Tom Brough takes us through the third installment in our blog series from the marine reserve monitoring project at Banks Peninsula.
I’ve been living on the glorious peninsula for four years, having moved here to study Hector’s dolphins for my PhD project with Otago University. My project focuses on trying to understand why dolphins hang out at certain ‘hotspots.’ Marine protection, if well planned and well managed can have great benefits for the habitat of dolphins, so I was naturally curious about what’s happening in the marine reserves on Banks Peninsula. As a marine biology nerd I’m always pondering about processes in our moana and how what we do as humans influences those processes. This Banks Peninsula monitoring project was a chance to develop a monitoring programme to figure out what shapes the abundance and distribution of fish communities in a truly magnificent part of Aotearoa.
To pick up where we left off on the last blog; after seven days of incredible weather, our baited underwater video (BUV) sampling was complete. Tangaroa truly smiled upon us for those days, with clear blue water, sunny skies, calm seas and not a breath of wind. Feeling a bit jaded after some long periods on the water, we took stock of our video footage and prepared for the most challenging part of the project: data analysis. With over 150 BUV deployments I had a solid 75 hours of video to go through. A good project for the dark Dunedin winters perhaps.
To know how many fish were at each video collection site we use a value called ‘MaxN’. MaxN for a given site is the maximum number of each species of fish counted within any one minute period of a video. When there are one or two fish present, this is a piece of cake. When you’ve got twenty blue cod swimming about with a handful of scarlet wrasse, blue moki and the odd tarakihi, counting this menagerie of fish life isn’t straight forward. Have a look at the video below and see how many you can count of each species.
As you can see, this takes a while! We also save images from the video to measure individual fish (using the scale bar as a reference), count the number of species to investigate diversity among deployments, and record the habitat types at the deployment location.
It took many months to process our BUV footage as an increasingly battered looking hard-drive was lugged between places as far afield as the Bay of Islands and the sub-Antarctic Auckland Islands. Daily immersion in the sparkling underwater world of Banks Peninsula began to have a meditative effect; offering some escapism from the trials and tribulations of impending PhD completion. The gentle swaying of the kelp and the scales of blue moki glinting in Canterbury summer sunlight put me right back in the field. After a while, large crayfish with razor sharp claws began to invade my dreams, and the facial features of close friends began to take on an uncanny fish-like resemblance. Just in the nick of time, the processing was complete.
The deployments were made across five different areas on the peninsula; two marine reserves (Pohatu and Akaroa) and three ‘control’ sites that were outside of the reserves. The final dataset is a marine nerd’s dream, offering tantalising opportunities to run statistical models to learn more about Banks Peninsula’s fish assemblages. How will fish abundance and size vary between marine reserve and control sites? What factors other than protection status may we need to be considered in interpreting our data now and in future surveys? Keep following – the results are up next!