White Shark (Carcharodon carcharias) photo by Howard Hall
History of PRBO's White Shark Project at the Farallon Islands
In 1969 PRBO biologists working on the Farallon Islands saw a large shark kill and eat a Steller's Sea Lion. At the time, biologists had no idea what kind of shark was involved. Today, the Farallones are recognized as one of the best places in the world to study Great White Sharks in their natural environment.
Our studies on the white sharks at the Farallones have gained widespread recognition in both popular and scientific arenas. We have undertaken long-term population monitoring through standardized watches from the lighthouse atop Southeast Farallon Island, studied the influences on sharks of oceanographic conditions and other environmental variables, investigated the reactions of sharks to decoys of various shapes and sizes, documented thermoregulation and individual and sex-specific occurrence patterns around the island, studied predator-prey relationships, and investigated various other aspects of shark behavior. In 1997 we documented the attack on a white shark by a killer whale (Orcinus orca) and the subsequent disappearance of white sharks at the island, an event that repeated itself in the fall of 2000. Our research led directly to a 1994 California State Assembly bill protecting white sharks in the state. Much of this research has been published in the scientific literature (see bibliography, below) and communicated to the public through numerous documentaries, popular articles, and lectures. All research involving decoys and tagging have been under permit with the California Department of Fish and Game.
The White Shark at Southeast Farallon Island: Uncovering the Real Story
by Peter Pyle
Rarely these days does raw primal fear completely control our neural circuitry. It has happened to me but once: upon my first close encounter with a great white shark. Just off Southeast Farallon Island in the fall of 1985, I was performing a routine "boat-day", the weekly operation during which we transfer supplies and personnel from a supply boat to the island via our 11-foot Boston Whaler and a crane that swings over a leeward gulch. I had just hooked up a box of provisions in the Whaler when I noticed, about 20 feet away, the shark's distinctive dorsal and tail fins meandering in my general direction. Although it was a "small" white shark by our standards - an estimated 12 feet long - I was stricken with panic and recklessly retreated as far into the gulch as surge and rocks would allow. I finished the landing by darting out and back from the depths of the gulch until, at last, the crane lifted the Whaler and my unsettled self to safety on the island. Nothing before or since has invoked in me such aboriginal fear as did the sight of those swaggering fins.
It was thus with some hesitation that, four years later, I considered Scot Anderson's request that we go out in the Whaler to observe a 16-foot white shark eating an immature elephant seal. As part of PRBO's ongoing research on white sharks, Scot had just witnessed the attack on the seal from the lighthouse atop the island. As is often the case, the shark had temporarily left its quarry drifting on the surface before returning to consume it. It was a calm, cloudy day in early October 1989, the type of day when the surrounding ocean is full of magic and the island comes to life. Though my fear of white sharks remained remained intact-- I had briefly met them twice off the landing since that first encounter-- the calm seas, a growing understanding of the shark's feeding behavior, and a sense of adventure became the deciding factors that moment.
As our Whaler is gently lowered upon the sea, that sense of forebodence begins to consume me. Somewhere under the mirrored surface prowls a dispassionate hunter significantly larger than our boat. How will it react to our approach? Will we frighten it off, or will it consider us a rival to be challenged? We approach the carcass and make a quick discerning pass. The six-foot seal is half decapitated, with impressive parallel gashes extending across its neck and chest. Our sense of vulnerability heightened, we retreat from the scene and await the shark's return. Although the ocean is eerily still, my mood becomes surprisingly detached. Has nine white shark seasons made me impervious to their presence, or am I just losing my mind? While admiring the island's austere silhouette, I contemplate the steady progress we are making in understanding this infamous but misrepresented predator.
The early years: A story emerges from the deep.
