Arxiu de la categoria: Marine mammals

The most recent extinct mammals because of humans

The history of life is full of extinctions of living beings, some massive and popularly known, such the one that extinguished dinosaurs. Extinction is a usual process, perhaps necessary, in biological evolution. Even so, the responsibility of the human species for the high rate of extinctions in recent years is alarming. We can even talk of a new geological era, in which the planet globally is changing due to our activity: the Anthropocene. In this post you will meet four mammals that existed only 300 years ago and we will never see alive again. Or maybe will we recover them back from extinction?

THE MOST RECENT EXTINCT MAMMALS BECAUSE OF HUMANS

1. THE THYLACINE

Thylacine, Tasmanian wolf or Tasmanian tiger. Despite its many names, the thylacine (Thylacinus cynocephalus) was not related to wolves or tigers (placental mammals), as it was a marsupial animal, like kangaroos and koalas.

One of the few thylacines that are preserved taxidermized in the world. Museo nacional de Ciencias Naturales, Madrid. Photo: Mireia Querol Rovira

The thylacine was a solitary and twilight hunter, who caught his prey by ambush, since it was not very fast. A unique feature was the ability he had to open his mouth: the powerful jaws could open at an angle of 120 degrees. Watch it in the following video:

In the same way as the rest of the marsupials, the offspring were not born directly, but instead developed in the marsupium (popularly known as the mother’s “bag”).

Extinction and protection of the thylacin

The last known wild specimen was hunted in 1930, and in 1933 the last captive specimen in a zoo died, 125 years after its description (1808). There are several hypotheses about its extinction:

  • Intensive hunting: As with the wolf in Spain nowadays, the thylacine was accused of killing cattle, so rewards were offered for dejected animals. Subsequent studies have concluded that their jaw was not strong enough to kill an adult sheep.
  • Reduction of habitat and prey: with the colonization of Australia, their habitats and habitual preys were reduced.
  • Introduction of invasive species and diseases: colonization also led to the introduction of species that competed with the thylacine (dogs, foxes…) and new diseases to which it was not immunized.

The protection of the species was approved 59 days before the death of the last individual. The law was clearly late and insufficient.

If you want to know more about the thylacine, we encourage you to read The thylacine: we extinguished it.

2. THE QUAGGA

The quagga (Equus quagga quagga) it was a subspecies of zebra that inhabited the plains of South Africa. The anterior half of the body had the typical black and white stripes of the zebra. The stripes blurred to give rise to a brownish color on its back, so it was initially believed to be a separate species from the common zebra (Equus quagga). The legs were white.

Its strange name belongs to the onomatopoeia, in the language of the Khoi, of the noise that quaggas made.

Cuaga quagga disecada ,taxidermia, taxidermy
Taxidermized quagga in the Museum of Natural History of Bamberg. There are only 23 quaggas dissected worldwide. Photo: Reinhold Möller

Extinction and recovery of the quagga

The last wild specimen died in 1870, and the last one in captivity died in 1883 at the Amsterdam zoo, only 98 years after its description (1785). Although the quagga began to be hunted by Dutch settlers to use their flesh and skin, the decline in population was accelerated until extinction because of the intensive hunting to exterminate wild animals in the area, and thus use the pastures for domestic cattle.

quagga, cuaga, animal extinto
Of the few existing photographs of a quagga, at the London Zoo (1870). Photo: Biodiversity Heritage Library (public domain)

At the time no conservation effort was made. Moreover, it was not known that the quagga of the Amsterdam zoo was the last one. However, quagga has the dubious honor of being the only extinct species that has “come back to life” thanks to a project called The Quagga Project, which began in 1987.

When it was discovered that the quagga was not a separate species from the zebra, but a subspecies, its DNA was sequenced and compared with zebra’s DNA. After all, if they were subspecies, zebras had to have quaggas’ DNA in their genes. By selective breeding of zebras with a tendency to disappearing stripes, some quaggas are currently grazing in fields of northern South Africa.

Although the first technique that is intended for the recovery of extinct species is cloning, in the case of quaggas it has been possible through the reproduction of selected zebras, thanks to the quagga DNA preserved in its genome, even if they are not 100% quaggas identical to their extinct ancestors.

In this video you can see current quaggas and the investigation process followed to “resuscitate them” (english subtitles):

3. STELLER’S SEA COW

Steller’s sea cow (Hydrodamalis gigas) was a sirenium, that is, a marine mammal of the same order as manatees and dugong. It was distributed by the Bering Sea, near Kamchatka (Eastern Russia). It was up to 8 meters long and weighed 5 tons.

vaca marina de steller, steller marine cow, esqueleto, skeleton, model, modelo
Model and skeleton of Steller’s sea cow. Photo: KKPCW

Unlike the rest of the sirenians, who live in the Indian Ocean and part of the Pacific, Steller’s sea cow lived in cold waters, had fewer teeth and was the best sirenium adapted to marine life. It was totally herbivorous (algae and plants).

