Could a Warmer Firth Harm Aquaculture

In the last few days, the sea temperature in parts of the Firth of Thames has risen to an astonishing 25°. This is about 5° or 6 ° above the average for December.


It’s not just the Hauraki Gulf which is warming so rapidly – large parts of the Tasman Sea between New Zealand and Tasmania are also 5° or 6 ° above the long-term average for this time of the year.


People may welcome warmer temperatures for swimming – not that anyone swims much in the Firth anyway. In reality, this warming trend is a serious concern. Scientists are becoming increasingly worried about the effect rising sea temperatures will have on marine life – particularly hard-shelled molluscs such as mussels and oysters, due to acidification of the ocean. Lower pH in seawater can make the shells of mussels and other shellfish much softer and brittle and there is increasing evidence of a drop in production for aquaculture due to this effect. Already the pH in waters in the Firth of Thames is higher than expected.

Firth low Ph

Local mussel farmers around Coromandel town are involved in a major research project to look at what the effects of warmer waters and lower pH might have on the whole aquaculture industry.   Industry insiders are aware of the threats.

NZIER HeaderWhich calls into question the rosy projections in an NZEIR Report commissioned by the Thames-Coromandel District Council has to be potential for growth in GDP, jobs and other economic benefits. The economists waxed lyrical about the future potential for growth in the industry.  But nowhere in their report will you find any reference to the threats to the industry from climate change, warming oceans and lower pH.

The evidence of rapidly rising sea temperatures is there in plain sight.  The Thames-Coromandel District Council and others who see aquaculture as a big part of the economic salvation of the District need to curb their enthusiasm. The Council would be wise to wait for more definitive research before trying to “pick winners” and committing ratepayer funds for wharf and other infrastructure for Marine aquaculture growth which may never eventuate.