Sightings of the species are becoming increasingly common as experts worry about danger posed by busy waterwaysA humpback whale was spotted on Thursday swimming in New York’s Hudson River, sparking a social media frenzy.Brad Hoylman-Sigal, president of Manhattan borough, was among those to share a photograph of the whale on Facebook, an image taken on Thursday morning and provided by Gotham Whale, a citizen science and education group that tracks marine mammals.