Reading Practice Set 1
Examining the Problem of Bycatch
1. A topic of increasing relevance to the conservation of marine life is bycatch—fish and other
animals that are unintentionally caught in the process of fishing for a targeted population of
fish. Bycatch is a common occurrence in longline fishing, which utilizes a long heavy fishing
line with baited hooks placed at intervals, and in trawling, which utilizes a fishing net (trawl)
that is dragged along the ocean floor or through the mid-ocean waters. Few fisheries employ
gear that can catch one species to the exclusion of all others. Dolphins, whales, and turtles
are frequently captured in nets set for tunas and billfishes, and seabirds and turtles are
caught in longline sets. Because bycatch often goes unreported, it is difficult to accurately
estimate its extent. Available data indicate that discarded biomass (organic matter from
living things) amounts to 25–30 percent of official catch, or about 30 million metric tons.
2. The bycatch problem is particularly acute when trawl nets with small mesh sizes (smaller
than-average holes in the net material) are dragged along the bottom of the ocean in pursuit
of groundfish or shrimp. Because of the small mesh size of the shrimp trawl nets, most of the
fishes captured are either juveniles (young), smaller than legal size limits, or undesirable
small species. Even larger mesh sizes do not prevent bycatch because once the net begins to
fill with fish or shrimp, small individuals caught subsequently are trapped without ever
encountering the mesh. In any case, these incidental captures are unmarketable and are
usually shoveled back over the side of the vessel dead or dying.
3. The bycatch problem is complicated economically and ecologically. Bycatch is a liability to
shrimp fishers, clogging the nets and increasing fuel costs because of increased drag
(resistance) on the vessel. Sorting the catch requires time, leading to spoilage of harvested
shrimp and reduced time for fishing. Ecologically, high mortality rates among juvenile fishes
could contribute to population declines of recreational and commercial species. Evidence to
this effect exists for Gulf of Mexico red snapper and Atlantic Coast weakfish. Because the
near-shore areas where shrimp concentrate are also important nursery grounds for many
fish species, shrimp trawling could have a profound impact on stock size.
4. Once the dead or dying bycatch is returned to the ecosystem, it is consumed by predators,
detritivores (organisms that eat dead plant and animal matter), and decomposers (organisms
that break down dead or decaying organic matter), which could have a positive effect on
sport fish, seabird, crab, and even shrimp populations. Available evidence indicates that 40–
60 percent of the 30 metric tons of catch discarded annually by commercial fishing vessels,
and even more of the noncatch waste (organisms killed but never brought to the surface),
does not lie unused on the bottom of the sea. It becomes available to midwater and ocean
bottom scavengers, transferring material into their food web and making energy available to
foragers (organisms that search for food) that is normally tied up in ocean-bottom, deep
ocean, midwater, and open-ocean species.
Examining the Problem of Bycatch
1. A topic of increasing relevance to the conservation of marine life is bycatch—fish and other
animals that are unintentionally caught in the process of fishing for a targeted population of
fish. Bycatch is a common occurrence in longline fishing, which utilizes a long heavy fishing
line with baited hooks placed at intervals, and in trawling, which utilizes a fishing net (trawl)
that is dragged along the ocean floor or through the mid-ocean waters. Few fisheries employ
gear that can catch one species to the exclusion of all others. Dolphins, whales, and turtles
are frequently captured in nets set for tunas and billfishes, and seabirds and turtles are
caught in longline sets. Because bycatch often goes unreported, it is difficult to accurately
estimate its extent. Available data indicate that discarded biomass (organic matter from
living things) amounts to 25–30 percent of official catch, or about 30 million metric tons.
2. The bycatch problem is particularly acute when trawl nets with small mesh sizes (smaller
than-average holes in the net material) are dragged along the bottom of the ocean in pursuit
of groundfish or shrimp. Because of the small mesh size of the shrimp trawl nets, most of the
fishes captured are either juveniles (young), smaller than legal size limits, or undesirable
small species. Even larger mesh sizes do not prevent bycatch because once the net begins to
fill with fish or shrimp, small individuals caught subsequently are trapped without ever
encountering the mesh. In any case, these incidental captures are unmarketable and are
usually shoveled back over the side of the vessel dead or dying.
3. The bycatch problem is complicated economically and ecologically. Bycatch is a liability to
shrimp fishers, clogging the nets and increasing fuel costs because of increased drag
(resistance) on the vessel. Sorting the catch requires time, leading to spoilage of harvested
shrimp and reduced time for fishing. Ecologically, high mortality rates among juvenile fishes
could contribute to population declines of recreational and commercial species. Evidence to
this effect exists for Gulf of Mexico red snapper and Atlantic Coast weakfish. Because the
near-shore areas where shrimp concentrate are also important nursery grounds for many
fish species, shrimp trawling could have a profound impact on stock size.
4. Once the dead or dying bycatch is returned to the ecosystem, it is consumed by predators,
detritivores (organisms that eat dead plant and animal matter), and decomposers (organisms
that break down dead or decaying organic matter), which could have a positive effect on
sport fish, seabird, crab, and even shrimp populations. Available evidence indicates that 40–
60 percent of the 30 metric tons of catch discarded annually by commercial fishing vessels,
and even more of the noncatch waste (organisms killed but never brought to the surface),
does not lie unused on the bottom of the sea. It becomes available to midwater and ocean
bottom scavengers, transferring material into their food web and making energy available to
foragers (organisms that search for food) that is normally tied up in ocean-bottom, deep
ocean, midwater, and open-ocean species.
