The Impact of Commercial Bottom Trawling

For some, bottom trawling is the only viable way to keep up with the demand for fish both locally and worldwide; for others, it’s nothing short of an environmental disaster. With this in mind, Momoko Burgess and Ethan Neville set out in search of answers.

Karl Warr has been bottom trawling in Hawkes Bay for a couple of decades. When we called him during Level 4 lockdown, he was about to process the fish he’d caught the day before, and even skin and fillet the fish that weren’t going directly to restaurants. But this practice isn’t common these days – not many fishers are left who catch, process and sell the fish themselves. Those who are actually on the water are, as Karl puts it, “a labour force”. It’s big business, in other words, and Karl’s the first to admit there are some problems with the industry, as well as with bottom trawling full stop.

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“Bottom trawling isn’t my favourite method, even though that’s what we do. So we’ve been working to try and lift our game basically,” he told us in the first two minutes of the conversation. 

For Karl, ‘upping the game’ has taken the form of one key innovation so far: adding smooth rigid apertures at the end of the trawl net, which allows small fish to easily escape at the same depth they entered the fishing gear. This one measure has reduced his juvenile gurnard catch by 90%.

But the pressure to make innovations like this one comes largely from the public, not from the industry itself. Bottom trawling is a hot topic in the media right now, and just the mention of this technique will get a number of environmentalists’, journalists’ and recreational fishers’ blood pumping. Most articles published these days outrightly condemn bottom trawling, and unreservedly conclude that it should be banned entirely. So, as recreational fishers ourselves, we decided we needed to find out if this criticism is fair – and if innovative fishermen like Karl have found a better way forward. 

What is bottom trawling?

Bottom trawling, in short, involves dragging weighted nets across the seafloor. The nets themselves, however, are not the sole cause of damage – well, at least not to the seafloor. At either side of the net are steel trawl doors, and these skid across the sand, or whatever else makes up the benthic environment, as they are pulled along the bottom. 

As Karl told us, “That piece of contact might only be six inches wide by six inches long, but it might be pressing down with about a 100kg or more of weight. So if you go diving after a trawler has been through, you’ll often see trawl marks left behind.”

Two ropes, called sweeps, are attached to the doors and these also drag across the bottom in front of the net. They act to herd the fish into the net, much like you would sheep into a pen. The fish that find themselves in the net are then dragged to the surface to be processed – and that is bottom trawling in a nutshell. 

The evidence of a bottom trawler passing through recently is clear.

The evidence of a bottom trawler passing through recently is clear.

There are obviously slight variations between how boats fish and the trawl gear they use (for example, some companies overseas use more than one net, while others use what are called otter boards and so on and so forth), but generally speaking, a net is still being dragged across the bottom of the ocean.

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In NZ, a wide range of bottom fish are targeted by bottom trawling. Baird & Mules (2021) using effort data from 297 trawl vessels over a period from 2008-2019 showed inshore trawl gear targets around 32 species, with around a third of the targeted being flatfish species. The rest is made up by 23% tarakihi, 13% red gurnard, 7% snapper, 5% red cod, and 5% trevally (lesser targets included john dory, barracouta, giant stargazer, and blue warehou). It’s also important to remember that this is the targeted catch and not bycatch, which includes a wider range of fish species, and even sea mammals.

Globally, an estimated 13.7 million km2 (which is about 50%) of the continental shelf has now been affected by bottom trawling, with much of this area being trawled multiple times each year. NZ, however, performs well in this area. 90% of New Zealand’s EEZ (Exclusive Economic Zone) has never been bottom trawled and a third of our territorial waters are completely closed to bottom trawling and dredging (it is worth remembering here that NZ has the fourth largest EEZ in the world). While this may be true, where NZ performs more poorly is in our inshore waters. 75% of the area swept by bottom trawls is located under 400m and 25% is located between 400-600m. According to the Ministry of Environment, almost half of the seabed in the shallow-water range was trawled at least once over a period of a decade between 1990-2011. These numbers are worrying at best.

