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Difficulty: MediumIdentifying Unstated Assumptions

To reduce the incidental bycatch of harbour porpoises, maritime authorities plan to require all commercial gillnet fishing vessels operating in the North Bay to install high-frequency acoustic deterrent devices on their nets. These devices emit acoustic pulses that cause porpoises to avoid the immediate vicinity of the nets without scaring away the commercial fish species targeted by fishermen. Authorities conclude that widespread adoption of these devices will result in a sustained decrease in harbour porpoise deaths attributable to commercial fishing in the North Bay.

Which of the following is an assumption on which the maritime authorities' conclusion depends?

  1. Harbour porpoises in the North Bay will not over time become habituated to the acoustic pulses in a way that diminishes the devices' deterrent effect.Answer
  2. B
    Installing high-frequency acoustic deterrent devices is the most cost-effective method available to protect marine mammals in commercial fishing zones.
  3. C
    Commercial fishermen operating in the North Bay currently suffer substantial financial losses due to net damage caused by entangled porpoises.
  4. D
    High-frequency acoustic pulses emitted by the devices will permanently drive targeted commercial fish species away from traditional fishing grounds.
  5. E
    If commercial fishing vessels install these acoustic deterrent devices, total harbour porpoise populations in the region will double over the next decade.

Answer

The argument depends on assuming that harbour porpoises in the North Bay will not gradually become habituated to the acoustic pulses, which would undermine the long-term effectiveness of the deterrent devices.
The conclusion asserts that equipping nets with acoustic deterrents will result in a sustained decrease in porpoise mortality. For this long-term prediction to hold true, the animals must continue to be repelled by the signals over time. If porpoises become habituated to the pulses, the devices will lose their effectiveness, causing the conclusion to fail. Therefore, non-habituation is a required unstated assumption.

Step-by-Step Solution

1
Identify the premises and conclusion of the argument.
Premise: Acoustic devices deter porpoises from gillnets without scaring away target fish. Conclusion: Widespread installation will lead to a sustained decrease in porpoise deaths from commercial fishing.
Understanding the core gap between the intervention (acoustic devices) and the intended outcome (sustained reduction in deaths) is essential for finding the unstated assumption.
2
Apply the Negation Test to candidate assumptions.
Negate the habituation statement: 'Porpoises WILL over time become habituated to the acoustic pulses, diminishing the deterrent effect.'
If the negated statement is true, porpoises will eventually ignore the signals and return to net areas, causing the conclusion of a 'sustained decrease' in deaths to collapse.
3
Confirm that alternative choices represent out-of-scope claims, extreme statements, or premise contradictions.
Claims regarding cost-effectiveness, fishermen's financial losses, fish displacement, or population doubling are either irrelevant, contradictory, or unnecessarily extreme.
An unstated assumption must be strictly necessary for the conclusion to hold, not merely helpful or plausible.

Key Concept

Identifying Unstated Assumptions using the Negation Test
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Topics

Identifying Unstated Assumptions

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