
A study has concluded that Stingrays at Grand Cayman sandbanks are stressed (with a subsequent depression of their immune systems making them more prone to disease) by tourists scuba diving with them (
http://www.guardian.co.uk/environment/2009/may/29/wildlife-tourism-stingray)%20even This seems to apply even when the fish are not physically touched. Other studies have suggested that penguins and dolphins (credited in some circles with almost 'mystical' healing powers) can also be stressed by swimming humans, leading to some popular ecotourism venues concluding that allowing these activities is detrimental for the animals that attract visitors in the first place. The situation is not, however, always this simple as some species appear to benefit from the presence of humans (who deter their predators and/or making their feeding more efficient, leaving more time and energy for reproduction). What we really need is proper evaluation in each case.