NEW YORK - "WHALE AT ONE O'CLOCK!"

Eager cruise passengers zipping around New York's southern shores rush to the starboard bow: a humpback whale is up for air, a breathtaking sighting set against Manhattan's iconic skyline.

Such scenes are no longer uncommon in the city's waterways, sparking excitement for animal lovers but also forcing new policy efforts to protect whales venturing into one of the busiest port regions in the United States.

Once hunted to near extinction, the rebound of humpback whales is considered among the conservation movement's greatest success stories.

And a growing cohort of mostly juvenile humpbacks are thriving off New York's coast, where food is now plentiful.

"People fly to different parts of the world to go on safari, and what I think a lot of people don't realize is that the marine safari is right out here," said Carl LoBue, New York oceans director at The Nature Conservancy.

The marine scientist who grew up on nearby Long Island told AFP that in the past, whale sightings were an "incredibly unusual event."

LoBue now spots the marine mammals basically every time he's out on the water. He generally sees humpbacks but sometimes other species, including the still critically endangered North Atlantic Right whale.

The new normal is "spectacular," he said.

"I never thought that I would see whales like this off the coast of New York."

- Cleaner water, climate change and more fish -

Humpbacks were once mainly migratory visitors, traversing the New York Bight -- the marine region that extends off the city, Long Island and New Jersey -- while travelling between foraging grounds further north and breeding areas in the Caribbean.

But more recently, a confluence of factors has made New York's coast less of a highway and more of a stomping ground.

One is the resurgence of whale populations thanks to government action, including the Endangered Species Act, as well as a cleaner habitat supported by air and water protections.

Another is the existence of relatively new statutes that support growing schools of the Atlantic menhaden, an oily fish with a variety of industrial uses like commercial bait and omega-3 supplements.

It is also a staple for whales, dolphins and seabirds.

Humpbacks, which can grow to the size of a large city bus, can feast on some 3,000 pounds (1360 kilograms) of fish a day.

Climate change also plays a role in the surge of New York-area whale sightings.

Warming waters are impacting baitfish distributions, encouraging whales to stray from tradition to find food, said Chris St. Lawrence, a naturalist who conducts whale-watching tours and also works for Gotham Whale, a marine research organisation that tracks whales in the Bight.

When Gotham began formally monitoring in 2012, they had just five whales in their catalogue.

Today, St. Lawrence said the organisation sees 80 to 100 unique whales annually, and just identified its 500th individual whale seen around New York City since tracking began.

Some routinely put on a show: NYC0318, a whale also seen by AFP on a recent outing, often charms whale watchers with sensational lunge-feeds, breaching the water and prompting shrieks of delight.

- Maritime traffic dangers -

Gotham is able to distinguish between the animals largely thanks to "fluke prints": whales have unique patterns on the underside of their tails, similar to human fingerprints, St. Lawrence explained.

But many whales are also identifiable by their scars, including from collisions with everything from tankers, cargo and cruise ships to fishing boats and recreational vessels.

While New York offers bountiful food, it also hosts heavy maritime traffic, posing fresh threats to the whale population.

In 2016, humpbacks in the New York area were delisted as endangered, but just one year later the US National Oceanic and Atmospheric Administration (NOAA) declared an "Unusual Mortality Event" along the Atlantic coast.

The designation under the US Marine Mammal Protection Act tracks unexpected die-offs and triggers investigation. For humpbacks, it remains in effect.

Vessel strikes and entanglements are leading causes of whale deaths, according to advocacy groups and government trackers worldwide.

Just this month, New York Governor Kathy Hochul signed the Whale Awareness Act, which requires integrating marine mammal protection efforts and education into state boater safety courses and vessel registration.

LoBue has worked to develop educational materials, including an online course that teaches seafarers how to recognise whale behaviour, report sightings and avoid collision.

He noted that even the most seasoned fishermen "didn't grow up driving boats around whales because they didn't used to be here."

"We're all needing to learn some new skills," he said.

"Nobody wants to hit a whale."

• by Maggy Donaldson (AFP)