Your recent post about touch tanks reminded me of something I've always wondered: why do the sharks and rays in them actively seek out contact? They don't just seem to coincidentally bump into hands or only go after food, so what makes them want to get touched?
For years, I’ve thought, if I had a research grant, this would be what I would study. The behavior of sharks and rays in touchpools.
Where I was proctoring them, we were taught we could never say that the sharks and rays ‘liked’ the interaction. All the species in the tank were eusocial species by nature - cownose rays live in large schools, and the smaller reef sharks are often found in fairly high concentrations in the wild and go as far as to sleep in piles in the mangrove roots. So, the messaging we were taught was that the rays and sharks didn’t find soft contact with human hands inherently negative because they were used to casual social contact from conspecifics (in contrast to like, solitary pelagic sharks who only get touched by food, mates, or things trying to eat them). As far as messaging went, I liked that way of doing it, because it wasn’t anthropomorphic and it allowed us to do some education about the natural behaviors of our animals while we explained.
Except for that part where, as a behaviorist who ended up spending a lot of time at that touch tank (it was the only one I could work for a period of time when I had an injury I couldn’t get wet) that really obviously wasn’t the whole story. I started noticing the same animals coming to the front repeatedly, and slowing down and rising up under certain hands (generally still, flat, calm, mid-way down the water) while they’d dive deeper under others (generally children’s hands, ones moving a lot, or those that were hovering just out of the water). I watched rays rostrum-bump hands that they’d slowed down under but that hadn’t reached down to pet them, and I watched other rays specifically circle back to a couple of hands multiple times - sometimes to the point of circling back as soon as they were out of reach. There was obviously something going on in terms of preferences and decision making with the fish and the hands they chose to interact with, but no amount of casual observation and anecdotes does a scientifically valid hypothesis make.
Point is, I don’t think we know. I personally believe that in really well designed tanks like the one I worked, where they had a huge amount of non-touch area and depth and current and natural habitat to spend time in, that there was definitely some preference for interaction with hands that behaved a certain type of way. I can’t tell you why and I’ll probably never have the money/time to take over an entire touch tank and quantify that hypothesis, though.