YOU SAID:

I haven't seen many dolphins in the past six years.

INTO JAPANESE

過去6年間、イルカを見たことがありません。

BACK INTO ENGLISH

I haven't seen dolphins in the last 6 years.

INTO JAPANESE

私は過去6年間イルカを見ていません。

BACK INTO ENGLISH

I haven't seen dolphins for the last 6 years.

INTO JAPANESE

私は過去6年間イルカを見ていません。

BACK INTO ENGLISH

I haven't seen dolphins for the last 6 years.