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Ocean to Table: A Guide to Commercial Fishing Methods Part One

Source: The TerraMar Project - April 18, 2017 in Featured, TMP

Ocean to Table: A Guide to Commercial Fishing Methods Part One
Photo: Rennett Stowe/Wikimedia Commons (CC BY 2.0)

Fish are the world’s last true wild-caught source of food. In order for that sushi roll to make it to your dinner plate, a crew of dedicated seafarers must first venture out to sea to catch that fish.

How does that fish you order in a restaurant or buy at market end up on your plate? How is that fish caught, how is it transported, how is it sold, how are they bought? What is the real cost, both financially and environmentally of that fish you are eating?

Depending on the fish you’re eating, the voyage can take anywhere from a morning of fishing close to shore, to weeks out at sea battling storms and high seas. Being a fisherman has always been one of the world’s most dangerous jobs and lifestyles. These people dedicate their lives to hunting on the sea, and chasing their life’s fortune in the currents. And sometimes they can strike gold, while others they are left with empty nets.

With the modernization of fishing technologies, vessels have improved their ability to find and catch more fish. But with great power comes great responsibility, and over-fishing around the world, combined with other threats to the fish in our oceans, have driven some fish populations to dangerously low levels.

Today, commercial fishing is a clash between past cultures and modern innovation. It’s a balance between making a living and causing irreversible damage to the oceans. But mostly it’s a challenge to understand the unknown, because the oceans will always remain unpredictable to both scientists and fishermen alike.

Schooling fish

Photo: Ellmax

Trawl Fishing

Overview

This is one of the most industrialized methods of fishing in the oceans today. And it can take many different forms.

Trawl boats are generally large boats meant to support a great deal of rigging and catch. And depending on their size and function, fish anywhere from a mile offshore to hundreds of miles out on the continental shelf.

The mouth of the largest trawl nets can be as wide as a football field (330 feet) and up to 40 feet tall. And as these massive nets sweep through the ocean, they catch everything that comes in their path.

When trawling for fish on the bottom of the ocean, large weights called doors sink the net to the bottom, where the sweep (bottom mouth of the net) drags along the bottom, kicking up any animals and vegetation. This method of fishing can be highly destructive to bottom habitats, and often results in significant levels of by-catch of non-target fish species.

Bottom Trawl Diagram

Image: NOAA

The destruction of bottom habitat is a serious concern with bottom trawl fishing. Ancient deep-sea corals can become wiped out by a single net, leaving the ocean bottom bare and devoid of life in its path. Bottom trawls have been significantly re-shaping the sea floor since the industrialization of commercial fishing, and the impacts of this habitat destruction are not hidden.

Bottoms trawls with small sized meshes often have the highest levels of by-catch, because undersized fish cannot escape from the end of the net. By-catch also varies based on what the boat is fishing for. Some types of fishing (ex: squid fishing) can be  “cleaner” due to the schooling nature of the animals. On the opposite end of the spectrum, shrimp fisheries often have the highest levels of by-catch, where for every 1 pound of shrimp caught, 6 pounds of other species are discarded back into the sea.

Another type of trawl is a pelagic trawl, which targets mid-water schools of fish (ex: herrings, mackerels, anchovies). These can be towed by 1 or 2 boats simultaneously, and are often clean catches of the target fish (since the fishes school together). However, they are associated with higher rates of cetacean, sea turtle, and other marine mammal by-catch. These nets don’t sink to the bottom, so they aren’t destroying habitat in the way that bottom trawls do.

cod

Photo: Massachusetts Office of Tourism/Flickr (CC BY-ND 2.0)

Innovations

There have been a few design innovations made to trawl gears to help them reduce by-catch.

One such innovation has come in the form of escape outlets for turtles and other non-target fish species. Called ‘Turtle Excluding Devices’ (or TEDs), these openings in the net allow larger animals like turtles to escape, while still trapping the target fish.

TED device diagram

Example of various types of bycatch reduction devices. Top left: Funnel bycatch reduction device – Uses an inner small mesh funnel to provide a passage for shrimp to the bag of the net while a large mesh outer layer provides a means for large fish to escape. The design creates an area of reduced water flow so the fish can easily swim out the large mesh openings. Top right: The Fisheye – A cone-shaped rigid frame forms on opening in the net for fish to escape. Bottom: Sorting grate – Shrimp pass through the grate, while fish that are not large enough to pass through are pushed out through the escape opening. Images and information from NOAA Fisheries.

In order to reduce levels of fish by-catch in bottom trawls, the size of the mesh used on the trawl is crucial. By using larger sized meshes smaller fish by-catch can swim out of the net alive. The results are often a net filled with only keeper fish, and a few larger non-target species of by-catch. This allows the populations of target fish to continue to grow and reproduce in the wild. It also leaves the crew onboard with less fish to sort through.

