Monitoring our marine reserves: 7 days of surveying

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

Leaning over Kahukura’s bulwarks, I watched the aluminium frame of our baited underwater video (BUV) telescoping into the yawning blue deep. The water was captivatingly clear, an unusual and momentous sight here at Banks Peninsula, where water visibility is notoriously poor. As I watched that first BUV unit disappear, I knew that these were exactly the right conditions to complete our first marine reserve survey.

Otago University researcher Tom Brough collects a BUV unit from one of the 150 sites. 📷: DOC/Jesu Valdes

In some ways, collecting BUV is like going fishing – choose your location and bait depending on the fish you’re targeting. Reef fish like blue cod were the target of this survey, so we lowered our BUV units at randomly selected sites along the reef edge and used pilchards as bait. But there the similarities to a relaxing kiwi fishing trip end. For a robust comparison between fish assemblages inside and outside the marine reserves, the survey needed to collect 30 minutes of video from each of 150 sites. Good teamwork would be critical.

Three of us were on the water during the survey – Otago University PhD researcher, Tom Brough, local ranger Derek Cox and myself – continuously setting and retrieving three BUV units. Between sets there were Go Pro camera batteries and memory cards to manage and variables like location, water visibility, weather conditions and depth to record. Although having several BUV units certainly increased our efficiency, sometimes we’d end up with BRUV units simultaneously set on opposite sides of the harbour. On these occasions engines would whine and hair would stand on end as Derek made full use of Kahukura’s horsepower.

In a ten hour day we could collect video from about 30 sites. When Kahukura was safely back in her shed for the night, Tom and I reviewed what we’d caught on camera. At the end of the first day, I remember eagerly sitting down to our footage, only to find that our videos were dominated by sand-dwelling species like spiny dogfish. We’d set the BUV units slightly too far from the reef edge.

With a day lost, there were some anxious glances at the weather maps. However, miraculously, the weather held and the ensuing days were some of the most memorable of my short working life. Day after day we’d wake to those crisp, calm, late summer mornings, and under cobalt blue skies we’d venture out of Akaroa Harbour and into the Pacific Ocean.

Out there, the wildlife made our work enjoyable. Hector’s dolphins regularly porpoised around the boat, white-fronted terns hovered in the sky and then deftly dropped to ambush bait fish flashing silver in the sun. Little blue penguins bobbed on the surface, vulture-like giant petrels waited patiently for something – anything – vulnerable, and Banks Peninsula’s volcanic cliffs were the roosts for cormorants lining ledges like ornaments in a shop window. But as wonderful as these sights were, I was most interested in what we saw beneath the surface.

Our footage may not be worthy of a David Attenborough documentary. But for Tom and me, who’ve always wondered what happened around the bait on the end of our fishing lines, the footage was an endless source of fascination. We spent the evenings watching the hierarchical behaviour of blue cod, the delicate fluttering of leatherjackets, the mysterious ways of hagfish, and the apparent audacity of large crayfish leaving the refuge of their caves to mount our bait box in broad daylight. On one particularly memorable occasion, Tom Brough literally jumped in his chair as a large sevengill shark swam into the screen. We really did find ourselves living in the fishes’ world!

Seven days, and more than 75 hours of undersea footage…Phew! How would we now transform the video footage into quantitative data useful for management? That’ll be the topic of the next blog.

This is the second blog in our series on Monitoring our Marine Reserves. Read the first blog about the background to our Banks Peninsula BRUV project here.