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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: Cobbler wobby — 12. June 2017

shark of the week: Cobbler wobby

Wobbegongs are a family of 12, but only one of them belongs to the genus Sutorectus: the Cobbler wobbegong (Sutorectus tentaculatus).

Since the meaning of “cobbler” is wide-ranging, I don’t attempt to explain the English name (but I don’t think it has anything to do with food), but the Latin name as well as the German name (“Warzen-Teppichhai” means warts wobbegong) are fairly self-explanatory, since it does have tentacle-like barbels and warts.

A Cobbler Wobbegong, Sutorectus tentaculatus, at Wool Bay, South Australia. Source: Chris Hall / MLSSA. License: CC by Attribution-NonCommercial-ShareAlike

Living off Southern and Southwestern Australia, Cobbler Wobbegongs are ovoviviparous and up to 36 in – 92 cm- long. Due to their small size they aren’t targeted, but constitute nevertheless 0.9% of all elasmobranch catches from gillnets in their habitat.

Sources: here and here

 

shark of the week: spotted wobby — 29. May 2017

shark of the week: spotted wobby

Last weeks dwarf spotted wobbegong has got a big brother: the spotted wobbegong (Orectolobus maculatus).

Spotted wobbegong.jpg
Orectolobus maculatus CC BY-SA 3.0, Link

The Spotted wobbegong is a bottom-dwelling ambush predator. It lives in relatively shallow water (up to 715 ft -218 m- deep) and can even occur in water barely deep enough to cover it. It has been observed climbing ridges between tide pools with its back out of water. But it don’t use its fins as legs in the process, like the epaulette shark does.

The Spotted wobbegong is ovoviviparous with about 21 living young every three years. Like most wobbegongs, it lives off Australia. It is one of two larger wobbegong species and reaches a length of 9.8 ft -3 m-, making it a target species in fisheries for its meat (smaller wobbegongs have not enough flesh on their non-existent bones to be lucrative). Fishing pressure led to a IUCN-classification as Near Threatened (and as Vulnerable regionally in New South Wales) up to 2015. But conservation measures like marine protected areas (MPAs) and new management regulations, both for commercial and recreational fisheries (for instance are recreational fishers allowed to “bag” no wobbegongs at all in New South Wales, and only two sharks per person in Western Australia and one shark per person in Queensland), seem to be working, resulting in an assessments as least concern. Fortunately, these regulations are not typal anymore, because it seems that it is very difficult to differentiate between wobbegong species (at least without a comparison specimen or a biology degree):

In New South Wales, O. is often confused with O. halei, but differs from O. halei by having more (6-10 dermal lobes at the posterior preorbital group) and saddles containing whitish rings and blotches (unlike O. halei).

In Western Australia, O. maculatus was previously synonymised with O. parvimaculatus. Taxonomic revision of Western Australian species showed that O. maculatus differs from O. parvimaculatus by having have relatively smaller and less densely distributed ocelli and dorsal fins lacking dark markings (blackish marginal blotches present in O. parvimaculatus). The dorsal fins of O. maculatus are also smaller and less upright than those of O. parvimaculatus (Last and Chidlow 2008).
Records from Japan and the South China Sea are likely to be mis-identified O. japonicus or another undescribed species.

Source: 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: Pacific Angel — 1. May 2017

shark of the week: Pacific Angel

You know that most sharks travel to bear their young in a special area (nursery) to protect them. Mostly it is a shallow bay or estuary, sometimes even a river, but the Pacific Angelshark (Squatina californica) does the very reverse: normally living on sandy flats or rocky reefs as shallow as 10 ft -3 m-, female Pacific Angelsharks wander as deep as 180 to 300 ft -55 to 90 m – to give birth to 1 to 13 living young (their number is independent from the size of their mother, unlike in other sharks). But that is not the only peculiarity of this species.

