Local Shark Scientists Explain Why There Are So Many Shark Attacks in Hawai‘i
Hawai‘i’s shark researchers are some of the world’s best. Here’s what they say about our recent spike of shark attacks.
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HONOLULU: What effect does culling sharks have?
H/M: Historical shark culling efforts in Hawai‘i did not stop shark bites, nor is there evidence of a reduction in shark bites associated with culling efforts. For example, the 1967–69 Shark Control Program killed 1,727 sharks (including 280 tiger sharks), yet 1969 saw more shark bites (two total) than any other year during the 1960s. Licius Lee was bitten while surfing at Mākaha (March 9, 1969), and a few months later (Nov. 11, 1969) D. McGinnis was injured by a shark while diving for lobsters off Barbers Point. The latter incident is particularly demonstrative of the ineffectiveness of culling programs, because 33 tiger sharks were removed from waters off Barbers Point alone during the 1967–69 program, yet a shark bite still occurred at that location in late 1969. The reason for this is likely simple—tiger sharks are highly mobile and the culled sharks were soon replaced by other animals moving into the area.
Given what our tracking and growth rate studies have shown, we can state that, in order for any culling operation to have any chance of success at reducing shark bite frequency, it would require a huge, costly and continuous fishing effort that (even if feasible) would result in an unacceptable perturbation of our marine ecosystem. And, as pointed out above, even this would not guarantee that shark bites will not occur.
HONOLULU: As a scientist, what would you like to see measured or quantified to bring clarity here?
H/M: Detailed information on the volumes and types of ocean recreation activities occurring over time around the coastlines of each island would allow much more detailed analysis of shark bite data. It would be useful to reassess the importance of turtles to the diets of tiger sharks—but this would require nonlethal ways of doing so, perhaps by using ultrasound to see inside the stomachs of sharks captured during research activities.
HONOLULU: Do sharks have memories?
H/M: We have good evidence that sharks have memories. Long-term, reciprocal movements between distant locations suggest tiger sharks possess detailed cognitive maps of resource availability. The precise, seasonal arrival of certain tiger sharks at French Frigate Shoals atoll in time for albatross fledging season (which occurs during only three to four weeks each summer) indicates these sharks may also use internal clocks to guide their movements. Not only do these results demonstrate “memory” but also a very sophisticated ability to navigate over large distances of ocean.
Repeated sightings of sharks at particular locations may arise because the same individuals return to these sites, and also simply because these locations may simply be good habitat for sharks.
HONOLULU: Tigers are perpetrators of severe and fatal attacks on humans, along with a possible great white shark visitor. Do Galapagos, sandbar, reef and hammerhead sharks ever cause fatalities, or can we call them biters but not eaters?
H/M: Based on victim descriptions, a very small number of unprovoked shark bites in Hawai‘i are likely due to small sharks other than tiger sharks, but identifying the specific species responsible has not been possible in most cases. A lack of clear species identification is common in shark bite incidents. Victims are concerned with survival and escape rather than species identification. However, tiger sharks are large, very distinctive in appearance and are also the only large shark species routinely found in waters used by humans for ocean recreation in Hawai‘i. Available evidence suggests tiger sharks are responsible for most shark bite incidents in Hawai‘i waters. All of the other species of sharks that you mention have been implicated in attacks somewhere around the world at some time or other—for instance, during ship disasters at sea (e.g., during war). In Hawai‘i there are no confirmed attacks from Galapagos sharks, although they are certainly big enough to cause damage. Our research indicates that this species very rarely comes close enough to shore to interact with swimmer or surfers. Worldwide, only one fatality has been conclusively linked to a Galapagos shark (LTJG John W. Gibson, age 25, April 20, 1963, Magens Bay, Saint Thomas, U.S. Virgin Islands).
Three species of shark (white, tiger, bull) account for the vast majority of severe shark bites worldwide.
Severe or fatal bites by other shark species are extremely rare. Sandbar sharks have only been implicated in five nonfatal bites worldwide (none in Hawai‘i). Seventeen nonfatal shark bites are attributed to the genus Sphyrna (hammerhead), but most of these are likely due to great hammerheads (rare in Hawai‘i).
