Category: Biosecurity

The most barbaric way to answer this question would be to drag a giant net around and count what you kill but you’re not allowed to do that in the inner Gulf where trawling is restricted… unless you have a research permit from Fisheries New Zealand (FNZ). Despite calls to stop bottom trawling in the Hauraki Gulf Marine Park (HGMP) (Sea Change 2017 & Hauraki Gulf Forum 2021) FNZ have started doing these trawls regularly, they justify the trawls are required to gather information on the Tāmure / Snapper population. They haven’t done research trawls like this since the Hauraki Gulf Marine Park Act came into effect in the year 2000 (NIWA 2019). In areas where trawling is restricted (c25% of the HGMP), the study was like bulldozing a regenerating forest to count the birds. A disgraceful act on private land let alone a national park.

How much seafloor was scraped?

The nets are massive, wider than a rugby field. FNZ were just interested in killing demersal fish (goundfish), they dragged theses massive nets along the seafloor smashing down anything that lives there and creating giant sediment plumes that contribute to climate change. In areas that have been closed to trawling for decades there are patches of horse mussel beds, sponge gardens and tubeworm mounds and other habitats regenerating after decades of abuse from heavy machinery. You can read about them in the report (NZFAR 2021) where they are described as ‘foul’ a horrible word which suggests there is something ugly about these beautiful benthic epifauna that are working hard (day and night) to clean up our pollution (they are nearly all filter feeding animals). In defense of FNZ they did try and avoid areas with a lot of immobile sea life but they failed so badly that they had to stop trawling on several occasions, this shows that a) the seafloor is recovering and b) echosound is no good for measuring trawling impact on benthic life.

Although the percent of trawled seafloor was small (less than 1% of the study area) the areas bottom trawled were huge:

39 rugby fields between Shakespear Regional Park and Rangitoto Island	Stratum 1386
54 rugby fields of the inner Firth of Thames	Stratum 1887
68 rugby fields of the mid Firth of Thames	Stratum 1268
88 rugby fields in a west-east band North of Waiheke Island	Stratum 2229
59 rugby fields around the western side of Waiheke Island	Stratum 1149
41 rugby fields north of Whangaparāoa Peninsula	Stratum 1284
40 rugby fields northwest Coromandel	Stratum 9292
60 rugby fields south of the line dividing the inner gulf	Stratum 1219
59 rugby fields from Bream Bay to Mangawhai	Stratum 1449
49 rugby fields between Aotea / Great Barrier Island and Ahuahu / Great Mercury Island	Stratum COLV
77 rugby fields north of the line dividing the inner gulf	Stratum LITB

A total of 615 rugby fields, 381 of those fields had not been physically impacted by trawling for decades. The trawls were about 1/10th as long as a commercial trawl which may impact 1–10 km² (MacDiarmid 2012). This is largely due to the horrific sediment plumes they create, especially on mud which most of the trawls in restricted areas were. This means the total trawl distance of 53.35km could have impacted up to 40km² (6,349 rugby fields) of seafloor – choking animals and smothering plants.

So where were all the fish?

The average catch weight per trawling station in restricted areas was 500% higher than areas where bottom trawling is not restricted (1,033kgs vs only 171kgs). That’s a huge difference, the commercial fishers pulling up the nets must have been blown away with the haul! There was no significant difference in the size of the trawls but there was a big difference in depth. Trawls in trawling restricted areas averaged about half the depth (23m) of those in regularly trawled areas (47m). So are the fish benefiting more from trawling restrictions or depth?

As you can see from Figure 1 & 2 there is no correlation between depth and catch weight (red line vs data). There could be many other factors involved (FNZ seemed to deliberately avoid trawling on sand in the inner Gulf so we can not directly compare substrates), but the 500% increase in catch weight in areas protected from trawling shows that protecting the seafloor from bottom trawling dramatically increases the amount of fish that live on the seafloor.

The survey is good news for recreational fishers who shouldn’t leave the inner Gulf to catch more Tāmure / Snapper. If you’re a fisher who wants to know where demersal fish are in the Gulf I recommend you read the report (NZFAR 2021). If you want to know which trawling station got the highest catch… I’m not telling! You will have to ask FNZ, you can send them an OIA request Official.InformationAct@mpi.govt.nz why don’t you tell them to stay out of the restricted areas and stop bottom impact fishing at the same time 😀

What happened to all the fish?

The total weight of fish (mostly Tāmure / Snapper) landed was 41,759 kilograms! 80% of the dead fish was sold for $128,449.35 which seems like a lot but with Tāmure at $20-$30 per kg at the supermarket they could have made more than one million dollars selling it direct to consumers. Of the total revenue from the two years of survey approximately 73% ($93,634.47) was absorbed in operation costs of the research vessel to process the catch. The remaining balance ($34,814.88) was returned to the Ministry of Primary Industry. That means even selling the dead fish dirt cheap the surveys make a profit for the Government. The self issued scientific permit to trawl in restricted areas is more profitable than some whaling trips the Japanese government justifies as science.

What else did they haul up?

