Swimming with dolphins is a very popular tourist attraction, but it may be time to give the animals a break. The National Oceanic and Atmospheric Administration (NOAA) is preparing to propose regulations that could ban swimming with Hawaii spinner dolphins.

Scientists are concerned that swimming with dolphins causes harm to the animals, as they are nocturnal and often come inshore - where they are corralled by tourists - to rest after foraging for food all night.

Hawaii's spinner dolphins primarily feed on fish and small crustaceans that surface from the ocean's depths at night. This way they avoid predators, such as tiger sharks, that they would otherwise run into and compete with during the day.

Allison Alterman, who likes to swim in the ocean for exercise near her home on Hawaii's Big Island, notes that the dolphins "come into the shore to rest and it doesn't seem like they're able to do that because they're surrounded."

With stricter regulation, the NOAA could ban swimming with Hawaii spinner dolphins or prohibit people from shallow bays when the dolphins are resting.

"Disturbing their resting behaviors can actually affect their long term health and the health of the population," said Ann Garrett, the assistant regional administrator of the National Marine Fisheries Service's protected resources division for the Pacific Islands. 

The Marine Mammal Protection Act prohibits harassing dolphins, but swimming with them falls into a grey zone under the law. To ensure the animals' safety, tour operators are taught to watch for the signs indicating dolphins are settling into their rest state, explained Claudia Merrill, co-owner of Dolphin Discoveries in Kailua-Kona on the Big Island.

For example, when spinner dolphins swim slowly and are seen occasionally surfacing for air, they may actually be sleeping or resting. In order to keep breathing they remain partially awake, allowing only half of their brain to sleep at a time. One key indication the animals are settling in for a nap is when a pod synchronizes its dives and swims. 

Current rules protecting dolphins from human swimmer are very loose. For instance, only some tour operators follow guidelines that local tours have established. This includes avoiding four of the area's dolphin resting bays between 10 a.m. and 2 p.m. Merrill added that she knows of only three out of 12 Kona coast tour operators that stick to that time table.

The NOAA plans to propose new rules in June, which could affect over 200 dolphin-related businesses operating in Hawaii, in addition to recreational swimmers and other ocean users.