Week 3: Diversity of Ross Sea fish
The Antarctic fish fauna is relatively small, with only around 325 species known and only about 135 reported to be found in the Ross Sea region. By comparison, coral reefs support very large fish communities ranging from about 400 species in the waters around Fiji to more than 2,000 in Indonesia. However, the fauna of fish from the Ross Sea have not been thoroughly sampled so, during this survey, we expected to find new species not known to scientists.
An Antarctic silverfish
The Antarctic silverfish (Pleuragramma antarcticum) can withstand very cold temperature and is the main food for many larger fish, seabirds, penguins, seals and whales living in the Ross Sea. They grow to about 25 centimetres long and live up to 10 years.
The most common group of fish we expected to find during the survey are called notothenioids. This is a group of about 125 diverse marine fish species, most of which are found in Antarctic and sub-Antarctic waters. One of the remarkable adaptations of these fish is their ability to withstand very cold temperatures. The average sea temperature in the Ross Sea is –1.9°C. Most fish would freeze at this temperature, but some Antarctic notothenioids have 'antifreeze' proteins in their bloodstream that prevent them from freezing.
Antarctic toothfish
The Antarctic toothfish (Dissostichus mawsoni) can grow to over 2 metres long, weigh more than 100 kilograms, and may live up to 50 years, it is also the target of bottom longline fishery.
Two of the most abundant notothenioids in the Ross Sea region are the Antarctic silverfish (Pleuragramma antarcticum) and the Antarctic toothfish (Dissostichus mawsoni)
The silverfish is the main food for many larger fish, seabirds, penguins, seals and whales living in the Ross Sea. They grow to about 25 centimetres long and live up to 10 years. In contrast, the toothfish can grow to over 2 metres long, weigh more than 100 kilograms and may live up to 50 years.
Antarctic icefish
Andrew Stewart is discussing the adaptations of the Antarctic silverfish.
Points of interest for teachers:
Students may want to discuss why the icefish does not have red blood.
Why is more oxygen dissolved in the Antarctic waters?
Consider the range of adaptations that icefish have developed.
IPY blogs week 3
Antarctic fish habitats
Antarctic fish have evolved to use practically all of the habitats in the Ross Sea. Fish live either in the water column (pelagic) or closer to the seabed (demersal), and some live in the sea ice (cryopelagic fish). Thigmotaxis is a special behaviour where an organism needs to be very close to something. This leads to schooling behaviour in pelagic species or being close to the seafloor for demersal species. Most fish species are pelagic during the larval stages and may ‘recruit’ to a seafloor habitat at a certain age, where they will spend the adult portion of their lives (demersal species), and sometimes species use different habitats depending on what time of day it is – for food or protection.
Written by Christopher Jones
An Antarctic icefish
An Antarctic icefish species (likely Neopagetopsis ionah) in its preferred demersal habitat, observed on 11 February 2008, using the underwater video system.
Antarctic ice cod
An Antarctic ice cod species, likely T rematomus eulepidotus, nestled amongst benthic invertebrates, observed on 11 February 2008, using the underwater video system.
Antarctic toothfish – the southernmost fishery in the world
The longline fishery for Antarctic toothfish that has operated in the Ross Sea region since 1998 is managed by the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR), who set catch limits for toothfish and fish taken as bycatch (e.g. rattails, skates and icefish). New Zealand scientists have been monitoring the toothfish population using a tag, release and recapture programme, and a catch limit of 2,700 tonnes has been set for the current season. Although this level of catch is believed to be sustainable for toothfish, the effects of the fishery on other parts of the ecosystem are poorly understood.
Written by Stu Hanchet
Whitson’s grenadier
Whitson’s grenadier (Macrourus whitsoni) – the most common bycatch species in the toothfish fishery and an important prey item of toothfish on the slope.
Crocodile icefish
Crocodile icefish (Chionodraco myersi) – a bycatch species of the toothfish fishery and an important prey item of toothfish on the shelf.
Dumbos and jumbos
Only a few cephalopods (octopus, squids and their relatives) are known from Antarctic waters and even less from the Ross Sea, but we hope to find new species during our voyage. The ‘dumbo’ octopuses have large floppy ‘ears’ and webbing between their arms. There are about 10 types of Antarctic squid that range from 10 centimetres to the jumbo-sized colossal squid at over 4 metres in length. The colossal squid is a voracious predator with large hooks on each tentacle and the largest beak known. All cephalopods have a strong horny beak, which looks like a parrot’s beak, and the beak’s shape often changes between species.
Written by Darren Stevens
A large ‘dumbo’ octopus
A large ‘dumbo’ octopus about 60cm long.
Collosal squid beak
A very large colossal squid beak (the left beak is about 12 cm across).
Photographing fish
We take digital photos of all fish species soon after capture to get a record of the fish as it might appear in real life. Colours fade quickly once the fish is preserved. The position, size and shape of the fins are important for identification of fishes. We prepare a fish for a photo by pinning the fins upright against a polystyrene sheet, then painting the fins with a small amount of concentrated formalin, which locks the fins in place. The formalin is then washed off and the fish is photographed. Here are photos of the same specimen of a crocodile icefish (Neopagetopsis ionah) before and after it was prepared for photography.
Written by Peter McMillan and Peter Marriott
Crocodile icefish before being prepared
This shows what a Crocodile icefish looks like before it is prepared for photographing.
Crocodile icefish after being prepared
This shows what a Crocodile icefish looks like after it has been prepared for photographing.
Fisheries acoustics
Fisheries acoustics uses sound to ‘see’ deep into the ocean. On the hull of Tangaroa are specialised echo-sounders that send out pulses of sound – pings. Each ping can travel hundreds of metres through the water and is reflected by the seabed and objects like fish and plankton. The reflecting sound (backscatter) from 4 different echo-sounders with different frequencies tells us how far away objects are. The total amount of backscatter from a group of fish tells us how many there are. We compare information of sound to help us work out what sort of animals we are seeing. When we’re not sure, we try and catch the fish using a trawl to identify them.
Written by Richard O Driscoll
Echo-sounder monitors
Monitors showing pictures from four echo-sounders.
Fisheries acoustic data
Fisheries acoustic data collected steaming from Wellington to the Ross Sea. Each ‘pixel’ is 20 km long by 50 m deep. The colours show the average amount of sound coming back from each depth (red = strong, blue = weak). Patterns north of 60º S are caused by daily vertical migration of fish to the surface at night.
Identification of Antarctic fishes - spot the difference!
Identifying the fishes – that’s the easy part, isn’t it? That couldn’t be further from the truth. Over 320 species have been discovered in the Southern Ocean since the first Antarctic fish was described in 1844, and new ones are still being found. However, it is often difficult to accurately identify the fish. For example, snailfish require examination of the number of vertebrae and fin rays – not easy when you, the microscope and the specimen are all rolling in heavy seas! Fish from depths between 1,500 and 4,000 metres are virtually unknown, and we expect new and rare ones when we sample deep water later in our voyage.
Written by Andrew Stewart
A snailfish species (Paraliparis spp.)
The taxonomy of this family is poorly understood and these could be new species to science. Compare this image to A different snailfish species and spot the differences.
A different snailfish species
The taxonomy of this family is poorly understood and these could be new species to science. Compare this image to A snailfish species (Paraliparis spp.) and spot the differences.
