REMINISCENCES | Two sharks: one real, one fake

FISHING/AQUACULTURE WEEK
Oceanic whitetip shark (Photo: Red Sea Project)

This story has two sharks involved, a real one, an oceanic whitetip (Carcharinus longimanus), sometimes called the shipwreck shark, and which are quite large, and something else masquerading as a shark. Initially there were four participants: me, fellow biologist Eugene Leroy Nakamura, a school of about a hundred aku (skipjack tuna; Katsuwonus pelamis), and (most importantly) the Fisheries Research vessel Charles H. Gilbert of the Honolulu Laboratory of the US National Marine Fisheries Service. The number of participants changed once the shark took up its station close to us. This all took place early one delightfully sunny morning in the summer of 1968.

Gene and I were Fishery Research Biologists – part of the Laboratory’s Behavior Program and went aboard the 120-foot-long research vessel Charles H. Gilbert for an overnight journey to the waters off the small Lanai Island port of Kaumalapa’u where we had been told it was easy to find schools of aku early in the morning about five miles offshore from the harbor. The purpose of our venture was to see how aku reacted to a new bait, threadfin shad (Dorasoma petenense) that we netted from Wahiawa Reservoir on Oahu, trucked them 30 miles to Kewalo Basin in Honolulu, acclimated them to 100 per cent saltwater and placed them in Gilbert’s bait well.

When Gene and I entered the water, we took with us a small container holding the threadfin shad. Our plan was to find a school of aku, get as close to it as possible, and then tip the container holding the shad and see what happened.

How many shad were in the container? Written records of the experiment are not available (as of this writing in 2017) but I recall about 300 to 500 shad were in the container. Besides our standard skin-diving equipment (fins, mask, knife, and snorkel) we had one other piece of equipment – a Shark Billy. This was a defensive pole about four or five feet long. It was made of aluminium and the anti-shark end of it was plugged with hard plastic. Sticking out from the plastic were five large nails that were imbedded in the plastic before it hardened. Each nail was about six inches long and faced outward in various directions.

“The shark was very elegant as it held motionless while watching the aku.”

The idea was that if a shark swam at the diver the Shark Billy would be jammed into the shark’s nose, causing pain to the shark and making it retreat. Texts on the anatomy of shark noses state their noses contain sensitive Ampullae of lorenzenini, electro sensing organs. We thought a shark would turn away if poked in the nose by the Billy.

Gene and I entered the water on a sunny calm day, basically no waves to contend with. Gilbert then backed down until it was 100 yards away. We were then ready for anything, so we thought, and started looking for a school of aku. Lo and behold in a few minutes a school of about 100 aku of five to 10 pounds size came cruising slowly across our line of vision and then coming to a complete stop. They did not pay any attention to us.

We were astonished as the aku became motionless. The water was crystal clear, and they were about thirty feet from us. The longitudinal stripes on their bodies were highly visible. But before we could do anything with the threadfin shad bait – there was another big surprise – an oceanic whitetip shark (Carcharinus longimanus) about six or seven feet long had taken up a position at the rear of the school two or three feet below the surface. It was also motionless in the water, not going up or down or sideways. It was obvious that it was doing the same thing that Gene and I were doing – conducting a reconnaissance of the school of aku.

The geometry was roughly as follows: Gene and I were about 25 to 30 feet on our side of the aku school. The shark was also about 25 to 30 feet from its side of the aku school and there was probably 25 to 30 feet between us and the shark. The shark was very elegant as it held motionless while watching the aku. It was simply a gorgeous large animal. The sun shining on the shark caused attractive mottled patterns along its flanks. There probably were three or four small striped pilot fish (Naucrates ductor) maintaining station next to the shark. Pilot fish are members of the jack family and are usually found swimming alongside this species of shark.

“Suddenly something grabbed me by the shoulder and shook it back and forth.”

There was no indication the shark had seen us; I thought it was so keen on watching the school of aku it simply did not see us. I thought discretion would be the better part of valor and to leave watching the aku to the shark, so I got Gene’s attention, pointed to the shark, and then pointed to the general location of Gilbert, he nodded, and we started swimming towards Gilbert. In the process, I lost sight of Gene as I thought he was off to one side or behind me. I also lost sight of the of the shark.

Suddenly something grabbed me by the shoulder and shook it back and forth. I was stunned as I thought the shark had attacked me. But then I saw Gene, the shaking stopped, and I realised he had shaken my shoulder to get my attention – probably to point out where the shark was. First, I was angry but then I realised what happened, and I gave Gene a great big grin.

Several years ago, when I told Gene I wanted to write this episode, he claimed it was an accident, but it did not seem that way to me. We then waved to Gilbert to pick us up, but the experiment never provided any answers on how the aku responded to the bait – which got lost in the commotion. We did find out later that shad are a very good bait when Gilbert took a bait well full of threadfin shad 4,000 kilometres south of Hawaii to French Polynesia to catch aku for subpopulations research by Dr Lucian Sprague, then the Assistant Laboratory Director.

Why Hawaii’s commercial aku fleet did not use threadfin shad as a regular bait is another story, one that caused me a lot of grief and gave me a lesson when it comes to selecting fishing vessels to try a new bait species or anything else that is new.

The above article is an excerpt from Swimming with Fishes, Mr Iversen’s memoir detailing his experiences as a fishery biologist. It is reposted here on Baird Maritime with the author’s permission.

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Bob Iversen

Bob Iversen is a retired Hawaii fishery biologist who spent 40 years studying tuna and other fish in the tropical Pacific Ocean. He is a former officer in the US Navy, and initiated the “mental health of seafarers” movement that has now taken off worldwide.