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shark of the week: graceful shark — 19. June 2017

shark of the week: graceful shark

The reason for shark names are sometimes mysterious. On example is the graceful shark (Carcharhinus amblyrhynchoides) that has got a similar name in several languages. But, living in the tropical Indo-Pacific from the Gulf of Aden to northern Australia in coastal waters, this rare species of requiem sharks is not graceful but rather tubby.

Carcharhinus amblyrhynchoides phuket.JPG
Von Tassapon KRAJANGDARA – http://www.fishbase.us/photos/thumbnailssummary.php?ID=860#, CC BY 3.0, Link

With a size of up to 5.6 ft -1.7 m- the graceful sharks is potentially dangerous, but has not been implicated in any shark attacks. It is oviviparous, and females bear litters of up to 9 living young (with a mean of three) after a 9- to 10-month gestation period every year. Once the developing embryos exhaust their supply of yolk, the depleted yolk sac is converted into a placental connection to the mother.

The graceful shark is regularly caught as bycatch in commercial fisheries and used for its meat, liver oil and fins. In northern Australia it made up 1.5% of the shark catch in gillnets and 0.2% on longlines. Nevertheless, it is only considered near threatened by the IUCN.

Sources: here and here

shark of the week: dwarf spotted wobby — 22. May 2017

shark of the week: dwarf spotted wobby

Last week I introduced one of the largest wobbegong species – now one of the smallest: the dwarf spotted wobbegong (Orectolobus parvimaculatus).

A Dwarf Spotted Wobbegong, Orectolobus parvimaculatus. Source: CSIRO National Fish Collection. License: CC BY Attribution

Before 2008, sharks of this species have been considered juvenile Spotted wobbegongs (Orectolobus maculatus). Now it is a separate species, and its name means both in Latin and Englisch (a little bit uninspired) nothing else than little (i.e. dwarf) Spotted wobbegong.

Like nearly all wobbegongs, the dwarf spotted wobby lives off Australia in a depth range of 30 to 443 ft -9 to 135 m. While its big brother, the Spotted wobbegong, can reach a length of 9.8 ft -3 m-, the little brother reaches only 37.1 in -94.3 cm- in length. Like all wobbegongs, it is a nocturnal, bottom dwelling ambush predator and ovoviviparous.

Due to its size, the Dwarf spotted wobbegong is not targeted directly but caught as bycatch (in gillnet- and longline fisheries and rock lobster pots), where it normally survives after being discarded.

Sources: here and here

 

shark of the week: Banded wobby — 15. May 2017

shark of the week: Banded wobby

Wobbegongs are known to bite and don’t let go, when provoked or disturbed. ISAF reports 32 unprovoked attacks of species of this family, but this report states even a number of 51 unprovoked attacks solely off Australia (as shown in Table 3, “attack” may be a tad exaggerated since even close encounters count as such, but wobbegongs are notorious for biting). Fortunately, all but 2 wobbegong species reach only 4.1 ft -1.25 m- in length, but there are larger ones, too, that you do not want hanging from your leg.

The Gulf or banded wobbegong (Orectolobus halei) is up to 9.5 ft -2.9 m- long and a strong and agile ambush predator, if it wants to be.

Confused with its significantly smaller look-alike Ornate wobbegong before, the Gulf wobby was revalidated in 2006, and it was proven genetically that it is more closely related to the equally large Spotted wobbegong. Camouflaged with colored skin pattern and dermal lobes, all wobbegongs are predestined ambush predators. They are bottom-dwelling and nocturnal.

Living off the southern half of Australia at depths up to at least 640 ft -195 m- , the Gulf wobby is ovoviviparous. Like all wobbegongs, its meat is used for fish- and-chips and its skin for leather. Targeted by recreational and commercial fishermen and as bycatch, it has been considered near threatened by the IUCN (and vulnerable regionally in New South Wales) since 2009. But management and protection efforts made an impact on this site fidelity species, resulting in an assessment of least concern in 2015.

Sources: herehere, here and here

Shark of the week: Shortfin Mako — 8. May 2017

Shark of the week: Shortfin Mako

The open ocean is a desert. You have nowhere to hide, either as prey nor as predator. And you have to catch any prey you can find to prevent starvation. One survival strategy of oceanic pelagic fish is speed, and the champion in it is the Shortfin Mako shark (Isurus oxyrinchus). As the fastest-swimming of all sharks, it is typically clocked at 31 mph -50 km/h- with occasional bursts of speed of at least 46 miles -74 km- per hour to catch really quick prey.

