Vol.12 No.2 - June 2004

Horse mussels growing on the sea bed. These shellfish are filter feeders and are vulnerable to the effects of suspended sediment in the water. For details of recent modelling work to assess these effects, see “Modelling the effects of muddy waters on shellfish”.

In this issue

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    Flood flushing of bugs in agricultural streams

    PDF of this article (2 MB)
    Natural flood event, Topehaehae Stream, 15 September 1999. (Photo: R. Davies-Colley)
    Flow, turbidity and faecal indicator bacteria concentrations measured in the Topehaehae Stream near Morrinsville during the natural flood event pictured above. (Click to see detail)
    Sampling at the front of one of the artificial flood events on the Topehaehae Stream. (Photo: Rob Davies-Colley)
    Response to a series of three artificial flood events showing water level, turbidity and faecal indicator bacteria concentrations.
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    Gambusia: a biodiversity threat?

    PDF of this article (388 KB)
    Cindy Baker
    Dave Rowe
    Joshua Smith
    Laboratory trials suggest that mosquitofish could be a potential threat to the whitebait fishery in northern New Zealand.
    Gambusia affinis is commonly known as the mosquitofish because it eats mosquito larvae. Gambusia are native to southern and eastern USA, but following translocation for control of mosquitos, they now have an extensive global distribution, including New Zealand.
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    Modelling the effects of muddy waters on shellfish

    PDF of this article (541 KB)
    Nicole Hancock
    Judi Hewitt
    Statistical models can assist in predicting the effects of different levels of sediment in the water for maintaining the health of coastal ecosystems.
    You may have noticed that after heavy rain and strong winds the sea along our coasts becomes brown and dirty. Some of this dirt (sediment) is from fine marine sediments being resuspended from the sea floor by wave and current action (see Water & Atmosphere 11(2): 20–21). But rain also washes sediment from the land into the sea, particularly during heavy rain or floods.
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    Lethal turbidities and native fish

    PDF of this article (644 KB)
    Dave Rowe
    Joshua Smith
    Erica Williams
    How muddy can water be before it’s lethal to native fish? The answer is extremely muddy for most fish, but some are more sensitive than others.
    When New Zealand rivers flood, they can become extremely turbid for up to several days at a time. Native fish may well be able to cope with such short spells of high turbidity. But it could be a different story in rivers where the forest cover is stripped away from the catchment and high levels of erosion occur.
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    NIWA news forum

    On this page
    Fish on the move
    New NIWA posters
    NIWA studies the top of the South
    Just published: Freshwaters of New Zealand
    The Living Reef shortlisted for the Montana Book Awards
    Shipboard air sampling through the western Pacific
    Study of nutrient enrichment in South Island coastal lakes
    NIWA and GNS co-host stable isotope conference
    The Southern Ocean and climate change
    Kelp on reefs under the February 2004 flood
    Recent publications by NIWA staff
    Fish on the move
    NIWA’s fish transport tanker. (Photo: N.
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    The Antarctic ozone hole and Southern mid-latitudes: the dilution effect

    PDF of this article (610 KB)
    Jelena Ajtić
    Brian Connor
    Modelling studies have confirmed that the Antarctic ozone hole is a major player in the lower summer ozone levels measured over New Zealand.
    Every spring NIWA scientists inform the public about the current status of the Antarctic ozone hole – how big it is, how much ozone has been depleted, whether it is likely to break early or late in the season, and if yet another record in its properties has just been set.
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    On-road remote sensing identifies the worst vehicle polluters

    PDF of this article (315 KB)
    Shanju Xie
    Jeff Bluett
    Gavin Fisher
    Gerda Kuschel
    A campaign to measure vehicle emissions using a remote-sensing technique has yielded significant information about pollution from vehicles under normal driving conditions.
    Every major city in the world faces problems associated with emissions of air pollutants from motor vehicles. In some cases these are severe and growing, with few prospects for short-term improvements.
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    Let sleeping fish lie

    PDF of this article (398 KB)
    Mark Morrison
    Glen Carbines
    Video photography of sleeping fish has proved to be an effective way of estimating fish population sizes.
    Many small marine fishes can be difficult to visually count and measure because of a mixture of cryptic colouration patterns and behaviours designed to avoid larger predators. We have experienced this trying to count juvenile snapper (less than 10 cm long) within habitats such as seagrass and horse mussel beds.
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    Reconstructing past environmental changes using speleothems

    PDF of this article (691 KB)
    Darren King
    Paul Williams
    Jim Salinger
    Growth rings in stalagmites can tell us about past climates.
    Speleothems – more commonly known as stalactites, stalagmites and flowstones – are limestone deposits that form when calcite (CaCO3) is released from water droplets that have percolated through rock into a cave.
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    Trophic modelling for sustainable New Zealand fisheries

    PDF of this article (818 KB)
    Matt Pinkerton
    Mary Livingston
    Managing marine fisheries through a whole-ecosystem approach requires an understanding of how different organisms interact.
    As long as people continue to exploit natural fish stocks, fisheries science will be needed to improve our understanding of the workings of fish populations.
    Many fisheries around the world are in decline, with over a quarter of exploited fish populations worldwide having been over- fished to some degree.
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    Drilling Lake Tutira for evidence of climate change

    PDF of this article (872 KB)
    The Lake Tutira drilling group
    Thanks to a multi-organisation collaborative project, Lake Tutira in Hawkes Bay is starting to give up some exciting information about climate conditions during its 7400-year history.
    In this rapidly warming world, realistic assessment of how climate will change relies upon dependable records of past climate. Unfortunately, such records tend to be short. Meteorological data for New Zealand covers, at best, the last 150 years.