9 Jul 2015

Spookfish and Other Deep Sea Sharks

From Our Changing World, 9:20 pm on 9 July 2015

By Alison Ballance

"They’re just so weird looking. When it was first suggested that I look at deep water sharks I was a little sceptical, because everyone wants to study your big typical pelagic species, the charismatic great whites and whale sharks. But spending a bit of time with them and just looking at them and all the weird features they have - there are some that glow in the dark, they have massive spines, and there’s lots we just don’t know about them so there’s lots of opportunity to learn."
Brit Finucci, PhD student and deep sea shark scientist, Victoria University of Wellington

Brit Finucci holding a long nose spookfish and a brown chimaera

Brit Finucci holding a long nose spookfish and a brown chimaera Photo: RNZ / Alison Ballance

Brit Finucci is a PhD student at Victoria University of Wellington, and she already knows more about six of New Zealand’s species of deep water sharks than almost anyone else in the world. She has spent many weeks this year dissecting more than 500 specimens of chimaeras that were accidentally caught by research boats working on the Chatham Rise and in the subantarctic, trying to find out as much as she can about these mysterious enigmatic creatures.

Chimaeras are ‘perhaps the oldest and most enigmatic groups of fishes alive today.’ Their closest living relatives are sharks, but they parted evolutionary ways about 400 million years ago. Chimaeras are deep sea sharks that are known by a number of different names, including spookfish, ratfish, rabbitfish, elephantfish and ghostsharks.

The name chimaera (or chimera) comes from Greek mythology, in which it was a fire-breathing monster composed of various animals: a lioness, a snake and a goat. 

Like sharks the skeletons of chimaeras are composed of cartilage, and the males have claspers for internal fertilization of females. Unlike true sharks, chimaeras have just a single pair of gills, and most species also have a mildly venomous spine located in front of the dorsal fin.

“They’re all characterised by having this big giant spine [on their back] which is probably a defensive mechanism,” says Brit.

As well as having flexible claspers with a spiked bulbous end, male chimaeras also have small sexual organs, which resemble a hooked club at the end of a stalk – known as tenaculum - on their forehead and in front of the pelvic fins.

Tenaculum (sex organ) on head of a male chimaera.

Tenaculum (sex organ) on head of a male chimaera. Photo: Brit Finucci

“It’s really odd with the chimaeras, males have this little organ on their head that’s the tenaculum,” says Brit. “When they’re mature the [tenaculum] get these tiny little hooks on them. They think it’s used to attach themselves to the female.”

Chimaeras are deep sea species. “Living in complete darkness at the bottom of the ocean they do have large eyes,” says Brit. “And they also have a tapetum, which is a reflective surface – you see that in cats, too, when you shine lights in their eyes and you get that reflection back.”

Not much is known about the diet of chimaeras. “Their teeth are more like rabbit teeth,” says Brit, “They have these tooth plates they use to grind their food.”

Beak-like grinding plates in mouth of a chimaera

Beak-like grinding plates in mouth of a chimaera Photo: RNZ / Alison Ballance

Sharks are a surprisingly diverse group of animals, ranging in size from the enormous whale shark, the world’s largest fish, to dwarf pygmy sharks (Squaliolus spp). Sharks, batoids (rays, skates and sawfish) and chimaeras form a distinctive group of cartilaginous fishes collectively referred to as the Chondrichthyans. There are more than 500 species of sharks, nearly 650 batoid species and 50 chimaera species, bringing the overall total of Chondrichthyans to about 1200 species.

Te Ara - the encyclopaedia of New Zealand says ‘in 2004 there were 70 known species of sharks, 26 skates and rays, and 12 chimaeras or ghost sharks in New Zealand … and at least four undescribed species.’

Prickly dogfish (Oxynotus bruniensis)

Prickly dogfish (Oxynotus bruniensis) Photo: Brit Finucci

Long nose spookfish (left), brown chimaera (centre), Pacific spookfish (right)

Long nose spookfish (left), brown chimaera (centre), Pacific spookfish (right) Photo: RNZ / Alison Ballance

Brit’s work is focusing on identifying when the six species she is looking at become mature, and she will look at stomach contents to see if she can work out what they’re eating. She is studying six different species:

The long nose spookfish (Harriotta raleighana) has a nose that can be up to half its body length. It belongs to a family of long-nosed chimaeras called Rhinochimaeridae, which has 8 known species in 3 genera.

The Pacific spookfish (Rhinochimaera pacifica) is another long-nosed chimaera.

The brown chimaera (Chimaera carophila) was only described as a distinct species in 2014. I t is only found in New Zealand, has a very blunt nose and large purple pectoral fins. There has been a resurgence in discovering and naming new shark species, both from existing specimens in museums and from new ones collected as more deep sea research is carried out. American taxonomist Dave Ebert alone has described 24 species, some of which he has found in Asian seafood markets.

The prickly dogfish (Oxynotus bruniensis) has a thick body, a prominent hump back with two very large sail-like fins and a very rough skin.

The black ghostshark (Hydrolagus homonycteris) lives at depths of 500 to 1,400 metres.

Owston’s dogfish (Centroscymnus owstonii) grows to 1.2 metres long, and is caught as by-catch in the orange roughy and oreo fisheries.