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Is chumming leading to more shark attacks?

A great white shark similar to this one recently attacked and killed a man off the coast of South Africa, raising concerns about the chumming by film a crew days earlier in the area. (Photo: File/ Terry Goss)

A fatal shark attack in South Africa has led to international headlines questioning the practice of chumming for sharks. Champion bodyboarder David Lilienfeld was killed by a great white shark in Kogel Bay near Cape Town last week. The four-meter shark severed the 20-year-old's right leg while he was in the water with his brother and friends. Some people are trying to place some of the blame on a documentary film crew for the National Geographic Channel show "Shark Men," which was filming in the area during the previous week and using chum to attract sharks.

I asked Robert Hueter, AAAS member and Director of the Center for Shark Research at Mote Marine Laboratory in Florida, about the risks and realities of chumming.

AAASMC: What is chumming and who uses it?
Robert Hueter, Director of the Center for Shark Research at Mote Marine Laboratory: Chumming is a practice used by shark fishermen, tourism operators, photographers, videographers, and scientists to attract sharks to a boat, fishing gear or other equipment.  It takes advantage of sharks' keen sense of smell by creating a "chum slick" in the water.  Ground-up fish, fish oil, or other shark food-resembling materials typically are released slowly into the water and currents carry the slick downstream.  This trail of odorant can lead sharks to the source where they can be caught, observed, tagged, or sampled for various purposes.

AAASMC: Is chumming necessary for research on sharks in the wild?
Hueter: Because ocean research can be very expensive and logistically challenging, it sometimes is desirable to chum to expedite encounters with sharks. Chumming cannot raise the abundance of sharks in a general region; it can only help to concentrate the sharks that are in the area. One misconception is that chumming draws sharks from great distances to an area that is not naturally inhabited by sharks. This rarely occurs. In most cases, the sharks are already in the area and scientists chum to decrease the waiting time to encounter a shark for study.  Chumming may also be used in behavioral experiments; for example, in tests of sensory orientation of sharks in the wild.

AAASMC: Critics say that chumming could bring sharks closer in shore, encourage them to search for easier prey, and associate humans with food. Have there been any studies on the effects of chumming? Is there any evidence that chumming influences shark behavior?
Hueter: Unless chumming is done on a constant and regular basis with a large amount of chum in the same area, chumming will not condition sharks to alter their natural behavior over the long term. There are cases where some onshore facilities, such as restaurants or processing plants, have released animal material into the sea on a regular basis, which has led to sharks learning where and when the potential food is released, and aggregating in the area. That is more a case of the sharks associating an area and time, rather than humans per se, with food. On the other hand, shark feeding dives are a tourism practice in which sharks are concentrated in a specific area with food in the water, for the purpose of allowing human divers to observe sharks up close.  In that case, sharks do learn that certain patterns of human activity in a specific spot -- such as dive boats arriving and guides entering the water with food -- are associated with the availability of food. Studies indicate, however, that sharks involved with properly operated feeding dives do not alter their overall behavior in a way that significantly affects animal health and ecology.  Furthermore, there is no evidence to support the premise that sharks generalize from these feeding dives to associate food with humans who are swimming or diving in other areas.

AAASMC: How should agencies that give out permits for chumming react? Should scientists be allowed to chum? What about filmmakers? Should it be restricted to certain areas or smaller amounts of chum?
Hueter: This should be handled on a case-by-case basis. Massive amounts of chumming in a confined area where people are in the water is obviously a bad idea. By definition, chumming attracts sharks that are motivated to feed, and bringing people and sharks into close proximity raises the risk that a bite or attack on a human will occur.  Rather than making value judgments on the type of activity associated with chumming, such as fishing, research, tourism, or filmmaking, it would be better to focus on the chumming itself and its potential effects.  Does the chumming bring sharks that would otherwise not be in the area in proximity to people in the water?  Does the chumming alter shark behavior in any significant way?  Does the chumming threaten ecosystem dynamics?  If the answers to these three questions are all no, then the chumming itself is not a problem.  As to how much chum and where, it is a matter of degree and relates back to the three questions.  My understanding of the research and filmmaking operation in question in South Africa is that about 24 kg (53 lb) of sardines were used to chum over a 24-hr period.  This is not an exorbitant or unusual amount or type of chum.

AAASMC: Researcher and photographer Dirk Schmidt issued a news release on April 11, stating that a high shark alert should be issued and maintained during, and for several days after, filming activity involving chum as a preventative measure. Do you agree with this? Do think this type of measure is enough to protect people and sharks from coming into contact?
Hueter: The coastal bay ecosystem near Cape Town, South Africa is an area that is dominated by large white sharks as top predators. The sharks are there to feed on the abundant prey in this area, especially seals. The fact is that the research and filmmaking operation in this case did not attract white sharks to the area, but rather the reverse: the natural abundance of white sharks in the area attracted the researchers and filmmakers to work there. There is always a risk to human swimmers when these large predators that feed on large prey are in the vicinity. Depending on how local authorities structure their shark education programs, a system of alerts could be in place during the duration of the white shark season in the South Africa bays. Based on the facts reported, an extraordinary alert over and above what should normally be issued during this time of year in the Cape Town region does not seem to have been warranted in this case.

To learn more about Robert Hueter's work, check out his Cutting Edge video on shark research

Representative Image Caption
A great white shark similar to this one recently attacked and killed a man off the coast of South Africa, raising concerns about the chumming by film a crew days earlier in the area. (Photo: File/ Terry Goss)
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Mary Bates, Ph.D.