Extinction and conservation of Steller’s sea cow

Steller’s sea cow has the sad record of being the fastest animal to become extinct since its discovery in 1741: only 27 years. The cause is, again, indiscriminate hunting by seal hunters and whalers, to take profit from the skin, meat, and fat. With hardly any predators, sea cows were easy prey. No effort was made to conserve the species.

Currently, there are only about 20 skeletons and few skin samples.

4. WESTERN BLACK RHINOCEROS

We finish the list of recently extinct mammals with the western black rhinoceros (Diceros bicornis longipes), a subspecies of the black rhinoceros. It was almost 4 meters long and could weigh up to 1.3 tons. Like all rhinos, they were herbivores.

rinoceronte negro occidental, wester black rino, rinoceront negre
Western black rhino. Source: savetherhino.org

Extinction and conservation of the western black rhinoceros

He lived in the savanna of central-western Africa only 8 years ago (IUCN declared it extinct in 2011). The causes of its extinction were:

  • Habitat loss.
  • Slaughtering by farmers to protect their crops.
  • And especially poaching, mainly to market with their horns and as hunting trophies. Rhinoceros horns are used in traditional Chinese medicine without any scientific evidence. If you want to know more animals threatened due to this activity, you can read The five most threatened species by traditional Chinese medicine.

There were 850,000 individuals registered at the beginning of the 20th century. Between 1960 and 1995, poachers reduced its population by 98%. In 2001, there were only 5 live rhinos left. In spite of the conservation measures taken at the beginning of the 20th century, the fight against hunting and enforcement of judgments against the poachers were declining over time, which led to the disappearance of the subspecies.

rinoceronte, rhino
Rhinoceros with their amputated horn. Foto: A. Steirn

Another subspecies of rhinoceros has become extinct in recent years: the southern black rhinoceros (Diceros bicornis bicornis) disappeared in 1850 due to excessive hunting and habitat destruction. The rest of the subspecies are critically endangered.

TO THINK ABOUT

The list of extinct animals in historical times and because of human action does not stop growing. Some species such as the Chinese river dolphin or Baiji (Lipotes vexillifer), have been declared extinct on more than one occasion. IUCN currently has it categorized as critically endangered-possibly extinct, although there is no solid evidence of its existence since 2007. The vaquita porpoise (Phocoena sinus) can be the next, with only 12 specimens detected in 2018.

baiji, delfin de rio chino, river dolphin, China, extinct, extinto extingit
This Baji was photographed before his death in captivity, 2002. Photo: Institute of Hydrobiology, Wuhan, China

Although animals, and especially mammals, include the most iconic species that the popular opinion wants to conserve, we must not forget the biological value of other species of animals, plants, fungi, algae and even bacteria, from which we should avoid their extinction. In a future post, we will write about some of these species.

How do cetaceans communicate?

We cannot imagine our lives without communication, but we are not the only animal species that use communication as a way to exchange information. In this post, we are explaining how cetacean’s communication is.

HOW DO CETACEANS COMMUNICATE?

Given that there are highly social species among cetaceans, it is essential to understand the role that communication plays in regulating social interactions in these species. When we think of communication, we usually tend to associate it with acoustic communication, and, in fact, this is the major way for cetaceans; but other types exists, such as chemical, visual or tactile communication.

ACOUSTIC COMMUNICATION: THE MOST DEVELOPED

Acoustic communication is the most important way of communication in cetaceans and the reason is that sound transmission in the water is very fast. It includes both vocal and non-vocal signaling. In some species, it can be very complex, since some of them have dialects.

Because of the fact cetaceans rely on sound, some activities such as seismic surveys may interfere in their behaviour and threaten their survival.

NON-VOCAL COMMUNICATION

Non-vocal communication consists of producing sounds without using the vocal apparatus, like using flukes or flippers to strike the water surface, jaw claps, teeth gnashing or bubble emissions. By slapping their tails, cetaceans convey a threat or distress.

Breaching is the typical behaviour of most cetaceans in which they leap vigorously into the air. The originated sound may travel several kilometres and it is thought to be a spacing mechanism, to keep acoustic contact or to inform about sexual stimulation, location of food or a response to injury or irritation. It can also be a manner to remove parasites and dead skin. More studies about the purpose of breaching are needed.

VOCAL COMMUNICATION IS VERY COMPLEX IN CETACEANS

Considering vocal communication, odontocetes and mysticetes  are very different. For this reason, we are explaining it separately.

