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Shark of the week: Borneo Broadfin shark — 26. February 2018

Shark of the week: Borneo Broadfin shark

As mentioned last week, the Broadfin shark had been categorized as Endangered by the IUCN. But this happened before its sister species, the Borneo Broadfin shark (Lamiopsis tephrodes), has been again considered as separate species due to biomolecular analyses. Discovered in 1905 (instead of 1839, where he wasn’t even alive) by zoologist Henry Fowler, it had soon been equalized with the Broadfin shark.

Lamiopsis tephrodes (FOWLER,1905).jpg
Lamiopsis tephrodes von Henry Weed Fowler – http://shark-references.com/species/view/Lamiopsis-tephrodes, Gemeinfrei, Link

Reaching only 4.3 ft – 1.30 m -, the Borneo Broadfin shark lives solely off Borneo. Due to fishing pressure in this waters and 2 separate species, the IUCN should maybe revise its classification.

Sources: here and here

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shark of the week: Broadfin shark — 19. February 2018

shark of the week: Broadfin shark

Another species of requiem sharks is the Broadfin shark (Lamiopsis temminckii). Living solely in shallow waters off India, China and Southeast Asia, it suffers greatly from habitat destruction, overfishing and water pollution. The IUCN considers this species as endangered.

Breitflossenhai (Lamiopsis temminckii) aus der Erstbeschreibung von Müller & Henle
Lamiopsis temminckii by Müller & Henle – Systematische Beschreibung der Plagiostomen pl. 18, Gemeinfrei, Link

Like almost all other requiem sharks, the Broadfin shark is viviparous. 4 to 8 embryos feed at first from yolk and later via a placental connection. After about 8 month they are born at 15 to 23 in -40 to 60 cm- length. Maximal length is 5.5 ft – 1.7 m.

Sources: here and here

Shark of the week: Blackspot shark — 12. February 2018

Shark of the week: Blackspot shark

Here the third shark of the triplet: the Blackspot shark (Carcharhinus sealei). Often confused with the whitecheek shark and until 2012 equated with Coates’s shark, it is also a rather small requiem shark, reaching a maximal length of 37 in -95 cm. After a gestation of about 9 month, only one or two pups of 13 to 17 in – 33 to 45 cm – length are born alive (viviparous).

Carcharhinus sealei terengganu.jpg
Carcharhinus sealei by Tassapon KRAJANGDARA – http://www.fishbase.us/photos/thumbnailssummary.php?ID=882#, CC BY 3.0, Link

The Blackspot sharks is even more widespread as the Whitecheek shark and not only inhabits shallow waters off northern and western Australia, but coastal waters all over the Indo-Pacific Ocean from South Africa and Madagascar over India to Indonesia. Despite living in intensively fished waters and often caught for its meat, it is only considered Near Threatened by the IUCN. If there where enough data, it may be very well meet the criteria of Vulnerable.

Sources: here and here

Shark of the week: Coates’s shark — 5. February 2018

Shark of the week: Coates’s shark

The classification of sharks is difficult. That’s true in particular for the species of requiem sharks that all looks quite alike. The Coates’s shark (Carcharhinus coatesi), named after the ichthyologist George Coates, was discovered in 1939, but had been equated with the Blackspot shark (Carcharhinus sealei) since 1982. As recently as 2012 they have been adjudged as 2 different species, after all.

A Whitecheek Shark, Carcharhinus coatesi. Source: CSIRO National Fish Collection. License: CC BY Attribution

The Whitecheek shark (Carcharhinus dussumieri) is a different species, too, but is synonymous with Coates’s shark in the source of my picture, that’s why it could be false.

The Coates’s shark is a small shark. Born alive (viviparous) at a length of 15 to 16 in – 38 to 40 cm -, it grows to at most 2.89 ft – 88 cm. It inhabits the surface to a depth of 404 ft – 123 m – off northern Australia.

