Question

the main, or central, idea of the passage is thanks to conservation efforts, florida manatee populations have increased. how does the detail in bold develop the main idea?
the florida manatee, a subspecies of the west indian manatee, is a large ocean mammal found in floridas rivers and coastal areas. unfortunately, the states population of manatees has dwindled significantly over the years. although the manatee has no natural predators, humans have contributed to many manatee deaths, mainly through boat collisions. the loss of warm - water habitats has also hastened the manatees decline. aerial surveys performed in the early 1990s found an estimated 1,267 manatees in florida. because of conservation efforts by several organizations, however, the number of manatees has rebounded recently. the creation of manatee protection zones—areas that boaters must avoid or drive through more slowly—has been particularly effective. as a result of these efforts, more than 6,000 manatees are found in florida today.
it highlights a successful conservation strategy.
it anticipates a potential flaw in conservation strategy.

Explanation:

The bolded detail "the creation of manatee protection zones—areas that boaters must avoid or drive through more slowly—has been particularly effective" shows a specific conservation measure (protection zones) that worked. This directly supports the main idea that conservation efforts led to an increase in manatee populations. It is a positive example of a conservation strategy (not indicating a flaw as there's no mention of problems with the zones).

Answer:

It highlights a successful conservation strategy.