Anderson Cabot Center for Ocean Life at the New England Aquarium
A new study, led by Anderson Cabot Center for Ocean Life at the New England Aquarium scientist Nick Whitney, Ph.D., found that blacktip sharks (Carcharhinus limbatus) have a better than 90 percent survivability rate for recreational catch-and-release fishing in Florida.
A new study, led by Anderson Cabot Center for Ocean Life at the New England Aquarium scientist Nick Whitney, Ph.D., found that blacktip sharks (Carcharhinus limbatus) have a better than 90 percent survivability rate for recreational catch-and-release fishing in Florida. Whitney worked with scientists at Mote Marine Laboratory.
The National Oceanic and Atmospheric Administration’s (NOAA) Marine Recreational Information Program estimates that blacktip sharks are the most commonly captured shark species in the Florida recreational fishery. According to the program, roughly 89 percent of sharks were released alive after capture.
Between September 2011 and April 2013, Whitney and his team caught, tagged, and released 31 blacktip sharks off the coast of Florida. Fitted with so-called acceleration data loggers (ADLs), the 31 tagged sharks provided a total of 838 hours of acceleration data.
“These accelerometers are the same technology found in smartphones, Fitbit™, and other electronic devices that can measure how you’re holding the device, how many steps you take in a day, or how you’re moving your hands while you play a game,” said Whitney.
For sharks, ADLs record every tailbeat and change in body pitch by measuring acceleration on three axes 25 times per second. Depth was also recorded every second. That provided Whitney and his team with more than 6 million data points per shark, per day.
Of the 31 tagged sharks, only three died, a post-release mortality rate of 9.6 percent. All of these mortalities occurred within two hours of release. Using the vast amount of data provided by the ADLs, Whitney and his team determined that, on average, blacktip sharks recovered around 10.5 hours after release. They also found that larger sharks had a significantly shorter average recovery time than smaller sharks.
This was the first study to examine post-release mortality in blacktip sharks.
“Before this study, managers doing population assessments on blacktip sharks had to guess at their post-release mortality rate using data from studies on completely different shark species in different parts of the world,” said Whitney.
This study collected data for up to three days before the ADLs were released, floated to the surface, and could be collected by the scientists. The scientists also observed no at-vessel deaths, which can be as high as 88 percent for blacktip sharks caught by commercial longline fisheries. “This finding suggests that the impact of recreational fishing (on blacktip sharks), is minimal,” said the paper. The mortality rate of less than 10 percent is well below the 20 percent mortality threshold that is considered “unacceptably high” for recreational fisheries.
“Our next step for this work is to move on to other species and fishing methods,” said Whitney. The scientists are currently working with commercial longline fishermen in Florida to study the post-release mortality of several species.
Understanding how species respond and rebound from catch-and-release practices can keep the oceans healthy and help ensure the sustainability of valuable marine species around the globe.