Sources: here, here and here

Shark of the week: Creek whaler — 29. January 2018

Shark of the week: Creek whaler

One of many shark species in Australian waters is the Creek whaler (Carcharhinus fitzroyensis). Inhabiting shallow waters off northern Australia, it can also be found in estuaries (first in the Fitzroy river estuary, thus the scientific name). Like almost all requiem sharks female Creek whaler are viviparous, that means the depleted yolk sac changes into a placental connection. Every year, up to 7 pups are born in special nursery areas. Newborns are between 14 and 20 in -between 35 and 50 cm- long and grow up to about 4.3 ft – 1.3 m.

Carcharhinus fitzroyensis csiro-nfc.jpg
Carcharhinus fitzroyensis by CSIRO National Fish Collection – http://www.fishesofaustralia.net.au/home/species/2888, CC BY 3.0, Link

Creek whaler pose no danger to humans and are only a minor part of shark catches off Australia (as bycatch). The IUCN considers them as least concern (but this classification from 2003 may be now in need of updating).

Sources: here and here

Shark of the week: Pacific smalltail shark — 6. November 2017

Shark of the week: Pacific smalltail shark

The Pacific smalltail shark (Carcharhinus cerdale), sister species of the Smalltail shark from last week, is an example for a misguided believe in authorities, in this case the experts Henry Bryant Bigelow and William Charles Schroeder. What happened? After this species was first described in 1898 by Charles Henry Gilbert, colleague Seth Eugene Meek and his assistant Samuel Frederick Hildebrand discovered between 1910 and 1912 several specimen on a fish market in Colón on the Caribbean side of Panama and reasoned that this species lived on both side of the Isthmus of Panama. Maybe they made an error in identification, or wrongly assumed the fish was also caught there, we will never know. Since the Panama Canal had not opened yet, neither the sharks nor the fishing vessel was able to reach the Atlantic side of Panama from the Pacific side afloat, but a fish transporter ashore sure did. Anyway, in 1948 Bigelow and Schroeder not only repeated the mistake of their colleagues, but insinuated that Meek and Hildebrand considered therefore the Pacific smalltail shark not as an own species but as synonymous with the closely related, on the Atlantic side native Smalltail shark. Only in 2011 this mistake was remedied by José I. Castro, but such important websites like the IUCN or the Florida Museum still don’t feature that fact and need an urgent update.

Carcharhinus cerdale SI.jpg
Carcharhinus cerdale by D Ross Robertsonhttp://biogeodb.stri.si.edu/sftep/en/thefishes/species/5290, Public Domain, Link

Just like its sister species,the Pacific smalltail shark is a requiem shark and viviparous. It inhabits coastal waters of the eastern Pacific from the Gulf of California to Peru.

Sources: here, here and here

Shark of the week: Smalltail shark — 30. October 2017

Shark of the week: Smalltail shark

Another example to prove the Plate tectonics, anyone? Well, the Smalltail shark (Carcharhinus porosus – named after really big pores behind its eyes) was considered, until 2011, to live in coastal waters on both sides of the Isthmus of Panama: in the western Atlantic Ocean from the northern Gulf of Mexico to southern Brazil as well as in the eastern Pacific from from the Gulf of California south to Peru. A momentous mistake that seems to continue until now (see IUCN Red list and homepage of the Florida Museum). In fact, its sister species Pacific smalltail shark (Carcharhinus cerdale) can be found in the eastern Pacific, and the Smalltail shark lives only in the western Atlantic part. Both had been separated around 2.8 million years ago and developed into different species (just like the Whitenose shark and the Blacknose shark a proof of evolution, as well).

Carcharhinus porosus SI.jpg
Carcharhinus porosus by D Ross Robertsonhttp://biogeodb.stri.si.edu/caribbean/en/gallery/specie/100, Public Domain, Link

This small (generally only up to 3.6 ft -1.1 m- long) requiem shark is slow growing and viviparous with two to nine young every two years after an approximately 12-month gestation period. It can be found near the bottom of coastal waters and estuaries and forms large aggregations segregated by sex.

