Artificial Reefs, a tool for restoring Tasman Bay

The vessel Kaydee - Proposed artificial reef.
Unwanted vessels such as the Kaydee can be placed on the seabed as artificial reefs.

Artificial Reefs, a tool for restoring Tasman Bay

Artificial Reefs,  a life long passion.

Since I first started studying marine ecology,  I have always been interested in artificial reefs.  In fact I spent a couple of years diving,  surveying,  photographing and being amazed by these overtly human structures being reclaimed by marine communities.  What makes wrecks so attractive to divers?  I think it is not just the high diversity that they host,  but a link to the past and a history that connects the visiting human to this otherwise alien realm.

In Tasman Bay,  our deep reef communities have been highly modified.  In the 50’s, 60’s and 70’s dredging and trawling has destroyed most of the biogenic reef habitat that was once there.  Sediment runoff from the land has smothered large areas of the sea floor,  resulting in less nursery and forage habitat for our favored target species such as Tarakihi,  Blue Cod and Snapper.  These fish are not just tasty food to humans, but important keystone species that influence the wider ecosystem.  This has left a hole in the niche that appears to have been filled by more adaptable species such as spiny dogfish and carpet sharks.  Anyone who fishes our bay will tell you that once these guys show up,  it is hard to catch anything else.

Restoration of Tasman Bay

We have a huge area of mussel farm in Tasman Bay,  this is an artificial reef,  it provides shelter and feeding opportunities for many fish.  If you want a kingfish, that’s where you go.  It does not offer protection from capture, it does however protect the seabed from trawling,  but is not a conservation tool.  Marine Reserves are an important tool in the protection of non-migratory species, but they also act like a magnet for fishers,  who increase pressure around the edges of the reserve in the hope of ‘over-spill’ from the reserve, this is known as the ‘edge effect’.  There has been little work done on pro-actively restoring the ecology of Tasman Bay.  In our proposal we introduce the idea of installing artificial reefs, such as shipwrecks and concrete structures on the outside of Tonga Island Marine Reserve in Tasman Bay.

Scientifically Monitored

We propose setting up a ‘no fishing’ buffer zone around the wreck which will enable us to study the recovery of the seabed from trawling,  by comparing it to the marine reserve and currently fished sites.  We encourage fishers to work the edges of the areas and monitor their catch per unit effort.  This will create baseline ground truthing data for wider modelling that is happening in NIWA’s Sustainable Seas Science Challenge.  The new zone will create a buffer from the edge effect for the existing marine reserve.  The artificial reef will provide a new dive site for Tasman Bay and it will be a great opportunity for the various stakeholders to work together on a tangible collaborative project.

In talks with the commercial fishing industry,  we have found that most of Tasman Bay’s fish stocks are acceptable from a fisheries perspective.  We want to exceed and protect these stocks by providing refuges for all species,  that can be harvested as they move between the structures.  This will not only benefit the ecology of the bay but also sustain and improve fishing opportunities for small scale fishing operations in the bay.

We’ll keep you posted on how it goes!

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