The current rate of species extinction in the world is estimated to 100-1000 times higher (spread across all types of life) than the background extinction rate (average over very-long time-scales), primarily as a result of modern/industrial human activity.

Some groups are experiencing much higher rates even than that though — amphibians, for example, are currently going extinct roughly ~45,000 times faster than the background extinction rate. Most/many amphibian species are expected to go extinct at some point in the foreseeable future — without large changes to the current trajectory occurring. (There are notable exceptions to this.)

Despite the growing rates of extinctions, research has shown that public interest and concern has actually been diminishing greatly over the last few decades. (Perhaps as backlash against the tactics/hypocrisy of many “environmental” organizations? Perhaps because less and less people grow up in rural areas and spend time in the “wild”? Perhaps because entertainment consumption, drug-use, and obesity, has all skyrocketed in recent decades? Hard to say…)

Many researchers have estimated that at current rates of extinction, up to one-half of all the currently existing plant + animal species in the world will be extinct by the year 2100. (For more on that, see: 10 Extinct Animals Of The Last 100 Years, And Before, List).

On that note — in a continuation of our previous coverage of species on the brink of extinction (see: Brink of Extinction — Giant Leatherback Sea Turtle, Siberian Tiger, Mountain Gorilla, North Pacific Right Whale, & Philippine Eagle) I’m going to highlight 5 more species nearing the point of no return as far as population numbers and genetic diversity goes.

The species in question to be highlighted in this article are: the Mediterranean Monk Seal, the Axolotl Mexican Salamander, the Tiger Spider, the Southern Bluefin Tuna, and the Alabama Cavefish.

Near Extinct Animals — Critically Endangered Animals Top 5 List

Mediterranean Monk Seal

The Mediterranean monk seal (Monachus monachus) is the rarest pinniped species in the world currently. The critically endangered species is now limited to just 450–510 (by the most recent estimates) individuals — spread out across a couple of different populations throughout the Mediterranean and the eastern Atlantic Ocean.

The species typically grows to reach lengths of up to 8-feet, and weights of up to 500-900 lbs. they can live at least as long as 45 years in the wild, but median lifespans are thought to be in the mid to late 20s.

Mediterranean monk seals were until relatively recently known to congregate in huge numbers on the open beaches of the Mediterranean, but in recent years owing to: hunting, expanding human activity/industry, and tourism; the species now seems to spend much of its time in inaccessible undersea caves.

Births, in particular, had previously occurred probably exclusively on open beaches, but pregnant Mediterranean monk seals now seem to exclusively use these inaccessible undersea caves for the process.

This is thought to have led to a large increase in infant mortality for the species — as pups are far more likely to drown in these caves than they are on open beaches.

The IUCN species factsheet put it thusly: “Pup survival is low; just under 50% survive their first two months to the onset of their moult, and most mortalities occurred in the first two weeks. Survival of pups born from September to January is 29%. This very low survival rate is associated with mortality caused by severe storms, and high swells and tides, but impoverished genetic variability and inbreeding may also be involved. Pups born during the rest of the year had a survival rate of 71%”.

Pups are usually weaned after 18 or so months, but actually start learning how swim only two weeks or so after birth. Gestation lasts a year or so, but sometimes longer. Physical maturity is reached at about 4 years of age.

With regard to the change in behavior seen in recent times, there’s this:

Scientists have confirmed this is a recent adaptation, most likely due to the rapid increase in human population, tourism, and industry, which have caused the destruction of the animals’ habitat. Because of these seals’ shy nature and sensitivity to human disturbance, they have slowly adapted to try to avoid contact with humans completely within the last century, and, perhaps, even earlier. The coastal caves are, however, dangerous for newborns, and are causes of major mortality among pups.

Several causes have provoked a dramatic population decrease over time: on one hand, commercial hunting (especially during the Roman Empire and Middle Ages) and, during the 20th century, eradication by fishermen, who used to consider it a pest due to the damage the seal causes to fishing nets when it preys on fish caught in them; and, on the other hand, coastal urbanization and pollution.

Mediterranean monk seals are active mostly during the day (diurnal), and feed on a wide variety of different animals, including: various fish species, octopus, squid, and eels. While they seem to do most of their hunting at depths of between 150–230 feet, they have been observed as deep as 500-feet below the surface of the ocean.

