It's a bit strange construction in English. The word "these" implies that specific dolphins are indicated. If I don't see them, then I wouldn't normally say "these dolphins. These" implies dolphins that I do see, unless it's some sort of situation where, "I hear these dolphins, but I don't see them." Normally, if I don't see dolphins, I wouldn't even know that there are any dolphins present at all, so the word "these" would not apply.
Imagine you are at an amusement park, looking through the glass of a dolphin tank . On the glass, on the side, there is a short description, illustrated by a few photographs. However, you can't see any dolphins through the glass, because they are currently being fed on the top, or something like that. So you point at the pictures and say: "I do not see these dolphins."
Bad example. You're implying the positive representation of "these dolphins" by the photos and description on the side of the tank. So in that context, specific dolphins (or types of dolphins) are represented. If your example didn't contain any description or any photos, then the ambiguity of the dolphins would be represented by "any dolphins." Even using the word "those" implies specific dolphins in that case. In an empty aquarium, you wouldn't say "I don't see these/those dolphins." Which dolphins? There are none. It's ambiguous. The proper statement would be, "I don't see (any) dolphins."
Alik made sure to include "a description with photos at the side of the aquarium." That provides the context for WHICH dolphins. In that case, "I don't see those dolphins."
In my scenario, there is no description or photos depicting any dolphins. You and I just walk up to an empty aquarium. I would say "I don't see dolphins." Or, "I don't see any dolphins." There was no context provided in order to refer to SPECIFIC dolphins. So if you say to me, "I don't see those dolphins," I would answer "What dolphins are you talking about?" this/that implies specificity
Good point. The better argument is that the absence of something is not indicated by affirmative indicators "these" or "those." It probably would make better sense in Polish, too, to change from the negative to the positive.
Widzę tych delfinów. "I see those dolphins." If this exercise's purpose is to teach negation, then the Polish sentence should be
Nie widzę delfinów.