Sustaining Marine Fisheries (1999) / Chapter Skim
Currently Skimming:
3 Fishing and Marine Ecosystems
3 Fishing and Marine Ecosystems
Pages 36-63
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From page 36... ...
Fishing is a major activity that can selectively remove large portions of animal populations and also significantly alter trophic interactions. Fishing gear that drags the bottom at times, such as bottom-trawls, pots, and longlines, can alter marine habitats, especially benthic or reef habitats.
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From page 37... ...
For example, it is hypothesized that overfishing, habitat changes, and changes in water quality associated with the removal of oysters from Chesapeake Bay (Rothschild et al. 1994, Lenihan and Peterson 1998)
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From page 38... ...
REMOVAL OF HERBIVOROUS FISHES FROM CORAL REEF ECOSYSTEMS One of the more dramatic ecological effects of removing herbivores, including fishes, from an ecosystem has been described by Hughes (1994) , Jackson (1997)
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From page 39... ...
. Otters consume these animal species, many of which are of recreational or commercial significance and clearly play a critical role in the structuring and organization of nearshore marine ecosystems.
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From page 40... ...
Other Ecosystem Effects of Fishing in the Philippines The Philippines were the first among Southeast Asian countries to develop a modern bottom-trawl fishery immediately after World War II. This fishery grew quickly, as did the pelagic fishery, which relied mainly on boats using light sources to attract fish into nets, and a coral reef fishery using a variety of mostly destructive methods, notably the persistent muro-ami technique of pounding reefs to scare fish into surrounding gillnets.
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From page 41... ...
(1994) reviewed the literature on worldwide bycatch and discards and concluded that marine discards in the period 1988-1990 amounted to approximately 27 million t per year, roughly one-third as much as the total marine capture fisheries.1 There is great variation in bycatch associated with 1Bycatch and discards are extremely difficult to estimate precisely, in part because they often are illegal or unregulated activities.
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From page 42... ...
For example, the red snapper (Lutjanus campechanus) taken in the Gulf of Mexico shrimp fishery presents a convincing example of how bycatch losses can affect a valuable nontarget species.
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From page 43... ...
Important finfish species included halibut and other flatfish species, especially yellowtail flounder (Pleuronectes ferrugineus) , haddock, and cod.
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From page 44... ...
The Bering Sea Recent declines of many populations of marine mammals and birds that live in and near the Bering Sea, a semienclosed basin of the North Pacific Ocean between Alaska and Russia, have attracted attention and have been attributed by many to the effects of fishing. The National Research Council recently reviewed the information (NRC 1996a)
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From page 45... ...
One issue that needs resolution is the effects on marine ecosystems of populations of marine mammals as they recover from very heavy exploitation. Baleen whales eat zooplankton and thus compete for food with many commercially important fish species; toothed whales eat fish and squid and thus compete directly with humans for food.
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From page 46... ...
The relatively simple community structure of the Barents Sea ecosystem is easily destabilized. Even in "simple" systems, interactions among species and the role of environment are complex and initially unpredictable.
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From page 47... ...
, large populations of krill (planktonic crustaceans, mainly Euphausia superba) , formerly large populations of whales, and some commercially valuable fish species.
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From page 48... ...
Finally, Merrett and Haedrich examined the community structure of various marine ecosystems and noted that many shallow ecosystems have several top predators other than human fishers -- for example, marine mammals, large sharks, and large birds. In such ecosystems, humans are competitors with those predators.
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From page 49... ...
Lenihan and Peterson (1998) described the degradation of oyster reefs caused by oyster-dredging in Chesapeake Bay and North Carolina's Neuse River, and showed that the physical degradation interacts with water quality to cause the observed pattern of oyster
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From page 50... ...
The major and closely related issues relevant to this study are the potential of mariculture to supplement marine capture fisheries and its environmental effects. Mariculture (excluding plants)
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From page 51... ...
. Nonetheless, it seems safe to say that the potential for present practices to supplement marine capture fisheries should be carefully evaluated wherever it is being used or proposed.
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From page 52... ...
Natural4 environmental changes have been implicated in several examples of changes in marine ecosystems, some of them described earlier in this chapter (e.g., the Bering Sea, the Barents Sea)
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From page 53... ...
concluded that a strategy is needed to protect ecosystems and encourage the natural regeneration of lost salmon habitat. Salmon productivity in the Pacific Northwest appears to be correlated with large-scale environmental changes in ocean circulation, temperature, and chemistry (NRC 1996b)
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From page 54... ...
. ENSO events can have dramatic effects on fish populations.
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From page 55... ...
Because the impacts do not act alone, we discuss here three ecosystems -- Chesapeake Bay, the Laurentian Great Lakes, and San Francisco Bay -- that have been subjected to numerous significant human impacts and environmental changes. Although the Great Lakes make up a freshwater system and Chesapeake Bay and San Francisco Bay are semienclosed estuaries, some people have argued that their condition represents a preview of the fate of the larger, more open marine ecosystems discussed earlier in this chapter.
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From page 56... ...
Other populations have proved remarkably resistant to damage from heavy exploitation by commercial and recreational fishers, most notably blue crabs (the dominant species in terms of harvest value) and menhaden (the dominant finfish species in terms of weight of catch)
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From page 57... ...
have invaded the Great Lakes in the past, severely affecting the native pelagic fish species. A combination of biocides to kill larval sea lamprey, fisheries for alewife and rainbow smelt, and artificial propagation of lake trout and Pacific salmon have been used to rehabilitate native populations and provide sport fisheries.
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From page 58... ...
. Runoff from the western slopes of the Sierra Nevada Mountains flows into the San Joaquin and Sacramento rivers and then into the San Francisco Bay and the Pacific Ocean.
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From page 59... ...
. Superimposed on this massive alteration of the San Francisco Bay estuary by human action are patterns of periodic major perturbations of the operation of the bay ecosystem in response to wide interannual variations in rainfall that affect salinity gradients.
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From page 60... ...
At present, there are 164 known introduced species of plants, invertebrates, and fish in San Francisco Bay, many of which have displaced native species (Cohen and Carlton 1998)
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From page 61... ...
Despite a gradual decline in striped bass populations, the sports fishery was still valued at $45 million in 1985. The populations in San Francisco Bay have continued to decline (California Fish and Game Department 1997)
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From page 62... ...
. Endangered Fish Species Several fishes are endangered in the San Francisco Bay estuary.
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From page 63... ...
In addition to fishing, anthropogenic impacts and environmental changes continue to occur and are important. Anthropogenic impacts, which include contamination with toxic and other chemicals, habitat alteration and destruction, and introduction of exotic species, can be identified and in some cases managed.
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