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)
14.
The passage is primarily concerned ████ █████████
a
the effects of █ ███████████ █████████ █████████ ██ ████████ █████ ██████████ ████████
The author isn’t trying to assess the effects of anything—she’s assessing the cause of the dolphin die-off. The bacterial infection is just part of one theory on how the die-off occurred. It’s unknown whether there really was a bacterial infection, and the author’s interested in assessing two different hypotheses on exactly what caused the die-off.
b
the process by █████ █████████ ██ ████████ █████ ██████████ ████████ ████ █████████ █████████
Two problems. The author doesn’t suggest that the dolphins were ever correctly diagnosed—in fact, she rejects the explanation given by the research team that investigated the die-off. She also doesn’t discuss the research process much at all, other than to note that the dolphins were examined and tested for toxins. And she accepts the results of those tests without any assessment or critique. What she does assess, meanwhile, is the explanation the researchers offer to account for what those tests showed.
c
the weaknesses in ███ ████████ ███████████ ████ ██ ███████ ███ ███████ ███████
Two problems. Yes, the author exposes weaknesses in one hypothesis for the dolphin die-off, but she doesn’t end there. She goes on to propose an alternative hypothesis. This tells us that her purpose isn’t just to critique the first hypothesis—it’s to find a better explanation. Also, her critique of the first hypothesis isn’t over its methodology. She doesn’t discuss methodology much at all, other than to note that the dolphins were examined and tested for toxins. And she accepts the results of those tests. Her critique is all about the explanation offered to account for what those tests showed.
d
possible alternative explanations ███ ███ ███████ ███████ ███████
The author assesses two alternative explanations—the brevetoxin hypothesis in P3 and the synthetic pollutants hypothesis in P4—in an effort to account for the cause of the die-off.
e
relative effects of ███████ ██████ ██████████ ██ ███████ █████████
The author doesn’t compare how deadly one pollutant is compared to another. Rather, she’s trying to find the correct cause of a single, large case of dolphin mortality. She does consider the kinds of effects that different pollutants can have on dolphins, but she doesn’t draw up a comparison between their relative effects—she just matches up the dolphins’ observed condition with the possible pollutant-based causes of that condition.