They typically rely on their great speed and agility while hunting, but are also known to move slabs of stone/rock on the ocean floor while searching for hiding animals.

The species previously possessed a range that “extended throughout the Northwest Atlantic Africa, Mediterranean and Black Sea, coastlines, including all offshore islands of the Mediterranean, and into the Atlantic and its islands: Canary, Madeira, Ilhas Desertas, Porto Santo… as far west as the Azores. Vagrants could be found as far south as Gambia and the Cape Verde islands, and as far north as continental Portugal and Atlantic France.”

That range is of course now greatly diminished, due to the aforementioned hunting, pollution, habitat loss, and human expansion/activity.

The remaining population numbers are spread out amongst various subpopulations often composed of fewer than 50 mature individuals — and sometimes far less than that. These subpopulations are often cut off from one another by human activity.

Unfortunately, owing to the rarity of the species, searching out the caves where these remaining animals live has become something of a tourist attraction for some. Once the seals realize that people know the location of the cave where they are living they generally abandon it.

On that note — “despite clear instructions, an incident occurred with a tourist harassing a seal. The whole event was filmed. Less than a month later on August 25, 2014 this female Monk seal was found dead in the Mrtvi Puć bay near Šišan, Croatia. Experts said it was natural death caused by her old age.”

Hmm….

Axolotl Mexican Salamander

The Axolotl Mexican salamander (Ambystoma mexicanum) is a type of neotenic salamander, pretty closely related to the nearby tiger salamander species. Despite the common name — “Mexican walking fish” — the species is a salamander, a type of amphibian.

The rather strange looking species of salamander is native to the previously numerous lakes of the area that’s now Mexico City (Lake Xochimilco, etc). The strange look of the species (the normal ones, not the pink albino above) is due to the fact that individuals reach adulthood without undergoing metamorphosis. Rather than developing lungs and moving to the land — as most salamanders do — axolotls instead remain aquatic and gilled their whole life.

In other words, exhibiting neoteny — the retaining of “juvenile” characteristics into adulthood. (Something that is common in domesticated animals as compared to their wild counterparts. Think of the differences between dogs and wolves, domestic pigs and wild boars, etc.)

It’s worth noting here that while axolotls look fairly similar to waterdogs (larval stage of the tiger salamanders that are somewhat common in parts of North America), they aren’t closely related. They aren’t closely related to mudpuppies (Necturus spp.) either, despite the superficial resemblance.

As of the most recent 4-month population survey in 2013, there were no surviving individuals found in the wild — down from 100 individuals per square kilometre in 2008; 1000 in 2003; and 6000 in 1998.

The main drivers of the extinction are habitat loss and pollution, via rising levels of urbanization in Mexico City. While they are still listed by the IUCN as being critically endangered, it seems pretty likely that they will soon be “extinct in the wild“. There are pretty large numbers of the axolotl in captivity though, owing to their common use in: drug/chemical testing; regenerating limb research; and the pet trade.

The axolotl is only native to Lake Xochimilco and Lake Chalco in central Mexico. Unfortunately for the axolotl, Lake Chalco no longer exists, as it was artificially drained to avoid periodic flooding, and Lake Xochimilco remains a remnant of its former self, existing mainly as canals. The water temperature in Xochimilco rarely rises above 20 °C (68 °F), though it may fall to 6 to 7°C in the winter, and perhaps lower.

Non-native fish, such as African tilapia and Asian carp, have also recently been introduced to the waters. These new fish have been eating the axolotls’ young, as well as its primary source of food.

Axolotls typically reach maturity at around 18–24 months — and range in size from 8–18 inches in length. Historical reports suggest that it previously probably reached larger sizes in the past, but environmental pressures have resulted in it becoming smaller.

For those wondering, the feather-looking things coming out of their heads are actually their gills — that’s how they breathe.

The natural habitats of the species are high-latitude bodies of water surrounded by relatively dangerous terrestrial environments — which is what’s thought to have lead to the development of neoteny in the species.

Despite the way that the Axolotl looks, it’s actually carnivorous — and preys mostly on worms, insects, and small fish. The approach to hunting seems to be based mostly on the use of smell, and the use of “vacuum force” to suck food into its stomach.

Tiger Spider

The Tiger Spider (Poecilotheria rajaei) is a species of tarantula that’s roughly the size of a human face.