As part of a cooperative agreement with the Fish and Wildlife Service, PRBO has manned and conducted research on Southeast Farallon Island (Southeast Farallon Island) every day since April 1968. On 9 September 1970 PRBO biologists witnessed their first white shark attack; the victim was a Steller's sea lion. Fifteen years of opportunistic observation ensued, during which time we logged nearly 100 predatory events and learned that shark activity at Southeast Farallon Island corresponded to that of its preferred prey, the immature northern elephant seal. Both the size of the sharks and the number of attacks witnessed increased through the 1970s and early 1980s, perhaps in response to an expanding elephant seal population during this period, and strong peaks of both shark activity and presence of immature elephant seals occurred in the fall. Despite year-round effort, we observed no attacks in April-June, and only two each in March and July. Although the shark's activity patterns were primarily related to those of immature elephant seals, approximately 20% of the attacks involved California sea lions, and bite scars were also noted among the smaller numbers of Steller's sea lions and harbor seals that take refuge on Southeast Farallon Island Numerous shark bites also pocked the carcass of an adult male Orca that washed up on the island in 1972.
Despite the white shark's public notoriety, little is known of its natural history. Except for our observations, almost all scientific knowledge has been derived from specimens, attacks on humans, or from sharks baited with blood and large hunks of meat. Specimens of juveniles suggest that pups are about 4 feet in length when born. As revealed by stomach samples, white sharks prey on fish and benthic organisms until they reach 10-12 feet in length (at an unknown age), at which time their prey switches to marine mammals, including pinnipeds, sea otters, dolphins, and whale carcasses. To accommodate this dietary shift, the shape of the white shark's teeth changes from narrow and pointed to broad and knife-edged, the latter form enabling the shark to remove blocks of meat through the outward and downward rotation of its upper jaws. Although lengths of 25+ feet have been reported, the largest documented white shark was a 21-foot specimen captured near Cuba in 1945.
Typical of apex predators, the white shark is rare, with local concentrations restricted to temperate areas inhabited by pinnipeds. Most of the worldwide adult population occurs off northeastern and western North America, South Africa, Japan, and southern Australia. Along the Pacific North American coast, juvenile specimens have been found only south of Point Conception, suggesting that pupping grounds occur primarily off southern and Baja California. But surprisingly, no pregnant females have been found, and virtually nothing is known about such integral aspects of white shark natural history as population size, longevity, age of reproductive maturity, migratory habits, and predator-prey relationships under natural conditions. This lack of human knowledge, accompanied by primal fear, has helped promote a universal lack of compassion for sharks.
PRBO steps up its on-scene inquiry
Realizing our unique opportunity to study the white shark in its natural setting, PRBO intensified its research from Southeast Farallon Island with the formation of a "shark team" -- Farallon biologists David Ainly, Phil Henderson, and myself joined by shark biologists Peter Klimley of Bodega Marine Lab and Scot Anderson, who has volunteered on the island every fall since 1987. Using a combination of high-tech equipment and long hours of observation, we set out to learn as much as we could about the natural history of the white shark at SEFI.
Shark biologists photograph White Sharks with underwater cameras attached to poles.
We began in 1985 with a program aimed at tracking long- and short-term movement patterns of Farallon white sharks, by attempting to affix directional transponders to the dorsal fins of baited animals. Day after day, Peter Klimley resolutely transferred blood and sheep carcasses from our 12-foot Zodiac inflatable to his 22-foot research dory (which was moored to a buoy in a northern cove of the island) and set the bait in likely spots. We initially discovered that the sharks were not as interested in the bait and blood as they were in live swimming animals. Several times while Peter (and earlier that season, Jacques Cousteau's filming team) were attempting to coax sharks to the surface, island biologists saw natural attacks within 500 feet of the bait. Late in the season Peter successfully attached a transponder to a 14-foot female, but just as he was tuning his receiver to it an 18-foot shark known to us as "The Cadillac" (due to its size and wide girth) paid a brief portentous visit to the dory. The tagged female quickly departed the island, and we never heard the transponder again. We then found our Zodiac, still tied to the buoy, bitten and partially sunk by a white shark. Subsequent measurements of the bite indicated that an 18- to 20-foot animal, perhaps "The Cadillac", was responsible. We were rapidly discovering why more is not known about white sharks.
