Sharks have been around for more than 450 million years and were well-established when dinosaurs were still the coming thing. As predators, sharks play a vital role in the oceans’ ecosystems by keeping other fish populations in check. Removing that control would have damaging, far-reaching and unpredictable effects on our oceans — the world’s largest and most important ecosystem. Yet in the past 80 years, an estimated 80 percent of the world’s sharks have been killed by the hands, nets and hooks of humans.

All three species of thresher sharks recently were added to the International Union for the Conservation of Nature Red List as vulnerable to extinction. Like many other sharks, threshers are very slow to reproduce. They take eight to 10 years to become sexually mature, and after a nine- to 10-month gestation period yield only one or two pups. They don’t spawn hundreds of eggs, as do some other fish. Despite that, in 2008, more thresher sharks were landed in the Santa Barbara area than in any other area in the United States, according to the California Department of Fish & Game.

The commercial shark fishery started about 1915 and hit its first peak in 1939, when more than 9.3 million pounds of shark were landed on the West Coast of America. The primary target was the soupfin shark, which earned its name from its fins being used to make shark fin soup. The sharks’ liver oil was used to make vitamin A until scientists found a way to produce it synthetically. From 1936 to 1944, more than 24 million pounds of soupfin shark were landed in America. The fishery collapsed in 1945 because soupfins had basically been wiped out. To this day, the population has not recovered.

From 1950 to 1976, commercial shark landings averaged less than 1 million pounds each year until the commercial shark fishery hit its second peak in 1979, when 11.6 million pounds of shark were landed on the West Coast of America. This time, the primary target was the spiny dogfish (actually a shark). The spiny dogfish was used to make fish and chips. In 1979, 9.4 million pounds of spiny dogfish were landed on the West Coast. Spiny dogfish are now on the IUCN Red List as having a high risk of extinction.

The commercial thresher shark fishery peaked in 1982, when more than 2.3 million pounds were landed on the West Coast. Since the early 1970s, scientists (Holden in 1973 and Hanan in 1984) have warned that it’s not possible to sustainably fish threshers or any other elasmobranch species without further research. Despite those warnings more than 40 years ago, thresher sharks continue to be targeted. The research considered imperative for a sustainable fishery has not been conducted. In 2008, 73,400 pounds of thresher shark were landed in the Santa Barbara area, a far cry from the peak in 1982. The majority of the threshers caught were 1 to 2 years old. Since thresher sharks mature sexually at ages 8 to 10, this means that most of the threshers caught didn’t have a chance to reproduce.

Thresher shark meat is sold to restaurants, markets and grocery stores. Shark meat contains unsafe levels of mercury, according to the Food and Drug Administration, the American Heart Association and the Environmental Defense Fund.

Drift gillnets are the method of choice when it comes to commercially fishing threshers, a method that has been responsible for a high number of marine mammal injuries and casualties as the result of bycatch. (Bycatch is a term used to refer to any species caught accidentally while fishing for another species.) Fortunately, electronic pingers have greatly reduced marine mammal interactions.

Bycatch is a huge threat to sharks. According to the Food and Agriculture Organization, there are few fisheries that don’t catch sharks as bycatch, and some fisheries actually catch more sharks than the targeted species. Estimates suggest tens of millions of sharks are caught as bycatch each year.

Longlining, trawling and gillnetting are responsible for most shark bycatch. Mexico and Japan have a joint commercial swordfish effort that is unregulated. The landing reports from these fisheries are inaccurate, so the extent of the bycatch is unknown. Longlines and gillnets are used to target swordfish off Baja, Calif., but a lot of threshers and other sharks end up as bycatch. Many threshers caught in local gillnets have hooks in their mouths, suggesting interaction with Mexican longlines.

Commercial fishing and bycatch are by no means the only threat to threshers. Sport anglers find great thrills in catching threshers. Thresher and mako shark tournaments are held three times a year right here in Southern California.

One big problem with fishing sharks for sport is that there is no way to accurately keep track of how many are being killed. Some shark tournaments require bringing the whole shark back to the dock, but others give the option to catch and release for conservation purposes.

However, in 2007, a collaborative study was initiated by the Pfleger Institute of Environmental Research, the Southwest Fisheries Science Center and the NMFS Southwest Region for Sustainable Fisheries Division to examine the post-release survival of common thresher sharks. In response to the growing recreational fishery for highly migratory sharks, the pilot project used pop-up satellite archival transmitters (PSAT) to study the movement patterns and post-release survivability of rod-and-reel-caught common thresher sharks.

The recovery of a PSAT provided high-resolution temperature and depth data, and determined that one mature female, estimated at 335 pounds, died within 48 hours of release. Preliminary results suggest that capture stress, especially in large individuals, may lead to increased mortality in this fishery. This type of research is long overdue.

Why do we still continue to kill sharks locally? Consider:

» The slow reproductive rate of sharks

» The warnings from scientists about sustainability

» Inadequate management by the Department of Fish & Game, as evidenced by steadily declining landings

» Historically high commercial landings, followed by severe population declines

» Inaccurate sport fishing landing reports, which make impact assessments impossible

» The unknown amount of post catch-and-release deaths

» The inaccurate bycatch estimates

» The inaccurate Mexican and Japanese landing reports

In a few words, we still kill sharks because of consumer demand.

We the consumers need to educate ourselves about the problem and stop this demand. Visit SharkFreeSB.com to view a list of local businesses that sell shark as well as a list of shark-free alternatives. “Think globally, act locally,” is one of its mission statements.

Shark Free Santa Barbara is a local campaign associated with a nationwide campaign, SharkSafeNetwork.com, both created to spread awareness about the importance of shark conservation and to get shark off the menus of restaurants. To help, the Monterey Bay Aquarium started a Seafood Watch Program to help consumers and businesses make choices for healthy oceans. Their recommendations indicate which seafood items are best choices, good alternatives, and which ones to avoid.

Shark meat is under the avoid list with additional warnings about mercury levels. Click here for more information.

— Santa Barbara resident Jonathan Gonzalez is the founder of SharkFreeSB.com.