Over the last 20 years, the amount of trawling has decreased, and this downward trend does provide some evidence that commercial fishing interests are listening to the general public – but it also may indicate that there are less fish to catch and/or the profit margins aren’t what they used to be (these are topics for another article).

So, how bad is bottom trawling really?

If there’s one thing everyone agrees on, including industry itself, it’s that bottom trawling is a less than ideal way to catch fish. The real question is whether trawling’s environmental cost outweighs its economic advantages. 

Benthic Impact

It is widely acknowledged that bottom trawling has negative impacts on benthic communities – as could be expected when you’re dragging something across the bottom. According to a DoC report, gear directly contacting the seafloor can dig in up to 30cm into seafloor sediment (DOC, 2019) and as research done in the Hauraki Gulf shows, trawl door marks are often visible on the seafloor (anecdotal reports from recreational divers also confirm this). Marine flora and fauna is, of course, crushed or buried as a result, which often leads to permanent damage or mortality of creatures and subsequent loss of biodiversity and structural diversity (Auster and Langton, 1999). 

Perhaps what is most worrying is that the recovery of these seafloor habitats and communities after disturbance is uncertain. It is estimated recovery times for species on hard substrate can take centuries to recover (Montagna et al., 2017; Yesson et al., 2017). Colonisers such as bryozoans are often the first to recover, but longer living benthic slow growing sponges and coral species are unlikely to recover and, if they do, it is over a longer period of time, potentially spanning decades (Clark et al, 2019). 

Another big issue which has had air time recently is that marine sediments are one of the biggest organic carbon stores and reservoirs in the world. Carbon can remain in marine sediment for thousands of years if left undisturbed, but when the sediment is disturbed by physical impacts such as bottom trawling, re-mineralization of carbon occurs and carbon is changed into toxic carbon dioxide (CO2), contributing to global carbon emissions on a significant scale. Comparable to terrestrial agriculture and farming practices, trawling and other physical disturbance of the seafloor is estimated to release around 20% of the atmospheric CO2 usually absorbed by the ocean annually. 

The Hauraki Gulf is still a productive fishery, but there are worries about the state of its benthic environment.

The Hauraki Gulf is still a productive fishery, but there are worries about the state of its benthic environment.

Ecosystem Impact

It is naive to think that damaging the seafloor and indiscriminately bulk harvesting fish won’t negatively impact the wider ecosystem – and that’s exactly what recent studies are demonstrating. In a 2017 MPI report, it was noted that the changes in benthic communities caused by trawling may have implications for fish that predate on bottom infauna and epifauna. Studies done in the North Sea have demonstrated that fishing pressure leaves less food for bottom feeders to prey on, which in turn results in reduced fish condition – and an MPI report notes that this could be happening in NZ as well. This makes complete sense; if you disrupt and largely destroy a food source, then the fish that rely on this food will suffer. We could also talk here about how midwater trawlers removing tonnes of baitfish has a similar impact on the wider ecosystem, but we will confine ourselves to bottom trawling for now. 

With a lot of research coming from Government organisations, it is fair to question why so much of our inshore waters is still being trawled on a regular basis. If these habitats can take decades to recover, then it is hard to believe that the economic benefits outweigh the environmental damage. But, as always, there are two sides to a coin.

So, why isn’t bottom trawling banned?

A report from economic researchers in 2017 estimated the total worth of the commercial fishing industry to be at 4.18 billion. The report, which measured a five year average, showed 13,468 people were directly employed in fishing and seafood processing alone, which is 0.7% of all New Zealand employment. Seafood is New Zealand’s fifth largest export by value and represents 3.2% of total exports. This here lies the key problem: bottom trawling is the most effective way to catch fish, and it provides a lot of jobs for Kiwis and value to the economy, as well as of course seafood to our supermarkets and restaurants.