Successful biological inquiry requires a healthy combination of both focused technical research and ample field observation of a subject species. Turning our attention to the latter, we standardized and expanded our observation program in 1987 by stationing one to two observers at the lighthouse during all daylight hours in fall, specifically to search for shark activity. Initiated by Scot Anderson, the shark watch has now produced five years of fall surveillance. During this time we have witnessed 40-60 predatory events per year, an increase from a previous maximum of twelve in 1986. By standardizing our observations, we can determine whether this perceived increase in shark activity is real or simply the artifact of enhanced observer awareness at Southeast Farallon Island It will also enable us to compare the occurrence of attacks with oceanic conditions, such as temperature, salinity, and clarity, which show wide inter-annual variation in the vicinity of the Farallones. Preliminary analyses suggest, for example, that attack frequency increases with colder sea surface temperatures in fall, disputing a widely believed theory that warmer waters (such as those associated with El Nino) bring more sharks into our region. Our findings also suggest that white shark attacks are positively correlated with water turbidity: perhaps the lack of visibility impairs the ability of pinnipeds to detect and escape the sharks. As both colder water and higher turbidity result from coastal upwelling, though, one or both of these correlations may be coincidental. We will soon perform multivariate analyses to see which oceanic conditions have the greatest effect on shark behavior.
Predator-prey interactions
Of general interest to humans is the manner in which white sharks handle their prey, as this will help define appropriate on-scene protocols for surfers or others who have been attacked. To further understand the white shark's feeding behavior, we are now videotaping attack sequences from the Farallon lighthouse. Relying strongly upon the element of surprise, Sharks typically accelerate to strike a pinniped from below or behind. Even though most attacks occur at or near the surface, we are rarely lucky enough to see the first strike and have yet to videotape this event. But what happens after the initial hit? Steinhart Aquarium's John McCosker has promoted a theory (originally suggested by David Ainley) that the shark waits for its prey to bleed to death, in order to avoid risking injury feeding on a live and struggling animal. Thus, if the first strike is not fatal, the prey is able to escape. Some of our observations are consistent with this theory. We have often watched bleeding carcasses float for 10-60 minutes after the initial hit before the shark returned to feed, and we have catalogued many pinnipeds hauled out on the island displaying distinct and at times surprisingly large, crescent-shaped scars-- escapees of the first hit. But we have also observed white sharks apparently pursuing wounded animals and, at times, sharks seem to hold and asphyxiate their prey below the surface. An alternate theory explaining the pause in the predatory sequence might be that the shark itself is partially stunned by the hit, or is in an agitated state and waits to recoup before feeding. By analyzing our videotape footage we can ascertain how often and under what conditions each prey-handling strategy is employed, and record the methods sharks use and the time it takes them to actually consume their meals.
Surfers have long known that certain locations or backdrops are "sharkier" than others. What, exactly, defines the optimal depth and topographic bottom features from which white sharks stalk their prey? To investigate this we are pinpointing the locations of attacks using theodolites, geological instruments that yield precise horizontal and vertical angles from the lighthouse. We hope to confirm our hypothesis that the sharks use their cryptic dorsal coloration to stalk pinnipeds. The white shark, named for the color of its undersides, is actually quite dark gray, even blackish on its upper surface, and may be able to exploit rocky and dark (versus sandy and light) areas found around the island. The surface above rocky ridges or precipices seem to be especially favorable locales for attacks. With the theodolite data we are defining a "high risk zone" in which a majority of the attacks on pinnipeds occur. Using our findings we hope to define high risk conditions, both topographic and oceanic, for humans as well.
