No big animals, no fertile Earth

A study recently published in the magazine Proceedings of the National Academy of Science (PNAS) reveals that animals play a key role in the transport of nutrients, but their contribution has been reduced due to the extinction or decline of many of the largest populations. In this post, we will review this study in order to understand the consequences of this fact.

INTRODUCTION

The ancient Earth was plenty of giant animals, with abundant whales in the oceans and large animals in the land. Nevertheless, their populations have been reduced for several reasons:

• The massive extinction during the late-Quaternary: about 150 large mammal (more than 44 kg) species went extinct.
• Recent and present extinctions.
• Widespread population reductions in great whales due to hunting: some whale densities might have been reduced between 66% and 99%, like blue whale (Balaenoptera musculus).
• Present environmental pressures: 27% of seabird species are threatened and anadromous fish’s populations have been reduced to less than 10% of their historical values (Pacific Northwest).

All this things are probable to have caused a shift in the global nutrient cycling. In concrete, Doughty et al. estimate a reduction to about 8% of the animals’ capability to spread nutrients in the land and about 5% in the oceans, compared with past values. Several animal groups have been identified to play a key role in this system.

1. Terrestrial animals: accelerates cycling of nutrients from more resistant  forms to decomposing matter. Some animals transfer terrestrial nutrients to aquatic environments, while others do the contrary. Even some animals, like bears and eagles, transfer oceanic nutrients to land environments by feeding on anadromous fishes.

   

   Moose (Alces americanus) transfer aquatic-derived N to terrestrial systems (Picture: BioLib).

2. Anadromous fish, fish that travel from sea to rivers to spawn their eggs (such as salmon or striped bass) and seabirds transport nutrients from sea to land.

   

   Striped bass (Morone saxatilis) is an anadromous fish (Picture: Ethan Dropkin).

3. Marine mammals, that include cetaceans, sirenians (with dugongs and manatees) and seals; have two functions in the cycling nutrient process: they transport nutrients vertically (from deep to surface waters via excrements and urine) and laterally due to migrations. [Read more about cetacean migration]

IS EARTH AS FERTILE AS IT WAS?

The answer to this question is “no”.

New findings reveal that the global nutrient distribution capacity on land has been reduced to 8% of its former value. Nevertheless, there is regional variation: most of the current capacity is on Africa because it is full of megafauna species, while in South America the capacity is at 1% of the past value. In the past, South America had the largest number of big herbivorous (more than 1,000 kg) but all of them went extinct. Nowadays, the largest animals in the continent weights about 300 kg. This difference explains the large reduction.

Arctotherium bonariense was a bear that live in South America during the late Pliocene (Picture: W.B. Scott, Creative Commons).

The current capacity of oceans is more than three times higher than for land. However, the reduction of its capacity is also important: 2% of its former value in the Southern Ocean and 14% in the Atlantic Ocean. Concerning the vertical transport of nutrients, the amount of phosphorus transported from deep to surface waters is nowadays a 23% of the original transport, with differences among oceans. Behind these reductions, hunting pressure to marine mammals is present. Nutrients that fall below the well-illuminated zone are considered to be lost. Marine mammals would have been responsible of returning nutrients to surface by feeding on the deep ocean and defecating and urinating on the sea surface.

Finally, seabirds transports 6.3 million Kg for square kilometre of phosphorous from sea to coastal environments each year (former values are not available) and anadromous fish capacity is 4% of the past value, possibly due to overfishing and habitat modification (such as damming of rivers).

Potential interlinked system of recycling nutrients. Grey animals represent extinctions.  (Picture: Doughty et al. 2015).

HOW CAN WE RESTORE THIS?

Doughty and his colleagues give some solutions to restore this situation:

• Future pastures may have less fences and more species to simulate natural pastures.
• Restoration of free-ranging wild herbivores.
• Restoration of whale populations.
• Restoration of seabird colonies and anadromous fish populations.

REFERENCES

• Doughty, CE; Roman, J; Faurby, S; Wolf, A; Haque, A; Bakker, ES; Malhi, Y; Dunning, JB & Svenning, JC (2015). Global nutrient transport in a world of giants. PNAS, doi: 10.1073/pnas.1502549112

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).

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).

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).

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).

