When we learn to dive, we are taught not to touch the seafloor. Not just because it’s covered in delicate ecosystems that are easily damaged, but because if you’re on soft sediments you will cloud the water for yourself and your dive buddy. After spending more than 100 hours on the seafloor of the Hauraki Gulf Marine Park, I can tell you it’s still good advice. Advice that doesn’t seem to apply to a fishing industry that won’t move with the times.
The heavy doors of bottom trawlers as they plough the marine park cause widespread destruction. The scale of the damage caused by different bottom fishing methods varies – with dredging (responsible for the collapse of the kūtai mussel fishery and now tipa scallops) thought to be the worst.
The fight to protect the seafloor of the Gulf from bottom trawling is more than a century old. Parliament was first petitioned with the arrival of the first steam trawlers in 1899. The most significant win was a protected part of the inner Gulf that pre-dates the Hauraki Gulf Marine Park Act 2000. A more recent win was the Sea Change – Tai Timu Tai Pari Marine Spatial Plan 2017, which sought the transition to seabed-friendly fishing methods by phasing out bottom trawling and Danish seining in the marine park. The authors of the plan made the recommendation because bottom-impact fishing damages habitats, removing food and homes for animals that are at the base of the Gulf food web.
I would describe the Government’s response to the Sea Change plan as timid at best. In 2021 it released a plan to instead restrict trawling to “corridors”. In a 2023 consultation document, the wording has changed to “areas”.
The one thing Sea Change and the Government’s plan agree on is stopping recreational dredging due to its impacts on the seafloor. This is significant, as it removes dredging from areas where trawling is already banned – in effect creating large benthic protection zones. However, it’s hypocritical to ban small recreational dredges because of their impacts on seafloor ecology when bottom trawling gear has a much greater impact.
The scale of the commercial impacts is greatly increased on soft sediments, which cover most of the marine park. The gear that is dragged along the bottom re-suspends sediment. These plumes choke filter feeding animals and smother photosynthesising plants.
The impact of these sediment plumes far exceeds the footprint directly impacted by trawling gear. By the time a fisher hauls in the first trawl of the day, it’s likely to have created a plume as big as the Goat Island marine reserve.
Scientists have recently found that when bottom trawlers stir up carbon from the seafloor it mixes with oxygen in the water to create CO2, a climate heating gas.
With all this evidence of impact, I find it incredibly frustrating that companies are not held to account for all the damage they do to the environment. The companies that directly caused the loss of 1500 square kilometres of the Gulf’s shellfish beds last century are not helping to restore them today. I’m not sure if the tipa scallop fishery will ever reopen. Natural recovery of many marine ecosystems may take centuries. Scientists are still in the pioneering stages of shellfish restoration, and I’m worried that such active restoration might not even be feasible for most of the other habitat-forming species in the Gulf (like sponge gardens, bryozoan thickets and tubeworm mounds). We must take a much more precautionary approach to managing commercial impacts on public resources.
There is no place for bottom trawling in New Zealand’s first marine park. The Hauraki Gulf/Tīkapa Moana/Te Moananui-ā-Toi is a national taonga with sensitive ecosystems and increasing pressures. It deserves a fisheries minister that cares about ocean ecosystems and leads the industry to transition to less damaging fishing methods.