An 11-day slow zone advisory expires today just off the coast of Ocean City, after serving its purpose of protecting endangered right whales as they passed through local waters.

The advisory cautioned all boats to travel at 10 knots or less in these zones and required it for vessels 65 feet or longer.

North Atlantic right whales are one of three species of right whales. With a “critical” designation, they are the most endangered of the three, according to International Union for Conservation of Nature (IUCN).

Boat collisions and fishing line entanglements are the leading cause of serious injury and mortality for the right whales, said Allison Ferreira, public affairs officer for the National Oceanic and Atmospheric Administration.

“Right whales travel at the surface of the water and they’re black, so they’re hard to see,” Ferreira said. “These slow zones enable — if the vessel does hit a right whale going at 10 knots or less, the whale is more likely to survive.”

Ferreira said the advisory zones are triggered by a certain number of right whales in a given area, which is common this time of year as they migrate south.

According to Kate Shaffer, rehabilitation manager at the National Aquarium in Baltimore, the North Atlantic right whale isn’t just the most endangered species of right whale, it’s among the most endangered of all large whale species, with less than 400 individuals remaining.

“The most recent population estimate is 336 individuals, which is the lowest estimate in over 20 years,” she said. “After years of slow steady growth, the population has been in decline since 2010.”

Shaffer attributed this trend to an “unusual mortality event,” in which 50 whales in the last five years have died or been seriously injured. Calving numbers have also dipped in that time.

The full range of the North Atlantic right whale in the western Atlantic Ocean spans from the coast of Florida in the cooler months all the way up to Greenland in warmer months.

Right whales migrate between their feeding and calving areas, Shaffer said. Mothers spend a few months in the calving areas while their young nurse and grow before migrating back north.

While they’re passing right off the Ocean City coast, seeing a right whale is incredibly rare. But other whales are a different story.

“There has not been a confirmed right whale sighting in Ocean City since 2007,” Shaffer said. However, you can spot other whales from Ocean City beaches regularly. The most common species we document are humpback, minke and fin whales.”

A Massachusetts-based research center monitors acoustic buoys off the coast, including one near Ocean City, which detect several species of baleen whales, Shaffer said. The local buoy detected right whale calls this year.

Those acoustic buoys are now used to determine where the NOAA slow zones are placed.

“Just because we don’t see the whales from shore doesn’t mean they are not traveling through the habitat,” Shaffer said.

This story appears in the print edition of the OC Today on Nov. 19.

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