Category: Restoration

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Brief for restoring extremely degraded seafloor ecosystems

Degraded seafloor - sediment - mudification

I don’t know how to solve this problem, so I am writing it up as a public brief for people smarter than me.

Brief for restoring extremely degraded seafloor ecosystems

Soft sediment marine ecosystems support diverse and productive biogenic habitats like shellfish beds, sponge gardens, tubeworm fields, and bryozoan mounds. Direct impacts such as mobile bottom contact fishing, and indirect impacts such as sediment pollution, reduce the function of these habitats. Stopping or reducing the impacting activities can help the habitats recover naturally over many decades. Active restoration (like mussel and oyster seeding) can be done in areas where the habitat is not recovering naturally; however, some environments can be too degraded for these methods.

Problem

In my opinion, at least tens of square kilometres of the Hauraki Gulf Marine Park are too degraded to restore with known techniques. In these extremely degraded areas, the seafloor is very soft, deep mud. It’s not lifeless; there are burrows and infauna present. But the areas would be more diverse and productive if the seafloor was less soft with less sediment in suspension. Even when pollution input has been reduced in these extremely degraded areas, legacy sediment is constantly resuspended – choking filter-feeding animals and smothering photosynthesising plants. It is difficult to visually convey the condition of these ecosystems, as visibility is usually less than 30 cm on a good day.

Solutions

To increase biodiversity in these areas, the benthic enhancement method must be low-cost at scale. This means traditional erect concrete and steel structures are not likely to be the solution. In my opinion, resurfacing the seafloor with demolition rubble or quarried aggregate is too extreme because it kills all the infauna. Anything heavy deployed will immediately sink into the mud, anything lighter than the mud will quickly be covered by sediment. A smarter solution might contain one of these elements:

  • Local pits or trenches to collect the most mobile sediment.
  • Dispersed erect artificial shellfish (think horse mussels) to slow benthic currents and allow sediment to fall out of the water column in fields or fences.
  • Regular deployments of waterlogged woody debris.
  • Biological concrete structures that grow using elements from the local environment.
  • Hardened local seafloor sediments (think mudbrick or mudcrete).
  • Growing dense algae at the surface which will 1) slow currents and surge to reduce resuspension 2) drop fragments for sequestration, feeding invertebrates, collecting sediment and seafloor hardening.

Caution

While these solutions will restore some ecosystem function they will not restore the original ecosystems. Hard surfaces will likely be first colonised by invasive species and the new habitat will offer more ecosystem services but be novel / new. We must first halt the destructive activities that degraded the seafloor ecosystems.

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Artificial Reef or Fish Aggregation Device?

Artificial reefs have significant potential to boost fish populations, even surpassing pre-fished levels or what is possible in marine reserves. However they have a checkered history overseas, with many reefs:

  • Failing to restore native biodiversity to levels of those of conserved natural reefs (Bracho-Villavicencio et al. 2023).
  • Creating hard surfaces which are favoured by invasive species (these species often travel to new areas on hard structures) (Gauff  et al. 2023).
  • Created as a convenient way to dispose of something which pollutes the marine environment (E.g. UnderwaterTimes.com 2006). They can also attract polluting activities (Zhang et al. 2019).

When considering building an artificial reef, it is crucial to determine whether it will provide additional habitat to support reef communities or merely function as a Fish Aggregation Device (FAD). Like artificial reefs, FADs are man-made structures which are attract fish to a specific area by providing habitat and shelter for marine life. The problem with FADs is that they decrease local fish populations by concentrating them in one area where they are easily targeted by fishers (Cabral et al. 2014) as illustrated below.

To define the size of the habitat required to avoid FAD functionality, you could base it on the home range of each fish species you want to increase. For example:

The most studied fish in the Hauraki Gulf is the tāmure / snapper, which show high site fidelity to reef habitats. Tāmure in deep soft sediment habitats are quite mobile, with a median distance of 19 km, and some movements up to 400 km. In contrast tāmure in shallow rocky reef habitats have restricted movements, with a median distance of 0.7 km (Parsons et al. 2011). You can see this in small marine reserves with shallow rock reefs, such as the 5 km² Cape Rodney – Okakari Point Marine Reserve (Goat Island), which effectively increase the size and abundance of this species. Additionally, tāmure around mussel farms have been found to be healthier than those in surrounding soft sediment habitats (Underwood 2023). The studied mussel farms were near rocky reefs and covered about eight hectares (200 x 400m).