This is not the place to get into a full-blown discussion of the QMS, but what we will say is this: 35 years on, we are still in a position where bottom trawling – a method almost universally condemned – is largely relied on to catch diminishing quota. 

As Karl put it, commercial fishers are “geared up to make fishing as efficient and voluminous as possible. They simply sit down and look at the overheads to produce fish – that’s the focus… The most amount of fish for the least amount of cost – that’s the game.”

 “They tend to perceive that this is a big job: we’ve got 450,000 tonnes of fish to catch in NZ; it’s jobs, it’s exports, it’s local food security.”

Under the current system, these companies need to trawl to catch their quota, to pay their employees, to provide seafood to our supermarkets and to keep making profit – which is, after all, what a company needs to do to survive. It is far too simplistic to view all commercial fishermen who bottom trawl as the enemy.

“The price of fish at the moment can’t go up realistically any more otherwise you won’t eat it will ya?” 

“They’re caught in a hell of a jam at the moment in terms of not having enough resources for what they currently earn from their fish,” Karl continued. “They’re kind of painted into a corner more or less.”

For tangible and widespread change to happen, it’s clear that the system is what needs improving. But Karl didn’t leave us without ideas.

Is there a way forward?

In short, there are two things that need to change according to Karl: what happens on the water, and what happens off it. 

On the water, there needs to be more effort to meet social expectations, which means less bycatch of unwanted species and releasing juvenile fish unharmed – and one of these problems has an easy-ish solution. The new system Karl designed and currently uses has, as mentioned, lowered his catch of juvenile gurnard by 90%. This is a small change for a lot of reward – it just takes a bit of time and money to roll out nationally.

The Government has also made attempts to try and improve bottom trawling. They partnered with Moana NZ, Sanford and the Sealord Group to create a fish harvesting device that has minimum impact on the seafloor. According to the acting manager of this programme Martin de Beer, the Precision Seafood Harvesting programme “was a success in developing a low velocity, low turbulence in-trawl environment that provided both environmental and economic benefits...” It was reported to both keep caught fish in better condition, and so raise their value, as well increase the survivability of released fish and the fish that swim out the escapement holes. However, the commercial viability of this system is still far from assured.

“Due to the complex science and regulatory framework, including the lengthy regulatory approval process, it meant the PSH PGP Programme did not fully achieve some of the intended outcomes and therefore benefits, particularly in relation to the commercialisation of the technology,” Martin explained.

Another big issue is that this method requires bottom contact, so it really can’t be considered a long term solution.

A bigger issue still is that there isn’t the resource or the desire to implement these and other similar innovations across the whole commercial fleet. As Karl explained, “No matter how much they spend in that area, if the fishermen can’t employ those results profitably, they’re not likely to have much of  a future.” 

If it was profitable to be more sustainable, then change would happen overnight, and to make sustainable fishing profitable, then the system itself has to radically change. As a fisherman who predominantly fishes and sells his fish locally, Karl is in the vast minority. But this is what has allowed him to get better returns on his catch, which in turn has allowed him to reinvest money into sustainable fishing practices. It’s a simple model, and one he believes can be rolled out industry wide. 

“The idea that I’m proposing… is getting fishing companies very well resourced so they can afford to take the time and spend the money on innovation and meeting the intentions of what the public wish to see the fishermen doing.”

“At the moment when you go to buy fish from the supermarket, half of the value of that fish is quite often going to the supermarket. They make no effort to help the fishery or fishermen or technology for fishing… They are taking half of your cake but bringing nothing to the game. Now, if all fish sold in NZ was only sold by fishers directly, then all of the income that New Zealanders are paying for their fish is available to incentivise and be used to do the best job possible.”

What gives us hope is the number of fishermen, both commercial and recreational, who are starting to innovate...
October 2021 - Ethan Neville
New Zealand Fishing News Magazine.
Copyright: NZ Fishing Media Ltd.
Re-publishing elsewhere is prohibited

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