应该是are,因为尽管“我”去是在过去,用过去时,但水族馆的鲨鱼始终在那儿的,现在仍在,就像公园里的花,如：
I went to the park with my friends on Sunday and there are a lot of beautiful flowers there.

希望对你有帮助

有found就应该用were,宾语从句时态应该主句一致