• 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

• Animal Diversity Web: Dugongidae
• Berta A, Sumich J & Kovacs K (2011). Marine mammals. Evolutionary Biology. Academic Press (2 ed)
• IUCN Red List: Dugong dugon
• Marsh H (2002). Dugong: Status Reports and Action Plans for Countries and Territories. UNEP.
• Marsh H (2009). Dugong: Dugong dugon. In Perrin W, Würsig B & Thewissen JGM (edit.). Encyclopedia of Marine Mammals. Academic Press (2 ed).
• Save the Manatee Club: Sirenians of the World 
• Sirenian International: Frequently Asked Questions 
• University of California – Museum of Paleontology: Introduction to Sirenia

Oil spill effects on marine environment

Oh the occasion of the accident of the Russian fishing boat called Oleg Naydenov close to Grand Canary (Spain), the article of this week is about the effects of petroleum on marine environment. Here, I am going to talk about the origin of the petroleum in the sea, which are the transformations that suffer and the effects on marine fauna and flora. 

INTRODUCTION

The accident of the Russian fishing boat called Oleg Naydenov off of Grand Canary, which has finished with its sinking, is causing the appearance of oil in an area of 12 square km. The reason is that it sank with more than 1,400 tonnes of oil, 30 of diesel oil and 65 more of lubricant.

ORIGIN OF HYDROCARBONS IN THE SEA

Despite oil tanker accidents have a huge impact in the media, they represent a small portion of the amount of hydrocarbons that get in the sea. In general terms, these are the main sources of petroleum in the sea:

• Industrial discharges and urban dredging: 37%.
• Boat’s operations: 33%.
• Oil tanker accidents: 12%.
• Atmosphere: 9%.
• Natural sources: 7%.
• Exploration and production of hydrocarbons: 2%.

Although this values can vary depending of the sources, in general they represent quite good the proportions. It has been estimated that, each year, are poured into the sea 3,800 millions of litres of hydrocarbon, equivalent to 1,500 Olympic pools.

HYDROCARBON TRANSFORMATIONS IN THE SEA

When hydrocarbons are spilled into the sea (accidentally or deliberately), their features and shape change. This changes are physical, chemical and biological. This are the mechanisms:

1. Evaporation: it allows that certain substances of the hydrocarbons go to the atmosphere, reducing about 40% its volume just in the first day. In any case, the surrounding atmosphere will be flammable.
2. Dispersion: it consists on the fragmentation of the oil patch into small drops. When these drops are small enough, they remain in suspension and they mix with water and favours the biodegradation and sedimentation.

   

   Oil dispersion is positive because it allows the biodegradation (Picture from Ecosfera)

3. Emulsification: consists on the absorption of water so the hydrocarbon’s volume increases between 3 and 4 times. This hampers the oxidation and biodegradation.
4. Solution: depending on the product’s composition, the water temperature and its agitation. Only the more volatile components can be dissolved.
5. Oxidation: the effect of the oxidation can produce a compound that is easier or more difficult to degrade.
6. Sedimentation: consists on the down vertical displacement of the hydrocarbon’s particles. Depending on its density (with respect to water), the size and the agitation of the sea.
7. Biodegradation: consists on the elimination of hydrocarbons by living beings, like bacteria and fungus.

PETROLEUM’S EFFECTS ON MARINE ENVIRONMENT

As we have said in the beginning of the post, the main goal of this is to comment which are the effects of petroleum (and other hydrocarbons) on marine fauna and flora. Let’s start!

The effects of petroleum on fauna are wide due to the high diversity of marine organisms. The main effects on the marine biodiversity are:

1. Direct contamination: petroleum sticks on feathers, fur and scales, what make difficult the thermal isolation, movements and other important functions. As a consequence, this kills fishes, marine mammals and birds.

   

   Marine mammals are effected by petroleum pollution (Picture from Channel Island)

2. Modification of gas exchange: the petroleum sheet reduces the content of oxygen in the water, what produce the dead of the plankton and fishes, what produce the dead of the organisms that feed on them.
3. Alteration of seafloor: when petroleum is placed over the seafloor kills and produce sublethal effects on benthonic flora and fauna.
4. Intoxication: petroleum poisons marine fauna, soaking into its digestive system and its skin and mucosa. The result is, on the one hand, the dead for suffocation and genetic disruptions on fishes, molluscs, marine mammals, reptiles and birds; and, on the other hand, the intoxification of other organisms like humans when they feed on them.

   

   Only a quarter part of the contaminated marine birds achieve the earth, the rest dead (Photo: Marine Photobank, Creative Commons).

