By Ross Daley, Research Project Leader
Harrisson’s Dogfish (Centrophorus harrissoni) is a small shark that occupies a narrow strip of continental slope off eastern Australia and remote seamounts in the Tasman Sea, 300 to 600 metres deep. It grows to about 1.2 metres and has large, iridescent green eyes that locate lantern fish in the near darkness of the seafloor. Males and females of the species mostly live apart, moving together every two to three years to breed.
CSIRO – in association with the fishing industry and supported by fisheries managers – has conducted comprehensive field surveys of this species, and the first electronic tracking surveys of the closely-related Southern Dogfish (Centrophorus zeehaani). The surveys gather information on species distribution and home range to assist their conservation and management.
Dogfish follow schools of prey up the continental slope at night
It has been estimated that Harrisson’s Dogfish populations have declined by more than 90% in key parts of their distribution off southern New South Wales and eastern Victoria. Healthier populations remain off northern New South Wales, eastern Bass Strait and on remote seamounts in the Tasman Sea. In June 2013, the species was listed as Conservation Dependent under the Environmental Protection and Biodiversity Act.
Historically, Harrisson’s Dogfish have been targeted for liver oil in Australian state and Commonwealth fisheries. Targeted fishing was essentially halted by 2005, but with very low breeding rates, even limited incidental fishing mortality can be a problem. Populations can take decades or longer to recover because females don’t breed until they are about 17 years of age and produce only one or two young every three years.
The Upper Slope Dogfish Management Strategy has been implemented by the Australian Fisheries Management Authority to halt decline and support recovery of Harrisson’s Dogfish and Southern Dogfish in offshore waters managed by the Commonwealth. Under the strategy, a network of areas − large enough to ensure males and females can meet to breed − is closed to all fishing.
Electronic tagging at the largest closure off South Australia indicates most Southern Dogfish stay inside the closure. Outside the closures the strategy is complemented by a code of practice for the release of live sharks caught as bycatch. New South Wales restrictions have limited combined catches of Harrisson’s Dogfish to 15kg per day in trawl, trap and line fisheries. A closed area off Sydney helps protect Southern Dogfish.
As the world’s human population escalates, demands for food and energy have seen resource use expand into the deep-sea. Closed areas are a key strategy to maintain biodiversity in the ocean, particularly for species that are largely sedentary. Fishing closures such as those for Harrisson’s and Southern Dogfish can also protect species known to move on a limited scale. But the economic costs of such closures are high and cumulative. For slow-growing, deep-sea sharks such as Harrisson’s Dogfish, recovery is uncertain and a precautionary approach supported by ongoing monitoring and research is warranted.
Meet the sea pig. It’s a little different from the land pig. Actually, other than it’s plump appearance, it has no resemblance.
The sea pig rules the dark and mysterious depths of the sea. They’re typically found at depths of 1000m on the sea floor of the Indian and Pacific Ocean. A type of sea cucumber, they have several large “legs” or tube feet, which are really noodly appendages. While noodly appendages are generally fascinating, these sea pig appendages are particularly monstrous. The sea pig has the ability to inflate and deflate the appendages using water cavities within its skin.
Sea pigs are deposit feeders, meaning that extract their food from particles in the deep sea mud. There are more amazing sea pig facts in this video (accuracy not guaranteed):
Blue Marlin: This week a blue marlin washed up on a suburban Adelaide beach. It is thought this is the first time a marlin has been found in the cool waters of Gulf St Vincent where Adelaide sits.
Scientists from the South Australian Research and Development Institute think the fish took a wrong turn at Kangaroo Island and ended up in the Gulf.
They also think that the 3.2m long, 250kg marlin swan along the WA and SA coasts in the warm Leeuwin Current which at this time of year flows down the WA coast and around into the Great Australian Bight.
Below is a picture of the current (red turning to yellow and green as it cools) whipping around the bottom of WA. The second image shows the SA coast with the relatively warm water flowing around Kangaroo Island.
More images of the ocean currents around Australia can be found at the Bureau of Meteorology site which gets the information through the Bluelink program run by CSIRO’s Wealth from Oceans Flagship in collaboration with the Bureau of Meteorology and the Royal Australian Navy.
Anyway, back to the blue marlin. There is a debate going on about the classification of the Atlantic blue marlin and the
Indo-Pacific blue marlin (Makaira mazara) as separate species. Genetic data seems to show that although the two groups are isolated from each other they are both the same.
The blue marlin spends most of its life in the open sea far from land and preys on a wide variety of marine life and often uses its long bill to stun or injure its prey.
Females can grow up to four times the weight of males and the maximum published weight is 818kg and 5m long.
Blue marlin, like other billfish can rapidly change color, an effect created by pigment-containing iridophores and light-reflecting skin cells. Mostly they have a blue-black body on top with a silvery white underside.
Females can spawn up to four times in one season and release over seven million eggs at once. Males may live for 18 years, and females up to 27.
Here’s a fun fact: the words “sarcastic” and “sarcasm” come from the Greek word sarkasmos, meaning “to tear or rend flesh”.
And so I introduce to you the Sarcastic fringehead – a ferociously fierce and territorial fish.
The ‘fringehead’ part of the name comes from the little fringe-like appendages above their eyes. And of course, the ‘sarcastic’ bit relates to their highly aggressive nature. I’m sure if they could talk, they would be nastily witty too.
Fringeheads are found in the Pacific Ocean off North America and tend to hide inside shells or crevices. They have also been known to live inside cans and bottles. Whatever the shelter used, they will fearlessly defend their home territory against any unwanted intruders.
When two fringeheads have a territorial battle, they wrestle with their mouths as if they are aggressively kissing…how romantic (and yes, I’m being sarcastic).
This is how they interact:
Dark Smiling Whiptail: I was trying to be smart and find a fish with some sort of connection to the Winter Solstice (today) to try and make the shortest day of the year bearable. So I started to search the ScienceImage database using words like solstice, daylight, night etc etc and came across the Dark Smiling Whiptail.
I have got to tell you there is very little of interest about this fish. It lives down to about 850m of water which is something, but apart from that, not much.
Then I started to have a look at the scientists who described the fish and named it in 1999 – T. Iwamoto & A. Williams. As it turned out Dr Tomio Iwamoto has been the Curator of Ichthyology for 37 years at the California Academy of Sciences.
Then I found a connection to CSIRO. Dr Iwamoto is named as one a number of scientists who have made a major contribution to the fishmap interactive database which is a part of the Atlas of Living Australia. Dr Iwamoto has done a lot of work in Australian waters and contributed an enormous amount of information and experience to marine science.
There is always something interesting about everything.
So, hopefully this has helped get you through the day. For those in the Southern Hemisphere, from now on things are looking brighter!
Also known as the toothpick fish or vampire fish, the Candiru is a slender, translucent parasite. These creepy critters are native to the Amazon Basin and live in the gills of larger fish, feasting on their blood.
While some Candiru species can grow up to 40 centimetres long, the majority are quite small. It’s these smaller species that are famous for their alleged tendency to invade and parasitise the human urethra, although the truth to this story remains unknown.
Nonetheless, if you plan to swim in the Amazon, it might be a good idea to go to the bathroom first.