Isurus oxyrinchus by mark conlin2.JPG
By Mark Conlin, SWFSC Large Pelagics Program – http://swfsc.noaa.gov/ImageGallery/Default.aspx?moid=532, Public Domain, Link

The Shortfin Mako lives in tropical and warm temperate waters all around the world. It is highly migratory (albeit seasonal) – tagging proved that a specimen swam 1,322 mi -2,128 km- in 37 days, another one traveled over 1,725 mi -2,776 km across the Pacific (by the way, genetic tests shows that they rarely cross the Atlantic). Its spindle-shaped body, large gills and huge heart and a heat exchange circulatory system named rete mirabile (Latin for “wonderful net”) like the salmon shark that enables the body to be 12.5 to 18 degrees Fahrenheit -7 to 10 degrees Celsius- warmer than the surrounding water allow a high level of activity. But that means the shark needs to consume 3% of its weight each day – in fish.

Like every other species of the family mackerel sharks, the Shortfin Mako is ovoviviparous. Litters of between 4 and 25 live young are born after a 15 to 18 month gestation period, during which they feed on yolk and unfertilised eggs (oophagy). Females are believed to rest for 18 months after birth before conceiving again. They mature at around 17 to 19 years of age and males at around 7 to 9 years. The maximum known age of a Shortfin Mako is 32 years. Altogether, like all apex predators Shortfin Makos have a low reproduction rate.

The Shortfin Mako is one of the most popularly consumed shark species. It is a favored game fish and famed for its fights with spectacular leaps of up to 20 ft – 6m- out of the water. It is also targeted commercially for its high-quality meat (containing high doses of methyl mercury like in all apex predators), fins (shark-fin soup) and liver oil (to make vitamin supplements). It is one of the few known predators of the Swordfish (however, those fight back and in turn can injure and likely kill it). Its predilection for commercially important fish (billfish, tuna or mackerel, but primarily bluefish) makes it a frequent bycatch, too. All in all, the IUCN considers the Shortfin Mako as Vulnerable worldwide and Critically Endangered in the Mediterranean, which seems an important nursery area.

Despite its size (in average around 10 ft -3.2 m- length, but up to 13 ft -4 m- and 2,200 lb -1,000 kg-), speed and strength, the ISAF recorded only one unprovoked fatal attack by Shortfin Makos in 5 centuries. This close relative of the white shark only bits humans when provoked (fighting for its life after being caught), but it can attack boats or spear fishermen if it considers them competitors for prey. When hunting, it does not rely on electroreception but smell, hearing, and most prominently, vision. It is fast-learning due to one of the largest brain:body ratios of all studied sharks.

Sources: here, here, here and here

shark of the week: Western wobbegong — 24. April 2017

shark of the week: Western wobbegong

A new but old shark species – how is that possible? Specimen of the Western wobbegong (Orectolobus hutchinsi) are well known wobbegongs in Australia, but the species has not been described scientifically until 2006.

Western Wobbegong, Orectolobus hutchinsi. Source: Barry Hutchins. License: All rights reserved

The Western Wobbegong lives in shallow coastal waters off southwest Australia. It has a maximum length of 4.9 ft -1.5 m- and is ovoviviparous with females breeding every two or three years and producing 18-29 young per litter (at a size of 8 to 10 in – 22 to 26 cm). Like all wobbegongs, it is well camouflaged with a symmetrical skin pattern (somewhat resembling that of a jaguar) and is a sluggish ambush predator.

Even if wobbegong flesh is called flake and sold locally for human consumption through ‘fish and chip’, Western wobbegongs are considerd too small and are often released alive if caught incidentally as bycatch. Wobbgongs are tough and post-release survival is high. As site attached species they benefit from habitat protection and marine protected areas (MPA), marine parks and nature reserves.

Sources: here, here and here

Shark of the week: Archbishop — 17. April 2017

Shark of the week: Archbishop

Did you know that there is a shark that eats slime to neutralize toxins of its prey? The Archbishop or Ornate Angelshark (Squatina tergocellata) is said to do that.

Ornate Angelshark, Squatina tergocellata. Source: Australian National Fish Collection, CSIRO. License: CC BY Attribution-Noncommercial

The Archbishop lives off south-western Australia in depths of 430 to 1320 ft -130 to 400 m (adults usually around 980 ft -300 m-, juveniles higher). Being ovoviviparous, females give birth to 2 to 9 living young every 2 years, what means a low reproductive rate. Ornate Angelsharks are at birth 13 to 16 in -33 to 42 cm- long and mature at a length of 30 to 35 in -80 to 90 cm- with a maximum length of 55 in -140 m. Like all angel sharks, the Archbishop is an ambush predator.

