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Shark of the week: Daggernose shark — 14. August 2017

Shark of the week: Daggernose shark

The genus Isogomphodon of requiem sharks only consists of one living species, but it seems that the Daggernose shark (Isogomphodon oxyrhynchus), known since 1839, soon joins the fate of its extinct sister species Isogomphodon acuarius.

Systematische Beschreibung der Plagiostomen (Plate 15) BHL6353140.jpg
Von Henle, Jacob; Müller, Johannes – http://www.biodiversitylibrary.org/pageimage/6353140, Gemeinfrei, Link

Female Daggernose sharks are viviparous (placental connection after the yolk sac of the embryo is depleted) and give birth to 2 to 8 living young every two years in nursery areas. Newborn sharks measure 15 to 17 in -38 to 43 cm- in length. Males mature at an age of 5–6 years and females with 6–7 years and reach up to 12 years and 4.6 ft -1.4 m- (males) and 20 years and 5.2 ft -1.6 m- (females).

The Daggernose shark lives solely in coastal waters (no rivers since it is intolerant of fresh water) of the Western Atlantic off Trinidad, Guyana, Suriname, French Guiana and northern Brazil. It is highly specialised (tiny eyes but elongated snout to properly use electroreception, a lot of pointed slender teeth -the most teeth of all requiem sharks- to form a fish trap) to hunt small schooling fish in muddy waters. Since humans are after the same fish, the shark gets the short end of the stick – caught as bycatch in gillnets (but also by fishery targeting sharks), it has been considered critically endangered by the IUCN since 2006 as a result. Between 1992 and 2002 it suffered a very large population decline (shown by more that 90% less catches), and moreover, mostly juvenile specimens have been found in the nets. And things may have gotten worse since then. There are simply no new data available regarding daggernose sharks, not for lack of trying but specimen, which means they are (despite being legally protected in Brazil since 2006, which is without enforcement not of much use) in reproductive collapse and on the brick of extinction.

Sources: here, here and here

shark of the week: Blacknose shark — 31. July 2017

shark of the week: Blacknose shark

The Blacknose shark (Carcharhinus acronotus) is a little (up to 4.3 ft -1.3 m- long) requiem shark. Its name refers to a black spot on the nose of juvenile sharks.

Carcharhinus acronotus noaa.jpg
Carcharhinus acronotus by NOAA – http://www.noaanews.noaa.gov/stories2009/20090724_sharks.html, Public Domain, Link

Blacknose sharks live in tropical or warm-temperate coastal waters of the western Atlantic from the southern USA, through the Gulf of Mexico and the Caribbean all the way to southern Brazil. There is segregation by size and sex: juveniles are typically found in shallow water while adults are located at greater depths. They are known to form large schools.

Blacknose sharks reach a maximum age of 10-16 years for females and 4.5-9 years for males. Both mature at 2 years and are relatively fast growing. Reproduction is viviparous with a yolk-sac placenta. After a 8-11 month gestation period, 3-6 15 to 20 in -38 to 50 cm- long pups are born annually (Gulf of Mexico) or biennially (Northwestern Atlantic) in shallow nursery areas like coastal bays or mangrove swamps, for instance Bulls Bay, South Carolina (U.S.).

Blacknose sharks are fished commercially as target and bycatch, but also as game-fish – as they are deemed decent fighters. This species is considered Near Threatened globally by the IUCN, and benefits from conservation measures (together with other small coastal sharks) in US waters. Although affected by high fishing pressure, Blacknose sharks seem to be in no danger in Brazil (since there are enough mature sharks to be found) but there aren’t sufficient data yet. For the Caribbean, too.

Sources: here, here and here

Shark of the week: Finetooth shark — 10. July 2017

Shark of the week: Finetooth shark

Another shark with a name leaving no doubt about the reason is the Finetooth shark (Carcharhinus isodon). Named after its nearly even, rather slender teeth in upper and lower jaw (isodon means „even tooth“), its name is also Eventooth Shark or Smoothtooth Shark, in German Feinzahnhai, in French Requin à Petites Dents and in Spanish Galana Dientefino or Tiburón Dentiliso (however, I don’t know why it is also named Night Shark or Tiburón de Noche).

Carcharhinus isodon in net.JPG
Von National Observer Program, NMFS/SEFSC – http://www.st.nmfs.noaa.gov/observer-home/about-nop/activities/index, Gemeinfrei, Link

The Finetooth shark inhabits extremely shallow coastal waters (no deeper than 33 ft -10 m- in the summer and 66 ft -20 m- deep in the winter) in the Northwest Atlantic, Gulf of Mexico and Southwest Atlantic (off Brazil) in distinct populations. In the past it was known to venture into rivers, though most of its paths are nowadays blocked by dams. That’s a problem, since the females move to special inshore nursery areas. There they give birth to 2 to 6 living, 19 to 25 in -48 to 64 cm- long young every 2 years after a 12 month gestation period. Like all species of the family requiem sharks, finetooth sharks are oviviparous, that means the embryo hatches in the womb and is born alive. Additionally, the depleted yolk sac develops into a placental connection to the mother after the embryos drain their yolk supply during their first 15 weeks (viviparous).

Although having a maximum length of 6.2 ft -1.9 m- (on average males reach only 5.2 ft -1.6 m- in length and females 5.4 ft -1.7 m-), the finetooth shark is no danger to humans. However, it thrashes and snaps at anything within reach when caught. It matures at 40 in -1 m- (at 4-5 years as males and 5-6 years as females, who are growing slower in general) and has a life span of 9 years – males- or 14 years – females.

Off the coast of North America the finetooth shark is known to migrate south seasonally (namely when surface water temperatures drop below 68°F -20°C-). It hunts in large schools for small fish. It is susceptible to habitat degradation (especially it nursery areas) and overfishing (as bycatch and targeted), but is considered (despite its low reproductive rate) as Least Concern – at least in the northern hemisphere, off Brazil however there is only a badly managed fishery which already pushed other shark species near extinction.

Sources: here, 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: 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 viviparous, 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