Difference between よく + verb, and verb + ことが多い


> アザラシは寒い海にいることが多い動物です。  
>  The アザラシ is an animal that often lives in cold seas.

I'm not entirely sure that 'often' is the right translation here. How does
this sentence differ in meaning/nuance from:

> アザラシは寒い海によくいる動物です。




In your specific case, 寒い海にいることが多い and 寒い海によくいる are interchangeable, and they
both mean "to be often seen/found in cold waters." (Note that these sentences
do not mean individual earless seals often migrate from cold waters to other
places.)

In general, ～ことが多い and よく are not always interchangeable. ～ことが多い means:

  1. often; frequently 

>     * 日曜日はテニスをすることが多い。 I often play tennis on Sundays.

  2. there are many things to ～ 

>     * 日曜日はすることが多い。 I have lots of things to do on Sundays.

よく also means several things depending on the context:

  1. often; frequently 

>     * 彼はバナナをよく食べる。 He often eats bananas.
>     * ここでタクシーをよく見る。 I often see taxis here.

  2. well; much; intensively 

>     * 彼はよく食べる。 He is a good eater.
>     * あのタクシーをよく見ろ。 Look at that taxi carefully.

That said, I think よくいる and いることが多い are almost always interchangeable.




In your specific case, 寒い海にいることが多い and 寒い海によくいる are interchangeable, and they
both mean "to be often seen/found in cold waters." (Note that these sentences
do not mean individual earless seals often migrate from cold waters to other
places.)

In general, ～ことが多い and よく are not always interchangeable. ～ことが多い means:

  1. often; frequently 

>     * 日曜日はテニスをすることが多い。 I often play tennis on Sundays.

  2. there are many things to ～ 

>     * 日曜日はすることが多い。 I have lots of things to do on Sundays.

よく also means several things depending on the context:

  1. often; frequently 

>     * 彼はバナナをよく食べる。 He often eats bananas.
>     * ここでタクシーをよく見る。 I often see taxis here.

  2. well; much; intensively 

>     * 彼はよく食べる。 He is a good eater.
>     * あのタクシーをよく見ろ。 Look at that taxi carefully.

That said, I think よくいる and いることが多い are almost always interchangeable.

