ANZ New Zealand's interim results show it gained share in the fast growing Auckland mortgage market over the last six months, fending off attempts by its rivals to grab any customers unsettled by the merger of the ANZ and National brands and systems in October. ANZ New Zealand's CEO, David Hisco, said he was pleased the bank had managed to retain and grow its customer base despite the brand and system changes, and campaigns by others targeting ANZ and National customers.Hisco told Banking Day that ANZ had lost a few low value customers who had few connections with ANZ's staff but had more than made up for this with new customers added, particularly in the Auckland market, where ANZ has previously had a relatively lower market share."We've acquired more high value customers who have on average three products, so we've more than offset those accounts of people who have left. Most of those who left were those who had accounts with balances of less than NZ$2000," Hisco said."There was a bit of a flick up (in customers leaving) in November. After that it all went back to normal," he said.Kiwibank, NAB's BNZ, Westpac, and CBA's ASB all launched long-prepared marketing and customer acquisition campaigns in the September and December quarters of 2012 to target National Bank customers unsettled by the rebranding of their branches, as well as any ANZ customers unhappy with the move to the National Bank's computer system and products.Kiwibank's internal name for its campaign was "Black Horse Down", referring to the dropping of the black horse logo synonymous with the National Bank brand in New Zealand. Hisco said ANZ and National customers accepted ANZ's assurance that only the branding had changed, and staff had been assured about their own positions and so were able to focus on retaining and adding customers, particularly in Auckland.ANZ said its share of new mortgages in Auckland rose to around 30 per cent in the September and December quarters, from around 25 per cent previously. This put it ahead of ASB, the former Auckland Savings Bank, which is on around 25 per cent. ANZ's overall share of New Zealand mortgages rose to 30.3 per cent in the half year, from 29.5 per cent in the previous half, while its household deposit share rose to 30 per cent, from 29.6 per cent.But ANZ's burst of activity to retain and grow customers in the second half of the calendar year 2012 came partly at the cost of a 10 basis point fall in its net interest margin, to 2.49 per cent, between the second half of the 2012 financial year and the first half of 2013. ANZ was active in offering discounted fixed mortgage rates during this time.Hisco said the margin compression has since stabilised and had been partly due to a system-wide shift from more profitable floating mortgages to fixed mortgages over the last year, as fixed rates had fallen below floating rates.ANZ New Zealand's net interest income fell three per cent, to