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Shark of the week: Ornate wobby — 25. September 2017

Shark of the week: Ornate wobby

One of many shark species living solely off Australia is the Ornate Wobbegong (Orectolobus ornatus). This species of carpet sharks is only up to 3.8 ft – 1.17 m – long and had been confused with juvenile Banded Wobbegongs (Orectolobus halei) until 2006.

Orectolobus ornatus great barrier reef.jpg
Banded wobbegong (Orectolobus ornatus) at the Great Barrier Reef, Queensland by Andrew J. Green / Reef Life Survey – http://fishesofaustralia.net.au/home/species/1976, CC-BY 4.0, Link

Ornate wobbegongs are ovoviviparous. Every 3 years around 9 living young are born with a size of 7.9 in -20 cm. The gestation period is only about 10 to 11 month long, but the follicles take two years to enlarge before ovulation.

Since they mature at about 31 in -80 cm- length, measures to protect juveniles of the bigger Banded wobbegong (a minimum catch size limit of 5.9 ft – 1.80 m -), implemented between 2008 and 2013, effectively protected Ornate Wobbegongs of all sizes and allowed their stocks to recover. There are management regulations in place for commercial wobbegong fisheries (where they are taken as bycatch and for their meat for fish and chips and their skin for leather), and a possession limit for recreational fishers of one shark in Queensland and zero sharks in New South Wales. That’s why the IUCN has been considered the Ornate wobbegong since 2015 as “Least Concern” (after “Near Threatened” in 2009).

Sources:here and here

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Shark oft the Werk: Leopard shark — 21. August 2017

Shark oft the Werk: Leopard shark

The Leopard shark (Triakis semifasciata) is a beautiful shark of the family of houndsharks. It lives in the northeastern pacific in several distinct populations off Oregon down to Mexico. They like the ground (sandy or muddy) near rocks or kelp forests in depths between 3 and 295 ft -1 and 90 m.

View from above of two leopard sharks lying on the sand side-by-side
By nugunslinger from Lafayette, USofA – Leopard Sharks….NOT Tiger, CC BY 2.0, Link

Female Leopard sharks are ovoviparous and give birth to 4 to 29 living young after a gestation period of 12 month. The 8 in -30 cm- long pups grow slowly and mature only after 10 years. Males are up to 78 in -2 m- and females up to 70 in -1.8 m- long. They live up to 30 years.
Leopard sharks form large groups, even together with different shark species. They search rather buried prey like crabs, worms and clams than feed from fish. Since their habitats are often endangered by human effluent and industrial waste, they tend to concentrate pesticides, polychlorinated biphenyls (PCB’s), and other toxic chemicals in the liver.
Leopard sharks are caught as game fish and fished commercially for their meat. They are often shown in aquaria.

Sources: here, here and here

Shark of the week: Carcharhinus tjutjot — 17. July 2017

Shark of the week: Carcharhinus tjutjot

The Carcharhinus tjutjot (sometimes also known as Indonesian whaler shark) is a little known requiem shark. There is no picture of this species to be found, but since it had been confused with juvenile Whitecheek sharks up to 2012, it has to look a lot like them.

Named after one of the Indonesian words for shark, the Carcharhinus tjutjot lives in shallow coastal waters (up to 328 ft -100 m- deep) of the South China Sea off Indonesia, Taiwan and Borneo. This litte shark species (up to 36 in – 93 cm – long) is, like all requiem sharks, ovoviviparous: there have been found 2 late-term embryos measuring 11 in -27.9 cm- length inside one pregnant female.

There is no IUCN Red List Status available, yet, but, since the similar Whitecheek shark faces extinction in its Asian habitats, the risk for the Carcharhinus tjutjot has to be equally high, especially due to the fact that it has got no managed Australian sub-species like its relative.

Sources: here and here

shark of the week: Whitecheek shark — 3. July 2017

shark of the week: Whitecheek shark

If you watch the video the name of the Whitecheek shark (Carcharhinus dussumieri) seems fitting (I don’t know about the reason for its other name: Widemouth Blackspot shark).

Whitecheek sharks are, like all other requiem sharks, ovoviviparous with on average two about 15 in -38 cm- long pups annually. Both males and females mature when they are about 28 in -70 cm- long and reach a maximal length of 39 in -100 cm. Only in 2012 it was found out that sharks of the species Carcharhinus tjutjot are no juvenile Whitecheek sharks (as believed since 1982) but a different species.

Living in coastal waters of the Indo-Pacific Ocean, the Whitecheek shark is usually caught as bycatch rather than as the target species, but is nevertheless facing extinction in several Asian regions. But a relatively large and fairly robust population in northern Australia, where it comprises a stable 2-3% of trawl catch (by biomass), saves this species – thus only considered Near Threatened by the IUCN.

Sources: here and here

 

Shark of the week: Whitetip Reef shark — 26. June 2017

Shark of the week: Whitetip Reef shark

Another case of mysterious naming is the Whitetip Reef shark (Triaenodon obesus). Not the English name, which is quite apt due to its white tips on dorsal and caudal fins and its exclusive habitat, but the Latin one is untrue: this slender shark is far from obese. On the contrary, as nocturnal hunter it can detect its prey by electroreception (using its ampullae of Lorenzini) and smell (with unique tubular nasal flaps) and follows it into their resting crevices (well adapted to this hunting practice due to its tough skin, sleek build, blunt snout and ridges to protect its eyes), and some sharks “actually squirm into a hole in one side of a coral head and exit through an opening on the other”.

Three gray sharks lying beside each other on the sea bottom.
By Dorothy from USA – sharks, CC BY 2.0, Link

The Whitetip Reef shark is gregarious (sometimes even hunts in groups) and can be seen resting in groups on the bottom or in caves during daytime. It doesn’t need to swim to breathe, unlike other requiem sharks. Not to be confused with the other Whitetip requiem shark (the Oceanic Whitetip), the smaller Whitetip Reef shark (up to 5.6 ft -1.7 m- long) isn’t dangerous to humans. Sadly, as opportunistic feeder it learnt to associate the sounds of boats and spearfishing with food – the curious shark can become bold and agitated and sometimes bites while trying to steal the fish.

Like all requiem sharks, the Whitetip Reef shark is ovoviviparous: every two years 2 to 3 living young are born at a length of 20 to 24 in -52 to 60 cm. There is a case of Parthenogenesis (asexually reproduction) in Whitetip reef sharks. They grow slowly, mature at about 3.4 feet -1.05 m- and live up to 25 years.

Whitetip Reef sharks live in coral reefs all around the world. They are homebodies and famous for their site fidelity. That means that dangers to their coral reef due to climate change, overheating and pollution have a deep impact on the shark population, too, in addition to commercial and recreational fisheries. They are considered as Near Threatened by the IUCN. Conservation measures like marine protected areas (MPA) seems to help, but only if they are completely no-entry. On the Great Barrier Reef, populations of Whitetip Reef sharks in fishing zones have been reduced by 80% relative to no-entry zones. However, populations in no-take zones, where boats are allowed but fishing prohibited, exhibit levels of depletion comparable to fishing zones, most likely due to poaching (IUU). Demographic models indicate that these depleted populations will continue to decline by 6.6–8.3% per year without additional conservation measures.

Sources: here, 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