It’s cownose ray mating season! This is the time of year when I’m frequently asked “What kind of fish is that swimming at the surface with two fins out of the water?”
That fish is a female cownose ray. If one looks carefully, they will see at least one male (often several) following her at a slightly deeper depth. When a female cownose ray displays her pectoral fin tips above water, she is ready to mate.
In Charlotte Harbor, cownose ray mating behavior can occur between October and June, but actual mating usually takes place from April to June.
Female cownose rays have two ovaries, but only the left one is functional. Males have modified pelvic fins called claspers that they use to deposit sperm when mating. During mating, the male bites the female to hold onto her. This often leaves visible wounds along the pectoral fins. Sharks and other rays also exhibit this biting behavior. Don’t worry; the wounds heal quickly.
Unlike the related skates, which lay eggs commonly called mermaid purses, rays give live birth. The gestation period for cownose rays is 11 to 12 months, after which time just one pup is born. Very rarely, a female may produce two offspring.
The cownose ray (Rhinoptera bonasus) is found in coastal and estuarine waters from southern New England to Brazil. In northern climates, cownose rays migrate south beginning around October each year.
Cownose rays can be observed in Charlotte Harbor year-round. This is probably due to our warmer climate. Cownose rays do not do well when the water temperature dips below 60 degrees.
In addition to our year-round population, we also likely see a population increase as migrating cownose rays from the northern Gulf make their way south for the winter. This may explain the very large aggregations we sometimes see.
Cownose rays are pelagic swimmers and can cover considerable ground. However, many tagged individuals from a Charlotte Harbor study exhibited small home ranges and could be observed in these areas for months at a time. This is a good indication that they were finding ample prey items to feed on within their limited home range.
What causes cownose rays to move is unclear, but it’s probably related to prey availability and predator avoidance. If you have nothing to eat or something is trying to eat you, it’s best to leave. This is good life advice for all of us.
Speaking of prey, cownose rays have a diverse diet of invertebrates including bivalves, marine worms, urchins, sand dollars, and a host of other things. Cownose rays eat during the day and at night.
Betty Staugler is the Charlotte County extension agent for the Florida Sea Grant Program. Contact her at firstname.lastname@example.org or 941-764-4346.