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ABC News
an hour ago
- ABC News
Lab Notes: Can bottom trawling be a sustainable way to fish?
Belinda Smith: If you've seen the recent documentary Ocean with David Attenborough... Ocean trailer: After living for nearly a hundred years on this planet, I now understand the most important place on earth is not on land, but at sea. Belinda Smith: Like me, you may have been blown away by the destruction caused by bottom trawlers. In super high resolution, we see a giant net weighted by heavy chains getting dragged quickly across the bottom of the ocean. Fish, squid, all manner of animals are scooped up and swept into the net, while the gouging chains churn up the seabed, crushing everything in their path. The documentary leaves you wondering how sustainable our appetite for seafood really is, and if anything is being done to reduce the impacts of bottom trawling. Hi, I'm Belinda Smith, and you're listening to Lab Notes, the show that dissects the science behind new discoveries and current events. To tell us about the state of bottom trawling in Australia is Denham Parker, a marine ecologist at the CSIRO. How much of the world's seafood is caught by bottom trawlers? Denham Parker: Approximately 25%, about a quarter of all seafood that is landed is landed from bottom trawling. Belinda Smith: 25%? That's a huge proportion. Denham Parker: So yes, it's a large proportion of the seafood that we have globally is derived from bottom trawling. Belinda Smith: But it hasn't always been this way. Denham Parker: So bottom trawling has been done for hundreds of years. It was really established in Europe, so it's a very old practice or form of fishing. Belinda Smith: But it's really ramped up for commercial fisheries too, hasn't it? Denham Parker: Yes, particularly around the 90s, 80s, 90s, 2000s, there was a significant increase in bottom trawling. Belinda Smith: And what spurred that increase? Denham Parker: So really, with a growing global population, seafood supplies at this point in time about 3 billion people with a form of nutrients and protein. Belinda Smith: Australia is no exception. We eat on average around 14 kilograms of seafood each year. That's about twice as much lamb as the average Australian eats annually. So what species are fished by bottom trawling in Australian waters? Denham Parker: The common ones in Australia is prawns. So we have a variety of prawn trawl fisheries. As you go south, you get trawlers that tend to target more fin fish, species like ling, grenadier, gummy shark, etc. Now Belinda Smith: Attenborough's latest and probably his last documentary was a really damning critique into the practice of bottom trawling. Was any of that criticism warranted, do you think? Denham Parker: So as someone who has a real passion for the ocean and as someone who has studied the ocean for a very long time, particularly fisheries, I was really excited to know that David Attenborough was making a documentary on oceans. It was great, to be honest, very hard hitting. But obviously there's limitations in terms of that sort of documentary making in terms of it needs to be entertaining as well as it needs to be in a relatively short period of time. So there are limitations as to what can be said. I suppose what I felt was there wasn't enough information as to the hard work that's gone into trying to improve bottom trawling in terms of sustainability and in terms of bycatch reduction and in terms of mitigating seabed destruction. So in the early stages of trawling, it was very destructive. A lot of work has gone into ensuring that mitigating that destructive side of trawling as much as possible. Belinda Smith: Yeah, okay. Let's talk about that destruction and how it can be mitigated, starting with bycatch. The Attenborough documentary says up to three quarters of what's dragged out of the ocean by bottom trawlers is bycatch. Denham Parker: What is very clear is that there's a large variation amongst trawlers as to what bycatch and that's largely to do with what they're targeting. So in general, trawlers that target smaller species such as prawn have higher bycatch than trawlers that target larger fish species. And that's simply got to do with the mesh size of the net that they trawl. And if you're targeting smaller species, that mesh size needs to be smaller. And as a result, you generally tend to catch more bycatch. Belinda Smith: Is there anything being done to minimise bycatch? Denham Parker: There are a number of measures that you can employ within the fisheries. And I think this is really where Australia has done a lot of research into ensuring that bycatch is kept to a minimal. One of the things that you do is all Australian trawl fisheries have a bycatch and discard work plan. These things include gear modifications. So in general, we talk about bycatch reduction devices. And essentially, these are different sort of gear modifications to the net, which help or aid any unwanted species to escape. So this can be anything from a portion of the net that is a different shape or larger mesh size to let animals escape. They have fish eyes, which are essentially a little escape slot in the top of the net. And then this reduction devices for larger animals, such as turtle exclusion devices, which is something that's been really successfully implemented in Australia. Belinda Smith: I guess that's one of the sort of more enduring images of documentaries, right? Seeing the poor old turtles, they always get caught up in fishing nets and things like trawlers are no exception. So how would a trawler turtle exclusion device work? Denham Parker: What it is essentially is a grate, a metal bar grate that's put into the net and angled slightly upwards. So as all the animals get kind of flushed into the net, the target species can pass through those bars. But large animals like turtles will hit up against that bar and will be forced upwards to the top of the net. And then at the top of the net, there is essentially a flap. So an escape little hole that the turtle can then pop out of and escape unharmed. So these are implemented in the late 1980s, early 1990s across a lot of the trawl fisheries in Australia. And having a look at the history of these fisheries, we see that in the northern prawn fishery, for example, there were 5,700 turtle interactions in late 1980s. And then in 2020, that was decreased down to less than 70 interactions. Of that, only five