Distinctive scar patterns on a White Shark
Using the exact distance from the lighthouse to attacks (as calculated from theodolite readings), we can estimate the lengths of sharks and prey by measuring their images on a video monitor. This will help us confirm suspicions that shark size and prey size are directly related. The size data can also be combined with video and photographic images of the fins to identify individuals. Like the color designs on the flukes of whales, the exact pattern of notches and scratches on the trailing edges of white shark fins are unique to each animal. Using these patterns, Scot has identified 10-15 individuals near the island from 1987 to 1991; at least five of these have been observed in multiple years. We have found returning individuals at about the same time and in the same areas around the island each season, and we have recorded as many as three elephant seals taken by one known shark in a single year. The known-individual data will also be critical to accurately estimating and monitoring the population of white sharks at Southeast Farallon Island
Our ultimate research objective: the overall story
Our ultimate research goal is to document coevolved life-history patterns in the white shark and its two principal prey species, the northern elephant seal and the California sea lion. What domestic and regional strategies do the sharks employ to track and feed on pinnipeds, and in turn, how have the pinnipeds adapted locally and evolutionarily to the presence of the sharks? During detailed observations of pinnipeds from the lighthouse we have noticed a distinct difference in pinniped behavior relative to the "high risk zone". We rarely see elephant seals within the zone in the fall, and we suspect that they commute through this area underwater, possibly along the bottom where the shark would lose its calculated advantage. Sea lions traverse the high risk zone during the fall in large porpoising groups that move too quickly for a shark to strike. Within the safety zone close to the island, in contrast, both pinniped species frolic and float lazily on the surface. Likewise, their behavior is more relaxed in the spring, when white sharks are absent from the area. Recently weaned elephant seals first learning about the ocean, for instance, venture frequently into the high risk zone in March-May when white sharks are not present at SEFI. These seasonal differences in the pinnipeds' behavior supports a theory promoted by David Ainley that the timing of the northern elephant seal's winter pupping season has evolved in response to the white shark's occurrence patterns along the California coast.
As amply demonstrated by PRBO's overall research programs at SEFI, the answers to such questions can only result from long-term studies. We will thus continue, with our lighthouse shark watch, to monitor the natural behavior of white sharks. In the on-going quest for the white shark's underwater story, Peter Klimley and others will be returning to SEFI to track movement patterns with transponders attached to the fins of baited animals. To minimize our effect on the sharks' natural movements, however, we will only offer bait directly following an attack. And so, we will continue pursuing and investigating post-strike events from our trusty Boston Whaler...
The distant cry of a western gull sharply punctuates the stillness. Glancing toward the hapless seal, we note the impressive head and back of the shark as it gently thrusts itself into the carcass, preparing to savor its initial bite. The irony does not escape us as we circle slowly in, approaching within fifteen feet: oddly, there seems no danger at all. Unlike the initial strike, the feeding is performed in peace. With a casual eye on us, the shark glides along the surface, first to nudge the carcass, then to take a healthy bite. Both shark and prey submerge, after which the carcass, missing another section, rises back upon the surface. With growing respect, we calmly watch as the shark in leisure consumes its prize. Even as it passes directly under the Whaler, briefly mistaking us for its prey, we are not alarmed. This is not the indiscriminate killer that the media portrays but simply one of the ocean's many organisms, tending to its livelihood.
The final chapter
With increased understanding, our fear of the white shark has been replaced by a fear for it. The field biologist's bane is to see well-intentioned research findings used to commercially or otherwise exploit a species. In the fall of 1982, four white sharks were killed by a thrill-seeker in Farallon waters, resulting in a noticeable decline in attacks observed from the island. In 1988, another was killed for trophies, and further attempts on sharks by humans have occurred each year since. Due in part to a lack of natural predators, sharks take a long time to reach sexual maturity; the white shark, at the top of the ocean's ecological hierarchy, probably takes the longest of all. The removal of but a few white sharks can thus have profound effects on both its own population status, already considered tenuous, and the demographic balance of all species under its apogee. Such upheaval has already happened in Australia, where a few fishermen in misguided valor rapidly wiped out the white shark population. We plan to use our increased knowledge to assist future efforts to legally protect the white shark. But more importantly, we wish to instill a fundamental change in human attitude.
The white shark may be the last of Earth's primary predators capable of invoking irrational fear and response in humans. Although landbound predators such as lions, tigers, and wolves once held this authority, they have all been subdued, nearly eradicated, and restricted to wildlife preserves, where we point at them from the safety of our automobiles. But Homo Sapiens remains out of its element on the ocean, and it is from this perspective that the white shark still lurks in the primal quarters of the human mind. By revealing the white shark's natural story, we hope to supplant fear and vindictiveness with respect and understanding for this beleaguered citizen of the sea.
This article is from PRBO's Observer, 1992.
For more on PRBO's ongoing research on White Sharks visit:
Individual Shark Identification
Shark Watch and Population Monitoring
Animal Planet website with more info on White Sharks!
