Self-study
P1
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. █████ ████ ██ ███ ████ ███████ █████ ██████ ███████ ███ ███████ ████████ ███ ██████████ ██████ ███████ ██ ███████ ██ ███ ██████████ █████ ███
Phenomenon ·
Almost a thousand dolphins washed ashore dead
Presumably many more died and didn't wash ashore. What caused this?
Phenomenon Details ·
Skin lesions; internal lesions in the liver, lung, pancreas, and heart
Evidence of massive opportunistic bacterial infection of already weakened animals.
P2
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Phenomenon Details ·
Autopsy found presence of brevetoxin and PCBs (synthetic pollutants)
P3
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Hypothesis ·
Brevetoxin poisoning
Causal Mechanism ·
Alga bloom, toxin, stress, release of synthetic pollutants, bacterial infection
Unusual bloom of P. brevis resulted in toxin accumulation in fish which was then eaten by dolphin. Dolphins then metabolized blubber which reduced their buoyancy and insulation and released synthetic pollutants (PCBs). This provided opportunity for bacterial infection which ultimately caused death.
P4
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Critique ·
No die-off in Gulf of Mexico; timing and location mismatch; brevetoxin effects unknown
Red tides are common in Gulf of Mexico but no dolphin die-off there; dolphins began dying in the north in June yet red tide bloomed in the south in October; effects of brevetoxin on dolphins are unknown.
Alternative Hypothesis ·
Exposure to synthetic pollutants
Sudden influx of pollutants triggered a cascade of problems in dolphins already heavily laden with PCB poisoning which is known to include symptoms like impaired immune system, impaired liver function, and skin lesions, all of which were observed.
Passage Style
Critique or debate
Phenomenon-hypothesis (RC)
21.
Which one of the following ███████ ██ ██████████ █████ ██ ████████████ ██ ███ █████████ ██████ ██ ████ ████████ █████████ ██ ███ ████████
a
the dolphins' diet
Only the researchers’ theory involves the dolphins’ diet.
b
the presence of ██ ██████ ██ ███ ████ ██ ██████
Neither theory involves the Gulf of Mexico. The author only brings up the Gulf of Mexico to make the point that the researchers’ theory is probably wrong. But her alternative theory is squarely focused on the Atlantic coast, just the like the researchers’ theory.
c
the wide variety ██ ██████ ████████ ██ ███ ███ ████ █████ ██ ███████ ████
Only the researchers’ theory involves the red tide bloom.
d
the presence of █████████ ██████████ ██ ███ █████████ ██████
Stated. Both theories say synthetic pollutants contributed to the dolphins’ deaths. In the researchers’ theory, brevetoxin caused the dolphins to digest their own blubber, which released the synthetic pollutants already stored in that blubber,
e
the bacterial infection ██████ ██ █ ███████████ ███████ ██ ███ █████████ ██████ ███████
Only the researchers’ theory points to immune failure and bacterial infection. In the author’s alternative theory, it’s ambiguous whether these factors played any part in the dolphins’ deaths. The author just refers to “