Counting kōura in the Sounds – Long Island Kokomohua Marine Reserve

Written by Casey Spearin.

Jutting from the water like a knife edge in the northeast entrance to Tōtaranui/ Queen Charlotte Sound is a chain of small islands nestled between Cape Jackson and Cape Koamaru. Accessible only by boat, most people reach it by launching from the port at Waitohi/Picton and enjoying the half hour ride along the beautiful drowned river valleys that make up the Sound.

Today there are seven of us on the DOC vessel Waitohi. We’re here as part of a yearly monitoring trip to the marine reserve. Established in 1993, Long Island Kokomohua Marine Reserve is the longest running monitoring project of a marine reserve in Aotearoa New Zealand. Since 1992, DOC and contractors (Davidson Environmental Ltd.) have been carefully monitoring the ecosystems in and outside of the reserve.

Marine reserves have been a hot topic recently. It’s good to remember that it’s not enough to simply establish new marine reserves – we also need to commit to properly manage and monitor them into the future, to make sure that they are effectively protecting the species and habitats they were created to protect. And that means lots of human hours diving, doing science, taking and analysing underwater video footage, and patrolling for people illegally fishing in the reserve. At Long Island-Kokomohua, we have nearly 30 years of data showing that the marine reserve is doing amazingly well at protecting species such as blue cod and kōura/crayfish – which is what we are counting today.

Long Island, a thin sliver, is mostly an exposed ridge plunging startlingly into the sea. Winds from the Cook Strait buffet the island around the clock. The seabed surrounding is a marine reserve made up mostly of rocky reef and exposed rock walls, with areas of sandy bottom. It’s connected to the neighbouring islands, the Kokomohua, by an underwater reef surrounding Kokomohua and extending further north for nearly half a kilometre.  

The ocean habitats around the islands are unique because they form a transition zone between the sheltered inner sounds and the wild waters of the Cook Strait.

Both the island and the marine reserve around it are completely protected. On Long Island you can find little spotted kiwi, tuatara, tīeke (South Island saddleback) and spotted shags. And if you were to chuck on a snorkel and mask, you’ll see blue and red moki, triplefins, butterfish, many different species of seaweed, crabs, octopus, horse mussels and plenty of fearless blue cod willing to nip at your fingers and any bit of exposed skin.

But its history goes back much further. Long Island falls in Te Ātiawa’s rohe and was known as Hamote when it was a fortified pā. In colonial times the native forests were burnt, and the island was used to run stock. In 1925, a ranger (organisation unknown) visited the island and recommended it become a scenic reserve – this was implemented the following year. In 1930, stock was removed from the island, and it reverted “vigorously” to native forest. In 1989, Marlborough dive clubs voluntarily stopped taking fish from around the island. In 1992 they recommended it become a marine reserve and began promoting the idea locally. Finally in 1993 it became the South Island’s first marine reserve and fell under DOC’s management.

The islands and their surrounds are teeming with life, and it’s because of the actions of many people, including the voluntary sacrifice to give up a legendary fishing spot, that lets us experience this rich biodiversity today.

In the 30 years since the marine reserve was introduced, sea life has bounced back with determination. “When you dive in the area, the difference is stark between the inside and outside of the marine reserve. Inside the reserve there is a huge abundance of kelp, kōura and blue cod. The kelp is so thick it’s hard to find the lobsters. Outside the reserve there is less of everything and way more bare rock,” says Monique Ladds, who leads DOC’s national Marine Reserve monitoring and reporting programme.

Every other year a different element is monitored for. This repeats on a two-yearly cycle, enough to detect trends in the different components of the ecosystem.

Today we’re out monitoring kōura (crayfish/rock lobster). We’re also recording habitat information including other key species such as seaweeds, sponges and invertebrates within each of the dive sites. Later, our monitoring team will cross reference the habitat types with the kōura information, to see if any trends exist.

Next year we will be conducting fish counts using SCUBA divers. Last year the team collected information on fish and pāua including diversity, abundance, and size. They found edible fish such as blue cod, red moki, and tarakihi were all more abundant and larger sized inside the reserve, a trend which has continued for many years. Butterfish were spotted inside the reserve but not at any control sites outside, and pāua numbers had increased – all these positive effects are directly results of the marine reserve protection.

This is day three for the dive team. They’ve already completed seven dive sites over the past two days, both inside and outside of the marine reserve. Today we have one more control site to monitor and two more inside of the reserve.

We begin at a control site to the east of the reserve, off Motungarara Island. The spot is fairly exposed, and the divers pop their heads up occasionally to check they are still tracking along the decided course. Together, they’re swimming three separate 25 m lines – a transect – and recording kōura information along the way.

The divers have an overwhelming array of tools and instruments dangling from them – flashlights, underwater note-taking equipment, a spool for measuring the transect, video cameras, plus all the normal dive gear – navigating all of it off the boat and into the water while in a wetsuit would make even a professional gymnast look uncoordinated.