mortality. So things like turtle exclusion devices, which have been developed over time with scientists as well as with the industry, they really have quite a lasting impact in terms of bycatch reduction. Belinda Smith: The other big environmental concern, of course, is the trail of destruction a bottom trawling net can leave in its wake. Denham Parker: Yes, obviously the interaction of trawling with the seabed does modify and disturb the habitat. One of the methods in which we try to mitigate that interaction is by ensuring that the gear that is towed is as light as possible so that it really doesn't penetrate deep into the seabed. So the points of contact are as few as possible and if possible, include things like rollers with rubber so that that interaction is minimised as much as possible. Belinda Smith: The seabed is a good carbon store and that carbon accumulates as dead animals and plants and their waste sink to the bottom of the ocean. But when trawlers come through, they disturb that carbon and it can be released into the atmosphere. So how much carbon does get released? Denham Parker: That's a very complex and difficult question to answer. The reason it's so complex is because it really lies at an intersect between understanding the carbon cycle, understanding the seabed, biota and understanding fishery science. There have been attempts to answer it. However, those attempts and the assumptions that they made in their model in terms of trying to quantify the carbon that is released as a result of trawling have been questioned. Like I said, not an easy thing to do. With Belinda Smith: this potential for carbon release as well as habitat destruction, how much of Australia's oceans are bottom trawled? Denham Parker: Australia has done a lot of work in mapping the seabeds and understanding where sensitive habitats lie and understanding where the trawl footprint lies relative to that. You'll be surprised to know that in recent years, the trawl footprint is only about 1.1% of Australia's economic exclusive zone. Belinda Smith: The economic exclusive zone being the area of ocean around 370 kilometres from the coastline where Australia has exclusive rights to do activities like bottom trawling. So how does that 1.1% compare to other regions? Denham Parker: There was a global research paper written that looked into a similar sort of trawl footprints across 24 regions in the world. What that found was that the average trawl footprint within an EZ is about 14% and on the higher sides of it in areas like the Mediterranean and the Adriatic Sea, it exceeded 50%. Belinda Smith: Really? Oh my gosh. Yeah, right. That's huge. Denham Parker: So in that sense, Australia is doing really well in that it is probably one of the world leaders in understanding spatial management and understanding where your sensitive habitats lie through mapping and where your trawling footprint is and ensuring that those two don't overlap. I think another important statistic is that 54.8% of Australia's EZ is actually protected from trawling. Belinda Smith: After an area has been trawled, how long does it take to recover? Denham Parker: That's an interesting question and that largely depends on the ecosystem that was there prior. Belinda Smith: So for say a seagrass meadow versus a coral reef, would one bounce back faster than the other? Denham Parker: Yeah, again, one would bounce back faster than the other, but it's not as simple. It also depends on the environment health outside of simply just the impact of trawling. A lot of those sort of questions can only be answered with experimental design where you really would have a trawled area that otherwise or later becomes a marine protected area and you would be able to monitor the bounce back then. Belinda Smith: Considering that bottom trawling is needed to meet our appetite for seafood, is there a way of doing it sustainably and how can we consumers know? Denham Parker: Yes, there is a way of bottom trawling sustainably and in fact there are a number of bottom trawl fisheries that are considered to be sustainable at this point. So globally I think there's approximately 70 bottom trawl fisheries that are certified by the Marine Stewardship Council, the MSC certification. Belinda Smith: The MSC is an independent body that checks if a fishery is operating sustainably, both in terms of the species they're fishing and their impact on their ecosystems. Denham Parker: As a consumer, if you're looking to make informed choices in terms of sustainability for your seafood that puts on your plate, look for the MSC green tick label on products. In terms of Australia, I think there's approximately 25 MSC certified fisheries, of that around eight are bottom trawl fisheries. Belinda Smith: Right, okay. It seems like a fairly low proportion of the total number of trawl fisheries out there. How do you get more people to think sustainably? Denham Parker: I suppose how you can force fisheries to become more sustainable is through government interventions, right? So like I said, Australia is really a world leader in terms of fisheries management because there is this interaction between researchers, governments and fishermen themselves. Belinda Smith: Ultimately, making fishing practices as sustainable as possible is a win for both the environment and the people fishing, a point also made in the Attenborough documentary. The fishermen are Denham Parker: not against sustainability. In fact, they're absolutely for sustainability. They realise that their investment is in the ocean and it's best that they conserve their investment as much as possible. We test a lot of mitigation devices with industry, so they take them out themselves and test them and collect data for us and we bring that back and see which are efficient and which are not. It's really that interaction that really helps us understand each fishery as an individual and how we need to or what we need to do to improve that fishery sustainability. Belinda Smith: That was Denham Parker, a marine ecologist at the CSIRO. Thanks for listening to Lab Notes on ABC Radio National, where every week we dissect the science behind new discoveries and current events. I'm Belinda Smith. This episode was produced on the lands of the Wurundjeri and Menang Noongar people. Fiona Pepper's the producer and it was mixed by Tim James. We'll catch you next week. You've been listening to an ABC podcast.
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