This means fished artificial reefs should be deployed at hectare scales to avoid acting as population sinks. For tāmure, an area about the size of eight rugby fields is a considerable undertaking, but to avoid your reef functioning as a FAD for fishing, it is essential to spread your structure over a large area. If this sounds more like ‘habitat enhancement’ than an artificial reef, then perhaps that is a better way to frame your design. Of course, this consideration is unnecessary if your artificial reef is not fished.

REFERNCES

Bracho-Villavicencio et al., 2023 https://doi.org/10.3390/environments10070121 A Review of the State of the Art and a Meta-Analysis of Its Effectiveness for the Restoration of Marine Ecosystems. Environments.

Cabral et al., 2014 https://academic.oup.com/icesjms/article/71/7/1750/664488 Modelling the impacts of fish aggregating devices (FADs) and fish enhancing devices (FEDs) and their implications for managing small-scale fishery

Gauff  et al., 2023 https://doi.org/10.1016/j.jembe.2023.151882
Unexpected biotic homogenization masks the effect of a pollution gradient on local variability of community structure in a marine urban environment.

Parsons et al., 2003 https://www.researchgate.net/publication/225304000_Snapper_Pagrus_auratus_Sparidae_home_range_dynamics_Acoustic_tagging_studies_in_a_marine_reserve Snapper Pagrus auratus (Sparidae) home range dynamics: Acoustic tagging studies in a marine reserve

UnderwaterTimes.com 2006
https://web.archive.org/web/20170912095117/https://www.underwatertimes.com/news.php?article_id=36210951740 Two Million Tire Artificial Reef to be Removed Off Florida Coast; Smothering Corals

Underwood et al., 2023 https://www.aquaculturescience.org/content/dam/tnc/nature/en/documents/aquaculture/AquacultureHabitatComparativeReport.pdf  Habitat value of green-lipped mussel farms for fish in northern Aotearoa New Zealand

Zhang et al., 2019 https://doi.org/10.1016/j.scitotenv.2019.134768
Microplastic pollution in water, sediment, and fish from artificial reefs around the Ma’an Archipelago, Shengsi, China.

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Record oystercatcher chick at Tahuna Torea

This summer Tōrea pango / Variable Oystercatcher have nested for the first time at Tahuna Torea Nature Reserve (written records began in the 1970’s). Its also the first time any bird has nested on the man-made shorebird roosts (or islands) in the lagoon. Tōrea Pango are recovering from being threatened with extinction and are one of the most endangered breeding birds in the Eastern Songbird Project area. The nearest breeding area is Motukorea / Browns Island which is a population sink for the species. The reserves name ‘torea’ does not come from this species but the South Island Pied Oystercatcher which once gathered here in great numbers.

The two egg nest was laid days after I trimmed the vegetation on Kuaka Island mid November 2023 as part of a roost restoration project. A team of local bird watchers kept a close eye on the nest. The mud in the lagoon keeps the cats out, but not the rats, the trapping team stepped up efforts and rats stopped turning up on the trail camera. One of the eggs was not fertile but the other one was and the bird watching team was thrilled when a chick hatched just in time for Christmas.

Tōrea Pango Chick on Kuaka Island. Photo by Shaun Lee.

The nest would not likely have survived a kiteboarding event in the lagoon. Thanks to the kiteboarders for volunteering to stop kiting in the lagoon at high tide. If you do see anyone kiting in the lagoon phone me 021 555 425 and I’ll have a chat to them.

Tōrea pango whanau at Cable Beacon Point. Photo by Basil Avery.

It was interesting that after nesting on Kuaka Island where I had trimmed vegetation and where a small amount of mangroves have been removed (not the majority) the parents then took the chick 400 m southeast to Cable Beacon Point. New mangrove stumps here were used by the chick to hide. I put up a sign and the bird watchers were on high alert for a few weeks until the chick fledged. The Tōrea pango whanau have stayed in the area which is a great endorsement of the reserve from our feathered friends and a huge win for our shorebird habitat restoration efforts.

