Effects of Trawling and Dredging on Seafloor Habitat (2002) / Chapter Skim
Currently Skimming:
5 Analyzing the Risk to Seafloor Habitats
5 Analyzing the Risk to Seafloor Habitats
Pages 48-56
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From page 48... ...
New research also might be required to clarify uncertainties, especially those about indirect effects on the resource species, on other parts of the ecosystem from which benefits could be derived, and on the response of the fisheries to new regulations as, for example, if disturbance of benthic spawning grounds by trawling led to a subsequent decline in fish recruitment. The slowed recovery of the exploited fish population could secondarily affect populations of prey species, and the continued decline in the catch could change the economic incentives of the fishery.
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From page 49... ...
~ ' 1 l l l Risk Characterization = population density x mortality per tow x tow frequency l J 49 The second method described here is comparative risk assessment. This method compares several types of risks and allows evaluation of the effects of a variety of stressors as opposed to a single stressor on seafloor habitat.
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From page 50... ...
Exposure assessment involves calculating the overlap between the spatial distribution of fishing effort and the nontarget species. At this stage we can distinguish between sensitivity (an organism's innate ability to withstand physical damage)
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From page 51... ...
Recognizing the practical impossibility of setting and monitoring compliance of reference points for every nontarget species in a community, the International Council for the Exploration of the Sea Working Group on Ecosystem Effects of Fishing Activities proposed the development of reference points for highly vulnerable indicator species (International Council for the Exploration of the Sea, 2000~. That proposal assumes that the documented conservation of a set of highly vulnerable nontarget species gives a high probability of also conserving other, less vulnerable, nontarget species.
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From page 52... ...
. The method is described below, both with a hypothetical case study for application to bottom trawling using criteria and scales adapted from the Houston Foresight Project and with a real-world example used in the Alaska groundfish environmental impact statement.
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From page 53... ...
Increased sediments and nutrient loads result in reduced light penetration; episodic hypoxia; a change in primary producers from benthic to planktonic organisms, increased incidence of toxic algal blooms, and sediment covering portions of the reefs. Uncertainty.
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From page 54... ...
Alternative 5 would shift fishing effort and its associated habitat effects from bottom trawl gear to fixed gear. Increasing socioeconomic benefits would increase the risk to benthic habitat because of greater bottom trawling effort.
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From page 55... ...
. nonllvmg substrates by bottom trawl gear Modification of 1nonllvmg substrates by fixed gear Much more removal/damage to HAPC biota Amount of bottom trawl effort is more than 25 percent greater than status quo Amount of fixed gear effort is more than 25 percent greater than status quo Marginally more removal/damage to HAPC biota Amount of bottom trawl effort 10 to 25 percent greater than status quo Amount of fixed gear effort 10 to 25 percent greater than status quo Same level removal/damage as status quo Same (+/- 10 percent)
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From page 56... ...
SOURCE: National Marine Fisheries Service, 2001a.
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