"Maybe New Zealanders are becoming more law abiding," he said.
Greater issuing of pre-charge warnings by police only affected low-level offending, so it was difficult to relate it to a reduction in new criminal cases, he said.
Crown solicitor Greg Hollister-Jones said the decrease in cases going to jury trials was a result of the reduction in crime and the impact of the Criminal Procedure Act.
Statistics New Zealand figures showed crime dropped 10.9 per cent in the Western Bay of Plenty in the last financial year, with 10,748 offences in the year ending June 30 compared to 12,061 in the 2012-13 financial year.
Nationally, district courts had fewer new, ongoing and disposed criminal and civil cases than in the previous year.
Fewer new criminal cases nationwide could be attributed to the police's greater use of pre-charge warnings that aimed to divert lower-end offences away from court proceedings, the Courts New Zealand report said.
The number of District Court jury trials was also down, while the number of cases held in the Youth Court fell to a record low.
New and active applications in the Family Court increased slightly but the number of disposals decreased.
Court of Appeal and High Court cases were down, while the number of cases the Supreme Court heard was up.
Statistics New Zealand data showed conviction rates for the year ending June 30 were the lowest in the 34 years statistics had been available.
The sector's Better Public Service targets, which were based on June 2011 crime levels, aimed for a 15 per cent reduction in total crime and a 25 per cent reduction in youth crime by 2017. At the end of March this year, the total crime rate was down by 16 per cent and Youth Court appearances were down 30 per cent, Mr Rutherford said.
