Monitoring our Marine Reserves: An eye beneath the water

We catch up with Tom MacTavish, a Marine Ranger, undertaking monitoring at Banks Peninsula’s marine reserves. This is the first blog in a series following his work with baited remote underwater video.

When I tell people that I’m a DOC Marine Ranger, the response is often a blank-faced ‘Cool… but… since when have DOC done marine stuff?’ This is not surprising, perhaps, when DOC manages 30% of New Zealand’s land area, and just 0.3% of the country’s ocean territory. While we know and love our land, the world beneath our ocean is out of sight and mostly out of mind.

Yet most of us live, work and play along the coast, and our ocean area is 16 times that of our land area. With a view to making us more aware of our country’s marine conservation estate, here is the first of a short series of blog posts on the Mahaanui District’s project to begin monitoring Banks Peninsula’s two marine reserves with baited remote underwater video (BUV).

Preparing to trial DOC Mahaanui’s new BUV units. Image: DOC/Tom MacTavish).

So, why is DOC still bothering to monitor marine reserves? Have their positive ecological effects not already been proven? Part of the answer is that marine reserve status alone does not ensure a desired outcome. The success of marine reserves can vary greatly depending on where we choose to put them, and how big we decide to make them. Monitoring can help us understand how to choose successfully.

A BUV unit. The Go Pro camera is mounted on an aluminium frame one metre above a bait box and a reference bar. Image: DOC/Tom MacTavish.

And because scientifically robust, long term monitoring regimes of our marine reserves are also useful non-fishing reference sites for managers of adjacent fisheries. At Banks Peninsula we’ve started to collaborate more closely with the MPI fisheries monitoring team and the Akaroa Harbour Taiapure Management Committee. However, as MPI blue cod potting monitoring only happens once every four years, we wanted to develop something complementary to that monitoring partnership, but more regular and marine reserve focused.

The conditions in our marine reserves here are challenging. Getting an eye down beneath the water to see what’s going on is not easy around Banks Peninsula. On the turbid, eastern coast of the South Island, clear, blue water is near-mythical, and, as a consequence, SCUBA is unsuitable. When faced with similar challenges, Callum Lilley from DOC Taranaki chose to adopt BUV.

BUV involves lowering an aluminium frame with baited remote camera to the seafloor. The fish attracted to the bait are videoed and later computer analysed to quantitatively record fish assemblages. By collecting video from a sufficient number of sites inside and outside the marine reserve, a scientifically robust monitoring regime can be established. This is cheap, requires no divers, and, most importantly for us, reduces field time and exposure to Banks Peninsula’s fickle underwater visibility conditions.

We began pilot work in December 2016 and quickly learnt that setting the BUV units was tricky, and that recording fish assemblages along Banks Peninsula’s deep and exposed outer coast would be fraught with difficulties.

Once, we accidentally landed the BUV unit on the edge of an undersea wall, from which it soon toppled, and, without sufficient rope to reach the bottom, began floating around several metres above the seafloor. On another occasion the surface buoy completely disappeared for 30 minutes, only to re-appear 200 metres away – the BUV had been relocated by Akaroa Harbour’s strong ebb tide.

Preparing to lower one of the BUV units. Image: DOC/Jesu Valdes

Yet these early mistakes also revealed how fascinating the project may be. Silver, snake-like barracouta had investigated the floating BUV unit with swim-bys and the occasional inquisitive snap of their teeth or poke with their slender heads. Similarly, a solitary skate had resolutely winged its way after the BUV unit that was dragged along the seafloor. Eureka! We were glimpsing another world.

Did we get good enough water visibility to carry out our first BUV survey at Banks Peninsula, and, if so, what insights may we get into New Zealand’s marine conservation estate? Stay tuned for the next blog.