Aorere Catchment - What's happening in the Bay?

August 2007

The Problem for shellfish companies:

Cockle and mussel farmers in Golden Bay have had their harvest days reduced to around 50% because of high E. coli levels in runoff from the land.  The main sources are believed to be dairy farms and domestic sewage.  Swans also pose a problem for cockle bed in the intertidal zone.

There are three classified Growing Areas in Golden Bay, where shellfish harvesting is carried out year round:

Collingwood Marine Farms covers around 80 hectares, farming Greenshell mussels (Perna canaliculus).  Production is around 4,000 tons per year with a value of $12 - 15 million dollars of processed product.  The product is predominantly exported.

Westhaven Shellfish is a cockle fishery, licensed for 749 ton/pa destined for the live export market, mostly to the USA.  It covers an area of around 900 hectares.

The Ferry Point cockle fishery is licensed for 300 ton/pa from an area of 40 hectares.

The harvest criteria for this area are based upon real time telemetry salinity data from buoys situated in water close to the farms.  When salinity drops it indicates increased runoff from the catchment and this is used as an indicator of likely increased levels of E. coli.

The dominant influence on water quality is the Aorere River catchment.  It covers 700 square kilometres with the river passing through areas ranging from pristine native bush in Kahurangi National Park (including the popular Heaphy Track) to a rich alluvial valley that is used extensively for dairy farming, and then to the sea.

In 2003, routine monitoring indicated bacteria at levels that did not comply with regulatory requirements for human consumption.  To ensure ongoing access to the EU markets, the Collingwood mussel farm's harvest criteria were adjusted several times between 2003 and 2004, severely limiting harvesting opportunities.  Originally the area was closed for harvest 28% of the time, now it is closed 50% of the time.  This has seriously impacted the viability of the farms and has wider industry implications in terms of lost opportunity costs, with harvesters unable to harvest and factories not having a constant supply of product.

At the same time, the two cockle fisheries were experiencing similar difficulties and were having severe restrictions for harvesting imposed on them.  In 2003, changed harvest criteria at Ferry Point led to the fishery shutting down in that area.  Westhaven Shellfish experienced similar problems but were able to avoid closure.

The potential pollution sources in the area were identified as:

1. Domestic waste

2. Wild life

3. Recreational water use

4. Agricultural run off

The consensus between scientists and regulators was that contamination was most likely attributable to stock crossings in creek beds and estuaries, plus stand off areas adjacent to streams.  However, this is a large catchment with many feral animals (particularly black swans), septic tanks and a poorly operating municipal sewage treatment system, so nothing could be ruled out.

A public meeting held in March 2005 appointed a working group consisting of representatives from both dairy and marine farming sectors and the Tasman District Council.  This group met several times and fast-tracked the start of a TDC/Fonterra survey of farms.  Most dairy farmers responded positively as they appreciated the difficulties faced by their marine counterparts and both share in the guardianship over the areas they farm.

Today, Ferry Point remains closed, Westhaven Shellfish has been closed for extensive periods because of serious bacterial contamination, possibly due to malfunctioning sewage systems and bird excrement.  Collingwood continues to operate with a restrictive harvest criteria.

 The Cawthron Institute has been working in this area developing an effective and economic way of determining whether the bacterial contaminations were of bovine, avian or human origin.

Helen Smale

The Marlborough shellfish quality program is a grower owned incorporated society, and Helen is employed by industry to manage the water quality on a day to day basis for the top of the South Island.  They are spending well over $1 million a year in ensuring the quality of the growing waters, and growers fund the operation for testing, and it is quite different from overseas where governments tend to pay.  All laboratory work is contacted out to NIWA and the Cawthron Institute.  Export requirements require that an independent accredited laboratory does all testing and certification.

The Bay that lies at the edge of the Aorere catchment is a significant growing area for cockles and mussels.  It is particularly significant for mussels because it is a source of spat, the seed mussels.  The 18 ha of green shell mussel farms produce about 4,000 tonnes per annum, while the cockle fisheries are on a quota system.

Exotic birds (swans) are a significant issue for the cockle fishery, because cockles are intertidal and that's where a lot of the birds tend to congregate as well.  When the tide goes out shellfish close up, but when the tide comes back in the shellfish start to feed again.  Unfortunately the faecal matter is at its most concentrated at this time because the birds have been spending much of this time on the beach.

Shellfish are filter feeders and they tend to concentrate what is in their environment.  Certain events increase bacterial concentration and it takes a certain number of days for them to pass through the fish and out again.  While that is happening harvest cannot take place.

At certain tides and wind conditions pollution from the river can come directly over the mussel farms, which has a negative impact and is when the farms are closed for harvesting. Telemetry buoys in the bay measure the rate of salinity drop so that companies know when to stop harvest.

This system has been used for 10 years and has been refined so that it protects the harvest but Helen explains that in the past few years it has meant that the mussel farm has been closed to harvest for almost half the time.  And delays can mean that harvested shellfish are past their best.

E. coli is used as an indicator species for pathogenic bacteria and viruses.  It indicates the level of contamination in an area.

"What we do on land inevitably has an impact on the marine environment and things like septic tanks, new subdivisions with sealed driveway are creating surface areas that cause runoff rather than rain soaking into ground, says Helen.

The testing we are doing is indicating issues that we should look at now while they are manageable rather than leaving it till they become serious and will take a whole lot more resources to resolve. It's not just a Golden Bay issue, we have councils throughout the country issuing permits to discharge and not thinking about what it is doing to the environment.

Helen believes that while the situation with farm effluent runoff and domestic sewage run-off etc may look pretty negative for the industry they actually have a great opportunity for forging networks and relationships.

This is quite a serious issue for our industry and also has an impact on the dairy industry because they are going to have to spend quite a bit of money in changing the management approaches, she says.

But we are seeing progress.  I think it is very positive that we are providing really strong linkages so that if we have issues in the future we will be able to address them quicker and people will understand better the impact that they can have on the environment.