Reading Comprehension

PT103 · S4 · P3 · Q14 Dolphin Die-off

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Between June 1987 and May 1988, the bodies of at least 740 bottlenose dolphins out of a total coastal population of 3,000 to 5,000 washed ashore on the Atlantic coast of the United States.

Topic

The cause of a massive die-off of bottlenose dolphins on the Atlantic coast in 1987–1988.

Framework

Answer / Explain

Main Point

The passage examines why a severe die-off of bottlenose dolphins occurred, presenting a commonly accepted explanation (brevetoxin poisoning from an algal bloom) but ultimately arguing that a sudden increase in synthetic pollutants, such as PCBs, was likely the main precipitating factor, with brevetoxin possibly playing a secondary role. (The “most valuable sentence” is at the end of the final paragraph: )

P1: The Scale and Features of the Dolphin Die-Off

Between 1987–1988, about half the coastal bottlenose dolphins died in an unprecedented event, with affected dolphins showing a wide variety of symptoms, likely due to a massive, opportunistic bacterial infection.

P2: Possible Toxins Identified

Researchers tested dolphin tissues for natural and synthetic toxins, finding brevetoxin from an algal bloom in some, and PCBs—a manmade pollutant—in almost all dolphins.

P3: Brevetoxin Hypothesis

The research team initially concluded the red tide algal toxin (brevetoxin) was the main culprit, as there had been a bloom of this alga in the area. The dolphins’ stressed, emaciated state also likely released more pollutants from their fat, making them even more vulnerable to infection.

14.

The passage is primarily concerned with assessing

  1. the effects of a devastating

    Cause, not Effect

    The passage is about assessing what caused the dolphin die-off, not about assessing its effects.

    4% picked this

  2. the process by which illnesses

    Opposite: correctly diagnosed

    The author was not assessing "the process by which they were correctly diagnosed". The author was assessing "the accuracy of the diagnosis". The author doesn't think that the researchers correctly diagnosed the dolphins.

    4% picked this

  3. the weaknesses in the research

    Wrong Emphasis

    The passage is all about assessing this explanation from the researchers. The main point is the assessment the author offers at the beginning of the 4th paragraph: "this explanation is not plausible". This answer is saying the main point was, "This methodology was not sound".

    12% picked this

  4. Correct

    possible alternative explanations for the

    Why this is right

    This answer is weirdly plural, when there's really only one alternative explanation considered (although maybe the "perhaps from offshore dumping" counts as a 2nd alternative explanation). But it's the only answer that correctly identifies that the passage is assessing what caused the dolphin die-off. The researchers explain the die-off by saying that it was primarily brevetoxin poisoning from a red-bloom, assisted by metabolizing pollutants, and capped off by some opportunistic bacterial infection. The author is considering the alternative hypothesis that it was primarily a sharp uptick in the dolphins' exposure to pollutants, assisted by brevetoxin poisoning.

    Skill tested: Primary Purpose · how this choice captures the passage's function is the move to repeat next time.

    77% picked this

  5. relative effects of various marine

    Out of Scope: relative effects

    This answer is saying that the author named various separate marine pollutants and then ranked their relative effects on dolphin mortality. We might be able to say that PCB and brevetoxin are both marine pollutants. But brevetoxin comes from algae, which is a natural marine organism. It's a stretch of language to call an algal bloom a marine "pollutant". Yes, it changes the chemistry of the water, but the term 'pollutant' is reserved for unnatural additions to an ecosystem (like humans dumping their chemical wastes into the ocean). Also the author isn't assessing their relative effects on dolphin mortality (she says that brevetoxin's effects aren't even really known yet). The author is only assessing whether PCB vs. brevetoxin was the primary culprit in this particular episode of dolphin mortality.

    2% picked this

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