Project

Does habitat-use change with age for cownose rays?

Species
  • Rays & Skates
Years funded
  • 2021
Status
  • Active
Project types
  • Conservation
  • Research
Description

Ashley is catching cownose rays to tag them with an acoustic transmitter. With this information, she can passively track where these rays move throughout their different life stages using the network of listening stations established in her research area. Ashley works in Apalachicola Bay, a large and highly productive estuary in the northeast Gulf of Mexico that is also a biodiversity hotspot and federally-designated National Estuarine Research Reserve. Her study on the movement patterns of these rays, which are highly migratory and vulnerable to overfishing, comes at an important time after an unregulated fishery has led to the population’s collapse.

Does habitat-use change with age for cownose rays?

Ashley Mackenzie Dawdy

Project leader
About the project leader

Fifteen years ago I visited the Georgia Aquarium on opening day and began using it as my window into the underwater world. Looking into the eyes of elusive species that I may never otherwise have a chance to see drew me into finding out more about them. While working in various aquariums, I have gained invaluable experience educating visitors of all ages about a diverse assemblage of marine species and have enjoyed innumerable exchanges about what we as humans can do to become conscious marine stewards and support efforts to protect the earth’s aquatic ecosystems. These conversations...

PROJECT LOCATION : Florida, USA
Project details

Ontogenetic Changes in Habitat Use of Cownose Rays in Apalachicola Bay, Florida

Key objective

The main objective of this study is to define the spatial use habits of cownose rays (Rhinoptera bonasus) in Apalachicola Bay, Florida, in effort to provide the opportunity for effective species management while guiding efforts in local oyster restoration projects.

Why is this important

The Atlantic cownose ray is highly migratory and vulnerable to overexploitation. It has become difficult to manage this species due to limited behavioural data in the Gulf. The historical implication in the collapse of several fisheries led to an unregulated cownose ray fishery with immeasurable population effects. As oyster restoration is becoming heavily pursued, now is a crucial time to launch a ray movement study to clearly define the potential interaction occurring between rays and oysters.

Background

Cownose rays are an extremely vulnerable species, due to the fact that it takes them 4-5 years to mature and then only give birth to one pup each year. These factors considered, it takes the population a long time to recover after instances of decline. While detailed movement studies of this species have been conducted along the eastern US coast, movement and space use data for Gulf of Mexico individuals are limited, contributing to the fact that no official stock assessment has ever been conducted. As key life-history traits differ between populations in the Atlantic and Gulf, it is likely that behavioural differences in space use and movement also exist. There are no existing data regarding seasonal residency or movement of cownose rays in Apalachicola Bay. However, it is likely that they are affected by fishing pressure from shrimp trawls during their seasonal window of bay use.

Cownose rays are considered mesopredators, primarily eating hard-shelled invertebrates such as clams and oysters, and are preyed upon by larger species of sharks. Reports of cownose rays depleting commercial oyster stocks in Chesapeake Bay, although challenged in the literature, led to the creation of a large and unregulated cownose ray fishery as pushed for by commercial fishermen, dubbed the ‘Save the Bay, Eat a Ray’ campaign. Lacking an official stock assessment, impacts from this fishery were immeasurable, which is particularly jeopardizing for a species so vulnerable to overexploitation. Crucial data gaps regarding spatial use and migratory habits are dangerous to let linger, especially in highly migratory mesopredators that are interacting with several different ecological habitats over different life stages.

Aims & objectives
  • Define the extent of seasonal habitat use of Apalachicola Bay by cownose rays, including the timing of when they enter and exit the bay each year. This information will fill in data gaps that inhibit species management.
  • Identify changes in core habitat preferences and space use of cownose rays over various life stages to guide future management strategies and commercial oyster fishery restoration efforts. Defining changes in proportions of habitat use between seagrass, oyster, and mud habitat in the bay as individuals age will give a rough idea of the potential prey items they are eating at different ages.
  • Determine if and to what extent Brazilian cownose rays are using the bay habitat and whether these species are mating with each other. The Brazilian cownose ray is another ray species that looks externally identical to the Atlantic cownose ray. We only recently discovered that the geographic range of these two species overlaps, which introduces management concerns for each species. It is important to identify whether both species are present in the bay, and if so, genetic analysis will reveal whether these closely related species are having mating interactions. This information is critical to inform biologically accurate stock assessments in the future.