5. Increase of the infections: because petroleum produces a reduction of the resistance to infections. This is specially important in birds because when they clean the feathers theirself, they swallow petroleum, so they present sublethal concentrations.
6. Negative effects on fertility, reproduction and propagation of fauna and flora.
7. Modification of the behaviour.
8. Destruction of food sources.
9. Incorporation of cancerous substances on food webs. 
10. Effects on the availability of light: we cannot forget that the petroleum patch in the sea surface produce an important reduction of light in the water column. This causes a reduction or elimination of photosynthesis, essential process for the maintenance of food webs because the algae growth depends on light, which is consumed by herbivorous (and so on) and produce an oxygen input into the water. Moreover, we have to take in consideration that algae communities are shelter for many larvae and youthful fishes.
11. Marine communities alteration: at community level, there is a gradient of vulnerability of oil spills. From less to more vulnerability, the communities are: exposed cliffs, exposed rock platforms, fine sand beaches, middle to big sand beaches, exposed tidal planes, big sand beaches, gravel beaches, protected rocky beaches, protected tidal planes, marshlands and mangroves, subtidal seafloors of sand and gravel, mud subtidal seafloors, batial and abyssal seafloors, infralittoral and circalittoral seafloors and reef corals.

REFERENCES

• Notes of the subject Ecotoxicology and marine pollution of the Master in Oceanography and Marine Environment Management of the University of Barcelona.
• EmerCoast Coast. “Training on marine pollution risks. Environmental risks in the littoral and marine environments”.
• Course”Marine Pollution” from EuroInnova.
• Greenpeace (2012). Environmental impact of petroleum (Brochuere).

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) (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, Wild Wonders of Europe)

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 (Photo: Sá, Wild Wonders of Europe)

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)

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).

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: 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

• Fauna Iberica: Foca monje
• IUCN Red List: Monachus monachus 
• MarineBio: Mediterranean Monk Seals
• NOAA Fisheries, Office of Protected Resources: Mediterranean Monk Seal
• The Monachus Guardian (main source)
• Wildscreen Arkive: Mediterranean Monk Seal

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Reasons to watch marine mammals in captivity (or maybe not)

The topic we are discussing this week is marine mammals in captivity, a very controversial subject. While some people totally agree with this practice because they defend that are beneficial (not only economical), others are against it.

INTRODUCTION

In the discussion about marine mammals in captivity; zoos, aquaria and and dolphinaria maintain that their shows have such a great value in conservation, people learn a lot and that marine mammals have a good life. On the contrary, animal protection groups and more and more scientists defend their lives are impoverished, people don’t receive a good information of the species and that captures of wild animals negatively impacts populations and habitats.

CAPTIVITY OF MARINE MAMMALS IS EDUCATIONAL (OR MAYBE NOT!)

Despite in some countries is compulsory to offer educational values in their shows, there is less evidence that the industry spreads information about marine mammals and their habitats. There are more than 1,600 centres in United States and just a negligible part are actually involved in educational and conversational issues, since most of them just aspire to entertain their visitors.

Tricks performed by sea lions, dolphins or whales are exaggerated variations of their natural behaviours and cause the audience loose the notion of the place they are: inside pools confined by Plexiglas. In a survey of 1,000 US citizens, the respondents overwhelmingly preferred to see captive marine mammals expressing natural behaviours rather than performing tricks and stunts.

Contrast of the behaviour between a killer whale (Orcinus orca) and a sea lion. In the right, the natural behaviour, which consists on a killer whale capturing a sea lion (Picture: Daniel Bianchetta). In the left, artificial behaviour in which a sea lion gives food to a killer whale.

In general, almost nothing is explained  about natural behaviours, ecology, demographics or population distribution during the shows. In addition, it has been demonstrated that the information is sometimes incorrect of distorted. For example: SeaWorld doesn’t use the word “evolution” as many visitors consider the theory of evolution to be controversial, they fool in the explanation of the drooping fin syndrome in killer whales or about their life span in captivity.

Another example is that many actions performed by dolphins in shows or observed being directed toward visitors or trainers that are portrayed as play or fun (such as the rapid opening and closing of the mouth and the slapping of the water surface with the tail flukes or flippers) are actually displays that in wild animals would usually be considered aggressive.

Aggressive behaviour of a dolphin, slapping the water surface with the tail flukes(Picture from Sara's Cetacean Stories).

