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Scientific American Blog Network: 30 Percent of Sharks, Rays and Related Species at Risk of Extinction | 30% der Haie, Rochen und verwandten Arten sind vom Aussterben bedroht — 16. August 2017
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

ideas.ted.com: Vertical ocean farms that can feed us and help our seas| Vertikale Meeresfarmen, die uns ernähren können und unseren Meeren helfen — 30. July 2017

ideas.ted.com: Vertical ocean farms that can feed us and help our seas| Vertikale Meeresfarmen, die uns ernähren können und unseren Meeren helfen

Bren Smith wants to create thousands of decent jobs, transform how we harvest food from the oceans, and blunt the effects of climate change and marine degradation — all at the same time. His big idea: small-scale marine farms.

see Vertical ocean farms that can feed us and help our seas — ideas.ted.com


Bren Smith will tausende von ehrlichen Jobs schaffen, verändern wie wir Nahrung aus dem Meer holen, und die Effekte von Klimawandel und Meereszerstörung abmildern- alles zur gleichen Zeit. Seine große Idee: kleine Meeres-Farmen.

Siehe Vertical ocean farms that can feed us and help our seas — ideas.ted.com

Shark of the week: Borneo Shark — 24. July 2017

Shark of the week: Borneo Shark

One shark species considered endangered by the IUCN was possibly nearly extinct, since it had not been recorded since 1937 and only five confirmed specimens were known. But in 2004, several specimens of the Borneo Shark (Carcharhinus borneensis) has been found again by scientists in fish markets (just like the Indonesian wobbegong), making images never seen before possible, like color images (of fresh specimens instead of preserved) or of its enlarged denticles.

Denticles c borneensis.png
Denticles borneo shark – By William Toby White i Pieter Last – White, W.T.; Last, P.R.; Lim, A.P.K.. Rediscovery of the rare and endangered Borneo Shark Carcharhinus borneensis (Bleeker, 1858) (Carcharhiniformes: Carcharhinidae), 2010. CSIRO Marine and Atmospheric Research, CC BY 3.0, Link

The Borneo shark has a slender body with a long, pointed snout, rather large, round eyes with nictitating membranes and oblique, slit-like nostrils. Unique is a row of enlarged pores above the corners of its mouth. Like most requiem sharks it is viviparous with up to 6 embryos, provisioned by the mother through a placental connection formed from the depleted yolk sac and born alive at close to 9.4 to 11.0 in -24 to 28 cm- long. Maturing at around 22 to 23 in -55 to 58 cm- in males and 24 to 26 in -61 to 65 cm- in females, the Borneo shark is a rather small shark (the largest known specimen measures 26 in -65 cm- long).

Formerly, the Borneo shark lived in shallow coastal waters of the Indo-West Pacific off Borneo, China and possibly Java. Now it lives maybe solely around the mouth of the Mukah River in Malaysia, where, due to high fishing pressure, it is in grave danger.

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

Fünf kluge Wege, um Essensverschwendung zu bekämpfen | Five smart ways to fight food waste — ideas.ted.com — 4. June 2017

Fünf kluge Wege, um Essensverschwendung zu bekämpfen | Five smart ways to fight food waste — ideas.ted.com

An estimated 30 percent of the planet’s food supply is needlessly discarded. Here are some imaginative ideas to stop the rot. We humans have a puzzling attitude towards food — it’s one of the few things in life that we absolutely need to survive, yet we can be shockingly careless with it. From a shriveled up…

über Five smart ways to fight food waste — ideas.ted.com

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