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Indiscriminate Slaughter at Sea

Audubon Society
Posted 18th May 2003

The Bycatch Problem

Indiscriminate fishing gear and unsustainable fishing practices unnecessarily and adversely affect the health of the marine environment by exacerbating the problem of over fishing and slowing or preventing the recovery of depleted fish stocks and other marine life. Massive numbers of unwanted species, juvenile or undersized individuals, and other marine wildlife are unintentionally caught and killed everyday. The resulting carnage is called "bycatch" or more appropriately "bykill.” Globally, the level of waste that is described by the term bycatch is staggering: more than 20 million metric tons (44,100,000,000 lb.) annually.

1 Roughly one-quarter of the annual global catch of marine fish, and more than four times the entire catch of U.S. fishers, is inadvertently killed and thrown back into the ocean as bycatch. To put this figure in perspective, the 44.1 billion pounds of marine life caught and discarded annually around the globe as bycatch is equivalent to the weight of 98,000 Statues of Liberty, or 60 Empire State buildings! This wholesale destruction of marine ecosystems has grave implications for the future health of the oceans. Ultimately, for animals caught as bycatch there are two possible outcomes: the animal either lives or dies. The unintentionally caught animal may be landed, in which case it is removed from the ecosystem, or it may be discarded. If discarded alive, there is no guarantee the animal will survive. Discarded animals which initially survive an encounter with fishing gear may die immediately afterwards or be weakened to the point where they are more vulnerable to disease or predation by other animals.

2 Depending on the species discarded and the type of fishing gear involved, survival rates can be as low as zero. Roughly 80% of the billfish discarded in the Gulf of Mexico and off the east coast of Florida by the U.S. commercial longline fishery die as a result of being caught and discarded.

3 Bycatch and dead discards can result in decreased levels of abundance, reduced spawning potential, and a diminished yield from fish stocks.

4 Over fishing and unsustainable fishing practices have depleted fish populations and destroyed fisheries around the globe. In recent years the worldwide catch of wild marine fish has stagnated at between 80 million and 85 million metric tons annually, despite large increases in fishing capacity. The reason: the seas are being stripped clean faster than they can replenish themselves. The Food and Agriculture Organization of the United Nations reported that by the early 1990s, 70 percent of the world's important commercial fish species were fully exploited, over exploited, depleted, or recovering from depletion. In the United States, more than 80 percent of marine fish populations that have been evaluated are classified as fully fished or overexploited.

5 What Is Bycatch?
In lay terms, bycatch is the unintended catch of animals associated with commercial fishing operations, the vast majority of which is discarded back into the ocean already dead or dying. Bycatch is pervasive the world's fisheries. It includes undersized or juvenile fish of targeted species as well as non-target species of fish, turtles, marine mammals, birds, and other wildlife. Bycatch is not inherent to all fishing efforts, it is the result of indiscriminate fishing gears, such as longlines and driftnets, and destructive fishing practices such as fishing in areas known to have large numbers of juvenile fish (nursery areas and spawning grounds).

Most damaging are non-selective gear types -- those that cannot target specific species of fish -- which catch and kill a huge volume and variety of marine species annually. Shrimp trawls around the world stand out as the fisheries with the highest bycatch and discard weight per landed target catch weight. However, high bycatch rates pervade most fisheries around the globe creating biological and economic waste of tremendous proportions.

The Hawaiian longline fishery for swordfish and tuna catches over 100,000 sharks annually as bycatch -- more than half are now killed as a result.

6 In 1996, the commercial U.S. Atlantic longline fishery discarded an estimated 40,000 dead juvenile swordfish because they were undersized.

7 In November 1996, the U.S. Northeast Atlantic drift gillnet fishery was closed on an emergency basis because of the threat it posed to endangered northern right whale populations. The fishery remains closed.
There are clean fisheries -- fisheries with low bycatch rates -- which use selective types of fishing gear or appropriate techniques. The Western Pacific pole and line fishery for tuna limits bycatch to less than one percent of total catch, and harpoon fisheries for swordfish and giant tunas have almost no recorded bycatch.

8 However, these fisheries are the exception rather than the rule. Bycatch associated with selective fishing gear generally consists of undersized or juvenile individuals of target species. Undersized or juvenile fish are often discarded either because of minimum size requirements or because the fish are not as economically valuable as their larger counter parts. Unfortunately, much of the bycatch ends up just as dead as the target species of fishes which are landed.

The solution is not to simply retain and use more of what is caught as bycatch, which would reduce waste, but do nothing to halt the emptying of the oceans. Rather, for species adversely affected by bycatch, such as sharks, sea turtles, whales, and other depleted species, the solution is to reduce bycatch rates and mortality by reducing encounters and increasing the survival rates of encountered wildlife, while managing fisheries based upon the biological imperatives of the most vulnerable species.

The Consequences of Bycatch

Bycatch has significant negative implications for the health and productivity of a fishery. Bycatch is particularly damaging in fisheries that are being overfished -- catching fish at a rate faster than they can be replaced -- or in fisheries that are already depleted. In slow-growing, rare, or less-productive fish stocks, even low discard rates can have significant impacts.