MYSTICETES

Sounds of baleen whales have a social function, such as contact when in long distances, assembly calls, sexual advertisement, greeting, spacing, threat and individual identification. It is probable that they use sound as a way to synchronise biological or behavioural activities, such as feeding or breeding. You can read more about communication in baleen whales here.

Scientists agree there are three (plus one) types of sound in mysticetes:

  • Low-frequency moans (1-30 seconds, 20-200Hz). These sounds can be pure tones, such as in the case of fin whales (Balaenoptera physalus), or complex sounds with harmonic structure. These sounds are used in communication at long distances. For example, 20Hz moans of humpack whales (Megaptera novaeangliae) can pass through most obstacles and travel hundreds of kilometres to reach conspecifics for signaling. It has been suggested that, without obstacles, these kind of sounds can travel from pole to pole. Amazing, isn’t it? You can hear the call of the fin whale here.
fin whale, rorqual comun, balaenoptera physalus, circe, whale communication, cetacean communication, comunicacion ballenas, comunicacion cetaceos
Fin whale (Balaenoptera physalus) (Picture: Circe).
  • Short thumps or knocks (< 1 second, < 200Hz). These sounds are known to be produced by right whales (Eubalaena sp), bowhead whale (Balaena mysticetus), gray whales (Eschrichtius robustus), fin whales and minke whales (Balaenoptera acutorostrata).  These sounds are related to social context and activity.  You can here the call of the gray whale here.
  • Chirps and whistles (>1kHz, <0.1 seconds). These sounds are produced by most baleen whales. 
  • Humpback whale songs. You can here some songs of humpback whales here:

ODONTOCETES

According to scientist, odontocete sounds can be divided into two categories:

  • Pulsed sounds. All toothed cetaceans produces this type of sounds and can be used for echolocation (the production of high-frequency sound waves and reception of echoes to locate objects and investigate the surrounding environment) or communication. echolocation, dolphin, ecolocalizacion, delfines, comunicacion odontocetos, odontocete communicationEcholocation in dolphins.

They can be subdivided into two types:

  • Pulse or click trains (clicks). Click trains consist of sequences of acoustic pulses (50μsec, 5-150kHz) repeated over time. They are related to echolocation. Species can have a broad spectral composition, such as in the bottlenose dolphins (Tursiops truncatus), or have a narrow-band composition, as in narwhals (Monodon monoceros). In this type of pulsed sound, animals produce from 1-2 to serveral hundreds of click per second. You can hear the clicks of the bottlenose dolphin here.
  • Burst-pulsed sounds (20-100kHz). These high repetition rate pulse trains; called barks, squawks, squeaks, blasts, buzzes and moans; consists of producing a pulse every less than 5μsecond, which is heard by humans as a continuous sound. They have  communicative and social functions. You can hear burst-pulsed sounds in an aggressive encounter among dolphins in this video:

  • Narrow-band tonal sounds (whistles) (5-85kHz). Whistles are thought to be produced only for communication purposes and not all odontocetes produce them. Because they are low frequency sounds, these sounds can travel longer distances than pulsed sounds. Some species, such as bottlenose dolphins can produce whistles and clicks at the same time, what permits to maintain communication and coordination during food search by echolocation. Even in some species, such as the bottlenose dolphins, exists signature whistles; that is a so distinctive whistle that serve to identify the animal, as if it was its name. Do you want to know more about signature whistles? Watch the video:

CHEMICAL COMMUNICATION IN CETACEANS

Chemical communication includes the smell and taste. Despite it is important in terrestrial mammals, in marine mammals it is limited.

The olfactory system in cetaceans is almost nonexistent, since there is no olfactory nerves, bulbs and tracts in adult odontocetes (cetaceans with teeth) and they are greatly reduced in adult mysticetes (baleen whales). In addition, all cetaceans close their blowholes under the water.

On the other hand, taste is more important. For example, bottlenose dolphins (Tursiops truncatus) have the ability to discriminate sour, sweet, bitter and salty solutions. However, they are least sensitive to different salt concentrations, being adaptive to the  marine environment.

delfin mular tursiops truncatus comunicacion cetaceos
Bottlenose dolohins (Tursiops truncatus) can discriminate sour, sweet, bitter and salty solutions (Picture: NASA, Creative Commons).

Other species, such as belugas (Delphinapterus leucas), release pheromones to alarm their mates and, with blood in the water, they quickly escape or become unusually excited.

VISUAL COMMUNICATION

Vision under water is limited by light levels, the organic matter and depth. Visual displays can be of different types, such as sexual dimorphic features, body postures and colouration patterns, which are simple; or more complex like sequences of behaviours, which indicate a context, species, age, sex or reproductive condition.

For cetaceans, visual signals are an alternative to acoustic communication when the animals are close. In the case of odontocetes, visual displays are behaviours, colouration and morphological traits.