I was surprised to see invasive species like Mediterranean fanworm (Sabella spallanzanii) turning up in the catch. They are very skinny and should fly through the nets. There must have been very dense beds in places. It was disappointing to hear from my Official Information Act request that Biosecurity New Zealand was not informed of which stations had high numbers of the Unwanted Organism. The lack of interagency communication (even with MPI) sucks but the double standard is worse. When restoring the seafloor from fishing damage the Mussel Reef Restoration Trust must notify an MPI technical officer if it accidentally releases an Unwanted Organism (a legal requirement of moving Unwanted Organisms under the Biosecurity Act 1993). Bottom trawlers however can move them around the Gulf with no regard to Biosecurity. This shows how Biosecurity NZ favours industry over community groups.

Will they do it again?

The surveys continue despite FNZ no longer having a public license to bottom trawl the HGMP. There is 84% public opposition to fishing methods that impact the seafloor (Hauraki Gulf Forum 2021). Most fisheries scientists take samples 100’s of times smaller or use baited underwater video cameras to count and measure fish. FNZ definitely don’t have a social license to trawl in restricted areas but they are ploughing on. Because I make a living doing science communication its not in my interests to criticise the research survey but I had to because I think what they are doing is wrong.

Notes

I included trawl stations in areas where Danish seining is allowed and trawling is restricted in the restricted totals. The three stations had an average catch weight that lowered the average restricted catch weight and increased the average catch depth.

References

Sea Change 2017. Sea Change – Tai Timu Tai Pari Marine Spatial Plan. Hauraki Gulf Forum, Ministry for Primary Industries, Department of Conservation, Waikato Regional Council, Auckland Council. 2017.

MacDiarmid 2012. Assessment of anthropogenic threats to New Zealand marine habitats. A. MacDiarmid. New Zealand Aquatic Environment and Biodiversity Report No. 93 2012

NZFAR 2021. New Zealand Fisheries Assessment Report 2021/08. Trawl surveys of the Hauraki Gulf and Bay of Plenty in 2019 and 2020 to estimate the abundance of juvenile snapper. 2021. https://fs.fish.govt.nz/Doc/24856/FAR-2021-08-Hauraki-Gulf-2019-Bay-Of-Plenty-2020-Trawl-Surveys-4125.pdf.ashx

Hauraki Gulf Forum 2021. Results of Hauraki Gulf Poll by Alex Rogers. The Gulf Journal

https://gulfjournal.org.nz/2021/11/results-of-hauraki-gulf-poll/ Accessed December 2021

NIWA 2019. NIWA to survey young snapper in Hauraki Gulf. https://niwa.co.nz/news/niwa-to-survey-young-snapper-in-hauraki-gulf Accessed December 2021.

I have begun doing some work with the Northern New Zealand Seabird Trust who invited me to come and help them with some field work on the Poor Knights Islands. My father had visited the Islands when he worked for DOC in the 1990’s, his stories about the reptile abundance really inspired me to do restoration work, and I jumped at the opportunity to go.

Landing on the Island is notoriously difficult and our first shot at it was delayed, we had to go back to Auckland to wait for better weather. The islands are surrounded by steep cliffs that made European habitation impractical, Māori left the area in the 1820’s. This means the island I visited has never had introduced mammals, not even kiore! I spent days cleaning my gear to get through the biosecurity requirements which are incredibly strict for good reason.

I have explored a few predator free islands including Hauturu / Little Barrier Island which has been described as New Zealand’s most intact ecosystem. However it was only cleared of rats in 2004. When I am photographing invertebrates at night in mainland sanctuaries or forests with predator control (like Tāwharanui Regional Park or parts of the Waitakere Ranges) I see one reptile every eight hours or so. On Hauturu / Little Barrier Island I see them every 20 minutes, but on the Poor Knights it was every two minutes! Bushbird numbers were lower than other islands, I expect this is because reptiles and birds compete over prey species. I wonder if reptile numbers on other islands might be slower to recover because they are preyed on by bushbirds. I reckon that the Poor Knights total reptile and bushbird biomass is much greater than the restored islands I have visited. One reason for this is that reptiles use less energy to hunt than bushbirds but the other reason might be because it has more seabirds.

While walking through the bush at night I would sometimes hear a crashing in the canopy followed by a soft thump on the ground. In an incredible navigational feat the seabirds somehow land only meters from their burrows. At night I heard Buller’s shearwater, grey-faced petrel, little penguins and diving petrel (fairy prion finish breeding in February). While monitoring birds at night I was showered with dirt by a Buller’s shearwater who was digging out a burrow. In my short time on the island I saw cave weta and three species of reptile using the burrows. Like a rock forest the burrows add another layer of habitat to the ecosystem. It was incredibly touching to see the care and compassion the researchers had for some of the chicks who were starving while waiting for their parents who often have to travel hundreds of kilometres to find enough food. The chicks who don’t make it die in their burrows and are eaten by many invertebrates, the invertebrates in turn become reptile or bushbird food. The soil on the island looked thick and rich, when it rains nutrients are bought down into the small but famous marine reserve which is teaming with life.

I was only on the island for three nights but I was very fortunate to experience a pristine ridge to reef ecosystem. Seabirds are incredible ecosystem engineers who were an integral part of New Zealand’s inland forests for millions of years. Communities are making small efforts to bring seabirds back to predator free island and mainland sites with no control over seabird food sources. If we really want intact ecosystems we will have to make sure our oceans have enough food for seabirds to feed our forests.