Sharks

Last week we joined our friends Ned and Susan on a snorkel trip to the pelagic zone offshore from Kona. Kona Diving Ecoadventures takes passengers about five miles offshore to waters around a mile deep. There they search for pelagic cetaceans—pilot whales, sperm whales, open-ocean dolphins—and other pelagic megafauna such as sharks and billfish. The passengers are allowed to get into the water and snorkel with anything interesting that is encountered, in a manner, we were told, intended not to unduly disturb the animals.

In stark contrast to the bustling nearshore reefs, the open ocean is mostly mile after mile of emptiness, so there’s a lot of searching and no guarantee as to what, if anything, you’ll encounter. On this trip we saw little in the open ocean—only a mixed pod of spinner and spotted dolphins that we observed from the boat.

Fortunately, open ocean is not all there is off the Kona coast—there are also fish farms operating in these deep waters. All sorts of marine life congregate near the aquaculture operations, partly attracted to wasted fish feed, and partly due to the shelter provided by the farms’ netting and associated structures where smaller organisms can hide from predators. Our boat visited one of the farms, where we had the opportunity to swim with Rough-toothed Dolphins (no decent photos though) and two species of shark.

This Silky Shark, about seven feet long, was quite curious about us, approaching very closely a number of times. Glad it didn’t take an exploratory bite. These fast swimmers are common in tropical and subtropical waters worldwide.

Here’s the other side of the same shark. It’s got a nasty, fairly fresh wound in front of its gill slits. There’s a remora attached behind the gill slits. The elongated rear edge of the second dorsal fin helps distinguish this species from similar sharks.

I’m not sure how many Oceanic Whitetip Sharks came up from the depths to check us out, but it was more than one. This one, again about seven feet long, is accompanied by several Pilotfish. Oceanic Whitetips are easy to recognize by their large pectoral fins and, of course, their white fin tips. The slow-swimming Whitetips are often found with the Silkies and are also found worldwide. In the nineteen-sixties this shark was so abundant that it was estimated to be among the most numerous large animals on the planet. Fishing pressure over the intervening decades has rendered the species rare through much of its range, but it’s still fairly common here in Hawaii.

We also visited a so-called fish aggregating device. They’re basically buoys moored in offshore waters for the purpose of attracting large fish and facilitating sport fishing. The FADs are placed and maintained by the Hawaii Division of Aquatic Resources. There were no big fish present when we were there, but there were a lot of interesting smaller fish. The boldly striped fish here are Pilotfish. The fish on the left are some sort of young jack. I think they may be escaped Kampachi (also called Almaco Jacks) from nearby fish farms, but they may be young Amberjacks.