For example, male narwhals have long spiral tusks and in males of several beaked whales there are lower teeth that protrude outside the mouth. In that cases, but they are not the only ones, these are sexually dimorphic features that may play an important role in regulating social signaling and mating.

narwhal, narval, monodon monoceros, comunicacion cetaceos
Male narwhals (Monodon monoceros) have a spiral tusk that may regulate social signaling and mating (Picture: NOAA).

Clear-water dolphin species show colour patterns in the body, such as spots, saddle patches, capes or longitudinal striping, such as the striped dolphin (Stenella coeruleoalba).

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

Finally, gestures are also important in cetaceans, such as open-jaw threat displays, aerial leaps, flared pectoral fins, tail lobs and S-shaped postures. Posture and behaviours may also inform about predators, prey or to synchronise actions among individuals in order to coordinate the group or for social interaction.

In this video, you can see a dolphin displaying the open-jaw threat behaviour.

In this one, a humpback whale is showing the tail lob display.

COMMUNICATION THROUGH TOUCH

Cetaceans may use their nose, flippers, pectoral fins, dorsal fin, flukes, abdomen and the entire body as a means of communication by touching other animals.  Tactile signals are usually used together with other types. This type of communication has been noted in all cetaceans. Not only do body contact serve as a communication display, but it also may serve to remove dead skin.

For example, gray whales (Eschrichtius robustus) of San Ignacio Lagoon (Mexico) rub under small boats and tolerate petting of tourist.  You can watch it here:

Atlantic spotted dolphins (Stenella frontalis), bottlenose dolphins, humpback whales and North Atlantic right whales (Eubalaena glacialis), among others, gently rub their bodies with congeneres and it is common between mothers and calves.

REFERENCES

  • Berta, A; Sumich, JL & Kovacs, KM (2006). Marine mammals. Evolutionary biology. UK: Academic Press.
  • Dudzinkski, KM; Thomas, JA & Gregg, JD (2009). Communication in Marine Mammals. In Perrin, WF; Würsig, B & Thewissen, JGM (Ed.). Encyclopedia of Marine Mammals (260-269). Canada: Academic Press.
  • Cover picture: Gregory “Slobirdr” Smith, Creative Commons.

Have you ever seen some of these types of communication in cetaceans? Share it with us on the comments!

Cetaceans and fishing: a dangerous relationship

The cetaceans are creatures that live in the seas and oceans of the Earth. Like other animals, not only must they cope with natural threats to their environment, such as predation or disease, but they also interact with human activities, such as fishing. Here we will see how fishing threatens the populations of these marine mammals. 

CETACEANS AND FISHING: A DANGEROUS RELATIONSHIP

According to a recently report published by Ecologists in Action, the main threats of anthropic origin that cetaceans have to overcome are fishing, aquaculture, submarine noise, collisions with boats, marine litter, chemical pollution, sighting tourism , research, climate change and dolphinariums.

amenazas cetaceos
Cetaceans have to face several anthropic threats and they might beach at coast (Picture: Bahnfrend, Creative Commons)

WHALING

During the last century, whaling activity captured more than three million individuals worldwide, especially in the southern hemisphere, where according to the IWC, about 750,000 individuals of fin whales (Balaenoptera physalus) and 400,000 specimens of sperm whales (Physeter macrocephalus) were captured, among others.

It is known that until the 1960s, hundreds of thousands of blue whales were captured, the largest animal that inhabits the Earth. Despite conservation efforts, currently only between 10,000 and 20,000 individuals survive, a small part compared to those that inhabited the Earth before the boom in the whaling industry.

industria ballenera, relacion cetáceos pesca
Picture showing whaling (Picture: Creative Commons)

In fact, according to a study by Tulloch et al. (2017), although there is currently an international moratorium and major conservation efforts are being made, in the year 2100 the populations of cetaceans that were the object of catches will reach, at most, by half of its original size.

Contrary to the prohibitions established in 1986, there are countries that continue to catch whales and dolphins. These countries are mainly Japan, Norway and Iceland. It is believed that they capture some 1,500 whales annually together, although the demand for meat from these marine mammals is low. In fact, since the ban, it is estimated that some 30,000 whales have been captured.

In Spain, the capture of cetaceans is also prohibited, although it is believed that there is a small illegal activity.

BYCATCH OF CETACEANS

We must bear in mind the impact of accidental catches, one of the main causes of mortality in cetaceans. It consists in the capture of species that are not the target of fishing.

Bycatch can cause a conservation problem when there are endangered species affected, such as the vaquita (Phocoena sinus), a critically endangered porpoise (there are only about 30 animals left around the world), according to the IUCN. mainly due to gillnets.

Bycatch is one of the main causes of mortality, although at European level some measures have been taken, such as Regulation 812/2004. Accidental capture with the use of driftnets was especially important, but this practice is currently prohibited throughout the Mediterranean. In any case, other fishing gears, such as gillnets, purse seines or trawls, are particularly harmful.

