6 Harmful Overfishing Practices and Types of Gear
As the global population continues to grow, so does our demand for fish-based protein. Developments in commercial fishing have made it easier to harvest fish with advanced gear, but at what cost?
Advancements in commercial fishing technology and gear mean we have the ability to wipe out entire fish populations in a very short period of time. We now face a crisis where 80% of our fisheries are either fully exploited or collapsing. These are the most prevalent and destructive fishing practices in the commercial fishing industry:
1. Longline fishing
A longline is a single, very long fishing line that is dragged behind a boat. It has thousands of smaller branchlines attached, each of which has a baited hook that’s used to lure and catch the target fish. Longlines can be used near the ocean’s surface or the seafloor, depending on the fish being targeted, and can stretch for up to 60 miles.
While they pull massive yields, longlines also easily attract and hook a variety of marine life, including non-target species like seals, swordfish, dolphins, sharks, rays, sea turtles, and seabirds. Even if these marine animals don’t take the bait, they can easily get snagged on a hook or become entangled in the line.
The non-target animals hauled up with the target species are called bycatch and dropped overboard already dead, dying, or gravely injured. Overfishing doesn’t just threaten target species, but any species that can be hauled up as bycatch.
2. Drift netting
Imagine a wall of netting so fine you couldn’t see it until you were caught in it. That’s exactly how drift nets work. Up to 30 feet tall and 30 miles long, a drift net is a free-floating net that’s either deployed in an ocean current or rigged with weights on one side that keep it on the seafloor while buoys on the other side keep it suspended vertically in the water.
These nets are nonselective and produce extremely high volumes of bycatch. This is especially problematic in pelagic fisheries, where dolphins, whales, swordfish, sharks, turtles, tuna, squid, seabirds, and salmon are commonly caught. When these nets are lost or abandoned, they still continue to fish, becoming death traps for all types of marine life in a phenomenon called ghost fishing. Lost and abandoned fishing gear like this account for 10 percent of all ocean litter.
Trawlers drag nets across the bottom of the seafloor to catch the marine life that lives on or near it. Commonly targeted species include shrimp, cod, rockfish, and flounder. Trawling is another unselective type of fishing that produces incredibly high volumes of bycatch. Up to 90% of a trawl’s total catch can be bycatch.
Even more alarming, trawling also damages the seafloor, uprooting vulnerable deep-sea corals, seagrass beds, and other habitats that provide food and shelter to a variety of marine species. The habitat destruction caused by trawling can be permanently damaging to the entire marine ecosystem. An ocean without healthy coral reefs is not a healthy ocean.
A gillnet is a particular type of drift net made from a mesh of monofilament line (like what you’d see on a normal fishing pole), which means fish and other animals can’t see it. The holes in the mesh vary in size depending on the species being targeted, but are designed to be large enough for the just fish’s head to fit through. When a fish is caught, it is trapped by the gills which means it can’t swim forward or backward to escape. These nets can be set at all different depths along the water column.
These nets are also indiscriminate and result in high volumes of bycatch. They entangle much larger, non-target species of marine life up to and including whales. The mesh netting can get caught arounds animals’ heads, fins, wings, and flippers and is so strong that it’s nearly impossible to escape from. Marine mammals drown when they are unable to escape to the surface for air. Animals that aren’t killed outright often suffer infection, mobility loss, or even limb loss when the thin, sharp net cuts into their flesh.
Gillnets are particularly dangerous to bycatch species. For example, gillnets are used in the Sea of Cortez to catch the totoaba fish, whose swim bladder is highly prized for its perceived medicinal value in places like China. However, these gillnets have decimated a species of porpoise called the vaquita. Despite a temporary ban in the small area of water they call home, it’s unlikely this species will recover; there are less than 30 of these animals alive today.
5. Purse-seine nets
Think of a purse-seine net like a lady’s drawstring purse where the pouch is filled up and the top is cinched shut. Now imagine one that’s 18 football fields long and two football fields deep. Fishermen use these nets to capture an entire school of fish in a single haul. Once the school is located, it’s encircled with net and the bottom is cinched, trapping the catch within the net. The net is then pulled alongside or onto the boat where the catch is collected.
A targeted school of fish can attract non-targeted species like sharks, turtles, and dolphins, which means those animals are often hauled in as bycatch. In the eastern Pacific Ocean, for example, dolphins and tuna frequently swim together and some fishermen use purse-seine netting to herd them both into a tight and easy-to-catch unit. While the dolphins are released before the catch is hauled onto the boat, there is still an impact on the dolphins that threatens their ability to recover. Mothers can be separated from calves during this process, which means the calves will die. High levels of stress caused by the chase can also cause female dolphins to abort pregnancies and have reproductive issues in the future. This practice has been banned in the U.S., which is why it’s important to look for dolphin-safe labels on any tuna you buy.
Marine protected areas and sustainable fishing practices can help end overfishing
Because many of these practices and gear are used in the international waters of the open ocean, where no single body has the ability to truly enforce protective regulations and quotas, commercial fisheries are often left to act in their own self-interest, which is rarely what’s best for marine life or the ocean. In the meantime, countries continue to debate the appropriate regulations while stocks continue to diminish and prices continue to rise.
By establishing marine protected areas, we can maintain biodiversity and provide refuge for endangered, overfished, and commercially important species where they can reproduce and grow to their full size, which increases both the size and quantity of catches in surrounding fishing grounds. Ending overfishing is a win for fish, for commercial fisheries, and for global food security.
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