Squatina californica.jpg
Squatina californica by Tony Chess/NOAA SWFSC (Public Domain)

Pacific Angelsharks are up to 5 ft – 1.5 m – long sharks living in coastal Pacific waters from Alaska to Chile in a number of genetically discrete subpopulations (or possible even different species like the Chilean Angel Shark (Squatina armata) off Chile). Like all other angel sharks, they have a flattened body with greatly enlarged pectoral and pelvic fins and are ovoviviparous (young hatch inside the womb). The embryo has at first an external yolk sac, but that begins to shrink as the yolk is transferred to an internal yolk sac. The embryo feeds from this yolk until it is fully resorbed (if the pup is born prematurely, it does not feed until everything is gone). Born after a 10 month gestation at 9 in – 23 cm- length, Pacific Angels mature at 35 to 39 in – 90 to 100 cm – (both sexes, unlike in other sharks). At what age is unknown, since, unlike in other sharks, their vertebral growth rings (analog to annual growth rings in trees) don’t indicate age but only size (and therefore feeding success). That makes age verification difficult. But tagging and recapturing indicates a relatively slow growth (adults around 0.79 in -2 cm- per year) with maturity occurring relatively late in life, and therefore a moderate fecundity.

As ambush predators, Pacific Angel Sharks bury themselves in the sand near rocky reefs, facing up-slope to better see the silhouette of prey against the sunlight, and lie quietly on the bottom. They appear sluggish, but high-speed videography has revealed that their “predatory strikes are sudden and dramatic: in about a tenth of a second, the front half of the shark’s body snaps upward about 90 degrees from the bottom, the bear trap-like jaws protrude a remarkable distance from the head, and snap shut with audible authority”. During the strike, the eyes roll backward into the head for protection. After a strike they bury themselves again. But, since prey animals often learn quickly where local predators tend to lie-in-wait, ten days later they move under cover of darkness to a new site up to 4.5 mi – 7.3 km – away.

To detect prey, Pacific Angel Shark nearly entirely depend on vision. Experiments showed that they caught fish models every time on vision alone, without scent, electrical or vibratory cues. Even at night, they detect prey indirectly by the faint greenish sparkle of bioluminescent plankton agitated in its wake (their retinal pigments suggest that this species’ peak visual sensitivity occurs at wavelengths almost identical to that produced by local bioluminescent plankton).

A fascinating shark, isn’t it? But humans nearly wiped out this species. Why? Due to fear for their lives? Hardly, since no human has been attacked by a Pacific Angelshark without provocation – they do snap when provoked, but even then don’t leave much damage. No, only for profit. The promotion campaign of a seafood processor in California named Michael Wagner in 1976 and later changed the former “junk fish” almost single-handedly to a tasty seafood, resulting in an annual caught of up to 1.2 million pounds -544,311 kilograms- of Pacific Angelsharks (in 1985) and making this species the number one shark fished off California. The eradication of this species was averted, as in the 90th the central Californian halibut and angel shark fishery (caught with the same gillnets with medium-sized mesh) was closed completely. Pacific angelshark numbers off California appear to be increasing, resulting in an assessment of Least Concern in the United States. Globally however, it is considered as Near Threatened, because the largely unregulated Mexican fisheries took over. This species is now absent from regions in Baja California Sur where it was historically found.

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: Hardnose shark — 10. April 2017

Shark of the week: Hardnose shark

Small sharks often fall prey to bigger sharks and usually survive by getting more pups. But the Hardnose shark (Carcharhinus macloti) has a low reproduction rate: only one or two pups are born after a twelve-month gestation period every two years, just like in apex predators.
Macloti karachi.jpg
Von Hamid Badar Osmany – FishBase, CC BY 3.0, Link

The Hardnose shark is a small species of requiem sharks living in shallow coastal waters of the Indo-West Pacific from Kenya through southern Asia to southern Japan and northern Australia. It is grey or bronze above and white below and was named hardnose because of the heavily calcified cartilages in its snout, unlike in other species of the genus Carcharhinus.

Female Hardnose sharks are oviviparous: one or two embryos hatch inside the uterus and are fed by yolk and later through a placental connection. Born alive at a relatively large size (18 in -45 cm-), they mature at 28 to 30 in -70 to 75 cm- and reach a maximum of only 3.6 ft -110 cm. Their skin is covered by overlapping, oval-shaped dermal denticles.

Hardnose sharks form large, sex-segregated groups and are homebodies (tagging data has shown that 30% of re-caught individuals having moved less than 30 mi -50 km- from their initial tagging location). Due to a high fishing pressure by artisanal and commercial fisheries and their low reproduction rate they are considered as Near Threatened worldwide (although in Australian waters as Least Concern).

Sources: here and here