Divers exploring warm waters around the world often encounter Chilean devil rays, gentle marine creatures that can grow up to ten feet long.
Scientists have just discovered that the rays harbor an impressive secret, however: they regularly undertake epic dives more than a mile deep.
These remarkable dives came as a surprise to researchers who reported the finding today in Nature Communications. In retrospect, they note, the rays’ physiology did hint at this ability.
Chilean devil rays possess a special organ called the retia mirabilia, which is also found in deep-diving species such as great white sharks. In those animals, the veined structure fills with warm blood that exchanges heat between vessel walls. This helps to keep the marine creatures’ brain warm when they descend to freezing depths. But Chilean devil rays, researchers assumed, spent all of their time at the surface. Why would they need such a structure?
To solve the puzzle, an international team of marine biologists attached satellite tags to 15 Chilean devil rays captured off the northwest coast of Africa, near the Azores archipelago. The team monitored the rays’ movements for nine months and found that the animals were tremendously active. They sometimes traversed up to 30 miles of ocean per day, with each covering a distance of up to 2,300 miles over the nine-month period. Even more impressive, however, was the rays’ diving abilities. They regularly dove below 1,000 feet, with a maximum-recorded depth of 6,062 feet. This means that Chilean devil rays undertake some of the deepest dives ever recorded for marine animals, the team reports.
The journeys into the deep seem to be no sweat for the animals. One individual, for example, dove nearly 4,600 feet six days in a row, and overall, the rays spent more than five percent of their time in deep water.
The deep dives explain the presence of the previously enigmatic retia mirabilia, the team writes. At the depths recorded by the trackers, rays would encounter temperatures as chilly as 37˚F, so the extra flush of warm blood provided by that organ likely makes those dives possible. Additionally, the researchers found that the rays spend more time basking near the water’s warm surface both one hour before and one hour after a deep dive, implying that the animals are preparing for and recovering from encounters with the cold.
The rays aren’t undertaking these dives just for fun, of course. Based on the animals’ movement patterns—oftentimes a quick bee-line descent followed by a slower step-wise ascent—the researchers think they are probably foraging on fish or squid that live well below the surface.
The unexpected findings, the authors write, demonstrate “how little we know” about Chilean devil rays and the role they play in ocean ecosystems. Given that these animals were recently listed as endangered (largely due to a growing demand for their gills by practitioners of traditional Chinese medicine), “this ignorance has significant conservation implications,” the team continues. As with any species, the more we know about them, the better equipped we will be for protecting them—and for knowing what we stand to lose should they disappear.
ONE OF THE world’s largest fishes, this strangely wonderful shark-like ray occurs in waters around the world. Individuals can grow larger than 6.5m (including the saw) and weigh up to 600kg.
They are named for their distinctive saw-like snout with about 14-23 protruding teeth (which are actually scales) on each side. They use the snout to find and stun prey, which includes schooling fish such as mullet, as well as molluscs and crustaceans.
Unlike many fish that either live in freshwater or marine environments, the sawfish can move through both (known as being ‘euryhaline’). Juveniles are often found in freshwater, whereas adults are most often in estuary or marine waters.
What were formerly considered separate species, P. pristis, P. microdon, and P. perotteti, are now listed under the one species P. pristis and thought to be subpopulations occurring in tropical waters in the Eastern Atlantic, Western Atlantic, Eastern Pacific and Indo-West Pacific oceans.
Our local sawfish (Indo-West Pacific population) population is one of the last strong ones, listed just as Vulnerable nationally; therefore, they are important to the whole species’ survival globally.
They are found in the muddy bottoms of Australia’s big northern rivers and estuaries, including the Fitzroy and Ord rivers in WA, the Adelaide and Daly rivers in the NT, and the Mitchell and Leichhardt rivers in Qld. They have been found 400km from the sea.
Sawfish are ‘ovoviviparous’, meaning that a mother incubates her eggs inside her until they are ready to be born. A litter ranges from 1-11 pups and individuals don’t reach maturity until about 8-10 years. The Australian population has been estimated to live for up to 35 years.
Threats to sawfish extinction
The shark-fin trade is a major threat to their survival globally, as is the traditional medicine trade. Their unusual saw-like snout is also a treasured item, which makes them a target for illegal trade.
Their snouts also cause them to easily become trapped in nets, so this type of fishing is also a threat.
A recovery plan for the species listed as Vulnerable in Australia is currently being developed.
The mandarinfish is one of only two known species that produces a blue pigment. (Credit: Jim Trodel/Flickr)
by Becky Crew
One of the most beautiful fish in the ocean, but the mandarinfish (Synchiropus splendidus) has got so much more going on for it than all those pretty colours.
At home in the sheltered lagoons and inshore reefs of the Pacific Ocean, ranging from the Ryukyu Islands off the coast of Japan, to warm Australian waters, this little dragonet is covered in tiny spines to inject a toxic mucus into anyone who tries to handle and/or eat it.
The mandarinfish contains two types of secretary cells in its colourful epidermis – one that produces a thick mucus coating to protect it from the elements, and another that produces a toxin to protect it from predators.
And not only is this toxic mucus coating dangerous, particularly if it makes it into a predator’s open wound, but reportedly, it smells disgusting.
“Every scientist and book [who] talks about the mandarinfish makes mention of its strong, unpleasant smell,” says Esther Inglis-Arkell at io9. “
That stink is not incidental. The mandarinfish needs the smell, and the spines, because it lacks one of the most basic protective measures in the marine world: It doesn’t have scales.”
There’s nothing like thick mucus and an unpleasant stench to turn someone off their potential meal.
The German ichthyologist M.H.C. Lichtenstein described the goliath grouper as Serranus itajara in an 1822 publication regarding the natural history of Brazil.
In an 1884 work, “The fishes of the Florida Keys,” David Starr Jordan proposed the inclusion of the goliath grouper in Epinephelus (Bloch 1793) and this combination remains in use today. Of incidental note is the fact that various authors have incorrectly spelled the specific epithet “itajara” as “itaiara.”
The genus name comes from the Greek epinephelos translated as cloudy. Synonyms of E. itajara include Serranus guasa Poey 1860 and Serranus quinquefasciatus Bocourt 1868.
A number of authors treat the name Promicrops itajara as valid taxonomy for the goliath grouper.
The goliath grouper occurs in the western Atlantic Ocean from Florida south to Brazil, including the Gulf of Mexico and the Caribbean Sea.
It is also found in the eastern Atlantic Ocean, from Senegal to Congo although rare in the Canary Islands.
The species is also present in the eastern Pacific Ocean from the Gulf of California to Peru.
Fins with transparent membranes give the ribbonfish its name. Image Credit: Joshua Lambus.
Up to 2m long the ribbonfish is an elegant deep-sea creature.
Named for the elaborate fins that ripple delicately after them as they swim, ribbonfish from the genus Trachipterus are found all over the world.
There are six known species, and Australia’s is the southern ribbonfish, a 2m-long silvery creature with black polka dots on its sides and bright red fins.
Found off the coast of southern Queensland and South Australia, the southern ribbonfish has also set up a population off the coast of South Africa.
This fish is pretty much a taxonomic nightmare, because while it’s certainly a single species, according to the Australian Museum no one can decide whether its correct scientific name is T. jacksonensis or T. arawatae.