Project Overview

The Atlantic cownose ray (Rhinoptera bonasus) is a type of stingray found in the Gulf of Mexico and along the eastern coasts of North and South America. These rays have a slow-growing population because they only give birth to one baby (called a ‘pup’) per year after a long, 12-month pregnancy.

In the past, cownose rays were blamed for declines in scallop and oyster populations along the East Coast. But there’s little evidence to support that claim. Still, this belief led to a widespread, unregulated culling of cownose rays—including pregnant females—through derbies and other fishing efforts during their breeding season. Because no formal population study has ever been done on this species, we don’t know how much damage this caused.

We know that cownose rays travel long distances each year between Chesapeake Bay and South Florida, thanks to acoustic tracking studies. But very little is known about their movements in the Gulf of Mexico. Our lab has been studying sharks in Apalachicola Bay, Florida, for years, and we’ve found both adult and baby cownose rays during the summer months. With the recent collapse of the oyster fishery in the bay—and a five-year ban on wild oyster harvesting—now is a critical time to learn more about these animals.

In this project, we used acoustic telemetry to follow adult and baby cownose rays in Apalachicola Bay. Our goals were to: 1) Better understand how these rays move around in the Gulf of Mexico, 2) Learn how both adult and baby cownose use different parts of the bay throughout the year, and 3) Compare where they go with how strong their bite is, to see whether they’re truly capable of eating oysters in this region.

Cownose rays have one of the slowest population growth rates of any fish, which means their numbers can’t bounce back quickly if they’re overfished. That’s why it’s so important to understand their movement behavior and habitat needs—especially if there is ever a need to conduct a full population assessment.

One of the biggest gaps in our knowledge is how these rays move and use their environment in the Gulf of Mexico. Since past concerns about their impact on scallop and oyster fisheries led to mass killings along the East Coast, we need solid science to understand whether cownose rays actually pose a threat to oysters in Apalachicola Bay—before similar actions are considered in the future.

As part of this project, we also collected and tested genetic samples of all rays caught, because a nearly identical species—the Brazilian cownose ray (Rhinoptera brasiliensis)—was recently found to overlap in geographic range with the Atlantic cownose ray (Rhinoptera bonasus). Confirming whether these two species are overlapping in the bay will allow managers to make smarter, more effective decisions for cownose conservation and management.

Resources

• Does habitat use change with age for cownose rays?
• Apalachicola Bay: an important ecosystem for Florida’s cownose rays?