More samples urged
The "learning by doing" approach to salmon farming relies on adverse effects being identified through monitoring, says Conservation Department planner Anna Cameron.
Ms Cameron gave evidence on Tuesday at the Environmental Protection Authority hearing in Blenheim to consider the application by New Zealand King Salmon to develop nine new salmon farms in the Marlborough Sounds.
Ms Cameron suggested changes to farming conditions proposed by King Salmon, aimed at protecting the water from the sea surface to the sea floor.
If farm conditions started heading towards non-compliance, King Salmon must step up seabed monitoring from once to three times a year, she said. Thresholds should be set and samples taken beneath farms and further afield, where effects were especially undesirable.
King Salmon lawyer James Gardner-Hopkins asked whether taking and analysing potentially hundreds of samples could be impractical.
DOC marine technical adviser Andrew Baxter advised three samples were needed to see a trend, Ms Cameron said. This sampling was not part of day-to-day farm operation but to help correct deteriorating conditions.
If farms became non-compliant, King Salmon must immediately reduce feed or de-stock then allow sites to fallow, she said. Fish could either be shifted or killed.
Mr Gardner-Hopkins said if fish were killed before they reached harvest weights, processing costs would exceed their value.
"On a terrestrial farm if there was a breach of a discharge standard would you expect a farmer to kill stock early?" he asked.
Ms Cameron recommended setting maximum feed nitrogen levels and recording the ratio of nitrogen taken up by fish and excreted.
Mr Gardner-Hopkins said salmon farmers already had a financial incentive to reduce protein and nitrogen and it might be impossible to measure feed conversion rates on active salmon farms.
Setting nitrogen limits was appropriate because feed was a major source of this pollutant around farms, Ms Cameron said. She understood that measuring feed conversion ratios involved a simple calculation after weighing fish at harvest.
Phytoplankton should be measured and identified from the day farms were established rather than after three years of monitoring, as suggested by King Salmon, Ms Cameron said. This would avoid setting a biased threshold after water conditions were changed by farm operations.
Phytoplankton populations were highly variable, Ms Cameron agreed with Mr Gardner-Hopkins. However, the fact a system was complex did not mean it should be ignored.
Ms Cameron recommended that the Marlborough District Council be required to check that King Salmon plans and reports were consistent with conditions.
"I do not think council should be in a position where the only way of rectifying a problem is prosecution," she said.
The hearing at the Floor Pride Marlborough Civic Theatre in Blenheim is expected to end today after eight weeks.
- The Marlborough Express