Question

goodbye, cod
the atlantic cod was once the mainstay of the united states fishing industry. however, warming of the ocean along the shores of new england has caused the stock of cod to disappear almost completely. according to scientists at the gulf of maine research institute, the gulf of maine is heating up faster than a majority of the rest of the planets oceans. as a result of warmer ocean waters, female cod produce fewer offspring, and these fish are less likely to survive to maturity. even though recreational cod fishing was banned in 2014, and strict limitations were placed on the number of fish commercial fishermen could catch, these measures have not been enough to protect the cod.
what is the main, or central, idea of the passage?
because the gulf of maine is warming unusually quickly, atlantic cod are disappearing.
female cod are producing fewer offspring in the gulf of maine.
because cod used to be abundant in the atlantic, it was once the backbone of the u.s. fishing industry.

Explanation:

The passage starts by stating that Atlantic cod was once the mainstay of the US fishing industry. Then it explains that the Gulf of Maine is warming faster than most of the planet's oceans. This warming leads to female cod producing fewer offspring and the fish being less likely to survive to maturity. Even though there are measures like banning recreational cod fishing and limiting commercial catches, these aren't enough. The overall focus is on the reason for the cod's disappearance (the warming of the Gulf of Maine). The second option only mentions one aspect (fewer offspring) and the third option is about the past (cod being abundant and the industry's past state), not the main idea of why they are disappearing now.

Answer:

Because the Gulf of Maine is warming unusually quickly, Atlantic cod are disappearing.