I saw the following sentence, and am wondering whether "mistake" should be replaced with "mistook."
Plastic bags have been found in the guts of dead sea turtles, which mistake them for jellyfish.
I'd appreciate your help.
The present tense is used, among other things, for general statements. Plastic bags have been found; this is something that has happened, so it is in the present perfect. Sea turtles in general think that carrier bags are jellyfish and try to eat them, so that is in the present tense.
This isn't to say that you couldn't use the past tense, in which case you would be saying the particular turtles that the bags were found in had mistaken them for jellyfish. Just that there is no problem with it being the present tense - to make it a general statement about sea turtles and plastic bags.