A monitoring dive isn’t a relaxing time to swim around and look at the fish (though Monique notes she got distracted by a six-legged octopus at one point and let her dive partner carry on with data recording). Aside from all the regular dive considerations – keeping an eye on your air supply, your depth, and your dive partner – you carry a waterproof tablet for marking complicated looking hieroglyphs, which I’m told correspond to species type and measurements for size and sex.

You also need to make sure you’re staying on the dive line and spotting the proper habitat for the species in question. For kōura it’s all about the rock walls and rocky reefs – sheltered places to hide from predators and the constant buffeting from the currents of the Cook Strait.

From there we anchor off the east side of Long Island for another transect.

Dirk de Vries, a DOC Ranger stationed over in Motueka, has been involved in the dive monitoring here for 11 years. In that time, he’s seen the results of the marine protection improve each year. “When I first got involved in 2012 the results were already impressive and have stayed that way.”

The weather and tides have been smiling on us today and we finish the last dive in the early afternoon. Before finishing, we stop for one final dive off the northeast tip of the Kokomohua Islands to get some footage on the GoPros.

Monique climbs back into the boat and hands me the camera. She’s spotted something unusual on the seafloor – a mass of tangled yellow strands perfectly resembling a clump of ramen noodles. Stew Robertson, Marine Reserves Ranger for the Tasman area, checks the footage and tells us it’s the eggs from a sea hare – a “marine slug” which can reach epic sizes. They also spot nudibranchs, sea anemones and some playful terakihi.

With the final dive done, it’s time to head back to port and unload the dive gear from the boat. This is only the start of the work though. With the data on hand, the marine monitoring team now has the job of auditing and standardising it, writing a report, and incorporating it into the last 30 years of data to understand the trends happening in the ecosystem.

One of the dive contractors, Tom (of TC Environmental), has been working on this reserve for six years. He tells me they’ve recently been observing a population explosion of a species of tubeworm (Chaetopterus sp.), though not much is known about them. Suspected to be invasive, they are colonising much of the habitat in this area. They can grow on both soft sediments (sandy and muddy seafloor) and on rocky reefs, meaning they’re causing issues across multiple habitat types including smothering rare and native tubeworm mounds (Galeolaria hystrix).

It might not seem like much (so what if you swap one tubeworm for another?) but it could mean disaster for the ecosystem if they take over. The native tubeworms create biogenic habitats for other species, meaning they provide hidey holes for small invertebrates and solid foundations for mussels and other filter feeders to attach.

“We don’t know what’s causing it yet,” says Tom. “It’s possible there could be some climate change influence with the warming water and marine heatwaves. But for the moment we are observing and trying to figure out what’s causing their incursion in this area”.

Overall, it appears the ecosystem is making a good recovery after 30 years of protection. In 2011 a study found there was more blue cod in the area (extending beyond the marine reserve boundaries) and there were more blue cod above 30 cm. In 2016 a “dramatic recovery of fish stocks” was reported.

Kōura have also made a dramatic recovery. When the reserve was established there in 1992 there were on average two kōura per 100m² transect. Their population stayed relatively low for the first nine years. Twenty years later that number has skyrocketed to 34 kōura per transect.

Despite the abundance of species in the reserve, the water quality is poor. The Sounds have a lot of pressure on them. Forestry and land use on the surrounding areas contribute sedimentation to the marine environment, and fishing pressure is high, both commercially and recreationally. Boat traffic is also high, particularly in the summer, and waves from passing ferries impact intertidal communities (animals that live between the high and low tide marks). And a NIWA study in 2020 found microplastics on the seafloor of the marine reserve – unsurprising considering microplastics are turning up nearly every place we think to look for them.

This is an area which is used intensively by many people and industries. We’re fortunate that people had the foresight thirty years ago to create the marine reserve and save a little slice of the Sounds to be left to recover.

30 years on, what can we say about the marine reserve? Well for one, it’s working. Not all marine reserves show such dramatic increases in species like kōura. This is often due to pressures other than fishing that marine reserves can’t control for, like sedimentation, pollution, and marine heat waves. But here at Long Island – Kokomohua, many previously fished species are recovering and spilling over into the adjacent areas.

Results like these give us hope for the future as more challenges are ahead for our oceans, like invasive tubeworms and marine heatwaves.

“Marine reserves are not only ‘wet libraries’, enabling us to better understand what the marine environment looks like with the absence of extraction, but they also provide resilience in the face of increasing pressures of climate change,” says Stew Robertson, Marine Reserve Ranger for Nelson/Tasman.

“With a healthy suite of native biodiversity, the natural functions of the reserve hold the best chance at coping with temperature extremes, degrading water quality and the threat of invasive species. Healthy populations ‘overspill’ into surrounding areas, increasing abundance outside the boundaries. Size really does matter, the larger the reserve, the more resilient and productive the area will be.”

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Learn more about Long Island – Kokomohua Marine Reserve here.