A day in the life of a ranger: Monitoring Banks Peninsula Marine Reserves

Have you ever wondered what it’s like to be a DOC ranger? Akaroa ranger Tom MacTavish tells us about a new marine reserve surveying initiative in the area, and what it’s like ‘potting’ for blue cod.

It’s not easy to survey Banks Peninsula’s marine reserves.  Here, giant sediment plumes from Canterbury’s braided rivers interact with strong currents, southerly storms and vertical volcanic cliffs to turn clear, oceanic-blue water into a murky-green cocktail – not a reliable place for diving, that’s for sure!  Indeed, it’s these prevailing conditions that forced the DOC Mahaanui Office to seek out an alternative marine reserve monitoring regime.

Blue cod potting was completed in Pohatu Marine Reserve in 2008 and 2012 with some surprising results.  Blue cod were found to be, on average, larger and more abundant inside the reserve than outside, and fish tagged in the reserve turned up as far away as Wellington and North Otago.  It’s on the back of these findings that DOC and MPI and NIWA have developed a partnership that will see both Pohatu and the recently-established Akaroa Harbour Marine Reserve included in MPI’s Banks Peninsula blue cod potting stock surveys.  The initiative gives DOC a unique opportunity to consider the impact of the marine reserves in the context of the wider Banks Peninsula fishery while providing MPI with ‘non-fishing reference sites’ that may help inform fisheries management.  But with the next MPI survey not until 2020, we were keen to complete a catch-up marine reserve survey in autumn 2017.  The eight day survey, co-funded by DOC and NIWA, has just been completed.

For those unfamiliar with them, pots are large mesh cages with entry holes that allow fish to swim into the cage but then restrict their ability to swim out again.  When baited with something fish like to eat – for example smelly paua guts – they can become an effective trap for blue cod and other unsuspecting carnivorous/scavenging fish.  The eight day survey involved lowering pots to the seafloor at a series of random locations either inside the marine reserves or at designated control sites.  Each pot had surface line and a buoy, so they could be left to fish independently for an hour.

Jason prepares the blue cod pots for the first set of the day

A winch is used to pull the pot back onto the boat

Pulling the pots is an exciting process. It would begin with the inevitable acrobatics required to reach elusive surface buoys, move to anticipation as screeching winch hauled baited cage from way down deep, and finish with discovery as precious creatures were lowered, flip-flopping, onto the deck of the boat.  Any fish that came up in the pots were quickly sorted into species and then placed in onboard swim tanks until they could be counted, weighed, and measured.  Everything was returned to the ocean alive.

A blue cod that was caught in the pot

Weight and length of each fish is recorded before they are released back into the sea

Although the majority of our catch was blue cod, we did get 20 or so other species in the pots.  There were Maori chief fish with their dark, bulging eyes and tattooed bodies, a slippery conger eel that came up in an otherwise empty pot with a suspiciously rotund stomach, and there were baby red cod that give hope that Akaroa Harbour may one day recover the famous red cod stocks of yesteryear.  Results are likely to be available in late 2017.

Maori chief

Camouflage crab

There were a couple of disruptive cyclones that didn’t appear to help this year’s catch rates, which underscores again the need to establish consistent, long term monitoring regimes in our marine reserves.  Nonetheless, it’s great to have completed the catch-up survey this year.  We’ve collected the first potting data from Akaroa Harbour Marine Reserve and we built a strong relationship with NIWA and MPI in the process.  Perhaps that murky green cocktail isn’t such a bad drop after all.