In the 1960s, the tuna purse seine fishery in the Eastern Pacific had a significant impact on dolphin populations. The reason is that the fishermen knew that under the groups of dolphins that swam on the surface there are schools of tuna that followed them to take directionality. Thus, knowing this relationship, they surrounded the cetaceans (and therefore the tuna) with the purse seines, killing the former. It is estimated that in 1986 alone, about 133,000 dolphins were captured. To stop this situation, the pressure of the society was fundamental to take the appropriate measures. In fact, currently less than 0.1% of individuals are captured.

relacion pesca cetáceos, pesca accidental delfines
Fishers related dolphins with tuna, so that purse seine affected them (Picture: Wally Gobetz, Creative Commons)

Now we will focus on a case of gillnets. Gillnets kill many different species of cetaceans, both dolphins and whales. Although whales often survive, they often have traces of fishing gear attached to the body, such as nets. Small cetaceans do not suffer the same fate and often die. We have already seen the case of the vaquita , but another porpoise, the harbour porpoise (Phocoena phocoena) is the cetacean that suffers most deaths from gillnets.

Finally, we will see the relationship between cetaceans and trawling. Many species of cetaceans, both dolphins and small whales, feed on the target species of trawling, so they are caught while they are feeding on their prey. In fact, 16 cetacean species have been reported worldwide that feed in association with trawling. The catches are much greater when nets are left at a medium depth than when fishing is done on the seabed.

Despite all conservation efforts, according to an estimate by Read and collaborators, about 300,000 marine mammals are accidentally caught around the world each year due to fishing operations.

COMPETITION FOR FOOD

Finally, we cannot forget that cetaceans and fishermen compete for the same resources. Therefore, we must bear in mind that some cetaceans also interact with fishing to get food. Sperm whales, bottlenose dolphins and killer whales have learned to “steal” food from fishermen.

In fact, they take captures from longline, gillnets and trawl nets, running the risk of being trapped.

In any case, some measures have been taken, such as installing devices that emit annoying sounds for animals. Despite the attempts, they have adapted to it and, in fact, in some cases interpret them as an indication of the presence of fishermen in the area.

REFERENCES

  • López López, L (2017). Cetáceos: los mamíferos más salaos. Informe sobre las interacciones entre cetáceos y actividades humanas. Ecologistas en acción.
  • Hall, MA; Alverson, DL & Metuzals, KI (2000). Bycatch: Problems and solutions. Marine Pollution Bulletin Vol. 41, N 1-6, pp. 204-219.
  • Northridge, S (2009). Bycatch. In Perrin, WF; Würsig, B & Thewissen, JGM (Eds). Encyclopedia of Marine Mammals (pp.167-169). Academic Press (2 ed).
  • Whale and Dolphin Conservation: Stop Whaling
  • World Wildlife Foundation: The Vaquita
  • Cover picture: Omar Vidal (source)

Dolphins and humans: 5 things in common

Dolphins awaken interest of most people, if not everybody. Some of them are attracted by these creatures for their intelligence. Others because they believe they have a special connection with them. Whatever the reason, the fact is that there are some behaviours and characteristics of these wonderful animals that are shared with humans. Do you dare to find out?

1. DOLPHINS HOLD CONVERSATIONS

According to a study published in August 2016 in the journal Mathematics and Physics, scientists have discovered what appears to be a type of spoken language of dolphins.

Specifically, they have found that two dolphins took turns at the time of producing sound pulse packs and they  do not interrupted the other while the partner was communicating. Some people should learn from the dolphins, don’t you think? Scientists have compared it to a conversation between two people.

Tursiops truncatus delfin mular
Two dolphins have been described holding a conversation, in the same way as people do it (Picture: Julien Bidet, Creative Commons).

It is the first time that this phenomenon has been detected. Now, thanks to microphones that distinguish the different “voices” of animals, it has been possible.

But they have not only reached this conclusion. They also believe that each sound pulse corresponds to a word and pulse packs are actually phrases, in the same way that humans do. This means that the two individuals were sharing some kind of message.

All this demonstrates the high level of intelligence and conscience of these animals, besides the level of development of their spoken language, comparable to humans.

Do you want to know about some cetaceans with dialects?

2. DOLPHINS ALSO HAVE A NAME

To be more correct, dolphins have identification whistles that allow the identification of individuals, called signature whistles. Calves develop over time its own whistle, which seems to be part of their imprinting.

Imprinting is a pattern of rapid learning and normally stable that appears early in life of a member of a social species, and implies the recognition of their own species. This may involve attraction to the first seen moving object, even another species.

It is not after two months of life that they develop their signature whistle. At the time of “choosing its name”, they seek a whistle different from the other members’ group to avoid confusion.

