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Difficulty: MediumNecessary Assumption

To combat the invasive lionfish damaging local marine ecosystems, coastal authorities introduced a financial bounty for every lionfish captured by recreational divers. In the twelve months following the program's implementation, the number of lionfish recorded during standardized visual surveys of the local reefs decreased by roughly 40 percent. Based on this decline, officials concluded that the bounty program successfully motivated divers to catch enough lionfish to significantly diminish their overall population in the area.

Which one of the following is an assumption required by the officials' argument?

  1. The decline in the number of lionfish spotted during the visual surveys was not primarily the result of the lionfish altering their behavior to evade the increased presence of divers.Answer
  2. B
    The financial bounty was the only factor that contributed to the reduction of the lionfish population during the twelve-month period.
  3. C
    A majority of the recreational divers in the coastal region actively participated in capturing lionfish for the bounty.
  4. D
    The recreational divers who captured the lionfish were already experienced in hunting invasive marine species before the bounty was introduced.
  5. E
    Standardized visual surveys are the most accurate method currently available for estimating marine population sizes.

Answer

The argument requires assuming that the decline in lionfish spotted during surveys was not primarily the result of the lionfish altering their behavior to evade divers.
The argument relies on a shift from observed data (fewer lionfish seen during visual surveys) to a factual conclusion about population size (fewer lionfish exist). For this logic to hold true, the officials must assume that the drop in sightings accurately reflects a drop in actual numbers, rather than a mere change in the animals' behavior, such as hiding from the increased diving activity.

Step-by-Step Solution

1
Identify the main conclusion of the argument.
The officials conclude that the bounty program successfully motivated divers to catch enough lionfish to diminish the population.
Understanding the exact claim being made is the first step in finding the logical gap.
2
Identify the premises supporting this conclusion.
A bounty was introduced, and subsequently, visual survey sightings of lionfish decreased by 40 percent.
Premises represent the evidence provided to support the conclusion.
3
Locate the logical gap between the premises and the conclusion.
The evidence is about a drop in 'sightings' (lionfish recorded during visual surveys), but the conclusion makes a definitive claim about a drop in the 'actual population'.
An argument is vulnerable where its evidence does not perfectly match its conclusion.
4
Evaluate the correct option using the Negation Test.
Negating the correct option yields: 'The decline in sightings WAS primarily the result of lionfish altering their behavior to hide.' If this is true, the population didn't necessarily drop, destroying the officials' conclusion.
A necessary assumption is one that, if proven false, completely undermines the argument.

Key Concept

Applying the Negation Test to identify a 'Defender' assumption that rules out an alternative explanation for the observed evidence.
Estimated Time:1m 45s
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Topics

Necessary Assumption

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