I have had the good fortune, or bad, to work with captive sea lions as an animal keeper and veterinarian for 30 years. They are quick learners if some kind of negative reinforcement is immediately paired with what they are doing, but it has to be consistent and immediate. So, if everyone could do something aversive the minute they swiped a bait from us, they would do the math and learn not to do it. However, they are really good mathematicians and always weigh odds and cost benefit. If they steal bait successfully 50 times and have something unfortunate happen once, they keep doing it. The problem with causing some unpleasant physiological event for them by giving them a "treat" (I could name some possibilities) in a fish is that it takes too long to take effect. It is like having tacos at Robertos. They taste fine, you're sick later, but you might not attribute the sickness to Robertos, so you keep going back.