Scientists are increasingly concerned with the effects of bycatch, including the removal of large quantities of juvenile and non-target species. Sexually immature fish of both target and non-target species comprise a particularly destructive form of bycatch. Killing juvenile fish prior to spawning not only removes the individual fish from the ecosystem, it also squanders the reproductive potential of that fish. Killing too many juveniles slows or prevents the rebuilding of depleted stocks and contributes to diminished yields from healthy stocks.

The importance of bycatch is that mortalities of animals, whether intended or not, can threaten population, ecosystem, and fishery sustainability.

9 Atlantic blue and white marlin populations are a good example of a species being devastated as a result of being caught as bycatch. Atlantic marlin populations, which are not commercially targeted by U.S. commercial fishermen, have been reduced to only 23% of the level needed to achieve maximum sustainable yield (MSY).

10 Over 500,000 pounds of marlin and 150,000 pounds of sailfish were discarded dead by the U.S. Atlantic longline fishers in 1996. In the two year period 1995-1996, the U.S. commercial longline fishery in the Atlantic Ocean, which does not target marlin, caught and discarded well over 1.1 million pounds of dead marlin -- all caught as bycatch.

11 The problem is compounded by foreign longline vessels which catch an additional 23 million pounds of marlin Atlantic-wide.

Giant Ocean Fish

Particularly hard hit by the problems associated with bycatch are the ocean's depleted giant fishes. Giant ocean fish -- the sharks, swordfish, billfish, and tunas -- are among the most unique fishes in the marine environment. These top predators are long-lived and highly migratory -- capable of migrating over vast distances -- sometimes crossing entire oceans. Bycatch of these species contributes to the problem of their over fishing and slows or prevents rebuilding of their populations.

The Emptying of the Oceans

Atlantic swordfish populations are in free fall, down 42%, and still declining as a result of targeted effort and bycatch.

12 Six out of ten swordfish currently caught in Atlantic U.S. commercial fishing operations are juveniles that will never have the opportunity to spawn and replenish the stock. Additionally, more than 40,000 juvenile swordfish were discarded dead into the Atlantic in 1996 by U.S. commercial fishers.

13 Juvenile swordfish mortality is a leading cause of stock declines and retards the recovery of the stock.

In 1996, for every 22 swordfish caught in the California drift gillnet fishery, one whale or dolphin was killed as bycatch. For every swordfish caught, nine other fish were caught, including on average, 3 sharks with a majority of these fish being discarded dead.

14 Atlantic blue and white marlin populations are down 77%, and are still declining as a result of domestic and foreign bycatch and directed fisheries.

15 U.S. commercial fishermen do not target Atlantic marlin, yet over 1.1 million pounds were discarded dead by the U.S. in the period 1995-1996. Depending on the area in which they are caught, between 50 and 80% of Atlantic marlin caught as bycatch by U.S. commercial longliners die. The species is depleted and being overfished as a result of being caught as bycatch.

Bycatch may cause more damage to shark populations than any other species. First, sharks' life histories (slow growth, late sexually maturity -- some sharks don't reach sexual maturity until age 21 -- and small litter size), make them particularly vulnerable to over-exploitation. Second, the majority of the global catch of sharks -- 30-70 million killed each year -- is taken as bycatch. Atlantic large coastal shark populations are down over 50% (some species down 80% or more) and may still be declining as a result of targeted effort and bycatch.
Western Atlantic bluefin tuna populations are down 87% as a result of targeted effort and bycatch.

16 Over fishing has been halted for the time being, but the stock remains severely depleted with bycatch retarding the recovery of this species. Eastern Atlantic bluefin tuna are also severely depleted. The catch of large fish as well as juveniles contributes to over fishing.

Gear Used in Fisheries for Giant Ocean Fish

Bycatch is not a consequence of the nature of fishing. It is a consequence of indiscriminate fishing gears and fishing practices. Many fishing gears and methods do not discriminate between commercially valuable fish and those that are too small to eat or sell, fish of limited commercial value, or fish that are illegal to keep. Some fisheries, including those for tunas and swordfish, have particularly high rates of bycatch. Multiple types of fishing gear are used in the capture of highly migratory species, some of which are indiscriminate and highly damaging to the marine environment. It is important to note that with all gear, where, when, and how the gear is deployed are all important factors in determining the level of bycatch. Common fishing gear types used in fisheries for highly migratory species include drift longlines, drift nets, purse seines, and rod and reel.

Drift Longlines

Drift longlines are indiscriminate killers. Any animal large enough to bite the baited fist-sized hook is captured whether or not it is commercially valuable, juvenile or adult, targeted or unwanted. Longlines are used around the globe and primarily target high value swordfish and tuna. Each year drift longlines unintentionally kill marine mammals, threatened sea turtles, seabirds, and tens of thousands of billfish, sharks, juvenile swordfish and tunas, many of which are discarded. In the Atlantic longline fisheries for swordfish and sharks, longlines kill 7 species of skates and rays, 38 species of coastal sharks, 9 species of pelagic sharks, 12 species of tunas and billfishes, 22 other species of fishes, 3 species of sea turtles, 8 species of seabirds and three species of whales and dolphins.