Nature Sightings: Spinner Sharks

Storms passing through over the last week in August and first week of September dropped enough rain to top up our local swamps, vernal pools and freshwater ponds. The rain also seemed to prompt our terrestrial turtle, the Eastern box turtle, out of its summer estivation: Many were seen moving about in search of food.

In terms of interesting nature sightings, the ocean beaches once again stole the show. In addition to the bottlenose dolphins and humpback whales that have been observed cruising along close to shore all summer, many folks witnessed the dramatic aerial displays of spinner sharks last week.

My first sighting of the display occurred at Indian Wells Beach on Friday morning. All I was able to make out were huge splashes far offshore, similar to the plunge dives of Northern gannets but much larger, and no gannets in sight. Possibly due to the low morning light, even with the aid of binoculars I could not discern what was making the splashes.

Later that day, at Atlantic Avenue Beach, I witnessed the same splashes and with binoculars was able to see a large fish or marine mammal leaping clear of the water, spinning along its longitude axis, and crashing back onto the water’s surface.

This was something I’ve never seen before. I assumed I was witnessing a display by bottlenose dolphins. A search on the internet revealed no mention of that behavior for that species, but a very similar behavior noted and videoed for a species appropriately named the spinner dolphin (Stenella longirostris).

According to the NOAA Fisheries website: “Regarded as one of the most acrobatic of dolphins, spinner dolphins are well known for their habit of leaping from the water and spinning up to seven times in the air before falling back into the water.” The site also mentioned that their maximum size is 7 feet, and their distribution is generally limited to warmer tropical and subtropical water, with Long Island being at the extreme northern limits of its range.

Could this be the animal I was seeing? I was not certain, so I reached out to some colleagues who are marine biologists. I also checked in with some of the East Hampton Town lifeguards.

It was lifeguard Jeff Thompson who first suggested that it was, instead, spinner sharks (Carcharhinus brevipinna), followed by an email from East Hampton Town Chief Lifeguard John Ryan Jr., who stated, “We have seen them all summer long. They have been feeding on the bunker all summer. The bunker [are] generally 150 to 200 yards offshore. The spinner sharks rip through the bunker pod. We have not seen any in close, mostly because the bunker has kept its distance from the shore. As long as they keep their distance and continue to feed on the bunker, they pose no threat to our beach patrons.”

NOAA Fisheries biologists Tobey Curtis, who is currently part of the shark research team affiliated with the South Fork Natural History Society, or SOFO, also weighed in: “The SOFO team has been seeing spinner sharks out of Shinnecock since July, chasing bunker nearshore. Greg [Metzger] tagged several of them, including with satellite tags and our fin-cam tag. CBS rode along with Greg a few weeks ago.

“Spinners look very similar to blacktip sharks [Carcharhinus limbatus], but we’ve only confirmed blacktips being caught farther west in warmer water. Only spinners off the Hamptons.”

According to the Florida Museum website, “When feeding, spinner sharks will often swim through schools of baitfish, spinning along their longitudinal axis, snapping at fish as they move through the water toward the surface. When they breach the surface they can be seen spinning in the air — sometimes as much as 20 feet above the water surface.

“They are frequently mistaken for blacktip sharks (Carcharhinus limbatus), as they have a superficially similar appearance. However, spinner sharks grow to a larger size than blacktips and have a distinctly marked black tip on the anal fin (in adults), where blacktip sharks do not.

“The spinner shark is a common species of nearshore waters in temperate and tropical regions. It also occurs offshore as a pelagic species. Although occasionally involved in shark bites on humans, the teeth are adapted for seizing small prey rather than tearing at large prey and therefore usually result in relatively minor injuries.”

This is a new and exciting species for me, and it confirms my belief that ocean lifeguards are an excellent source of information about our marine wildlife! Many thanks to all — ocean lifeguards and marine biologists — who helped me pin down the identification.

To view a video of spinner shark aerial acrobatics, visit: youtube.com/watch?v=-wZ-mWeaj9E.

For a link to the CBS broadcast about SOFO’s groundbreaking shark research, visit: newyork.cbslocal.com/2021/08/06/shark-sightings-south-fork-natural-history-museum-shark-research-and-education-program/.