Along the northern Brazilian coast, where some of its nursery areas are, the Smalltail shark is the most common shark, and in Trinidad the most economically important shark (under the name puppy shark). Fishing pressure as bycatch as well as targeted (for its meat, fins, cartilage and liver oil) caused a significant decline in numbers, resulting in an ICUN-classification as vulnerable in Brazil, where mostly juveniles have been caught, but only data deficient overall. Since its habitat is much more narrow as previously assumed (see above), the IUCN should revise that urgently (in my opinion).

Sources: here and here

shark of the week: Tiger shark — 23. October 2017

shark of the week: Tiger shark

Like last weeks Blacktip reef shark, many sharks are targeted by recreational fisherman. After the film “Jaws” it became cool and manly to catch “man-eating” sharks as big-game fish, either alone or in tournaments. Rarely they are of use after (unlike in artisanal fisheries) – it is only for the thrill. And the kill, even if some tournaments try a catch-and-release-approach (if the shark survives the injuries and stress, and even the pull-up can be dangerous for example for deep sea sharks or highly pregnant females). Since the Tiger shark (Galeocerdo cuvier) has the reputation of a man-eating killer machine, it is a main target. As pointed out here, this results in many killings. In California alone, tiger sharks caught recreationally outnumbered the commercial side 6-to-1. Commercially, they are taken as bycatch or targeted for their fins, meat (the mercury content of this shark’s flesh is lower than in other large requiem shark species due to their diet), skin, cartilage and liver oil.

Yes, sharks can bite. And due to its size (females up to 16 ft 5 in – over 5 m- and males up to 13 ft 1 in – 4 m- length), power and dentition, an adult Tiger shark can cause significant harm -its serrated teeth are able to slice through turtle shells, after all. According to the ISAF, it is second only to the White shark in number of reported attacks on humans, many of them fatal. But if you watch this video, they seems rather docile and sluggish. They are big, curious and potentially dangerous, but no evil killing machines.

Tiger sharks live in tropical and subtropical waters all around the world and undergo a long-distance seasonal migration. As opportunistic feeders they prey mostly on fish, cephalopods, crabs, sea snakes, sea birds and carrion, but also with age more and more on seals, turtles, dugongs, dolphins and injured whales. As Neil Burnie said: “Tiger sharks like the dead, the dying and the dumb” (I would add dump, since they sometimes eat garbage, too), because they can’t be picky. To grow to such a size in relatively nutrient-poor warm waters is no mean feat (White sharks inhabit mostly cooler waters).

Tiger sharks are unique among their family. Firstly, they have got spiracles and a capacious stomach with a muscular wall that is proportionately three times thicker than that of any other requiem shark. Also unlike any other requiem shark, the female Tiger shark is ovoviviparous and not viviparous. That means the pups hatch in the uterus, but are not feed by a placental connection after the yolk supply is depleted. During the gestations period of up to 16 months the mother does provide unfertilized eggs (oophagy) and the one or other sibling to nibble on (in-utero cannibalism). But, other than in the Sandtiger shark, many survive, resulting in big litter sizes of 10 to 80 pups (unlike almost all other requiem sharks).

The 20 to 30 in -51 to 76 cm- long newborn Tiger sharks stay in their shallow nursery areas and grow fast. That is necessary, since their slender and delicately built bodies with over-sized fins and unique tail structure (an elongate upper caudal lobe) condemns them to an eel-like wriggle, an inefficient swimming style that renders them extremely susceptible to predators like bigger sharks (even other Tiger sharks). They do not outgrow their ‘awkward stage’ until they reach a length of about 8 feet -2.4 metres- at about four years of age. After that, their powerful build and fins make them successful predators with startling speed bursts.

Like the Blacktip reef shark, the Tiger shark has got large eyes with a reflective tapetum lucidum like a cat for nightly hunting. Normally they enter shallow, coastal waters at night and spend the day offshore in deeper water. But if their prey, like the Hawaiian Monk Seals, remains near shore during daylight hours and forages in deeper waters under cover of darkness, the Tiger Sharks adapt and revers their usual day-night pattern, remaining inshore during the day and moving offshore at night.

