin of multilevel societies in sperm whales as an example.

In sperm whales, the upper level of the multilevel society are clans of individuals that communicate between them using similar codas. These clans are originated from cultural transmission via biased social learning of codas, when they learn the most common codas (conformism) from behaviourally similar individuals (homophily). Thus, the result are groups with increasingly homogeneous behaviour with a strong integration. The cultural transmission plays a key role in the partitioning of sperm whales into sympatric clans (clans that live together but without interbreeding). So, it is in these clans where distinctive behavioural patters may appear, like dialects. The lower level, social units, are originated from ecological, cognitive and time constraints and benefits.

Multilevel societies (Picture: Marc Arenas Camps).
Multilevel societies. Individuals (stars and filled circles) are the lowest level and in association (black lines) with other individuals they constitute social units (empty black circles). Socials units with acoustic similarity (orange lines) form vocal clans (blue and green). It is in vocal clans where dialects can emerge (Picture: Marc Arenas Camps).

HUMPBACK WHALES: A DIFFERENT CASE

The differences in the songs of humpback whales (Megaptera novaengliae) cannot be considered dialects since they happen between geographically isolated populations. Due to a geographic and reproductive isolation, these differences have appeared as a result of genetic distinctions among populations.

REFERENCES

  • Cantor, M; Shoemaker, LG; Cabral, RB; Flores, CO, Varga, M & Whitehead, H (2015). Multilevel animal societies can emerge from cultural transmission. Nature Communications. 6:8091. DOI: 10.1038/ncomms9091
  • Conner, DA (1982). Dialects versus geographic variation in mammalian vocalizations. Animal Behaviour. 30, 297-298
  • Dudzinski, KM; Thomas, JA & Gregg, JD (2009). Communication in Marine Mammals. In Perrin W, Würsig B & Thewissen JGM (edit.). Encyclopedia of Marine Mammals. Academic Press (2 ed).
  • Ford, JKB (2009). Dialects. In Perrin W, Würsig B & Thewissen JGM (edit.). Encyclopedia of Marine Mammals. Academic Press (2 ed).

Difusió-anglès

The dugong

Maybe, cetaceans (dolphins, whales and other species) are among the most well-known marine mammals, but other groups are also included: the polar bear, the pinnipeds (which contain walrus and seals), sea otters and sirenians (with manatees and the dugong). In this post, we are talking about the dugong, one of the four living sirenian species. 

INTRODUCTION

Sirenians, also known as sea cows, are an order of four living species, which contain 3 species of manatees (Trichechus) and the dugong (Dugong). The order originated 50-55 million years ago in the African or European region, depending on the sources. All their activities, also the fact of giving birth, take place in the water, so they are totally aquatic mammals. The four species live in warm waters with abundant seagrass and vegetation, since they are herbivorous. Until 18th century, a fifth species existed: the Steller’s sea cow (Hydrodamalis gigas), that was 9 metres long and was hunted to extinction.

Steller's sea cow (Hydrodamalis gigas) (Picture: Encylopaedia Britannica).
Steller’s sea cow (Hydrodamalis gigas) (Picture: Encylopaedia Britannica).

THE DUGONG: DESCRIPTION AND BIOLOGY

Despite nowadays there is a single extant species of dugong, 19 extinct genera have been described by scientists.

Dugongs (Dugong dugon) are sirenians with a gray and smooth skin, the mouth opens ventrally beneath a muzzle and present a dolphin-like tail, which is different from manatees and allows its identification. Due to its strongly downturned snout, dugongs are obligate bottom feeders. Males have tusks, but not females. The flippers are short and lack nails. They may weigh 400 kg and measure up to 3.5 m in length.

Dugong (Dugong dugong) (Picture: WWF).
Dugong (Dugong dugong) (Picture: WWF).

Dugongs inhabit in the tropical and subtropical region of the Indo-Pacific, including Red Sea; in shallow water less than 10 m deep. This represents a potential area of occupancy of more than 125,000 square km. They feed on seagrass rhizomes (more than on leaves) and other plants, which are rich in available nutrients (such as nitrogen) and starch, are easily masticated and poor in fiber. In some cases, they eat invertebrates mainly during the winter at the higher latitudes of their range.

Dugong distribution (Picture: Dugongs Endangered).
Dugong distribution (Picture: Dugongs Endangered).

They are quite difficult to observe because they surface very discreetly, with only their nostrils out of the water. Different from manatees, dugong spends all its life in the sea.

