From November through March, humpback whales migrate into Banderas Bay to breed and give birth, and the waters around Sayulita become one of the more reliably productive spots on the Pacific coast for watching them. The peak is January and February, when sightings are common enough that most tours offer a money-back guarantee.
Several operators in Sayulita run whale-watching tours from the beach, typically lasting two to three hours. Boats head out into the bay and look for the characteristic blow and breach of humpbacks; encounters often include breaching, tail-slapping, and sometimes mothers with newborn calves. Dolphins are an almost constant companion on the crossing, and occasional encounters with Bryde's whales and orcas add variety.
The same boats often double as Marietas Islands tours and fishing charters — it's worth asking around the beach front to compare what each operator offers before booking. Tours are best in calm morning conditions; afternoon sea breezes can make the return trip rough.