September 24, 2021 — Longlining, a commercial fishing technique that drags a main line with baited hooks through the water, is convenient when catching massive amounts of swordfish and tuna, but it also traps what experts call “bycatch” — unintended victims that may face dark fates after release back into the ocean.
Sharks are often attracted to and caught on these baited longlines; it’s one of the many culprits behind declining shark populations. Certain rules called “no-take regulations” require fishermen to release some species when accidentally hooked, but a new study of over 300 sharks found that some are much more likely to die after “catch and release” than others. The study was published Sept. 15 in the journal PLOS One.
“The assumption behind no-take regulations is that the shark will swim away and live out its normal life after it’s released, but we know that for some sharks, that’s not true,” study lead author Dr. Nick Whitney, senior scientist at the New England Aquarium’s Anderson Cabot Center for Ocean Life in Massachusetts, said in a news release.
After five years of longline fishing that targeted five of the seven most commonly caught species in the Gulf of Mexico and Florida Keys, the researchers learned as many as 42% to 71% of blacktip and spinner sharks will die after being caught and released alive. Others, such as sandbar and tiger sharks, were more resilient; only 3% or fewer died after release. Bull sharks were also one of the more hardy species. The animals were caught near Madeira Beach, Key West and Naples, Florida.
The team learned 90% of the post-release deaths occurred within five hours of returning to the water, and 59% occurred within just two hours. Blood samples and tracking data revealed the stress of the capture process, or injuries acquired during it, leads to the unnecessary and disproportionate demise of some sharks.