Numerous shark species share the oceans with humans but for how long?
The numbers are “Jaws”-dropping: More than 100 million sharks killed each year. One billion pounds of shark fins imported annually into China alone – for soup. Of the 390 known species of shark, 110 classified as endangered, threatened or vulnerable.
The long, slender blue shark, plying Southern California waters, can reach 13 feet long.The last number may actually be higher, but scientists say they don't know enough about many sharks' biology or circumstances to say for sure.
That uncertainty extends to many of the sharks – and their cousins, the skates and rays – living off of the coasts of Southern and Baja California. Some of these creatures, from the notorious great white shark to the communal bat ray, reside or pass within wading distance of millions of people each day, but they remain shadows in the sea.
“Virtually nothing is known about local shark populations,” said Jeffrey Graham, a marine biologist at Scripps Institution of Oceanography. “We have a few ideas about mako and thresher sharks because they have some commercial importance. We can count how many get caught. But we have very little knowledge about anything else, especially south of the border where few species are quantified. We don't know how many of these animals are out there, or even where they are.”
To remedy the situation, Graham and colleagues have created the Southern California Bight Elasmobranch Consortium, a collaboration among U.S. and Mexican scientists, fisheries managers and public officials to study and promote greater awareness of elasmobranches (sharks, skates and rays) living in the bight, a 450-mile stretch from Point Conception near Santa Barbara to Cabo Colonet in Baja California.
“We want to develop a cohesive voice with a common interest, which is to better understand these animals and better preserve them,” said Graham. “There are easily 30 to 40 species of elasmobranch (pronounced ee-lazmo-brank) living within five miles of Scripps. But nobody has a real appreciation of what they're doing or how they are faring. What are their ecological roles?
“A lot of species appear to be in decline. Are they sentinels for the environment? If so, what are they telling us about the rest of the sea?”
Graham is a shark specialist. He has spent years studying their remarkable physiologies and abilities. They are capable of great feats of strength and endurance. For example, the estimated bite strength of the shortfin mako shark, found in San Diego waters, is several tons per square inch. Blue sharks, also seen locally, are global swimmers, migrating thousands of miles each year in pursuit of food and temperate waters.
A different shark warning
The International Union for Conservation of Nature and Natural Resources lists the following 20 sharks on its Red List of endangered species:
Angular angel shark
Smoothback angel shark
Smoothtooth blacktip shark
Grey nurse or sand tiger shark
Great white shark
School or tope shark
At least 10 other shark species are believed to be endangered, but data remains insufficient to declare them so.
Thresher shark Java or pigeye shark Kitefin shark Salmon shark Megamouth shark Broadnose sevengill shark Bigeye sand tiger shark Narrowmouth catshark Great hammerhead shark Argentine angel shark Some sharks – the mako, salmon and great white – are “warmblooded.” That is, body heat generated in red muscle is used to warm the circulatory system, allowing the fish to swim and live in cold waters rich with prey.
But despite their notable attributes, most sharks appear ill-equipped to deal with the pressures of modern life, at least those posed by men: over-fishing, pollution, habitat loss.
“In that sense, they have obvious biological flaws,” said Graham. “They grow slowly and have limited reproductive capability. That makes them less likely to survive this great pressure of human expansion over the next 50 years.”
If sharks are to survive, Graham and others will have to learn a lot more about how to save them. It's not an easy task, particularly with pelagic or open ocean species like the mako, blue and thresher.
“These aren't fish most people encounter very often,” said Suzanne Kohin, a research biologist for the National Marine Fisheries Service in La Jolla. “Unless they get caught in a commercial drift gill net, you have to really go looking for them.”
Scripps researchers have recently been doing just that, venturing out in small boats for hours on end, chumming ocean waters off San Diego to lure mako sharks close enough to be temporarily caught and tagged.
The tagging program, funded by California Sea Grant College Program, is intended to reveal the natural behaviors of mako sharks. While not a primary target of California's gill net fishery, makos are frequently trapped in the expansive nets as they drift below the ocean surface. The larger sharks have some commercial value; smaller makos are typically discarded.
Once a mako shark is caught by Scripps researchers, it is fed a mackerel stuffed with a pinging acoustic device that allows researchers (following in a boat) to track the sharks' swimming patterns and depth preferences for the next 24 hours, sometimes longer.
