When channel swimmers talk about their sport with the uninitiated and dryland athletes, they often face the following questions:
- Are there sharks?
- Aren’t you afraid of sharks?
- What happens when you face a shark?
The immediate questions are generally not related to distance or water temperature or conditions. But sharks, the most feared apex predator, remain on the minds of many. This is true in the Cook Strait in New Zealand to the Catalina Channel in California, but also from the Strait of Gibraltar in the Mediterranean Sea to the Tsugaru Channel in Japan.
In response, some swimmers use Shark Shields and other shark deterrent devices. Some swimmers utilize shark divers who stand alert on their escort boats, from Yonaguni Island in Okinawa to the Straits of Florida.
Even shark cages have been used for decades, from Susie Maroney in the 1990’s to Mohammad Kobadi in the Persian Gulf in 2012 (see below).
Even International Marathon Swimming Hall of Fame and International Swimming Hall of Fame dual inductees Kevin Murphy and Des Renford conducted their famous 1977 race in Sydney Harbour in shark cages in the first race of The Great Duel (see below).
While there have been shark encounters and attacks of channel and marathon swimmers in various places (from Charlotte Brynn‘s attack by a leopard shark in the Catalina Channel to Regent Lacoursiere‘s encounter with a Great White Shark in a 1968 professional marathon swim in Rhode Island, but there is no single location where shark encounters and shark attacks have been as frequent as in the channels in the State of Hawaii.
Upper photo shows Michael Spalding in the hospital recovering from a bite from a cookiecutter shark in the Alenuihaha Channel between the Big Island of Hawaii and Maui.
There are 9 main channels in the Hawaiian Islands where swimmers attempt crossings:
- Auau Channel (or the Maui Channel) between Maui and Lanai
- Kalohi Channel between Lanai and Molokai
- Alalakeiki Channel between Kahoolawe and Maui
- Pailolo Channel between Maui and Molokai
- Alenuihaha Channel between Hawaii and Maui
- Kaulakahi Channel between Kauai and Niihau
- Kealaikahiki Channel between Kahoolawe and Lanai
- Kaiwi Channel (see kayaker and a swimmer in the Molokai Channel below)
- Kaieiewaho Channel between Oahu and Kauai
These encounters have been noted since Greta Andersen attempted a Molokai Channel swim in 1958 where she was forced out due to tiger sharks, but none have been as witnessed as often as the tiger shark encounter that Ranie Pearce experienced in 2016 (see below). Captain Mike Twigg-Smith had three channel swimmers in a single season encounter sharks during a few month period in 2019.
Channel swimmer Dr. Steven Minaglia and open water swimming biostatician Melodee Liegl recently wrote a scientific paper Moonless night sky increases Isistius species and live human contact for bioRxiv, an open access preprint repository for the biological sciences co-founded by John Inglis and Richard Sever.
The abstract reads, “The nocturnal feeding behavior and zoogeographical habitat of cookiecutter sharks Isistius brasiliensis and Isistius plutodus (Isistius spp.) greatly reduces interaction of this species with live humans. Attacks on live humans are exceedingly rare with 7 cases reported worldwide, 6 of them in Hawai‘i, and 5 of these occurring among channel swimmers.
Published research suggests that periods of bright moonlight may increase Isistius spp. contact with live humans and does not otherwise identify significant trends or risk factors.
Yet 5 of the 6 Isistius spp. bites on live humans in Hawai‘ian waters occurred with the moon set and after nautical twilight end and before nautical twilight start.
From 1961-2023 in Hawai‘i, 129 successful solo channel crosses and 5 Isistius spp. related injuries in the habitat of cookiecutter sharks were analyzed across two groups:
- one where both the moon and sun were set (dark group) and,
- one where the moon and/or sun was in the sky (light group)
There was a significant difference for swimmers bitten by Isistius spp. in the dark 4 (12%) versus light groups 1 (1%), p=0.012, RR 12.6 (95% confidence interval: 1.5-108.9). Swim start time and year was also significant (Pearson correlation 0.566, p <0.001).
Swimmer gender and use of shark deterrent devices and artificial illumination were not significant.
The growing popularity of channel swimming in Hawai‘i and swim start times have contributed to an increasing likelihood of live human and Isistius spp. contact and a moonless night sky is a significant risk factor for this interaction.
A PDF of the paper can be downloaded here and read in its entirety.
Dr. Minaglia writes, “The data is small and the paper in review, but I think it is timely and will influence behavior in a positive way. It shows a striking risk profile (1-in-8 chance of cookiecutter shark bite with moon and sun set with no light in the sky versus a 1-in-101 chance with moon and/or sun in the sky) when crossing the deepest part of the deep channels in Hawaii. The paper is worth disseminating at this time because of its commentary on human safety.”
Download here – it is a fascinating read.
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