Dugongs are generally solitaries, since the only long-lasting social unit is between the mother and her calf. Females usually have their first calf when they are 6 to 17 years old and the time between births ranges from 3 to 7 years. The usual litter size is one and the gestation period lasts for 13 months. The oldest dugong found in a research was estimated to be 73 years old.

CONSERVATION STATUS AND THREATS

According to the IUCN Red List, dugongs are classified as a vulnerable species. Moreover, the total population size is unknown. Dugongs are vulnerable to several anthropogenic influences:

  • Habitat loss and degradation: the sensitivity of seagrass ecosystems is high and may be destroyed by mining, trawling, dredging, inland and coastal clearing and boat propellers, among others; which reduce the light intensity and, therefore, the growth of these plants.
  • Fishing pressure: the accidental entangling in gill nets, mesh nets and traps, both in the artisanal fisheries and in the industrial scale, is a major threat.
  • Indigenous use and hunting: dugong products are used in most of the countries with available information. These products include meat, leather, oil, medicaments, amulets and other. Fortunately, in many countires, dugong hunting is banned.
Dugongs hunted by the indigenous people of Australia (Picture: Earthrace Conservation).
Dugongs hunted by the indigenous people of Australia (Picture: Earthrace Conservation).
  • Acoustic pollution: there are just few reports of the impact of boat traffic in dugongs, but some suggest a ceasing to use areas with high traffic. Other studies with military detonations suggest potential indirect effects to dugongs such as injury, social disturbance, habitat damage and displacement. Moreover, effects of marine seismic surveys on dugongs might include: interference with their natural communication signals, damage in their ears and behavioural changes.
  • Chemical pollutants: dugongs accumulate high levels of heavy metals, but there is no evidence to be harmful to them; and pesticides.
  • Diseases: dugongs are susceptible to infectious and parasitic disease, like those produced by helminths, protozoans and other parasites.

REFERENCES

Difusió-anglès

Mediterranean Monk Seal: Until when will it survive?

In this post, we will do an approach to Mediterranean Monk Seal (Monachus monachus), a critically endangered species that, in fact, is the most endangered pinniped species in the world. Here, we are going to do a short historical review and we are going to talk about its natural history, its habitat and distribution, its threats and status and, finally, its conservation. 

INTRODUCTION

Mediterranean Monk Seal (Monachus monachus) is one of the three species included in the genus Monachus (Monk Seals). The other two species are Hawaiian Monk Seal (Monachus schauinslandi), which is critically endangered, and Caribbean Monk Seal (Monachus tropicalis), which is extinct.

mediterranean monk seal, monachus monachus
Mediterranean Monk Seal (Monachus monachus) (Photo: Sá, Wild Wonders of Europe)

Mediterranean Monk Seals were hunted for fur, oil and meat since Prehistory. Romans were responsible of an important decline, but thanks to the empire’ fall the animals were able to recover. More recently, the two world wars, the industrial revolution, the explosion of tourism and industrial fishing have produced the reduction and disappearance of the species in some regions.

MEDITERRANEAN MONK SEAL’S NATURAL HISTORY

When they are born, their length is 94 cm and their weight is 15-20 kg. Until weaning (at about 16-17 weeks), growth takes place fast. The pups’ pelt is soft and downy and the coat is black to dark brown, with a white patch in the belly.

Adult individuals have a length of 2.4 m (from nose to tail) and weigh 250-300 kg. Males are only slightly bigger than females. Juveniles and adults have very short hair. While adult males are black with a white patch in the belly, adult females are brown and grey with a lighter belly colouration. In any case, they can present more patches on the throat (males) and back (females).

Female individual of Mediterranean Monk Seal (Photo: Sá,
Female individual of Mediterranean Monk Seal (Photo: Sá, Wild Wonders of Europe)
Male individual of Mediterranean Monk Seal (Photo: Sá,
Male individual of Mediterranean Monk Seal (Photo: Sá, Wild Wonders of Europe)

Males and females reach sexual maturity between 5 and 6 years. After a gestation lasting 9-11 month, one pup is born (generally in autumn).

They feed on fish and cephalopods.

HABITAT AND DISTRIBUTION

This species’ habitat is inaccessible caves with underwater entrances. The truth is that in ancient times, they inhabit open beaches of sand and rocks. Mediterranean monk seals can be found in warm temperate, subtropical and tropical waters of the Mediterranean Sea and the east Atlantic Ocean.

