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2017

Finding fish in the Southwest Pacific

By Will McKay
Wednesday, 2nd August 2017

The first four days of the trip have been absolutely mind blowing. As Jeremy Barker from Te Papa put it, it’s 'like living in a National Geographic documentary'.
 
One of the key purposes of this expedition is to fill knowledge gaps on fish diversity in the South West Pacific. To achieve this researchers from Auckland Museum, Te Papa and the Australian Museum are employing several different mechanisms.
 
So far, diving has been the main method for fish collection, setting rotenone stations at a variety of depths and substrate forms. Rotenone is a natural product made from the roots of the barbasco plant. It is mixed into a solution on board and then administered to a small section of reef where it inhibits oxygen transfer across the fishes' gills. As a result, cryptic and elusive fish which would otherwise not be caught are flushed out of their coral hiding places in search of clear water and then they're able to be collected by our scientists and scientific divers who are waiting with their hand nets. (In scientific terms a 'cryptic' fish is one that's able to camouflage itself in its natural environment particularly well because of its coloration and markings. So they're extra good at hiding from us!)

 
Once back on board it’s time to work out what we've got. Fish experts Tom Trnski (Auckland Museum), Sally Reader (Australian Museum), Mark McGrouther (Australian Museum), Carl Struthers (Te Papa) and Jeremy Barker (Te Papa) pick through the specimens identifying each species. Tissue samples are taken by making a careful cutting of the right hand side before fish are pinned left side up and prepared for photographing.
 
One of the most extravagant fish we've caught so far is the leaf scorpion fish at the North Western corner of Walpole Island. Catching the eye as a flash of vibrant yellow weaving in and out of coral heads at 12m depth on the shelf edge leading to a further 20m drop off. It required a bit of trickery and care to get into the net, avoiding contact as some of these fish can be venomous.

Handle with care: the fish team had to take care when collecting this leaf scorpion fish as they can be venomous.

Auckland War Memorial Museum Tāmaki Paenga Hira

Another amazing species we came across is Pseudanthias squamipinnis. A beautiful display of sexual dimorphism, the male is purple in colour with an elongated 3rd dorsal spine, while the female is orange. If you’re not sure what sexual dimorphism is these two fish below are a perfect example - it’s the differences in appearance between males and females of the same species, such as in colour, shape, size, and structure.

The male Pseudanthias squamipinnis (left) is purple in colour with an elongated 3rd dorsal spine, while the the female (right) Pseudanthias squamipinnis is orange.

We’re currently having ‘a rest day’ from diving at Ellet Bank - but we won’t actually be resting. There’s always work to be done, whether it’s working through the discoveries to date or preparing for upcoming research activity on the expedition. We’ll also be putting out fish and invertebrate traps and collecting more BRUV footage - we’re hoping for some up close and personal shark encounters!

  • Post by: Auckland Museum

    Auckland War Memorial Museum tells the story of New Zealand, its people, and their place in the Pacific.