The scalloped hammerhead, commonly found in Hawai‘i, is a much smaller species than the great hammerhead. Three Hawai‘i shark bites have been attributed to hammerheads. Although the specific hammerhead species was not identified, two of the incident locations are known nursery areas for scalloped hammerheads:
Sept. 2, 1953, Waiau, Pearl Harbor, O‘ahu, Daniel Gonsalves, bitten on leg and foot by 5-foot hammerhead shark while crabbing;
June 3, 1984, Kāne‘ohe Bay, O‘ahu, Susan Buecher, bitten on the foot while towing her sister on a plastic ski board. Incident happened at 5 p.m. in water 5 feet deep, about 400 yards from shore. Surgery and lower leg cast required to repair damaged tendons. Four- to 5-foot hammerhead shark believed to have been responsible; and,
Jan. 20, 1989, Waialua Beach, Moloka‘i, Earl Dunnam, 10-year-old boy bitten on the foot by a 6- to 8-foot hammerhead shark while riding a body board 200 feet from shore. Wound required 8 stitches. Bite occurred to a naked foot, and not to the foot wearing a swim fin.
These incidents reflect the fact that hammerhead sharks have quite small mouths and their teeth are not designed for taking large chunks out of large prey.
We do have the oceanic blacktip (Carcharhinus limbatus) in Hawai‘i coastal waters (the “oceanic” part of its common name is a misnomer—it is a coastal shark). This species has been implicated in 29 bites worldwide and is thought to be responsible for less-severe bites along the U.S. eastern seaboard, but definitive species identifications are lacking in most incidents.
The severity of damage from shark bites is really a matter of (bad) luck—even a “small” bite from a small shark on an artery can be very serious if no help is at hand. This is why the single best safety tip is to never be in the ocean alone.
HONOLULU: Colin Cook’s rescuer, Keoni Bowthorpe, said the tiger he shoved off was very skinny for such a large shark. Would this indicate a very hungry female post-pupping? The “ravenous gravid shark” theory gets a lot of play. Your thoughts?
H/M: There are natural cycles in shark biology that may help to explain seasonal patterns of shark bites. For example, in Hawai‘i, we typically see more shark bites during the fall pupping season for tiger sharks.
However, although we can identify these broad, seasonal patterns, it is important to remember that shark bites occur in all months of the year, and not all shark bites are caused by pregnant female tiger sharks.
We also need to understand that any single shark bite is a unique event resulting from a confluence of factors that bring a person and shark together. This makes individual shark bites hard to decipher because we invariably know almost nothing about the particular shark involved in any given incident.
We should not over-emphasize the “hungry gravid female” concept. I am not familiar with the circumstances of the rescue of Colin Cook but I do know that the shape of things (like sharks) can be very deceptive when viewed from above water: I don’t know how good a look the rescuer got at the shark. Plus, there is no reason why a shark that has recently pupped should look “skinny”—it should just go back to looking like a regular, non-pregnant shark.
HONOLULU: What do we make of a situation like that on the island of Reunion, where seven fatalities since 2011 have actually resulted in a ban on swimming? What would you do if a similar spike were to occur here? Is there an emergency protocol in the state?
H/M: The incidents on Reunion Island were a combination of attacks from tiger sharks and bull sharks. Fortunately for us, bull sharks are not found in Hawai‘i. Bull sharks are bad news because they occur in shallow coastal waters (and can swim hundreds of miles up into freshwater rivers and lakes) and have evolved to hunt in shallow water. Therefore they overlap with swimming/wading/surfing humans on their hunting grounds. [As for banning swimming,] Reunion is a French protectorate—the French can be much more autocratic about these things than some other nations. I doubt that a total ban on swimming or surfing would get very far in Hawai‘i—and may not even have legal status.
HONOLULU: Any other considerations?
H/M: One of the outcomes of the occurrence of shark attacks in Hawai‘i is that it has led to local and federal funding of shark-related research. This has put Hawai‘i in the forefront of this field and especially in the development and deployment of increasingly sophisticated tracking devices that are now allowing us to not only track the sharks but also learn about their feeding habits, social interactions and the oceanographic properties of the water through which they are swimming.
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