Mediterranean Monk Seal habitat
Mediterranean Monk Seal habitat (Photo: Sá, Wild Wonders of Europe)
Mediterranean Monk Seal on beach
Mediterranean Monk Seal on beach (Photo: Hellio & Van Ingen)

In ancient times, the species’ distribution was bigger than now. While now they just are present only in the northeast Mediterranean and in the northeast Atlantic, long ago they were present in all through the Mediterranean Sea, Black Sea, Atlantic coast of Africa and some Atlantic islands.

Distribution map of Mediterranean Monk Seal (Monachus monachus) (Picture: TheAnimalFiles.com)
Distribution map of Mediterranean Monk Seal (Monachus monachus) (Picture: TheAnimalFiles.com)

STATUS AND THREATS

With just 350-450 individuals (maybe 550), the Mediterranean Monk Seal is one of the world’s most endangered marine mammals and is the most endangered pinniped species and it is described as critically endangered by IUCN.

Mediterranean Monk Seal is critically endangered, according to IUCN (Picture: IUCN).
Mediterranean Monk Seal is critically endangered, according to IUCN (Picture: IUCN).

The main threats against the species are:

  • Habitat degeneration and loss by development in the coast. The driving causes to this may be hunting, mass tourism, pleasure boats and diving. The result is that the caves occupied now are not adequate for their survival, so the recovery is only possible if they return to sandy beaches.
  • Killing them on purpose by fisherman and fish farm operators because they find it a nuisance that destroys their nets and steals their fish. In Greece, deliberate killing accounts for 43% of the deaths of adult and juvenile animals.
Deliberate killing of a Mediterranean Monk Seal (Monachus monachus) (Picture: A. Karamanlidis, MOm).
Deliberate killing of a Mediterranean Monk Seal (Monachus monachus) (Picture: E. Tounta, MOm).
  • Accidental entanglement in fishing gear. It is unknown if this has an important impact nowadays, but in the recent past it was and, in fact, it has played a significant role in the elimination of the species from some parts.
  • Decreased food availability due to overfishing. Malnourishment; susceptibility towards pathogens; affected growth, reproduction, juvenile survival and mortality rate and dispersion are the possible effects of this.
  • Unusual events: disease (like morbillivirus), toxic algae, rockslides, cave collapses or oil spills.
  • Pollution, maybe caused by organochlorine compounds used in pesticides.
  • Inbreeding depression, that results in reduced fecundity and pup survival. This factor is not a significant threat in the short term, but it can be a future threat because this causes reduced fertility, increased infant mortality and a distorted sex ratio.

CONSERVATION

Since 1970s, conservation measures have been developed, but the improvements are hardly seen. Conservation measures include:

  • Development of marine protected areas (MPA) in Madeira, Greece, Turkey and Cabo Blanco. In fact, what is necessary is a network of MPA.
  • Orphaned and hurt animals are rescued.
  • Educational programs.
  • Scientific investigation to identify its habitat areas.
  • International coordination of conservation activities.

On the other hand, ex situ conservation measures (like captive breeding and translocation) are not used because the species is so sensitive to human disturbance that it could be another threat.

REFERENCES

If you enjoyed this article, please share it on social networks to spread it. The aim of the blog, after all, is to spread science and reach as many people as possible. Your comments are welcome. 

This publication is under a Creative Commons License:

Llicència Creative Commons

Common names of Mysticeti

In this publication, there is a table that relate the scientific name of the different species of Mysticeti cetaceans (cetaceans with baleens) with their common names in Catalan, Spanish and English. You can observe that the most part of them have several names.

Nom científic

Català

Espanyol

Anglès

Nombre científico

Catalán

Español

Inglés

Scientific name

Catalan

Spanish

English

Eschrichtius gibbosus Balena gris Ballena gris Gray whale
Caperea marginata Balena franca pigmea Ballena franca pigmea