The fledged Tōrea pango chick. Photo by Shaun Lee.
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LegaSea’s displacement argument

LegaSea are asking their supporters to object to the Hauraki Gulf Marine Protection Bill due to concern’s about displacement.

“We do not believe the proposed protection measures go far enough to restore fish abundance and biodiversity in the Hauraki Gulf. Marine protection and fisheries management controls need to go hand-in-hand, otherwise all we will do is shift current fishing effort into our neighbour’s waters. We want 100% of the Hauraki Gulf seafloor protected from destructive, mobile fishing methods including bottom trawling, Danish seining and dredging. And, we want Ahu Moana, a joint iwi/hapū and community driven solution to resolve local depletion issues.” (Full email published here).

If we forget about the many non-fishing benefits of marine protection, then also forget about the fisheries benefits of marine protection (nursery and spillover) then forget about the fisheries plan which aims to rebuild stocks including Ahua Moana we are left with LegSea’s naïve argument over a limited amount of fish. Does it stand up?

No, the recreational losses for all species fished in the HPAs total 293 tonnes, the proposed commercial reductions from the corridors will total between 632-1017 tonnes.

Update January 2024. Marine scientists at the University of Auckland have done some excellent work looking at the displacement argument.

Math + references:

Calculating the weight of recreational catch lost to HPAs

Recreational fishers harvested 2,068 tonnes of snapper from the HGMP in 2017/18 fishing year. 9.58% of the recreational fishing effort is in the proposed High Protection Areas. The HPAs will reduce recreational fisheries catch of snapper by 198 tonnes. 

Recreational fishers harvested 517 tonnes of kahawai from the HGMP in 2017/18 fishing year. 9.58% of the recreational fishing effort is in the proposed High Protection Areas. The HPAs will reduce recreational fisheries catch of kahawai by 50 tonnes. 

– https://www.doc.govt.nz/globalassets/documents/getting-involved/consultations/2022/revitalising-the-gulf-2223/stage2-revit-gulf-economic-impact-assessment.pdf

These two species represent 82% of the fish (by weight) caught in the Gulf in the 2017/18 fishing year. 

– https://gulfjournal.org.nz/wp-content/uploads/2020/02/State-of-our-Gulf-2020.pdf

Recreational catch in the HPAs for the 2017/18 fishing year = 248 + 18% (45) = 293 tonnes. 

Calculating the weight of commercial catch lost to trawl corridors

Option 1 would result in an estimated reduction in landings of approximately 632 tonnes of fish per year. Option 4 would result in an estimated reduction in landings of approximately 1017 tonnes of fish per year.

– https://www.mpi.govt.nz/dmsdocument/58729-Discussion-document-Bottom-Fishing-Access-Zones-in-the-Hauraki-Gulf-Marine-Park

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Submissions on the protections proposed by Revitalising the Gulf

I spent a few days going through the 7,550 submissions on protections proposed by Revitalising the Gulf. I’m estimating 77%-90% of the submissions were positive about the protection proposals. However huge numbers concerned about the continuation of bottom impact fishing outside the protected areas and cultural take inside them. So there is a general need for more protection. This level of public support for marine protection can be expected and can be seen in Polling from the Hauraki Gulf Form, Submissions on the recent Waiheke Marine Reserve Proposal and the Live Ocean Barometer 2023.

Most of the names were redacted from the submissions but the organisation names were left public. Here are the names of the organisations that made significant submissions.