Another study from 2013 concluded that dolphins respond when they hear that another individual “says its name.” It also showed that in case animals are exposed to signature whistles that are not of any member of the group, they do not respond.

You can find more information in this video from National Geographic:

3. MOTHERS TALK TO THEIR BABIES WHEN THEY ARE IN THE UTERUS

What pregnant woman has not sung or spoken to her babies as they were being developed in the womb? According to experts, this helps the baby to recognise her voice. We now know that we are not the only species who do it.

A research suggests that mothers talk to their babies. Specifically, they sing their own name. This is believed to help the baby to recognise her mother’s voice.

delfín útero feto
Dolphin mothers sing to her babies while they are in the womb (Picture: National Geograhic).

The songs are intensified two weeks before birth and last until two weeks later. The funny thing is that the rest of the group significantly reduce production of its signature whistle during the first two weeks of life of breeding.

4. SEX: BEYOND THE PROCREATION

How many animal species do you know that have sex for pleasure? It is known that several species of dolphins, like humans, bonobos and other species, have sex beyond procreation.

This is known to be true because females have been watched having sex beyond their period of ovulation. It is also known that killer whales, the larger dolphin species, have homosexual behaviours.

In addition to feeling pleasure, these “encounters” can serve to strengthen the links between the different members of a group.

I leave this other video of National Geographic in which promiscuity dolphins is explained:

5. DOLPHINS USE PROTECTIONS TO AVOID INJURY

A study reported that bottlenose dolphins (Tursiops truncatus) use sea sponges, supposedly to avoid getting hurt with rocks when  they are looking for something to eat or to avoid the pincers of crabs.

delfin sponging tursiops truncatus delfin mular
A bottlenose dolphin (Tursiops truncatus) with a sea sponge in the snout (Picture: Eric M. Patterson)

This behaviour has been named sponging. This practice cannot be extended to all individuals of the species, as it has only been described in a region of Australia.

It is believed that this behaviour has passed between generations, from mother to female offspring (very little in males), but there was only one inventor, that had the occurrence between 120 and 180 years ago.

In addition, scientists have found that females who use sponges, compared to those in the area which do not use them, are more lonely, spend more time in the depths and spend more time feeding, without compromising the future of their offspring.

5+1. DOLPHINS LOVE TECHNOLOGY

OK… That is not true! But look this video of a captive dolphin, which steals woman’s iPad.

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Which of these facts have you found more surprising? Do you know other dolphin behaviours that are similar to humans? Leave your answers in the comments.

REFERENCES

Difusió-anglès

The elderly organisms of the oceans

Have you ever wondered which are the longest-lived organisms of the seas and oceans of the Earth? The sea turtles are well known to have long lives. But, ¿which is the oldest organism of the ocean (and the planet)?

BOWHEAD WHALES

The bowhead whales (Balaena mysticetus), also called Arctic right whales, live most of the year associated with sea ice in the Arctic ocean. These marine mammals are among the largest animals on Earth, weighing up to 75-100 tons and with a length of 14-17 m on males and 16-18 m on females.

Bowhead whale (Balaena mysticetus) (Picture: WWF).
Bowhead whale (Balaena mysticetus) (Picture: WWF).

More than 20 years ago, in 1993, it was discovered by chance that bowhead whales have a longer life than previously thought. Their lifespan was considered to be about 50 years, but the unexpected discovery let to know that they live more than 100 years. In fact, some individuals are known to have lived for about 200 years.

Which was that fortuitous discovery? An Alaskan Eskimo hunted an individual with the tip of a harpoon inside its blubber. This harpoon was created with a technique not used for 100 years.

They are among the mammals that get much older, even among other whales. And the explanation to this fact lies on the extreme cold of their habitat: they have to invest so much energy in maintaining the body temperature that their first pregnancy is usually at 26 years and, therefore, they have a long life expectancy.

SEA TURTLES

In the famous Disney movie Finding Nemo, Marlin, Nemo’s father, meets Crush, a 150-year-old sea turtle. However, do sea turtles live so much?

Do you want to discover the amazing life of the sea turtles? Do you want to know the reason why sea turtles are threatened?

Sea turtles have long lives, but their age is unknown (Picture: Key West Aquarium).
Sea turtles have long lives, but their age is unknown (Picture: Key West Aquarium).

It is well-known that sea turtles have a long life, but their ages are barely known. It has been confirmed that growth lines in some turtle bones are laid down annually, but due to growing at different rates depending on the age, this cannot be used to estimate their age.

However, scientist believe that these awesome reptiles may live long like whales. Those turtles that outlive the first stages of life can expect to live at least 50 years. In addition, biological aging is nearly suspended for these animals.