Ballena franca enana

Pygmy right whale
Balaenoptera musculus Balena blava Ballena azul

Rorcual azul

Blue whale

Sibbald’s Rorqual

Suphur-bottom Whale

Pygmy Blue Whale

Balaenoptera physalus Rorqual comú Rorcual común

Ballena de aleta

Ballena Boba

Fin whale

Finback whale

Fin-backed whale

Finner

Herring Whale

Razorback

Common rorqual

Megaptera novaeangliae Iubarta

Balena amb gep

Yubarta

Gubarte

Ballena jorobada

Jorobada

Rorcual jorobado

Humpback whale

Hump whale

Hunchbacked Whale

Bunch

Balaenoptera borealis Rorqual boreal Rorcual boreal

Rorcual norteño

Rorcual de Rudolphi

Rorcual sei

Ballena boba

Ballena sei

Sei whale

Rudophi’s Rorqual

Coalfish Whale

Pollack Whale

Balaenoptera edeni Rorqual tropical

Rorqual de Bryde

Rorcual tropical

Rorqual de Eden

Rorqual enano

Ballena de Bryde

Bryde’s Whale

Tropical Whale

Common Bryde’s Whale

Eden’s Whale

Pygmy Bryde’s Whale

Balaenoptera brydei Rorqual de Bryde Rorcual de Bryde

Ballena de Bryde

Bryde’s Whale

Tropical Whale

Common Bryde’s Whale

Eden’s Whale

Pygmy Bryde’s Whale

Balaenoptera acutorostrata Rorqual d’aleta blanca (Hemisferi nord) Rorcual aliblanco

Ballena de Minke común

Ballena enana

Rorcual menor

Common Minke Whale

Northern Minke Whale

Lesser Rorqual

Little Piked Whale

Dwarf Minke Whale

 

Balaenoptera bonaerensis Rorqual d’aleta blanca (Hemisferi sud) Rorcual austral

Minke antártico

Antarctic Minke Whale

Southern Minke Whale

Balaena mysticetus Balena de Grenlàndia

Balena franca àrtica

Ballena de Groenlàndia

Ballena boreal

Greenland Right Whale

Bowhead whale

Eubalaena glacialis Balena franca glacial

Balena franca comuna

Balena basca

Ballena franca glacial

Ballena de los vascos

Ballena franca del norte

Ballenga

North Atlantic Right Whale

Northern Right Whale

Right Whale

Black Right Whale

Eubalaena australis Balena franca austral Ballena franca austral Southern right whale
Eubalaena japonica Balena franca del Pacífic Nord Ballena franca del Pacífico Norte North Pacific right whale

Feeding behaviour of Humpback whale

This publication talks about Humpback whale (Megaptera novaeangliae). In particular, we are going to do an small introduction and we are going to focus on feeding behaviour of this animal, specially in a particular strategy devoloped for a group in west coast of Alaska.

 

Humpback whale, Megaptera novaeangliae, is a cetacean of the Balaenopteridae family that live in all the oceans, in oceanic and coastal waters. They measure between 12 and 16 meters (the females are lightly bigger than males) and they weight between 25 and 35 metric tons.  They eat krill and fishes.  We can identify them using different things: the caudal fin, with a visible central groove and with a cut edge, raises before it dives; the pectoral fins are very big and rounded, with a dark top and light bottom; the head is wide and has nodules on the top and also has nodules on bottom mandibule; and they have a big body, with a black – dark grey back and sides and a white abdomen.

Humpback_Whale_fg1_cropped

SOURCE: http://en.m.wikipedia.org/wiki/File:Humpback_Whale_fg1_cropped.JPG

 

About feeding behaviour, they have developed different amazing methods. The most known is called the bubble net, used to capture shoals of fishes. Other least sophisticated methods consists on swim against the fishes or hit the water with fins to stun them.

Now we are going to talk about the net bubble method. This one has been observed in a population from west coast of Alaska. During the summer, in the Alaska’s fjords there is a lot of plancton, what attract the herrings (Clupea harengus), which used to live in the depths to be protected from the predators. When humpback whales detect the fish, they do jumps and hits to advertise the other members. This method needs a lot of coordinaiton. Following the leader, they dive together and then each one adopt its position: there are the shepherds, who surround the shoal with fin movements with the goal of avoid the fishes escape; another member is placed under the shoal and produce a shout of 120 decibels to force the fishes to go up; and there is another member in the top that expel an air current to create a bubble net. The other members are under the fishes and jump against them with the mouth totally open. This technique allows to capure a half ton of fish every day.
bubble net

Author: Richard Palmer

I recommed seeing this video:

If you want more information, you can look for it here:

– DAY, Trevor. Guía para observar ballenas, delfines y marsopas en su hábitat (Ed. Blume)

– KINZE, Carl Christian. Mamíferos marinos del Atlántico y del Mediterráneo (Ed. Omega)

– PERRIN, W. F.; WÜRSIG, B; THEWISSEN, J. G. M. Encyclopedia of Marine Mammals (Ed. Academic Press, 2ª edició)

– Gigantes del mar, episodi 2: http://www.youtube.com/watch?v=lSQ6d02L1jc

 

Licencia Creative Commons
Licencia Creative Commons Atribución-NoComercial-CompartirIgual 4.0 Internacional.