There are of course many spiders commonly referred to as being “tiger spiders”, but the one that we’re going to talk about is the giant one that’s to native the forests of South Asia. Owing to widespread deforestation in recent years, and the species preference for large old-growth trees, population numbers appear to be declining rapidly.

The Tiger Spider Tatantula isn’t quite as large as the largest tarantula in the world, the Goliath Bird-Eater, but it is quite big — adults grow to possess legspans of up to 8 inches.

With the loss of much of its native habitat, the species can sometimes now be found living in old abandoned buildings in the region, in rural areas.

The venom of Poecilotheria rajaei is pretty strong, but nowhere near strong enough to cause real problems for a grown human. It is strong enough to kill the the spider’s prey though — rodents, snakes, small birds, and lizards, mostly.

Deforestation in the region is unlikely to stop anytime soon — as a result, most/many researchers expect the species to likely disappear from the world at some point in the relatively near future.

Southern Bluefin Tuna

The Southern Bluefin Tuna (Thunnus maccoyii) is a species of tuna classified in the family Scombridae. It’s found (or was found) throughout the open waters of the Southern Hemisphere.

The species is quite large, and regularly grows to be over 8-feet in length, and over 550 lbs in weight. It’s one of the largest remaining species of bony fish in the world.

Like most other pelagic tuna species, Southern Bluefin Tuna are able to raise/maintain their body temperature substantially higher than the temperature of the surrounding waters, via a complex, unique physiology.

This ability to keep a high body-temperature allows the species to maintain a high metabolic-output, to swim very fast, and to be a very effective predator. The species feeds on practically anything — from other fish, to squid, to salps, to crustaceans, etc.

The southern bluefin tuna is a predatory organism with a high metabolic need. These are pelagic animals, but migrate vertically through the water column, up to 2500 meters in depth. They also migrate between tropical and cool temperate waters in the search for food. The seasonal migrations are between waters off the coast of Australia and the Indian Ocean. Although the preferred temperature range for souther bluefin tuna is from 18-20 °C, they can endure temperatures as low as 3 °C at low depths, and as high as 30 °C, when spawning.

This wide range of temperature and depth changes poses a challenge to the respiratory and circulatory systems of the southern bluefin tunas. Tunas swim continuously and at high speeds and, therefore, have a high demand for oxygen. The oxygen concentration in the water changes with the change in temperature, being lower at high temperatures. Tunas are, however, driven by the availability of food, not by thermal properties of water. Bluefin tunas, unlike other species of tunas, maintain a fairly constant red muscle (swimming muscle) temperature over a wide range of ambient temperatures. So, in addition to being endotherms, bluefin tunas are also thermoregulators.

Southern bluefin tuna, as other tuna do, take the oxygen coming in via the gills and diffuse it throughout the body much more rapidly than most other fish do. They are also adapted to take up more oxygen from the incoming water than most other species — utilization rates for tuna are as high as 50-60%, as compared to 27-50% for other teleost fish.

They generally forage during the winter months in the temperate waters around Australia, before then heading to the tropical waters of the north-western Indian Ocean from the spring to autumn to spawn.

The preferred temperature range for the species appears to be around 64-68 °F (18-20 °C) — with over 91% of their time spend below 70 °F (21 °C). They can function in water temperatures at least as low as 36.5 °F (2.6 °C) though, or as high as 87 °F (30.4 °C).

While Southern Bluefin Tuna spend much of their hunting in depths of between 150-600 meters during the day, they typically spend the night in waters less than 50 meters in depth.

Here’s more on the complex physiology of the species:

Heat exchange in southern bluefin tuna is a unique adaption among teleost fishes. They are endotherms, which means that they can maintain their internal temperature elevated above water temperature. Heat is lost through heat transfer throughout the whole body surface and the gills, so prevention of metabolic heat loss is important. This is an adaptive feature, because it is far more difficult for an organism to maintain a temperature differential with its environment in water than in air. It allows tunas to have faster metabolic reactions, to be more active, and to exploit colder environments. A disadvantage is that they require a high energy input and insulation, and there is potential for greater heat loss, because of the high temperature gradient with the environment. To reduce heat loss, southern bluefin tunas have reduced their heat conduction by the presence of oxidative muscle tissues and fat, as muscle and fat have low heat conductivity, according to Fourier’s law of heat conduction. Their heat convection is also reduced. Since the heat transfer coefficient depends on an animal’s body shape, tunas increased their body size, adopted a fusiform shape, and their internal tissue arrangement is based on different thermal conductances.

