Picture of the week: Artist impression of the bullshark

This painting by Jeremy Stafford-Deitsch is based on a picture he took at Walkers Cay, Bahamas some years ago. Bull sharks show up regularly at baiting sites in the Bahamas, where they normally keep a safe distance from their bigger rivals, the tiger sharks. Bulls sharks are one of the view species of Carcharhinus that are able to survive in saltwater as well as freshwater of estuaries and rivers. See also our Biology Blog for the remarkable ability of bull sharks to tolerate freshwater.

Highlighted: bird navigation

The western osprey (Pandion haliaetus) is a fish-eating bird of prey with a cosmopolitan range.  After been practically extinct, they have returned to several locations in Holland such as the Biesbosch and Oostvaarderplassen. After their annual migration to Africa, they return in springtime with great precision to their nest, after a flight of almost 6000 km. Most migratory birds such as geese, godwits, and swifts, learn their flying routes from their parents or other migratory birds following the same routes.  Birds like the osprey however migrate alone and rely on a complex -probably innate- system of navigation using the earth's magnetic field, using magnetite mineral sensors buried in their skulls. Other birds like the buntings may use the starry sky,  and shearwaters seem to use their smell, allowing them to smell the coastline when flying over the sea. Day flyers like pigeons use the sunlight and position of the sun.  These factors may also interact with one another, like sunlight and the earth's magnetic field both affecting navigation.

Source: NRC Weekend. Nienke Beinntema April 4 2021

News: why whales dive deeper

Sampling of squid environmental DNA (eDNA) in the foraging zones of Risso’s dolphins (left) and Cuvier’s beaked whales (right). Picture taken from: Visser et al., Science Advances 2021; 7: eabf5908 GEOMAR, C. Kersten)

Whales that dive deeper need more energy to do so. It is only worthwhile to dive deeper if the dive also yields more energy (calories) from prey. This theory has recently been confirmed and expanded by a  joint Dutch/German study using environmental (E) DNA samples of water layers a different depths. By sampling the seawater at different depths off Terceira Island at the Azores, researchers could determine which squid live at the depths where the whales hunt. 'The small amounts of squid eDNA in those water samples were analyzed in the laboratory and compared to the known DNA of squid species’, says Véronique Merten of GEOMAR, Helmholtz-Centre for Ocean Research Kiel in Germany. The study showed that Risso's dolphins caught prey between depths of 12 and 623 meters. Cuvier's beaked whales hunted much deeper, between depths of 800 and 1,700 meters and at the deep-seafloor. 

 

 

Higlighted: Savanna elephants returning in Congo

Photo by Anthony Caere, Virunga National Park

Savanna elephants have returned en masse to Virunga National Park, in the Democratic Republic of the Congo,  a region plagued by violence to man an animal for decades. ''The return of big herds of elephants to Virunga has cheered rangers in an otherwise gloomy year. They hope that the elephants' impact on the grasslands will have positive effects for the park’s other grazers, too’. Source: National Geographic April 1, 2021

 

 

Highlighted: Colors along the wall

De Red Sea contains many deep walls such as the southern point of the Sinai surrounded by fringing coral reefs that emerged after a change in the coastline 70,000 years ago and has vertical overhangs at least 100-1000 m deep.  The limestone plateau of Raja Ampat Indonesia also has  steep walls covered with soft and hard corals, sea fans, and giant barrel sponges. For UW photographers, however,  the more shallow parts of the wall are of more interest. Shooting upwards can be an effective way to create a contrast between a colorful (preferably red) object close to the lens, a gloomy and darkish steep wall, and a blue sunlit surface. Taken with the Tokina 10-17mm,  8 mm Pansonic fisheye, and dual DS 161 strobes. Camera was either Nkon D7200 in Ikelite housing, or E-PL5 in Olympus  PEN housing. 

  • barrel sponge from Raja Ampat

Highlighted: Sponges of the Caribbean and Indian Ocean

Barrel Sponge (Xestospongia testudinaria)

Sponges like the giant barrel sponges (Xestospongia muta)  and tube sponges are highly effectivee filter pumps Water is continually pumped into the sides of the sponge, through the sponge body, and out of the osculum at the top of the sponge. Small pores in the sponge body are connected to channels lined by collar cells each with a flagellum and the beating of these flagellae draws water through the channels. Incoming particles, particularly microscopic bacteria  (Source https://en.wikipedia.org/wiki/Giant_barrel_sponge)

E-Book. Click on the Icon to download thePDF file

 This ‘E-book’  contains an updated collection of around 80  blog articles from the last three years.  I here provide two separate content lists, a list in which the articles are ordered according to the five most often recurring themes, and a chronological list. A simple click on the title will hopefully guide you to the article of your choice. For download,  click  next to the  PDF icon 

E-book