A mother spinner dolphin and a calf.

Whether it’s off Kealakekua Bay on the island of Hawaii or along the Napali Coast on Kauai, dolphin-watching excursions have become a popular attraction, giving visitors the chance to see spinner dolphins leap and spin in their natural habitat.

The spinner is the most commonly seen dolphin in Hawaii’s waters. But a new study showing fewer calves among a spinner dolphin population is raising more concerns about how human activity may be affecting the marine mammals.

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Dolphin tourism, including boat watching tours and swimming excursions, has increased dramatically in the past several decades, and scientists have long questioned whether those experiences come at a cost. One 2018 study found that spinner dolphins off the island of Hawaii were exposed to human activity, such as being approached by kayakers, swimmers and boats, for nearly 83% of their daytime, which they largely spend resting. And “if disturbed during daylight hours they can become stressed, fatigued and less effective at hunting and reproduction,” according to Hawaii Marine Animal Response.

Part of spinner dolphins’ vulnerability has to do with........

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