Jane Nees BOP Regional Councillor www.janenees.co.nz

Bay of Plenty Regional Council supports a research programme on the Tauranga Harbour.

Recently, the council provided financial support for a PhD study on the effects of black swan grazing and contaminants on the health and growth of seagrass meadows in Tauranga Harbour.

Seagrass meadows play an important role in the productivity of harbour ecosystems and coastal fisheries. Previous studies to map vegetation in Tauranga Harbour had shown significant reductions in the extent of seagrass between 1959 and 1996.

Unsurprisingly, loss of seagrass beds shows a strong spatial relationship to catchment run-off. However, the PhD study showed that black swan grazing created circular de-vegetated patches in seagrass meadows. At the most heavily grazed site, annual seagrass loss was estimated to be around 20 per cent. The recovery of seagrass in these heavily grazed areas was estimated to take three or more years.

The swan numbers in Tauranga Harbour during summer have increased from an estimated 1900 birds in 1979 to 5100 in 2010. As intensive black swan grazing has the potential to place pressure on the condition of seagrass beds in Tauranga Harbour, council staff recommend that discussions be initiated with the Eastern Region Fish and Game Council on control options for black swan in Tauranga Harbour. This may involve negotiating a maximum population threshold for swans in the harbour.

If you have any views on this or any other issue, email: neesj@xtra.co.nz or phone 07 579 5150. Or you can check out my website: www.janenees.co.nz