I ate mostly shrimp at the sushi restaurant today.
Shrimp was pretty much all I had at the sushi restaurant today.
どちらも「今日は海老のお寿司ばかり食べた。」という言い方になります。
海老ばかり食べたけど、他のお寿司も少しは食べたというニュアンスもあります。
1) I ate mostly shrimp at the sushi restaurant today.
「寿司屋で主に海老を食べた」
mostly で「主に」
2) Shrimp was pretty much all I had at the sushi restaurant today.
「寿司屋で食べたのは海老がほとんどだった」
pretty much で「ほとんど」
ご参考になれば幸いです!