A solitary mako shark patrols waters off San Diego. Makos appear to be relatively plentiful, but researchers know very little about their habits and biology. A recent paper published in Marine Biology on the tagging program reported that makos spent at least 80 percent of their time in the upper 39 feet of the ocean, almost never venturing below 78 feet. The finding buttresses a state law that mandates gill nets must be set at least 36 feet deep. The law was written to protect marine mammals, but appears also to benefit mako sharks.
Another Scripps program, also funded by California Sea Grant, involves attaching paper clip-sized electronic tags to the dorsal fins of thresher sharks, which are a primary target of commercial fishermen. The tags record the movements of released sharks – how far they swim each day, where and at what depths in the water column. Stored data from the tags is recovered when the sharks are caught. Each tag returned to Scripps brings a $50 reward.
Dan Cartamil, a graduate student in Graham's lab who is conducting the thresher program, says the expanded database of thresher shark movements and patterns will help scientists identify areas or water depths especially important to the species. These places could then be factored into future conservation programs.
Graham said the consortium's first goal is to better organize the efforts of diverse scientists and organizations in Southern California studying elasobranchs, and to find new sources of funding.
“We want everybody to know what everybody else is doing,” said Graham, “and for that information to get to people who can use it, not just scientists, but also commercial fishermen, sport fishermen and the general public.”
Scripps Institution of Oceanography researcher Dan Cartamil releases a tagged thresher shark - a favorite of commercial fishermen. The tags record the shark's movements, helping scientists determine how to protect the species from overfishing. The second goal is to expand and improve the flow of scientific communication with researchers, fishermen and the public in Mexico, said Cartamil, one of the consortium organizers.
“Sharks in the Southern California Bight certainly don't respect international boundaries. Migratory patterns lead them to spend part of the year with us, part of the year in Mexican waters.”
But what happens to them once they venture south is even more of a mystery than what happens to them in Southern California waters.
Based on admittedly scant data, Kohin at the National Marine Fisheries Service believes local shark stocks are reasonably stable, with a few notable exceptions like the Pacific angel shark, whose numbers have declined sharply due to overfishing. A few species like the mako, she said, may even be increasing in population, based on counts of caught fish.
One reason for the improvement, said Graham, has been the tightening of rules governing shark “finning,” in which a shark's fins are removed for sale (dried fin sells for more than $300 per pound in Asian markets and is used to make soup), while the rest of the still-living fish is tossed back into the sea to die.
In 2000, President Clinton signed the Shark Finning Prohibition Act (introduced by former Congressman Randy Cunningham) which mandated that any harvested shark fin brought into port must still be attached to the rest of the fish.
In 2002, a U.S. Coast Guard ship seized an American transport vessel a few hundred miles off Acapulco carrying 32 tons of shark fins ultimately bound for the Asian market. Graham says it's estimated the cargo represented 11,000 to 12,000 sharks killed.
“If fishermen have to keep the sharks intact for market, they can't carry so many back to port. The anti-finning act has curbed U.S. fin production, but it's still a huge problem worldwide,” he said.
Including, perhaps, to the south.
“Fishing rules are lax in Mexico,” said Cartamil. “There's barely any sort of enforceable regulation.”
No one knows how many sharks are harvested in Mexican waters for their fins, or how many die in drift gill nets intended for other fisheries. Graham hopes the consortium, through existing and new partnerships with organizations like Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (CICESE), a Mexican science agency based in Baja California, will spur both research and action.
“We want to foment new ideas. This can't really be done very easily through federal or state channels. There are too many binational issues and complications. But if we can get scientists and others on both sides of the border talking, if we can get students moving back and forth between science institutions like Scripps and CICESE, then we explore common interests and what needs to be done.”
Dead in the water
For much of their recent history, sharks have been perceived simply as unthinking eating machines, neither of which is true. Experts say they possess a particular intelligence and curiosity. Like dolphins, who enjoy a reputation for being brainy, sharks can be trained. And they eat periodically, depending on their metabolism and the availability of food. While large species like the great white, which can grow to 20 feet and weigh 4,000 pounds, are capable of consuming whole seals, other sharks eat less than 2 percent of their body weight each day.
Sharks have been around a long time, more than 400 million years. But there are real concerns that some species won't survive the century, perhaps not even the decade due to hunting, indiscriminate fishing techniques and human greed. According to projections by some environmental groups like the International Union for Conservation of Nature and Natural Resources, perhaps 20 shark species could go extinct by 2017, among them the great white shark (Carcharodon carcharias), the last known surviving member of its genus.
Now that's scary.