Separator devices are another new design in some trawl gears. When fish encounter a trawl net underwater, they react differently according to the conditions and their general behaviors. For example, Cod and Flounders are known to swim down in the bottom half of the net’s mouth when encountering a trawl net, while Haddock will swim up. By separating the trawl net horizontally into 2 halves, and including an escape outlet in the bottom half, only the target Haddock are caught in a Haddock separator trawl. 

Gill-Netting

Overview

Gillnets are a commonly used fishing method in coastal waters around the world. The vessels that carry gillnets are smaller than most trawl vessels, and can range from the size of a small dingy, to the size of a larger offshore sport fishing boat. Since the fishing is done closer to shore, gillnet fishing trips generally don’t last much longer than a day.

Gillnets are long panels of net walls that are hung vertically in the water column, and trap any fish unlucky enough to swim into them. As per their name, gillnets ensnare fish by the gills, where they remain trapped until the net is retrieved. They are made up of the net panels, weighted line on the bottom, and a line with floats on the top. Anchors can be used as well at the bottom of each end to secure the net. The “string” of net panels is connected at the surface to a set of floats at each end, which is how captains retrieve their nets.

gillnet diagram

Image: NOAA

There are 2 common methods of gillnet fishing: anchored gillnets, and drift gillnets. Anchored gillnets are secured to the seafloor via an anchor, and they can either be set on the bottom, or float up in the water column. Drift gillnets can be made to sink to the ocean floor, or drift in the middle of the water column as well. Except these nets are not secured in place and move with the ocean currents.

Gillnet fishermen will often set their nets by looking at fish-finders for schools of fish, or using the bottom contours to determine good habitat for their target species. The time that the string of gillnets soak in the water for can influence what is caught, and how much.

Gillnet fisheries generally have lower levels of non-target bony fish by-catch than trawl fishing, but they have high rates of interaction with marine mammals (whales, dolphins, porpoises, seals, sea lions), seabirds, sea turtles, and sharks. When these animals encounter gillnets, they become ensnared in them and can suffocate underwater before getting free. Some animals are actually attracted to the fish stuck in the nets, viewing them as free food, but can become stuck trying to steal a quick meal. This is why the time the net soaks is important, because the longer the net is in the water, the greater the chance marine mammal, sea turtle, or shark might get caught in it.

It’s not uncommon to hear tragic stories on the news of whales having to be saved and cut out of gill nets by teams of rescue workers. And harbor porpoises are one of the more threatened animals by gill nets because they spend their time closer to shore in the same areas that these nets are used to fish. Before scientists stepped in, 1,800 harbor porpoises were being caught and entangled in these fishing gears each year.

Gillnet boat

Photo: Rex Gary Schmidt/NOAA

Innovations

To help reduce levels of by-catch in gillnet fisheries, changes in net design have been made and are required to fish in certain areas of the world.

Weak Links were created to help large marine animals such as big sharks, whales, and dolphins to break free if they become tangled in the gill-net string. The weak links are attached to each panel of gillnet, and are designed to break under a specific amount of pressure or force. It isn’t a perfect system, as the animal could still remain stuck in parts of the net, but it gives the animal an opportunity to escape and make it to the surface for air.

Pingers are another innovation used in some places around the world to deter marine mammals from feeding on the net. These small devices are placed with the net’s floats, and are designed to “ping” every few seconds in a tone that’s meant to deter animals such as porpoises and dolphins from coming to feed on the fish in the net. There is some debate about whether or not these “pings” act as a “dinner bell” to actually display a free meal to these marine mammals, but for certain species, pingers have been proven to be an effective deterrent.

Pingers

A few different Pinger designs used in Gillnet fisheries. Photo: NOAA

Long-Lining

Overview

Long-line fishing is aimed at catching the top predators of the world’s oceans. These boats can venture on the high seas for anywhere from a few days to months at a time, depending on their luck and what they are fishing for.

The way long-line fishing works is that a central thick line is laid out, attached to buoys every couple hundred feet. Hanging from this central line are many shorter lines with baited hooks dangling from them. These long-lines can be set in the water column (pelagic long-lines), or can be set on the sea floor. Pelagic long-lines are designed to catch large, open-ocean species of fish such as Tunas, Mackerel, Mahi-Mahi, and Swordfish. While bottom long-lines are designed to catch Groupers, Halibut, Cod, and Sea Bass.

A single long-line can stretch for up to 30 miles across the sea, and be equipped with over 12,000 baited hooks! That’s a lot of bait used for a line-of-death over 500 football fields long, left to float in the high seas and catch whatever top predators happen to be curious enough to take a bite.

longline diagram

Image: NEFSC/NOAA

There are 2 big problems with long-line fishing: They are very good at catching sea birds and sea turtles, and the fish that they target are slow-growing top predators in the ocean.

