If you stroll along the Inner Harbor, you just may see the fins of cownose rays poking through the water.
It’s summer, which means cownose rays (Rhinoptera bonasus) have returned from their Floridian wintering grounds to the Chesapeake Bay. Their plans for the summer: give birth, eat shellfish and mate.
The migratory fish (yes, rays and sharks are fish!) use the Chesapeake Bay and its tributaries as both a nursery and a place to meet local singles. Females arrive in Maryland and, after a nine- to 12-month gestation period, give birth to one or more pups. Before summer’s end, they’ll find a mate and do it all over again. In fact, if you look closely, you might see bite marks on the tips of the female’s fins. That’s because males woo females by nibbling on their fins before the two intertwine and sink to the ocean floor in copulation.
By late August, males head even farther north to live the bachelor life near New England for a few weeks while the females and pups loaf around Maryland. Eventually, the chill of autumn urges the males to regroup with the rest and they all swim back to Florida, completing the migratory cycle. Thousands of rays sometimes group together in “mega-schools” in the open ocean while migrating south, said Jack Cover, general curator at the National Aquarium. But don’t expect to see that many in the Inner Harbor.
Cownose rays have a spotty relationship with the public. Starting about 15 years ago, the migratory animals were accused of hurting the Atlantic oyster industry and subsequently slaughtered en masse. But they’ve since been acquitted of the crime because they reproduce too slowly to have any threatening population booms that would harm oyster harvests. Instead, cownose rays should be welcomed as delightful part-time residents of Baltimore’s harbor, Cover said.
Since rays are not especially sensitive to environmental conditions, their presence does not indicate much about Baltimore’s water quality, Cover said. But the fact that they still come here annually says something positive about the Chesapeake, he said.
If you see a cownose ray, you can log it in the app iNaturalist to help scientists learn more about these creatures.