Despite unknowing the age of the oldest wild sea turtle, it is said to be a 400-year-old captive sea turtle in China.

THE OLDEST KNOWN ANIMALS

Black corals are the oldest known animals on Earth. Notwithstanding, they are not the oldest organisms on the planet.

Leiopathes sp. is a genus of black corals that can live several millenniums (Picture: CBS News).
Leiopathes sp. is a genus of black corals that can live several millenniums (Picture: CBS News).

These coal-dark-skeleton corals grow a great deal less than a millimetre per year, such as the Mediterranean red coral. Despite its name, they usually show yellow, red, brown and green colours. Although they are considered deep-sea corals, they are found worldwide and at all depths.

Research in 2009 demonstrated that a Hawaiian black coral individual included in the Leiopathes glaberrima species had been living and growing since the building of Egyptian pyramids; 4,600 years ago.

Like sea turtles, in case an individual survives the first century of age, there is every likelihood of  living for a millennium or more.

THE IMMORTAL JELLYFISH

It is a fact of life that all living beings die; except for Turritopsis nutricula, the immortal jellyfish. This small (4.5 mm) bell-shaped jellyfish is immortal owing to the fact that possess the capability to age in reverse.

The immortal jellyfish, Turritopsis nutricula (Picture: Bored Panda).
The immortal jellyfish, Turritopsis nutricula (Picture: Bored Panda).

This species starts its life being a mass of polyps growing in the seafloor, which in some point produce jellyfishes that develop gonads to create the following generation of polyps, and then die. This has nothing special in comparison with other jellyfishes. Learn more about these beautiful animals here.

This cnidarian species, under the presence of a stressor or injury, transforms all its cells into larval forms. It is that changes from an adult to a larva. Then, every single larva can transform into a new adult. That process is named transdifferentiation. Little do scientists know about this process in the wild.

Transdifferentiation in Turritopsis nutricula (Picture: Bored Panda).
Transdifferentiation in Turritopsis nutricula (Picture: Bored Panda).

THE OLDEST ORGANISM ON EARTH

The oldest organism on Earth is neither an animal, algae nor a microorganism. The most elderly organism in the planet is a plant. In concrete, a marine plant known as Posidonia oceanica, commonly known as Neptune Grass or Mediterranean tapeweed. Do you want to know the reason why the Posidonia ecosystems are considered the marine jungles?

pradera posidonia oceanica
Posidonia oceanica meadow (Picture: SINC).

Spanish researchers found out that in Formentera (Balearic Islands) there is a 100,000-year-old Posidonia clone. This means this is the longest-living organism on the biosphere.

The key to understand its age is the clonal growth: it is based on the constant division of cells placed in the meristems and on the extremely slow growth of its stalk (rhizomes).

REFERENCES

  • Arnaud-Haond S, Duarte CM, Diaz-Almela E, Marba` N, Sintes T, et al. (2012) Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica. PLoS ONE 7(2): e30454. doi:10.1371/journal.pone.0030454
  • NOAA: Black corals of Hawaii
  • Palumbi, S.R & Palumbi, A.R (2014). The extreme life of the sea. Princepton University Press
  • Reference: The oldest sea turtle
  • Rugh, D.J. & Shelden, K.E.W. (2009). Bowhead whale. Balaena mysticetus. In Perrin, W.F; Würsig, B & Thewissen, J.G.M. Encyclopedia of Marine Mammals. Academic Press (2 ed).
  • Schiffman, J & Breen, M (2008). Comparative oncology: what dogs and other species can teach us about humans with cancer. The Royal Society Publishing. DOI: 10.1098/rstb.2014.0231
  • WWF: How long do sea turtles live? And other sea turtle facts
  • Cover picture: Takashi Murai (Bored Panda)

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What lies beyond the death of a whale?

Have you ever wondered what happens after the death of a whale? When a whale’s life ends, its body turn into a new ecosystem for many life forms. Do you want to learn more about whale falls? Which are the stages of a whale fall? Do you want to discover some incredible new species? 

INTRODUCTION

Whales are amazing animals and they play a significant role in the marine ecosystems, as well as other cetacean species. Take the humpback whale for instance. This species feeds using a unique system called the net bubble method, in which seabirds can take advantage of it due to the fact that whales drive prey to the surface. Another key role they play is the transport of nutrients. Finally, another example is the one that we are going to explain in this post: the whale falls.

WHAT IS A WHALE FALL?

Whale corpses are known to serve as a host for animals that live in the bottom of the oceans. When the whale carcasses fall to the bottom of the sea, concretely in the bathyal or abyssal zone (at depths of 2,000 m or more), they are called whale falls. These animals take benefit from the dead whales since they serve as a source of food for them.

Whale fall (Picture: Ocean Networks).
Whale falls are ecosystems by themselves (Picture: Ocean Networks).