Scientists predict that between 150,000 and 300,000 seabirds are killed by long-line fishing every year. Species such as albatross are especially vulnerable to long-line fishing because they spend nearly their entire lives wandering the sea in search of food, and when they pick up on the scent of bait in the water, they can track it down and become the next victim of the fishery. These species of birds are also some of the ocean’s top predators, and like sharks and other large animals, they grow very slowly. The result has been seen in the listing of many albatross species as Endangered or Critically Endangered by the IUCN Red List.

Other sea bird species such as Gannets and Gulls fall prey to long-lines at sea as well. When these sea birds dive down to catch these fish, they consume the hook as well and become trapped underwater where they often drown. The same scenario happens with sea turtles that encounter these baited hooks on their oceanic travels. The turtles see a free snack, but end up trapped underwater with a hook in their throat.

Shark by-catch is also a major problem with the pelagic long-line fisheries that target tunas and larger predatory fish. Sharks share a similar position in the food web to these animals, and are often found in the same places.In the Pacific Ocean alone, each year 3.3 million sharks are caught as by-catch in longline fisheries.

longline bycatch

A Big-Eye Thresher Shark caught on a long line. Image: NOAA Fisheries

There’s also a large amount of waste in these fisheries. Fishermen will often catch target species that are too small to keep, and so will throw them back into the sea either dead or dying from being caught on the long-line.

By targeting the ocean’s top predators, long-line fishing perpetuates a phenomenon known as “fishing down the marine food web”. Removing these predators from the ocean creates huge voids in the top structure of these food webs. Without the ocean’s top carnivores, the whole system shifts. Each living creature in our world’s oceans has a part to play in the web of life, and each animal is connected to one another in ways that we even still do not fully understand.

Innovations

There are a few different strategies that have been developed to reduce by-catch in long line fisheries.

Bird streamers are being used in pelagic long line fisheries to deter birds from approaching the fishing lines. This innovation is really a win-win situation for the fishermen, who save money on lost bait to the sea birds as well.

streamers

Image: NOAA fisheries

Scientists have also found that using circle hooks instead of J-shaped hooks reduces the by-catch of sea turtles in these fisheries. And this really doesn’t influence the target catches for the fishermen.

Circle hook diagram

Image: Western Pacific Regional Fishery Management Council

The type of bait used by the fishermen can also influence what kind of by-catch is caught. By using whole fish as bait instead of squid, less sharks and turtles are caught in the lines.

As a whole, long-line fishing can be extremely harmful to the environment in terms of the by-catch in the fisheries, and the top-down effects of removing the ocean’s top predators. Other than more intense regulation on where these vessels can fish, and the kind of gear innovations they are required to use, the best option for the conservation of these animals is a phase out of long-line fishing gear to the use of greenstick gear and buoy gear to catch these ocean animals. Both of these new fishing methods used to catch tuna and swordfish have been shown to be able to reduce the numbers of by-catch in this kind of fishery.

Pots and Traps

Overview

Pots and Traps are designed to lure a target animal into the cage, which is designed to let the animals in, but make it difficult to escape. These can come in all different shapes and sizes depending on the fishery. Pots and Traps are mostly used to catch species such as lobsters, crabs, whelk, and shrimps.

The vessels that perform this type of fishing vary by region, and by the fishery. For example, large Alaskan crab fishing boats can go out for weeks at a time at sea, while smaller lobster fishing boats of the Northeast US will only fish by the day.

Levels of by-catch in these fisheries are generally pretty minimal. This is mostly because the trapped fish are not necessarily killed, and can be returned to the water alive if they are too small or illegal to keep.

However they still are a threat to some marine life. Whales can become tangled in their buoy-lines and seas turtles can occasionally be attracted by the bait used inside the cage and suffocate in the trap.

tangled whale

A humpback whale in Hawaii entangled in fishing rope line. Photo credit: NOAA

The biggest problem with pots and traps is that they are easy to lose at sea, and contribute a great deal to ‘ghost fishing’ in the world’s oceans. This is a phenomenon that occurs when fishing gear is lost at sea, but continues to catch or trap fish. If you were to take a walk down any beach in the world, chances are you’ll run into a rusted and algae-covered pot or trap lying on the beach.

Image: NOAA

Innovations

Simple changes to the design of pots and traps can make a big difference. For example, escape rings and outlets are made to allow non-target fish to escape, while still trapping the target fish. And excluder devices can prevent the non-target species from ever even getting into the trap to begin with.

To prevent larger marine animals such as whales and large sharks from becoming tangled in the rope, fishermen can use weak links on their line, which as with gillnet fishing gear, are designed to break under enough pressure.

Generally speaking, pot and trap fisheries are one of the “greener” methods used around the world.

Still to come:

We will explain 3 more common fishing methods: Purse Seines, Handlines, and dredges.

So far, we have only just begun the journey of where your fish comes from. Next, we dive into the journey of the fish from the boat’s fish-hold, to your dinner plate.

Become a citizen of the world’s oceans today by visiting us at: www.theterramarproject.org

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