Since the start of industrial commercial fishing (overfishing) of the species in the 1950s, the total population has fallen by an estimated 92%. As a result, Southern Bluefin Tuna are now classified by the IUCN as being Critically Endangered.

The politics of the fishing-stock decline and the various fishing organizations involved is quite complex, but here’s an excerpt that might give you some idea:

Current quota limits reflect the vulnerable nature of wild stocks, with quotas being reduced for the 2010/2011 seasons to 80% of years previous. Thus the global total allowable catch (TAC) has been reduced from 11,810 tonnes from the previously allocated global TAC to 9,449 tonnes. Australia currently has the highest “effective catch limit” with 4,015 tonnes, followed by Japan (2,261), Republic of Korea (859), Fishing Entity of Taiwan (859), New Zealand (709), and Indonesia (651).

However, fishing pressure outside the allocated global TAC is still a major concern. For instance, the Australian government stated in 2006 that Japan had admitted to taking more than 100,000 tonnes over its quota over the past 20 years. The new quotas reflect this, as Japan’s was cut by half, as supposed punishment for overfishing. In 2012, Japan expressed “grave concerns” that Australian catch numbers were falsely counted. In response, Australia committed to implementing video monitoring to verify their catches. However, in 2013 Australia withdrew its commitment stating that such monitoring would impose a “excessive regulatory and financial burden”.

Lmao. I’m willing to venture a guess that nobody keeps their word, or is even willing to try to do so, in that industry. Too much money on the line I guess — to the minds of those involved anyways.

It’s an open question how long the fishing stocks of the species will last at current rates of exploitation — but I’d venture that it’s not more than a few decades.

Alabama Cavefish

The Alabama Cavefish (Speoplatyrhinus poulsoni) is an animal that you’ve probably never heard of, and may have not even realized was a possibility. It’s one of the rarer species of cavefish still in existence, and is listed by the IUCN as being critically endangered.

As it’s name implies, the species lives in underground lakes in Key Cave, in northwestern Alabama. The species is found nowhere else, and though it isn’t vastly different from the other species of troglobitic fish native to northeastern North America, it is placed in its own genus.

The Alabama Cavefish was discovered only relatively recently (with regard to “scientific discovery” — these caves have been in use for over 10,000 years, I’m sure that people were aware of the fish) in 1974. The species was discovered living underneath a colony of gray bats — whose guano fuels the “ecosystem” where the fish live.

As it stands, only 9 individuals have been observed in recent years — and researchers estimate that there are probably fewer than 100 individuals left.

Its longevity ranges from five to 10 years, but it reproduces slower than all other cave-dwellers. Because its known range is limited to a single cave, the Alabama cavefish has an uncertain future, being threatened by changes in groundwater quality and level, changes in aquifer characteristics, and diminished organic input. It also may compete with the syntopic southern cavefish, Typhlichthys subterraneus.

On average the Alabama cavefish measures about 3 in (7.6 cm) long and has no eyes or discernible pigmentation — appearing semitransparent with a slight pink hue. Its large head makes up more than one-third of its length. It is the only species in its genus, and can be distinguished from other cavefish with its very elongated, flattened head with a laterally constricted snout and a terminal mouth. The cavefish lacks pelvic fins, and its fin rays are unbranched with the fin membranes deeply incised between the rays. It has an elaborate system of sensory papillae, arranged in ridges on the head and sides, an adaptation to the dark environment.

The species seems to feed mostly on copepods, isopods, amphipods, and other fish — all of which are supported more or less entirely by the guano input deposited by the bats that live there. The cavefish species also apparently sometimes eats mites, millipedes, spiders, and beetles, as well though.

Interestingly, it’s thought that the Alabama Cavefish carries its young around in its mouth for incubation — as many other cavefish species do (and other distantly related animals such as crocodiles, as well).

The reproductive cycle of the species appears to be heavily dependant upon specific environmental triggers — as a result it doesn’t reproduce every year. It’s speculated that the reproductive cycle might be linked to occasional seasonal flooding of the caves — which then trigger hormonal changes in the fish via unknown mechanisms.

That theory would help to explain how the species would/does colonize new caves.

There’s not any evidence to prove the theory though, and the species is fast approaching the end of its time in the world…

Image Credits: Ranil Nanayakkara; Public Domain, Screen Capture