The Ornate Angelshark is commonly caught as bycatch or targeted for its meat by trawling and longline fisheries. But due to it deeper range it seems to be somewhat protected. That’s why the IUCN regards it as Least Concern, unlike other angel sharks. Additionally, in Australia general fishery management measures have been taken, and there are marine protected areas by the Commonwealth Marine Reserve Network.

Sources: here and here

Shark of the week: Zebra bullhead shark — 27. March 2017

Shark of the week: Zebra bullhead shark

One of only nine (potentially ten) species of the order Heterodontiformes (or bullhead sharks – sharks that have been around longer that nearly all other sharks: for 200 Million years) is the Zebra bullhead shark (Heterodontus zebra), also known as Barred Bull-head Shark, Barred Shark, Bullhead Shark, Cat Shark, Little Shark, Striped Bullhead Shark, Striped Cat Shark, Zebra Horn Shark or Zebra Port Jackson Shark. Just like all its sisters, for instance the Horn shark and Port Jackson shark, it looks cute with its pig-like snout, small puckered mouth and chubby little body, but has got spines in front of its two dorsal fins.

Zebra bullhead shark Beijing Aquarium 17 Sep 2010.jpg
Von Jason QuinnEigenes Werk, CC BY-SA 3.0, Link

Living on continental and insular shelves in the central Indo-Pacific from northern China and Japan to northern Australia, the Zebra bullhead shark is mostly found in depths shallower than 160 ft -50 m. It lays flat, auger-shaped egg cases with small tendrils at one end (oviparous). It is caught as bycatch and may also be under threat from destructive fishing practices within its range (such as cyanide and dynamite fishing in Indonesia) and habitat destruction.

Zebra bullhead sharks have a distinct and attractive color pattern: zebra stripes in dark brown or black (even russet in juveniles) on a white, light grey or light brown body and are between 6 in -15 cm- (after hatching) and 4 ft -1.2 m- long. That makes them suited for using in aquariums, but the small (roughly 5 ft -1.5 m- diameter) cylindrical tank in the picture seems hardly appropriate. I only hope this one is tough.

Sources: herehere and here

Shark of the week: Carribean reef shark — 13. March 2017

Shark of the week: Carribean reef shark

Despite being the most common shark in reefs of the Caribbean Sea, the Caribbean reef shark (Carcharhinus perezii) is one of the least-studied large requiem sharks. It looks a lot like its sister species Dusky shark, but lives solely on or near coral reefs in the tropical western Atlantic Ocean from Florida to Brazil.

Carcharhinus perezi bahamas feeding
Caribbean reef sharks by Greg Grimes from Starkville, MS, USA – pic_0655, CC BY-SA 2.0, via Wikimedia Commons
Caribbean reef sharks are nocturnal and can be found resting in caves or on the sea floor by day (once famous in Mexico as “sleeping sharks”). They mature at 5 to 5.5 ft -1.5 to 1.7 m- (males) or around 6.5 ft -2.0 m- (females) and can reach a length of up to 9.7 ft -3 m, making them one of the largest apex predators in the reef ecosystem. Females are ovoviviparous and give birth to 3 to 6 24 to 30 inches -61 to 76 cm- long living pups every 2 years.

Despite their size Caribbean reef sharks are normally unaggressive toward divers, except in the presence of food – spear fishermen can get accidentally bitten (there are 4 registered unprovoked non-fatal attacks by this species), but sometimes also members of baited diving tours. Attracting sharks by feeding is a controversial by-product of ecotourism (and banned in Florida). Associate humans with food by the sharks (like by bears) seems only a problem if the species usually feed on mammals (like White sharks), but the artificial concentration of predators (like in the image above) and the intensified removal of fishes from the environment for use as shark bait (instead of using fish offal) could be a concern. Showing sharks to tourists, but also photographers and filmmakers, is more profitable than killing them – and provides a sustainable livelihood for ex-fishermen in times of overfishing. Unless, of course, their colleagues exploit this changed behavior of sharks to catch them all, not on film but on the thousands of baited hooks of longlines.

