LSAT 103, Section 4, RC Passage 3, Dolphin Die

RC Passage 3 Explanation

Paragraph Summaries

1. A very large number of bottle-nose dolphins died. It seems a weakened population was hit by a deadly bacteria.
2. Brevetoxin and PCBs were found in most dolphins tested.
3. Some say brevetoxin was the likely cause.
4. But it’s unlikely brevetoxin was the cause. It’s more likely that PCBs released by toxic dumping weakened the dolphins.

Analysis

The passage starts with the facts. A large number of dolphins died. The second paragraph introduces two suspects: brevetoxin and PCBs.

The rest of the passage has a simple structure. Paragraph three introduces the researchers’ theory. Unusual amounts of P. brevis algae released large amounts of brevetoxin.

Note that the researchers don’t claim that the algae always harms dolphins. They just say that large algae blooms called red tides are harmful.

The researchers claim that brevetoxin had a few effects. It made the dolphins skinny, and they lost their blubber.

This blubber released PCBs, which further harmed the dolphins. The weakened dolphins were vulnerable to a bacterial infection.

It sounds like a strong case. But in the fourth paragraph, the author shows that it is nonsense. First, the cause (massive algal blooms) occurs without the effect in the gulf of Mexico.

Second, the timing of the algal bloom was wrong, meaning that the effect happened before

the proposed cause.

Third, the author points out that we don’t know the effects of brevetoxin.

Having weakened the argument, the author presents his own theory. A large spill of toxins killed the dolphins. The author never says if bacteria had anything to do with it. The bacterial infection from lines 12-14 was only “suggested”.

It’s a pretty weak alternate theory. There’s no evidence that there was any toxic spill.