Tasmanian scientists demand salmon out of Long Bay – the case for science

For the past seven years, open pen salmon farming in Long Bay, Port Arthur has caused serious pollution, algal blooms, seagrass loss and damage to reef ecosystems. Based on an independent scientific review, we believe that this lease and the associated licenses should not be renewed.

The Tasmanian Independent Science Council has released a report on the impact of salmon farming in Long Bay. Long Bay is a small, shallow, poorly flushed bay located directly north of Port Arthur. This bay is highly diverse, with extensive seagrass beds and rocky reef ecosystems that provide a haven and breeding area for flathead, crayfish, abalone and other species targeted by recreational and commercial fisheries. Long Bay is also an important recreational and tourism asset, and a sheltered access point for boaters and anglers.

For these reasons, Long Bay would not be considered suitable for finfish aquaculture based on the marine spatial planning tools recently developed by IMAS.

Excess nutrients have stimulated chronic nuisance algal blooms in the bay and a catastrophic decline in seagrass cover by 75 to 100%. Reefs adjacent to the lease, and in the poorly flushed areas of Long Bay to the north of the lease, showed extensive signs of eutrophication, including the proliferation of nuisance algae and a lower reef canopy cover. These impacts were shown to be persistent, without the typical seasonal recovery that normally occurs.

Nitrogen is a known pollutant in marine systems, causing algal blooms where it is discharged at high levels over extended periods of time. While nitrogen is produced by multiple sources including sewage, fertilisers and livestock, a detailed nitrogen loading analysis undertaken by the TISC clearly identified salmon wastes as by far the largest source to Long Bay.

Even under the most conservative scenario, the salmon pens in Long Bay accounted for 95% of the human-derived nitrogen inputs. This is the equivalent of the sewage discharged by more than 25,000 people.

• Read the report here