How to study canaries in the Hauraki Gulf

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    Hidden 133 pages into the quite magnificent 160-page State of our Seabirds 2021 report into our feathered neighbours of the Hauraki Gulf comes a frightening analogy.

    “Seabird species in the region are distri-
    buted in accessible colonies across the Gulf, feed on a range of prey from zooplankton to fish and squid caught from inshore to more oceanic waters at a range of depths. This offers the exciting possibility of utilising these birds as sensitive indicators of change in the marine environment at different spatial and temporal scales. Seabird breeding and foraging performance should reflect changes in the distribution and abundance of key prey species and hence key trophic interactions within food webs upon which they and potentially other marine predators depend. A maritime take on the ‘canary in the coalmine’ scenario.”

    As exciting as this potential study may be, the choice of the report’s authors to draw on miners’ traditional use of songbirds to forewarn of the buildup of deadly gases in mines shows the level of dread with which the scientific community is approaching their study of the complex food webs within Waiheke’s surrounding waters.

    This week in Gulf News, Erin Johnson reports on what seems to be a worrying increase in reports of sick and injured seabirds – including kororā and kāruhiruhi, pied shags – around the island. Notably, a common theme within the story is that seabirds are being discovered that are seriously underfed and underweight. 

    Now, there are plenty of caveats to such anecdotal reporting, none more so that our increased awareness of the poor state of the Hauraki Gulf has made us more likely to look for and report sick and injured birds and animals, but over recent months both seabirds and seals have now made headlines for washing up on our shores either in poor health or dead.

    It’s now four weeks since the Department of Conservation announced it was investiga-
    ting reports of dozens of seal deaths within the Hauraki Gulf Marine Park, since when there has been at least one other report on the iNaturalist website that researchers are using to gauge the extent of the problem.

    Talking specifically about seals, DoC marine science adviser Laura Boren has told Gulf News that “climate can influence prey availability and can cause animals to travel further to look for food, and mean they may have to travel further and not find as much”. 

    Having read the State of the Seabirds report, this rung bells. 

    Using the chemical composition of feathers from living birds as well as museum specimens going back as far as 140 years, scientists can see how the diet of Hauraki Gulf seabirds has changed over time. Knowing that the overall number of fish that birds prey on has plummeted over the past century and a half, it could be expected that the predators may have adapted what they’d eat – but no.

    “Results demonstrate how species ‘carve up’ available prey sources with species such as pied and spotted shag and terns targeting primarily fish; little penguins exploiting a mixed diet of fish, squid and marine zooplankton; and red-billed gulls foraging primarily on lower trophic level prey such as marine invertebrates.” 

    In other words, these seabirds tend to stick to a familiar menu.  

    “However, feather carbon isotope data indicated shifts in the foraging habitats of Hauraki Gulf seabirds in the period between 1878 and 2019. Large pursuit divers, including pied shag, spotted shag, and little penguin, showed major declines in carbon isotope values indicating a shift away from inshore habitats to more offshore environments. 

    “The shift is likely explained by declines in inshore prey brought on by overfishing and the destruction of inshore reefs and benthic structure through dredging and sedimentation. Boat traffic has also been implicated in the disturbance of seabirds that pursue prey underwater, and growth in the commercial and recreational boat fleet utilising the inner Gulf could potentially play a role in forcing birds away from areas of high boat traffic and disturbance.”

    This all seems to echo Laura Boren’s comment on seals that “they may have to travel further and not find as much”.

    In coming weeks it’s highly likely that the relaxing of Covid travel restrictions will see a familiar summer stampede of Aucklanders back to holiday hotspots around the Hauraki Gulf. It’s our playground and, for many of us, a pretty well-stocked larder. But it’s becoming much more obvious that it’s also a barometer of New Zealanders’ negative impact on the environment.

    The disruption of human activity to the Hauraki Gulf food web is undeniably putting stress on populations of animals that exist at the top end of the chain – the predators. 

    And it seems a tragedy that the best we can do is treat these animals as a “canary in the coal-
    mine”. Remember, those canaries had only served their purpose once the miners were back safely above ground and the birds were snuffed out at the bottom of their cages.

    • James Belfield

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