Carried Away: Bags Unpacked
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At the time Pārekareka or spotted shags, Phalacrocorax punctatus, along with most other cormorants (commonly known as shags) in New Zealand, were considered uncharismatic marine ‘wildfowl’. Wildfowl were competitors for fish and so were hunted widely.
Today, however, there is a far greater appreciation for shags as well as for New Zealand’s position as the ‘centre of the shag world’. New Zealand has at least 13 of the world’s 40 shag and cormorant species breeding here. With many of these species under threat, analyses of museum specimens, such as the birds Griffin collected and preserved, have provided researchers with critical insights and understanding of the birds.
In the case of Hauraki Gulf spotted shags, the population has undergone a catastrophic decline in the 20th Century. They have gone from being prevalent on both Auckland’s west and east coasts, to today having only one major colony in the Firth of Thames with just 300 breeding pairs.
Concern over the ongoing decline of Auckland’s spotted shags has, until recently, been balanced against the knowledge that spotted shags have a New Zealand wide distribution with large populations in the South Island, and therefore little concern for the decline of the Auckland colonies.
Surely immigration from these large southern populations should safeguard the Hauraki Gulf population from going extinct, right?
Image caption: A photograph of the Spotted Shag Diorama created by Louis Griffin in Auckland Museum's Princes Street Building. The diorama was dismantled and no longer exists, however some of the specimens remain in our collection.
The Auckland Spotted Shag, © Edin Whitehead Photography www.edinz.com
Working with researchers at the University of Otago, Te Papa and Canterbury museums our Curator of Land Vertebrates, Matt Rayner, set out to discover just how genetically distinct, if at all, the birds in the north and South Island were with the results recently being published in the international journal The Condor here.
Led by Nic Rawlence and his team at the Otago ancient DNA lab, mitochondrial and nuclear DNA sequences were extracted from beach wrecked spotted shags and from birds held in museum collections around New Zealand, including Auckland Museum’s specimens collected from the Hauraki Gulf by Louis Griffin in 1914. The results were surprising. DNA sequences showed first, that two of spotted shag populations in the South Island, previously considered distinct were indistinguishable from each other. And second that Hauraki Gulf spotted shags represent a genetically distinct, isolated and critically endangered population whose survival is important for maintaining genetic diversity of New Zealand spotted shags in general.
Image credit: Spotted Shag from Auckland Museum's 1914 Diorama and from which DNA was taken for this research.
With the current ban on hunting, the primary threats to the Hauraki Gulf spotted shags are a changing marine environment and set-netting that can trap and drown birds when they dive into the ocean to pursue prey. Museum collections are helping to fill in the blanks and put numbers on what is happening out there in the wild. An analysis of molecules, called stable isotopes, in the feathers of spotted shag specimens in our collection, of bird specimens collected over 150 years, shows a marked change in the shags’ foraging habitat and diet over time. In a nutshell, over the last 150 years, the birds have begun feeding further away from shore and eating less fish, while eating more of other animals lower down the food web, such as squid, than they did in the past. Further work is planned to study the foraging biology of spotted shags in the wild through GPS tracking and analysis of diet. This study will enable us to understand where the birds are most at threat from interaction with set nets.
Image credit: The Auckland Spotted Shag © Edin Whitehead Photography www.edinz.com
Without conservation intervention, Hauraki Gulf spotted shags could go the way of the kohatu shag, Leucocarbo septentrionalis: extinct. Bones of this previously unknown and extinct northern New Zealand shag species were, for over a century, considered to be those of King shags, Leucocarbo carunculatus, found in the Northern parts of the South Island. However, a recent study by Rawlence, Rayner and others again using genetic sequencing of museum bone collections, revealed they were a new “lost” species that have been wiped out, most likely, by human hunting1. The kohatu shag joins the ranks of approximately 55 other extinct New Zealand birds lost since the arrival of humans to Aotearoa. Hopefully our study of the unique Hauraki Gulf spotted shag can stop its decline before it is too late.
1. Science Direct, Speciation, range contraction and extinction in the endemic New Zealand King Shag complex, 2017
Blog written by Auckland Museum Curator, Land Vertebrates, Matt Rayner
Header image © Edin Whitehead Photography