Tiger sharks are considered “near threatened” by the IUCN due to fishing pressure and questionable shark control programmes. But their widespread distribution and high growth and reproductive rates give reason to hope. It has been discovered that juvenile survivorship increases where adult Tiger Shark populations have been depleted by fisheries and hence predation of young is lessened.

Sources: here, here and here

Shark of the week: Blacktip reef shark — 16. October 2017

Shark of the week: Blacktip reef shark

The Blacktip reef shark (Carcharhinus melanopterus – derived from melas = black and pteron = wing or fin (see Pterosaurs)) is another requiem shark living in coral reefs. It inhabits nearshore waters of the tropical and subtropical Indo-Pacific from South Africa to Hawaii (even colonized the eastern Mediterranean Sea by way of the man-made Suez Canal) and prefers more shallow waters than its colleagues grey reef shark and whitetip reef shark. Their nursery grounds (females are viviparous and give birth to living young after feeding them from yolk and via placental connection) can be so shallow that the pups have to swim with their dorsal fins above the water looking “like a flotilla of tiny sailboats” (quote from here).

An expanse of clear water and white sand, and several sharks swimming with their black-tipped dorsal fins protruding above the water
Carcharhinus melanopterus by Leon Brocard from London, UK – PIMG_2915, CC BY 2.0, Link

Not only pups prefer to stay in groups for protection, but also adult Blacktip reef sharks form stabile groups for social purposes and hunting. Their prey are fishes, crustaceans, molluscs and squids, but also terrestrial and sea snakes and even rats and birds. They have got large eyes with a reflective tapetum lucidum like a cat, indicating that they can excellent hunt at night.

Due to their extremely small home ranges and strong site fidelity, Blacktip reef sharks are susceptible to habitat degradation and fishing pressure (only as bycatch by commercial fisheries, but targeted by artisanal fishermen for their meat, liver oil and fins, and also by recreational fishermen and for aquarium trade). Their small litter sizes (only 2 to 5 pups) and long gestation periods (up to 16 month) are no help, either. They are considered “near threatened” by the IUCN. They are normally timid and despite their size (typically up to 5.2 ft -1.6 m-) no danger to humans, but sometimes bite the legs or feet of waders encroaching into their space or spear fishers for their catch.

Sources: here, here and here

Shark oft the week: Silvertip shark — 2. October 2017

Shark oft the week: Silvertip shark

The Silvertip shark (Carcharhinus albimarginatus), despite being easily recognized due to its eponymous white margins on all fins (even pectoral fins, unlike all other “whitetip” shark species), it often confused with its smaller brother Grey reef shark. Both are requiem sharks and can be found on or near coral reefs in the tropical Indian and Pacific Oceans. They are known to form mixed-species aggregations and both perform (slightly different) ritual threat displays to chase away threats (like other sharks or divers) and protect their personal space. The mock attack of an up to 10 ft -3 m- long Silvertip shark (as described here) remind me of male gorillas. While it seems aggressive, I consider this as defensive behavior. Remarkable that they rather flee or chase away instead of attack, in which case they would, more often than not, prevail due to their size.

0979 aquaimages.jpg
Silvertip shark, Image taken by Clark Anderson/Aquaimages – Originaly uploaded to the english wikipedia, Image:0979 aquaimages.jpg, CC BY-SA 2.5, Link

Like all other requiem sharks, Silvertip sharks are viviparous. Females bear every other year litters of around five young after a gestation period of about one year. They grow slowly and mature at around 6.6 ft -2 m- with 20 years.

Silvertip sharks are caught in direct shark fisheries, as bycatch and by illegal practices (IUU) mostly for their fins and meat, but also for cartilage, liver, teeth, jaws and skin. This resulted in areas like Scott Reef off northern Australia, where they are now extinct because of Indonesian fishers. Hence the IUCN considers them as “Vulnerable“. However, there are no species-specific management measures in place.

Despite their inquisitive and aggressive behavior (see above) and being able to take on large prey (due to their dentition, size and power), Silvertip sharks are not known to attack humans. The ISAF lists only 4 provoked, none fatal attacks under this species.

Sources: here and here