The watchers identify the whales by their tail flukes, which are as unique as human fingerprints.
In the last decade or so, Gotham Whale has spotted up to 100 whales a year.
Before 2018, it only spotted 10 to 30 a year.
Experts say the warming ocean temperatures in New England and Canada push humpbacks and other species further south to our area.
"Every whale documented is another giant step toward understanding and protecting the remarkable wildlife living just beyond New York City's skyline," said Gotham Whale Board Vice-President, Paul "PJ" Sieswerda.
The milestone is significant for the region and highlights the importance of whales in the ecosystem.
The New York City Humpback Whale Catalog (NYCHWC) was founded in 2012 when Gotham Whale began collecting whale sightings reported by local boaters and members of the public.
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