Scalloped hammerhead

CORROBORATION IMPROVED. Two independent sources now support a cold-upwelling hammerhead season, though they disagree on extent: ZuBlu gives March-November with Sep-Nov strongest, Alor Underwater Explorers gives a Sep-Dec pelagic season. Encoded to the overlap plus the stronger claim. Still no research literature located, so this remains a commercial-consensus claim rather than a verified one. Do not book Alor solely for this.

Dec-Mar is the rainy season: visibility drops and some resorts reduce or suspend operations, though there is no formal closure. Apr-Aug is the calm high season with 30-40m+ visibility, best for photographers and first-timers. Sep-Dec is the pelagic season with stronger currents and colder water. The two 'best' windows serve different divers, which is the useful thing to know.

Present year-round with reported increases in the cooler Feb-Apr window. Schooling behaviour here is less consistent than at Cocos or Galapagos.

RESOLVED BY TIER 1. CONANP, the Mexican protected-areas authority, states the tourist diving season as November to June, 07:00-18:00, with a park fee of $3,760 MXN per person per day. That corrects the commercial sources, which variously gave Nov-May and Nov-Jun/Jul. Encoded Nov-Jun open, Jul-Oct closed. The closure is operational and regulatory, not biological: mantas, silvertips and dolphins are resident through it.

Present year-round; schooling behaviour peaks in the Jun-Oct rainy season, which is also when visibility is at its worst. That trade-off is the central booking decision for Cocos and most operators do not spell it out.

Liveaboards run year-round; there is no closed season. The seasonal split is a quality trade rather than an access one: Jun-Oct rainy season gives the best hammerhead schooling and the worst visibility (9-20m), Dec-May dry season gives up to 30m visibility and less consistent schooling.

Present year-round at Darwin and Wolf. Schooling behaviour is reported strongest in the warm season (Dec-May); the reason for the aggregation is still debated in the literature. Note this cuts against the common assumption that the cold season is uniformly better for big animals.

Open year-round with no closure; the split is a quality trade, not an access one. Cool season (Jun-Nov) means whale sharks, big-animal density, cold water and rough seas. Warm season (Dec-May) means calmer water, better visibility, more hammerhead schooling and more comfortable diving. Liveaboard permits are capped, so availability rather than weather is the practical constraint.

El Bajo. The historic schooling aggregation was heavily reduced by fishing in the 1980s-90s and sightings are reported as increasing again. Encoded 'shoulder' not 'peak' in the best months, because the reputation runs ahead of the current reality.

Diving runs year-round, but Los Islotes, the single biggest draw, is closed 1 June to 31 August for sea lion breeding. That is a hard site closure inside an otherwise open destination, which is why Jun-Aug reads 'limited' rather than 'open' or 'closed'. Hurricane season overlaps the same window.

Jan-Mar reported as the peak window, at depth in the passes.

Open year-round; the sharks do not have a season. Nov-Apr is the wetter, warmer, more humid half with more rain and occasional cyclone risk, and May-Oct is drier. Neither closes anything.

Daedalus, typically deep and on the first dive of the day.

Sources disagree on whether this is a closure or just bad weather. Some operators list the itinerary as running year-round; others describe winter wind limiting access to the offshore sites, and the Egyptian marine park has historically restricted Brothers and Daedalus in the winter months. Encoded 'limited' for Dec-Feb rather than 'closed' because the evidence does not support a hard closure. See OQ-29. Note the tension in the two arrays: the best shark months (Jun-Nov) are not the best condition months (Mar-May, Sep-Nov). Low operating

Described as occasional with no season given. Encoded unreliable in all months rather than inventing a window.

Trips run year-round but the crossing is the constraint: 20 hours of open ocean each way means the Coral Sea leg is dropped or rerouted in weather far more often than the sheltered Ribbon Reefs are. Dec-Feb is cyclone season in the region, hence 'limited'. Low operating

Jan-Mar schooling off Irizaki. Single source for the window; no research literature located. Unbaited.

No formal closure, but two separate limiting periods. Jan-Mar is the hammerhead window and also winter: north-east monsoon wind cancels a high proportion of days, so you can book a week and dive twice. Jul-Sep is typhoon season in the Ryukyus. This is the sharpest example in the dataset of the thing you came for and the conditions that let you see it being in direct opposition. Low operating