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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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Photo: Juan Oliphant

(page 1 of 3)

 

Early in his research for this month’s story on shark attacks (available on newsstands now), HONOLULU Magazine senior editor Don Wallace contacted Kim Holland and Carl Meyer, Hawai‘i’s go-to shark scientists. The resulting back and forth moved Holland, of the Hawai‘i Institute of Marine Biology, and Meyer, of the University of Hawai‘i at Mānoa, to prepare this exclusive executive summary and Q&A, portions of which were excerpted in the main article. (The questions have been abridged, but not the answers, which were also copyedited for style.) Among the surprising findings: The rise of the Dow-Jones Industrial Average closely parallels attacks in the U.S. (and if science says it’s so, you know it’s true). Of perhaps greater interest is their observation that sharks have memories—and very good ones when it comes to where and when to find the best food sources. In other words, they’re a lot like us. 

 

HONOLULU: Why do we see an increasing number of shark bites over time in Hawai‘i?

Holland/Meyer: The annual number of shark bites in Hawai‘i has increased over time in concert with increases in the human population of the Hawaiian Islands. Not only are there now more people living in Hawai‘i than previously, but we also have more visitors to the Islands every year. These increases have resulted in ever larger numbers of people using the ocean for recreational purposes. Over time, we are also inventing new types of ocean recreation, many of which take us further offshore into shark habitat than was previously the case. Long-term, ongoing increases in the numbers of people using the ocean, and changes in the types of recreational activity, could easily explain increases in shark bites over time in Hawai‘i, and similar trends have been seen in other locations around the world. Although speculation persists about other environmental factors contributing to an upward trend in shark bites, there is currently no scientific evidence to support these claims. 

 

A graphic of Hawaii shark attacks.

Hawai‘i human population versus shark bite incidents.
Source: International Shark Attack File

 

It is also important to understand that, although we may see correlations between the number of shark bites and other phenomena, these relationships are not necessarily causal. For example, there is a strong (95 percent), long-term correlation between the Dow Jones Industrial Average and the number of shark bites in Hawai‘i. No-one would reasonably expect share values to drive shark bites, as this is obviously absurd, but other apparently more plausible correlations may be equally coincidental, so we should be cautious when interpreting trends, especially when we lack empirical data to prove a causal link.  

 

Dow Jones Industrial Average (ten year average) versus total number of Hawaii shark bites per decade (1900-2015).

Dow Jones Industrial Average (10-year average) versus total number of Hawai‘i shark bites per decade (1900–2015).

 

We should also note the very uneven year-to-year pattern in shark bite frequency. For instance, in 2011 there were three unprovoked shark bites, whereas in 2013 there were 13. Certainly nothing about the biology of sharks, the number of sharks or the number of people in the water changes that fast—so there appears to be a large “chance” factor in play. Similarly, there are as many sharks in Hawai‘i on the 359 days of the year when there are no shark bites as there are on the six days a year (e.g., 2014) when they do occur. In the past decade, the average number of unprovoked shark bites averages about 5.5 per year—very different from the 13 that occurred in 2013.

 

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Honolulu Magazine November 2018