Because Caribbean reef sharks have been targeted by longline and gillnet for their meat, skin, jaws, fins and liver oil or taken as bycatch, resulting in its Near Threatened status. It is the most common shark species landed in Colombia, but protected in the U.S., Bahamas and some marine protected areas off Brazil. Illegal fishing and habitat degradation (coral bleaching) are dangers, too. Caribbean reef sharks off the coast of Florida have been found with dangerous levels of methyl mercury – higher than the FDA guidelines, anyway, the European guidelines are different and incomprehensibly (imo) permit higher levels for large predator species.

Sources: herehere and here

 

Shark of the week: Dusky shark — 6. March 2017

Shark of the week: Dusky shark

After introducing the homebody Atlantic nurse shark last week, this weeks shark is the opposite: the Dusky shark (Carcharhinus obscurus). It can be found worldwide in warm waters along the coasts (and offshore following ships, too) of America, Australia and Africa (and parts of Europe and Asia). It is nomadic and strongly migratory (even if genetic tests suggest that Indonesian and Australian Dusky sharks represent distinct populations) and wanders seasonally (between the poles in the summer and the equator in the winter) up to 2,400 mi – 3,800 km.

Despite being one of the largest members of the requiem sharks (it reaches on average 10 ft -3.2 m- and up to 14 ft -4.2 m- in length) and having a (maximal of all tested sharks) punctiform bit pressure at the tooth tip of 60 kg (just like human bites, by the way), the Dusky shark is no danger to humans (the very few unprovoked attacks attributed to this species are most likely cases of mistaken identity).

Being apex predators, Dusky sharks are one of the slowest-growing and latest-maturing sharks, not reaching adulthood until around 20 years of age. Female dusky sharks are ovoviviparous and give birth to at most one litter of 6 to 12 young every three years. They use shallow inshore habitats as nursery areas, since juvenile Dusky sharks (in contrast to their parents) do have natural predators, namely other large sharks. Off KwaZulu-Natal (South Africa), the use of shark nets to protect beaches has reduced the populations of these large predators, leading to a dramatic increase in the number of juvenile Dusky sharks (a phenomenon called “predator release”). In turn, these juvenile sharks have decimated populations of small bony fishes, causing monocultures of small Dusky Sharks.

Nevertheless, due to their very low intrinsic rate of increase (renders them among the most vulnerable of vertebrates) and fishing pressure Dusky sharks are considered Vulnerable worldwide and Endangered in the Northwest and Western Central Atlantic. They are targeted for highly valued fins, meat, liver oil and skin and have a high mortality rate when taken as bycatch.

Sources: here and here

Shark of the week: Nurse shark — 27. February 2017

Shark of the week: Nurse shark

Did you know that the Nurse shark (Ginglymostoma cirratum) has the lowest metabolism of all sharks? It needs only 18% of the energy of the agile shortfin mako shark – while swimming. If it swims at all. It is nocturnal and spends the days lazily in its resting sites, together and sometimes on top of many other Nurse sharks.

 

Living in shallow coastal tropical and sub-tropical waters, nurse sharks are bottom-dwelling with two fleshy barbels on the lower jaw (chemosensory organs to help find prey hidden in the sediments). Or they form with their bodies fake caves for prey. These are then sucked in like with a vacuum cleaner. Due to their frugal life they don’t eat much – caught sharks more often that not didn’t have anything in their stomach.

Nurse sharks are brownish in color and reach 7 ft to 10 ft -2.2 to 3 m-, while females are longer than males. They are ovoviviparous, giving birth to 21–29 living young every two years. Like with dogs, scientists found DNA from up to 4 fathers in one litter. Nurse sharks frequent the same nursery and mating areas and resting sites nearby their whole lives (called strong site fidelity), makes them homebodies. They are shy and docile and despite their size no danger to humans, but when provoked, they can bite and are difficult to detach due to the suction.

It seems that the pacific subpopulation of the nurse shark is a species of its own (called Pacific nurse shark), restricting the nurse shark to Atlantic waters only (thus its new name Atlantic nurse shark). Since it doesn’t migrate I wouldn’t be surprised if the Eastern Atlantic subpopulation turns out to be a separate species, too. By the IUCN the Western Atlantic subpopulation is considered as Near Threatened, even as Vulnerable off South America. It is reported locally extinct in some areas off Brazil. Nurse sharks are hunted for their liver oil, fins, flesh and skin and juveniles also for private and commercial aquariums (despite their maximum size). When caught accidentally as bycatch, post-release survivorship is high. Habitat destruction endangers their nurseries and requires additional protective maesures (like in the Florida Keys).

Sources: here, here and here