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The top four, all with market capitalisation greater than $1billion, collectively declined by $2.01billion or 9.7% in market capitalisation - the value of each share on issue.
Collectively, the 28 companies' capitalisation declined 9.2% to $23.59billion.
Ryman Healthcare recorded the largest decline in both dollar and in percentage terms, falling by $1.63billion, or by 23.3%, while EBOS Group and Synlait Milk both declined, respectively down 10.6% ($363million) and 17.1%, ($331.6 million).
Meridian Energy was the only one of the top four to record an increase for the December, rising by $307.5million, or 3.7%.
Deloitte corporate finance partner Scott McClay said the performance of the top companies on the index was likely to do with ``global headwinds more generally''.
``The decline within the top four appears in part to reflect global market forces rather than specific company performances or announcements,'' Mr McClay said.
The index decline had reversed the growth achieved in the previous two quarters.
The index tracks companies with a large exposure in the South Island.
Outside of the top four, the index's best performers in percentage terms were SLI Systems, up 94.1%, SeaDragon, up 61.1% and Pharmazen, which was up 35.3%.
Conversely, the largest capitalisation declines outside the top four, in percentage terms, were Chatham Rock Phosphate, down 28.6%, Connexionz, down 24.6% and Kathmandu Holdings down 17.1%.
Of the 28 companies, 16 declined in value and nine rose, and three made no gain at all.
Of the nine companies which grew in market capitalisation, Silver Fern Farms grew by more than $10million, Pacific Edge rose by $16.9million, while Blis Technologies was flat.
The index report noted Pacific Edge increased the number of shares it had on issue during the quarter, resulting in an 11.1% increase in market capitalisation.
During the quarter it released its half year 2019 report, noting a 29% increase in total revenue and a 13% improvement in net loss.
Dunedin's specialist engineering company Scott Technology returned a 9.1% quarterly decline, ending with a market capitalisation of $211.2million and Queenstown tourism operator Skyline Enterprises fell 4.2%, to $936.3million.
South Port at Bluff declined 6% to $173.2million and Synlait Milk was down 17.1%, to $1.61billion.
In the primary sector five of the nine participants recorded declines.
Synlait Milk and PGG Wrightson had the largest percentage declines, falling 17.1% and 16.4% respectively.
- Three participants were removed from the index, because both Heartland Group Holdings and EnergyMad no longer predominantly operated from the South Island, while Windflow Technology was delisted from the NZX.