OPPOSED PARTIALLY SUPPORT SUPPORT
Legasea
2xs Charters / Balmain Boating Services
Alan Seasprite Charters
CRA 2 Rock Lobster Management Co
Dr Hook Charters
Fisheries Inshore NZ
Kina Industry Council
Mercury Bay Game Fishing Club
NZ Rock Lobster Industry Council
New Zealand Charter Boat Association
New Zealand Sport Fishing Council
Paua Industry Council
Princess Carol Charters
Provider Adventures Ltd
Sea Urchin NZ Ltd
Seahawk Fishing Charters
Slipper Island Residents Association
Snap Attack
Specialty & Emerging Fisheries Group
Tairua Adventures Ltd / Artisan Fishing Co
Te Ohu Kaimoana
Te Ra Charters
The New Zealand Angling & Casting Association
Whitianga / Coromandel Peninsula Commercial Fisherman’s Association		 Aldermen Islands Marine Reserve Group
Friends of the Hauraki Gulf
Mama Fish
Sanford Limited		 Forest & Bird
Revive Our Gulf
Auckland City Centre Residents Group
Auckland Conservation Board
Auckland Council
Auckland Sea Kayaks
Auckland Sea Shuttles
Coromandel Marine Farmers Association
Devonport Yacht Club
Environmental Defence Society
Foundation North
Friends of Taputeranga Marine Reserve Trust
Goat Island Dive and Snorkel
Good Fishing
Hahei Residents and Ratepayers Association
Leigh Penguin Project
Live Ocean Foundation
Meadowbank School Marine team
Motuora Restoration Society
Mountains to Sea Conservation Trust
New Zealand Conservation Authority
New Zealand Geographic
New Zealand Marine Sciences Society
Ngāti Hei
Ngāti Manuhiri Settlement Trust
Ocean Voyages Inc
Pakiri Community Landcare Group
Pest Free Kaipātiki
Ports of Auckland Limited
Shakespear Open Sanctuary Society Inc
Sir Peter Blake MERC
Stet
Supporters of Tiritiri Matangi
Te Whanau o Pākiri
The Friends of Te Whanganui‐A‐Hei Marine Reserve Trust
The Glass Bottom Boat Whitianga
The Hauraki Gulf Conservation Trust
The Hauturu Supporters Trust
Tāmaki Estuary Protection Society
Tāwharanui Open Sanctuary Society Inc
Waiheke Marine Project
Waikato Regional Council
Wakatere Boating Club
Yachting New Zealand
Most of these submitters were upset about continued bottom impact fishing in the Gulf. Most of the Charter fishers all sent in the same submission. These submitters indicated support for marine protection but did not express that much support for the proposed measures: Most of these submitters wanted more protection than what was proposed and also wanted bottom impact fishing banned.

I have not published the names of many organisations who used the LegaSea form as those submissions contained dramatically less information than those from the above organisations. They were mostly small owner operator companies who are also keen fishers. The big Purse Sein operator Pelco NZ Ltd and Te Ahu wai o Tangaroa sustainable ecological aquaculture did make significant submissions but they did not speak to the protection proposal.

In response to the submissions the Department of Conservation has reduced the amount of protection. Submissions are now open on the Hauraki Gulf / Tīkapa Moana Marine Protection Bill.

P.S. These bottom impact fishing effort maps were made public by Fisheries Inshore NZ and are useful in considering the proposed ‘trawl corridoors’.

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Submissions on the Hauraki Gulf Fisheries Management Plan

Over 10,000 submissions on the Hauraki Gulf Fisheries Management Plan are likely to be the largest data set of opinions on fisheries management in Aotearoa and definitely the largest in the Hauraki Gulf Marine Park.

This copy is displayed when asking for public submissions:

Submissions are public information
Note that all, part, or a summary of your submission may be published on this website. Most often this happens when we issue a document that reviews the submissions received.

People can also ask for copies of submissions under the Official Information Act 1982 (OIA). The OIA says we must make the content of submissions available unless we have good reason for withholding it. Those reasons are detailed in sections 6 and 9 of the OIA.

If you think there are grounds to withhold specific information from publication, make this clear in your submission or contact us. Reasons may include that it discloses commercially sensitive or personal information. However, any decision MPI makes to withhold details can be reviewed by the Ombudsman, who may direct us to release it.

I’m disappointed that Fisheries New Zealand has not released all the submissions citing section 18(f) of the OIA—that the information requested cannot be made available without substantial collation or research.

I’m going to read over the submissions provided (which are substantial) before asking for more detail.

My request

FNZ response

Submissions Part 1

Submissions Part 2