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Difficulty: Very hardIdentifying Underlying Assumptions

Historical records from 19th-century oceanic expeditions indicate a 40 percent decline in sperm whale sightings along the North Atlantic migration route between 1840 and 1860. Marine historians attribute this decline exclusively to overharvesting by commercial whaling fleets operating in the region. However, archival logbooks from active whaling vessels during those decades reveal that the average catch yield per vessel remained entirely constant throughout the twenty-year period. Which of the following statements represent necessary assumptions upon which the marine historians' argument depends? Select all that apply.

  1. The total size of the commercial whaling fleet active along the North Atlantic migration route did not decrease substantially between 1840 and 1860.Answer
  2. The reduction in whale sightings was not primarily caused by oceanic environmental shifts that prompted sperm whales to alter their migration routes away from customary observation zones.Answer
  3. C
    Natural mortality rates of sperm whales due to apex predator attacks in the North Atlantic increased markedly between 1840 and 1860.
  4. D
    Whaling vessels operating along the North Atlantic route employed navigation techniques that were technologically superior to those used in other ocean basins.
  5. E
    The observed decline in sperm whale sightings occurred strictly within the North Atlantic and was absent in all other global ocean basins during the same timeframe.

Answer

The correct assumptions are that the total size of the commercial whaling fleet did not decrease substantially, and that the reduction in sightings was not primarily caused by whales altering their migration routes due to environmental shifts.
The argument concludes that commercial overharvesting was the sole cause of reduced sightings despite steady per-vessel yields. For this conclusion to hold, total harvest must not have dropped (requiring that overall fleet size did not collapse) and reduced sightings must reflect actual population drops rather than behavioral spatial shifts away from observation zones. Negating either statement invalidates the conclusion.

Step-by-Step Solution

1
Deconstruct the argument structure
Premise: Sightings along the route dropped 40% between 1840 and 1860, but catch yield per vessel remained constant. Conclusion: Overharvesting by commercial whaling fleets was the exclusive cause of the decline in sightings (and population).
Identifying the explicit premises and conclusion is essential before evaluating unstated assumptions.
2
Apply the Negation Test to fleet size trends
Negating the statement regarding fleet size yields: 'The total fleet size DID decrease substantially.' If fleet size fell dramatically while per-vessel catch stayed constant, total whales harvested fell, undermining the conclusion that overharvesting drove the decline.
A necessary assumption must break the conclusion when negated.
3
Apply the Negation Test to migration path shifts
Negating the statement regarding migration routes yields: 'Environmental shifts DID cause whales to alter their migration routes away from observation zones.' If whales simply moved elsewhere, sighting drops reflect spatial redistribution rather than overharvesting depletion, destroying the author's causal claim.
Ruling out alternative explanations for reduced sightings is logically required for a claim of exclusive causation.

Key Concept

Identifying Necessary Assumptions via the Negation Test
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Topics

Identifying Underlying Assumptions

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