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Discovery - Virtual tours of the underwater world
Mark Norman, Museum Victoria
Coffinfishes are flabby bottom-dwelling fishes that occur in deep waters around the world. They can walk along the seafloor on short leg-like fins. These fish often come up in the nets swollen into a ball. Like the pufferfishes, they can swallow large amounts of water to inflate themselves, presumably making it harder for predators to bite into them. The lateral line system (a series of sensory pores that can detect vibrations and chemicals) is very obvious on their smooth bodies. Coffinfishes have a small lure on their head (like their anglerfish relatives), consisting of a short rod and a small glowing bulb at the tip used to lure its prey. The eyes of the fresh fish are speckled with iridescent green looking like a pair of spectacular opals. Our animals are around 20-30 cm long.
Electric rays (or numbfish) are special rays that have evolved the ability to generate strong electric charges. You have to be very careful handling these rays as they can give off repeated electric shocks of up to several hundred volts. They have special organs on their undersides that build up electrical charge, just like capacitors. The ray uses these shock pulses to stun its prey. You must pick up these rays by the tail to avoid a shock. Electric rays spend most of their time buried under sand or mud, waiting to detect passing prey. This species also occurs in shallower waters over the continental shelf. Our specimen is a mature male at about 60 cm long, but they have been found up to twice this size.
One of the exciting finds in today’s trawl was two male specimens of an undescribed small species of shark. Known as spiked dogfish (genus Squalus), these two animals double the known number of specimens in the world. The largest was around 60 cm long. Research on related dogfish species elsewhere found that they can form large same-sex schools. The fact that we caught two males in a single haul suggests that the net may have skimmed a male aggregation. The long narrow spines on the dorsal fins are characteristic of this species. Some species of dogfish with much thicker spines use the spines to wedge themselves under rock ledges. The long good condition spines in our species suggest a free swimming lifestyle. Poison glands are present at the base of dogfish spines. This new species is only known from this region. According to shark expert, Dr Peter Last of CSIRO, each seamount chain seems to have different groups of these small sharks, New Caledonia, east Australia and New Zealand each have their own groups. These small sharks are highly vulnerable to fishing pressure as they produce very few pups and are probably slow growing. In some areas they are now rare and are considered good indicator species of fishing pressures.
Some of the invertebrates captured include long armed crabs (genus Platymaia), a bush of black coral, some squid and a huge soft-bodied red prawn (Plesiopanaeus edwardsianus).
This large deep-sea crab belongs in a group of crabs known as anomurans, which includes the hermit crabs. Some scientists suggest hermit crabs evolved from crabs such as these. It has long protective spikes and large crushing claws, presumably for crushing other crabs and shellfish. It has a soft tail held up under its body, showing its relations to the soft-bodied hermit crabs. Only eight legs are well developed, a small fifth pair is held up with the tail under the body. This specimen is a male, recognised by the genital opening at the base of the last arm pair. Although it looks very bright and colourful to us, the red colour probably helps hide it in the deep sea. In low light levels, red looks black, so it would blend in well in the darkness. Its eyes are very small; in some deep-sea crabs they have lost their eyesight completely.
Black corals are a group of corals with a dense hard black skeleton that comes in many different forms, but often look like small shrubs or bonsai trees. The living tissue of this coral lives on the outside of the hard stems and trunks. These corals form the homes of many interesting small animals including barnacles, scale worms, oysters, small crabs and serpent stars. Dr Tim O’Hara, an expert on board, describes serpent stars as “house fairies for black corals”. Their long arms sweep the coral clean of detritus in return for a perch high above the seafloor. The serpent stars that live on the corals are also unusual because they can reproduce by splitting into two separate animals. Some new species have been discovered on this voyage, brightly coloured red, orange and black.
In one trawl, our cruise has more than doubled the known number of specimens of this beautiful small angelfish. It was originally described by Gilbert Whitley in 1959, based on a single specimen collected off Ballina in northern New South Wales. More than twenty years later, Ken Graham of the NSW Fisheries (also on board this voyage) caught a single animal off NSW, took a photo of the fresh specimen and sent the photo and the fish to the Australian Museum. Before our cruise, these were the only two records of this rare fish in the world. Its rarity lead to it being formally recognised as threatened. In one short trawl at around 90 m deep near Ball’s Pyramid, we collected three specimens and excellent fresh photographs taken by Kerryn Parkinson. It appears that this species may be quite abundant in this special region.
This species occurs in the South Pacific and off Japan, at depths 700-1300 m. It reaches 1.2 m long. This genus of deep-sea chimaeras goes under different names in different countries. In the USA it is known as a Long-nosed Chimaera while in Europe they use the common name Cyrano Chimaera, named after the fictional French character Cyrano de Bergerac, who had a very long nose. This strange cartilaginous fish uses its long snout to scan over the seafloor for the electrical impulses of its prey that bury in the muddy seafloor, just like a metal detector. Like other chimaeras (such as ghost and elephant sharks), these animals lay horny egg cases in which their young are left to develop, potentially for up to one year.
This large species occurs right around the world in deep water. It was described in 1887 from an animal collected from the nearby Kermadec Islands, north of New Zealand. It is the second largest member of this diverse family of deep-sea fishes. Rattails get their name from their long narrow tail. Different species have very different head shapes, depending on their lifestyles. This large species has a rounded head and a mouth which faces forward to catch squid and fish that swim up off the seafloor. As in most other rattails, the males of this species have a special drum machine on their swim bladder that is used to attract females. They have to be careful though, as other fish like morid cods have hydrophones on their swim bladders to hunt down the sources of such noises.
The jewel squids are one of the strangest occupants of open-ocean waters. Firstly they have wonky eyes, the left eye is always much larger than the right. In some species the left eye is telescopic while the smaller right eye is normal. These squids have a funny slant on life, literally. They hang at a 45° angle and use the huge eye to look up for passing prey. Meanwhile the normal eye looks below for any signs of attackers. The common name comes from the scattering of small iridescent spots over the undersides of the body, head and arms. These are tiny directional light organs like tiny car headlights. When the squid is hanging at a 45° angle, all the light organs aim down and produce just enough light to cancel out the silhouette of the squid against the weak light from the surface above. They can even adjust the lights for different depths or time of day. Jewel squids are able to float mid-water by filling their soft flesh with pockets of ammonia solution that is less dense than seawater and cancels out the weight of their muscles. They make these solutions out of their body wastes: urine is turned into buoyancy.
