Monitoring our marine reserves: Different sights to see – Octopus invasion?

We catch up with Tom MacTavish and Tom Brough, Marine Rangers, undertaking monitoring at Banks Peninsula’s marine reserves. This is the first blog in the second season of monitoring, following the previous, season one  series. Take it away Tom!

Tom Brough and I were at it again, getting goggle-eyed as we watched long sequences of underwater footage from another BUV survey of Banks Peninsula’s two marine reserves and surrounding coast. Are we just gluttons for punishment, or is there a good reason to repeat these surveys bi-annually.

In 2017, armed with three GoPro cameras, a bit of aluminium, some rope and some pilchard bait we’d had an adventure – we’d slipped into another world right on the doorstep of New Zealand’s second biggest city. Yet after collecting 75 hours of undersea footage in the first survey you could be forgiven for wondering if there’d still be anything new to see in the 2018/19 summer?

Fish scattered as the warty, multi-legged monster burst into view.  “ANOTHER octy!” came Tom Brough’s surprised voice. We watched, captivated, as the octopus – eyes dilated and bulbous head pulsating – settle on the bait box of our baited underwater video (BUV) unit. Seconds later it was off again, jetting into the water column and colliding with another octopus in an explosion of tentacles. ‘Wow!’

The octopuses were emphatic proof that there most certainly would be different sights to see. Although we’d seen just one of them in the entire first survey, in December 2018, after reviewing the first 20 sites of our second survey we’d already seen six. Was this some sort of octopus invasion? 

Actually it shouldn’t be a surprise to us that repeat surveying with our BUV units will reveal new and different things. That is because there are many factors – food supply, temperature, habitat availability and fishing pressure (to name just a few) – that will be affecting the species attracted to our bait.  These factors change from day-to-day, month-to-month, and year-to-year.  Repeat surveying, or scientific monitoring, therefore allows us to begin considering the effect of time on what we see with our BUV

And how is that relevant to the management of our oceans? Ongoing surveys are probably the only way in which we can hope to develop an objective understanding of how time-dependent processes like climate change and sedimentation may be affecting marine ecosystems. Moreover, marine reserves are the only places where the impacts of these processes are at least partially isolated from the ongoing impact of fishing pressure. 

Unfortunately, in order to have a dataset extensive enough to address these broader management questions today we would need to have begun our monitoring regime decades ago – when Go Pros didn’t exist! What is it that they say, the best time to start may have been 20 years ago, but the second best time is today…?

Our inaugural 2017 BUV survey gave us an initial snapshot of the size and abundance of taonga south island fish species like blue cod and moki in the two marine reserves. By planning to repeat the survey again in the summer of 2018/19 we were aiming get a first insight into how time would influence Banks Peninsula’s fish populations both inside and outside the two marine reserves.

But repeating 150 x 30 minute BUV deployments along Banks Peninsula’s exposed, turbulent coastline wouldn’t prove easy. Alas, in December 2018 there would be no more exciting nights reviewing novel undersea footage.  The weather remained frustratingly unsettled and so did Banks Peninsula’s silty seafloor.   

By mid January 2019 it hadn’t got any better either, and I began to wonder if the conditions in February 2017 had been a fluke. Would we ever manage to complete this Banks Peninsula BUV survey again? Stay tuned for the next blog to find out.