PLACIDA, FL -- Tagging sharks for research is nothing new. For years, scientists have been logging all kinds of information about shark movements and the types of areas where they like to hang out. And while attaching satellite, streamer and acoustic tags to these top predators, researchers are also able to take DNA, blood and tissue samples for later study.
What is new is the level of detailed information scientists from Sarasota’s Mote Marine Laboratory are getting on the animals’ behavior, physiology and survival after they are caught and released by anglers. The object is to find out the post-release mortality of blacktip sharks – an important species for recreational and commercial fisheries in Florida.
“Nobody has tied the physiology with the behavior, so we’re kind of trailblazing in that respect,” said Paul Anderson, a scientist with the Florida Aquarium in Tampa.
With the help of Port Charlotte light-tackle guide captain Robert Moore, Anderson, Mote staff scientist Nick Whitney and their colleagues have caught 16 blacktip sharks on rod and reel in the Charlotte Harbor area since last fall. Leaving each shark in the water, secured by ropes to keep it still, Anderson draws a small blood sample and immediately puts it into a small field analyzer unit that can spit out results in two minutes.
Meanwhile, Whitney and Mote biologist Jack Morris and college intern Tauras Vilgalys attach an acoustic transmitter tag with a built-in accelerometer. The accelerometer records the animal’s body posture, tail movements, water depth and temperature every few seconds following its release. The tag is set to pop off within a couple of days and transmits a radio signal that enables the scientists to find and recover it using an antenna receiver. They haven’t lost one of the $1,400 reusable tags yet.
The combined information of the shark’s physiology as measured by the lactic acid, carbon dioxide, ph level and other factors in its blood and its post-release attitude and movement as detected by the accelerometer provide a clear picture of the animal’s physical condition and its response to stress.
The scientists are also looking at whether j-hooks or circle hooks contribute to more shark deaths after they are released. The team hopes to tag another 16 animals before their $192,000 NOAA Fisheries research grant runs out this fall.
“It’s amazing how little we know about their post-release mortality,” Whitney said.
He says it’s too soon to draw any conclusions, but the sharks’ swimming movements tend to be “weaker” after they are caught and released.
“We’ve seen a [recovery] range of between a few hours and 12 to 18 hours depending on the individual,” Whitney said.
He said two of their study subjects died after being tagged and released, but he said neither was in great shape when it was first brought alongside the boat.
Fishing with Moore, the scientists have caught sharks on nearly every trip, except when rough weather kept them from venturing into the open Gulf.
Said Whitney: “Rob Moore is on it.”