Salmon farms don’t cause algae blooms
It is a commonly heard assertion by anti-salmon farming activists that waste from salmon farms equals the sewage from cities of so and so many thousands of people. But the fact that most of the waste from salmon farms comes in the form of biological waste from fish that already live in our oceans is never acknowledged, and neither is the fact that this waste is vastly different than that coming through a human waste stream. Another assertion frequently favoured by environmentalists is that the nutrients released by fish in pens often cause harmful algae blooms.
Heading an article in the New Zealand Marlborough Express earlier this week was the statement that “Algal blooms overseas have been caused by fish farms, an expert appearing for NZ King Salmon conceded yesterday”. King Salmon is in the middle of an Environmental Protection Authority hearing in Blenheim to consider an application for the company to develop nine new fish farms in the Marlborough Sounds region. But under cross-examination, the expert- Cawthron Institute scientist Lincoln MacKenzie- conceded that ‘those were "extreme examples" and were nothing like the circumstances in the Marlborough Sounds’. "In the history of this industry, even when we were farming in unsuitable areas, there is no evidence of salmon farms being involved in exacerbating harmful algal blooms" he was quoted by the paper’s web site. (Mr. MacKenzie is a Council Member of the International Society for the Study of Harmful Algae (ISSHA) and he sits on the Editorial Advisory Board for the “Harmful Algae” journal at Elsevier Science).
Mr. Mackenzie said algal blooms were mainly caused by oceanographic forces impacting on coastal waters. There were some examples of human activity causing them, such as the heavy runoff from the dairy industry on Lake Ellesmere in Canterbury. "I've trawled heavily through the international research and was surprised how little association there is between marine farming and anthropogenic bloom [caused by human activity]." Under questioning from Conservation Department lawyer Shona Bradley, he said there was an "extreme example" from Finland, where there were fish farms in small, confined bays with very shallow waters. "These situations are completely different from the types of environment we're talking about here in the Marlborough Sounds."
According to another article by the Marlborough Express, New Zealand King Salmon could lift production from about 8,750 tonnes a year to about 22,000 tonnes a year if its application is successful. King Salmon operations and contracts manager Mark Gillard, who managed the proposed expansion project, said demand for fish grown by the company was outstripping ability to supply. Mr Gillard told the board that the proposed sites were mostly;
- deep, because there was more space to farm fish
- cool, so fish efficiently converted feed to flesh and stayed healthy
- fast-flowing, to wash away waste
- sheltered, so cages were not damaged by swells
- distant from significant landscapes, homes and beaches
- unlikely to clash with other uses like boating, fishing and tourism.