So, the exhibition of marine mammals does exactly the opposite of what the industry rhetoric claims: instead of sensitizing visitors to marine mammals and their habitats, it desensitizes humans to the cruelty inherent in removing these animals from their natural habitats and holding them captive.

ZOOS HELP TO THE CONSERVATION OF SPECIES (OR MAYBE NOT)

Zoos, aquaria and dolphinaria have increasingly promoted themselves as conservation centres, emphasizing their role as Noe ark. In fact, they do no more than produce new individuals of a limited group of species and do not maintain true conservation programs.

While several zoos have programs to breed endangered species in captivity with the intention that these animals be used in restocking depleted populations, this is not the case with dolphins. Only one facility attempted a captive breeding program for baiji or Yangtze river dolphins (Lipotes vexillifer).

Baiji or Yangtze river dolphin (Lipotes vexillifer) (Picture: Mark Carwardine, Arkive).

Moreover, the number of centres that invest money in conservation programs are few in number and the amount of money is less that 1% of their benefits. Fewer than 5 to 10 percent of zoos, dolphinaria and aquaria are involved in conservation programs, either in natural habitat (in situ programs) or in captive settings (ex situ).

Nevertheless, in Europe these centres are obliged for law to develop conservation programs to free the animals breeding in captivity to the nature. The truth is that the overwhelming majority of marine mammal species currently being bred in captivity is neither threatened nor endangered. In addition, the success of these programs would be in the capability to introduce the animals in the nature, what has been done in few chances.

What is worse is that many dolphinaria and aquaria are buying animals directly captured in the wild populations.

CAPTURE OF WILD ORGANISMS

All cetacean capture methods are invasive, stressful and potentially lethal, despite the method generally considered the better consists on chasing them by small boats and then herded together and encircled by a net. The process is so traumatic that mortality rates shoot up six-fold in the first five days of confinement. The dolphins not selected and released from the net may experience a similar risk of dying once the capture operators have left the area.

Capture of dolphins in Japan during a seine-net capture (Picture: Adrian Mylne, Reuters)

The most violent and cruel method of collecting cetaceans for dolphinaria is the drive fishery, used primarily in Taiji and Futo, Japan. A fleet of small ships produce underwater noise with metal pipes to force the dolphins to go into shallow water. Some of the animals are set aside for the public display facilities, while the rest are killed for human and pet food and other products.

Dolphin slaughter in Taiji (Japan) (Picture: unknown author).

ZOOS, AQUARIA AND DOLPHINARIA HAVE PROGRAMS TO HELP STRANDED ANIMALS (OR MAYBE NOT)

The one area of activity in which dolphinaria and aquaria can legitimately claim to serve a conservation function is work involving rescue, rehabilitation and release of stranded marine mammals. Indeed, there are some very good stranding rehabilitation programs, but the interests are not always clear.

Usually, the real interest is to promote a good reputation of themselves, so they promote themselves as altruists centres that care for marine mammals in the wild. In addition, they use a stranding as proof that marine mammals’ natural habitat is a dangerous place full of human-caused and natural hazards. The public receives a skewed picture in which an animal’s natural environment is hostile and captivity is a benign alternative.

Also disturbing is the fact that these industries appear to evaluate each animal in terms of display potential. Species that are highly desirable or rarely observed in captivity may be determined to be unsuitable for release.

MARINE MAMMALS IN CAPTIVITY ALLOW RESEARCH (OR MAYBE NOT)

Almost always, dolphinaria and aquaria claim that they foster research and scientific study of marine mammals, thereby contributing to both education and conservation. However, much of what can be learned from captive marine mammals has in fact already been learned (reproductive physiology length of gestation, visual acuity and general physiology). Moreover, most of the results given by studies made on captivity animals have been demonstrated to not be correct, specially those related with behaviour.

There may be some research questions that the study of captive animals can answer most directly, but due to advancements in technology such as biopsy darts, electronic tags and underwater video, as well as improvements in capture and release techniques, it can be studied in wild animals.

Use of a metabolic dome to study the metabolism of sea lions (Picture from Vancouver Aquarium).

REFERENCES

• Kleiman, D.G.; Thompson, K.V.; & Kirk Baer, C. (2010) Wild Mammals in Captivity. Principles and Tecniques for Zoo Management. The University of Chicago Press (2 ed).
• Rose, N.A; Parsons, E.C.M & Farinato, R. (2009). The case against Marine Mammals in Captivity. The Humane Society of the United States and the World Society for the Protection of Animals (4 ed)

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