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    1. What We Do
      1. Reducing Impacts
        1. Fishing
          1. Bycatch
            1. The Issue

Bycatch victims

An enormous number of different marine species are caught as bycatch. Many do not survive and low reproductive rates make many species especially vulnerable to bycatch related mortalities.

Some of the most affected animals include:

The good-will and expertise of fishermen are part of the solution to the bycatch problem. These gentle giants need fishermen to be part of the collective effort to save them for our grandchildren to see.

Carlos Drews, Regional Marine Programme and Species Coordinator for WWF's Latin America and the Caribbean Programme

Marine turtles

Leatherback turtle (<i>Dermochelys coriacea</I>) caught in a net off the coast of Sao Tome and Principe. Thousands of sea turtles are caught (and killed) by accident each year.
Modern marine turtles arose in the oceans over 100 million years ago, yet over the past 100 years numbers have dropped dramatically. Hundreds of thousands of these ancient reptiles are caught each year as bycatch, especially on longlines, in shrimp trawlers, gill nets and purse-seine nets. As many as 50% can die as a result.

Bycatch deaths are believed to be among the main causes of the drastic decline of Pacific leatherback turtles, whose numbers have reduced by 90% since 1980 to as low as 2500 females in the eastern Pacific Ocean.

While there are uncertainties about the precise, relative contribution of bycatch to global marine turtle declines, it is beyond any doubt that turtles cannot sustain current bycatch rates. Global longline fisheries, for example, caught more than 250,000 endangered loggerhead turtles and critically endangered leatherback turtles in 2000.

More on marine turtles

Cetaceans

Vaquita (<I>Phocoena sinus</I>) killed in a fishing net, Gulf of California, Mexico.
With over 300,000 small whales, dolphins, and porpoises dying each year from entanglement in many types of fishing gear, bycatch is causing one death every 2 minutes and is the single-largest cause of mortality for small cetaceans. While large whales can usually break free, entanglement can nevertheless cause debilitating injuries and eventual death.

Bycatch reduction may make the critical difference in the fight to save 9 of the 15 cetacean species or populations classified as endangered or critically endangered. These include New Zealand’s maui’s dolphin, Mexico’s vaquita, North America’s north Atlantic right whale, the Philippine’s irrawaddy dolphin, Europe’s harbour porpoise, and South America’s franciscana dolphin.

More on whales and dolphins

Young fish

Discard from trawl, Gahiramatha, Orissa, India.
Vast numbers of juvenile fish, including the young of commercially valuable species, are caught in many fisheries around the world, only to be discarded as they are under-size. Most do not survive. Even those that are small enough to escape through the net can die as a result of injuries/stress.

This loss of fish contributes to over-fishing and hampers the recovery of already depleted fish stocks. For example, the North Atlantic cod fisheries, once some of the most productive on the planet and which played a pivotal role in the economic and social development of the northern hemisphere are now being pushed to the brink because cod juveniles and spawning adults are killed in nets that target other fish

Seabirds

Several species of albatross and petrel are killed in longline fishing operations in the Benguela Current ecoregion.
Many seabird species are victims of bycatch, particularly albatrosses, petrels, shearwaters, and penguins. Around 300,000 seabirds drown each year after diving for bait set on longlines and becoming hooked.

Such deaths threaten 26 species, including 17 species of albatross, with extinction. Tens of thousands more seabirds die in drift nets, trawls nets, and gillnets. Seabirds also die after hitting trawl warps (the rope that attaches the net to the boat) often while feeding on fish offal discharged from on-board fish processing.

 

Sharks

Juvenile shark in gillnet. Mafia Island, Tanzania.
Bycatch accounts for about half of global shark catches. Longlines are mostly responsible, but bycatch in nets is also important. In the Pacific Ocean alone, 3.3 million sharks are caught each year as bycatch on longlines. Indeed, in terms of numbers, sharks are the most significant bycatch species in the world’s major high seas fisheries. They are also particularly vulnerable to over-fishing due to their relatively slow reproductive rate, with several species showing recent drastic declines.

Blue, hammerhead, shortfin, mako, thresher, and great white sharks are among the species most affected by bycatch. In the north east Atlantic Ocean, for example, 89% of hammerhead sharks and 80% of thresher and white sharks have disappeared in the last two decades as a result of bycatch. Deep-water sharks are also increasingly at risk.

More on sharks

Corals

Smashed and dead cold-water coral fragments in a trawling ground on the Norwegian continental shelf.
Bottom trawling is responsible for most coral bycatch. Such bycatch particularly threatens cold-water coral reefs which are extremely slow growing and so cannot recover easily from even one trawler pass.

Large amounts of such corals are caught / destroyed: 40 tonnes per year in the North Pacific Ocean, for example, with over 2,000 tonnes taken around the Aleutian Islands alone between 1990 and 2002.

Even though the technology to trawl on cold-water corals has only existed for a couple of decades, the damage is already widespread. On heavily fished seamounts off southern Australia, 90% of the sea bed where cold-water coral used to grow are now bare rock, while 30-50% of cold-water coral reefs off Norway have been damaged or destroyed, most likely by trawling equipment.

More on coral reefs

Invertebrates

Bycatch
Enormous numbers of starfish, crabs, sea urchins, brittle stars, mollusks, sponges, worms, and other bottom dwelling creatures are caught by bottom trawlers and dredgers targeting shrimp, Nephrops (Norway lobster), scallops and fish such as plaice and sole.

North Sea bottom trawl fisheries, for example, have been estimated to discard up to 150,000 tonnes of invertebrates annually. This is having a dramatic affect on the ecosystem of the seafloor and altering this balance may well negatively impact commercial species which prey on bottom living invertebrates.

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