It is believed that whale falls may have provided a stepping stone for deep-sea species to colonise the sea floor. In addition, the more research, the more new species described and the more potential commercial applications.

STAGES OF COLONIZATION

A dead whale creates by itself a new and rich ecosystem because produces intense organic enrichment in a very small area. After this, successive stages of colonization take place. Species found in these areas are similar to those in hydrothermal vents. According to researchers, whale falls pass through three stages:

  1. Mobile scavengers stage
  2. The enrichment-opportunist stage
  3. Sulfophilic stage
Decomposition of a whale carcass in Monterey Canyon over 7 years (Picture: MBARI).
Decomposition of a whale carcass in Monterey Canyon over a 7-year period (Picture: MBARI).

It is thought that tens of thousands of organisms from about 400 animals species depend on a single whale fall. Astonishingly, scientists estimate that one whale corpse provides with the nutritional equivalent of 2,000-years worth of normal biological detritus sinking to the seafloor.

1. MOBILE SCAVENGERS STAGE

The first stage is dominated by mobile scavenger species. In this stage, the dead whale is covered by a dense aggregaton of hagfishes, small numbers of lithodid crabs, rattail fish, large sleeper sharks and millions of amphipods.

These animals are responsible of the disappearance of the soft tissue. They can eat 40-60 kg per day. In a 5-ton carcass, it lasted for 4 months, while in 35-tone carcasses for 9 months to 2 years.

Grey whale decomposition, 2 month after deposition (Picture: Hermanus Online).
Grey whale decomposition, 2 and 18 month after deposition (Picture: Hermanus Online).

2. THE ENRICHMENT-OPPORTUNIST STAGE

During the second stage, the animal’s skeleton is surrounded by dense aggregations of polychaete worms, cumaceans (crustaceans) and molluscs such as snails. There have been described some whale fall specialist species, previously unknown. These animals feed on the rest of the body, including the sediment surrounding because it is full of decomposing tissue.

Se (Picture: Hermanus Online).
During the enrichment-opportunist stage, the skeleton is surrounded by many species of animals (Picture: Hermanus Online).

3. SULFOPHILIC STAGE

This is by far the longest stage in whale falls: it might last from 10 to 50 years, or more. The so-called sulfophilic stage owes its name to the sulfide produced by bones due to the action of chemosynthetic bacteria, who use sulfate to break down the lipids inside the bones and produce sulfide. The sulfide allow the presence of dense bacterial mats, mussels and tube worms, among others. It have been found more than 30,000 organisms in a single skeleton.

Sulfide stage (Picture: Hermanus Online).
Sulfophilic stage (Picture: Hermanus Online).

NEW SPECIES DISCOVERED

As it has been mentioned above, new species have been described in whale falls. In this section, we are going to present only some of them.

The anemone Anthosactis pearsea is a small, white and cube-shaped species. Its importance lies on the fact that it is the first anemone found on a whale fall.

df (Picture: MBARI).
Anthosactis pearseae (white animals) (Picture: MBARI).

Species included in the genus Osedax have also been discovered. Their common name, bone-eating zombie worms, reflects exactly their task: to eat bones. These animals have neither eyes nor mouth, but they present reddish plumes that act as gills and some kind of green roots, where symbiotic bacteria break down proteins and lipids inside the bone, which supply nutrients for the worms. The macroscopic form of the animals is always a female, who contains dozens of microscopic males inside its body

Osedax frankpressi (Picture: Greg Rouse).
A female Osedax frankpressi (Picture: Greg Rouse).

Another strikingly awesome worm is the bristleworm, Ophryotrocha craigsmithi. In spite of lacking any particular adaptation, it is thought that they are exclusive at whale falls or similar ecosystems.

Ophryotrocha craigsmithi (Picture: Live Science)
Bristleworm, Ophryotrocha craigsmithi (Picture: Live Science)

A final example to take into consideration is the gastropod Rubyspira, whale-fall specialists molluscs which are 3-4 cm in length.

Rubyspira snails on whale bones (Picture: MBARI). Lat= 36.61337280 Lon= -122.43557739 Depth= 2895.4 m Temp= 1.683 C Sal= 34.618 PSU Oxy= 2.31 ml/l Xmiss= 84.1% Source= digitalImages/Tiburon/2006/tibr991/DSCN8049.JPG Epoch seconds= 1148489479 Beta timecode= 07:21:57:03
Rubyspira snails on whale bones (Picture: MBARI).

I encourage you to watch these videos about whale falls. In the first one, you can see a diving on the Rosebud whale fall carried out by the team of E/V Nautilus, searching for the life it supports. In the second one, you can see a feast in the deep in a whale fall in Monterey Canyon, recorded by the Monterey Bay Aquarium Research Institute (MBARI).

REFERENCES

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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

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