Please help with 「しじみがとれる」, I'm not yet able to take on walls of kanji in Google search, nor do I know descent Japanese databases to look for idioms and netslang. Thanks.

Finally got this one.

It's Japanese netslang. In this video dude is gathering freshwater clam for TV program. He is sending a message to teenagers, who are recently being said to be unenthusiastic.

松岡修造 said:

「あきれめるなよ、あきらめんなよ、お前！」
Don't give up. Don't give up, guys!
「どうしてそこでやめるんだ、そこで！もう少し頑張ってみろよ」
Why do you quit so easily? Go for it a little more!
「ダメ、ダメ、ダメ、ダメ、あきらめたら」
NO, no, no, no, don't give up!
「周りのことを思えよ、応援している人達のことを思ってみろって」
Look around you. Think about people, who cheer for you.
「あともうちょっとのところなんだから」
You're almost there!.
「俺だってこの-10℃のところ、しじみがとれるって頑張ってるんだよ！」
I'm too doing my best gathering clamp in this -10℃ water!
*The sentence in question
「ずっとやってみろ、必ず目標は達成できる」
Keep on trying! You definetely can achieve your goals!
「だからこそ、ネバーギブアップ！」
So, never give up!

Thanks to an awesome native Japanese speaker, who went trough the pain of explaining all of this to me.