Thanks to some excellent weather conditions, we made much better headway than expected after departing French Frigate Shoals, arriving at Lisianski early Sunday morning. Whereas we had originally expected (at best) a late afternoon start yesterday, we now had nearly a full day of diving, combined with a full day of diving today as well. And now that we’ve completed those two days of diving, there is one word that comes to mind to summarize our experiences here: SHARKS!
In the Main Hawaiian Islands, sharks are rarely seen by divers. In my experience diving off Oahu, the species most commonly encountered by divers is the Reef Whitetip Shark (Triaenodon obesus), followed by the Sandbar Shark (Carcharhinus plumbeus), and the Scalloped Hammerhead Shark (Sphyrna lewini). Other species, such as Grey Reef Sharks (Carcharhinus amblyrhinchos), Galapagos Sharks (Carcharhinus galapagensis), and Tiger Sharks (Galeocerdo cuvier), are only infrequently seen, and usually only in specific areas. By contrast, sharks are encountered extremely often up here in the Northwestern Hawaiian Islands. Tiger Sharks are often seen from the surface at places like French Frigate Shoals and Midway Atoll, especially during the summer seabird breeding season. From our perspective, however, the dominant species we encounter while diving up here is (by far) the Galapagos Shark. Typically, the sharks are already near the boat before we even have a chance to get our gear on, and we see them during the descent, while on the bottom, and throughout most of the decompression. This has been the case during the past two days of diving here at Lisianski, except it’s not just Galapagos sharks that we’ve been seeing. We’ve also seen more Reef Whitetip Sharks here than we have ever seen before, and also several Sandbar Sharks and even a few Blacktip Sharks (Carcharhinus limbatus).
On two occasions, we’ve seen a shark that we haven’t been able to identify. Rob Whitton managed to capture one of them on video as it swam past us briefly during decompression. Our best guess is that it is a Bignose Shark (Carcharhinus altimus) — a species that has been recorded from Hawaii before, but only very rarely. We don’t have a positive identification yet, but based on what we can see from Rob’s video, as well as the process of elimination of other plausible shark species, the identification as a Bignose Shark seems the most likely. This unusual diversity of sharks at Lisianski aside, by far the most common sharks — especially during decompression — are the Galapagos sharks.
At one point, we counted at least 45 individual Galapagos Sharks at one time. In years past, we have felt somewhat intimidated by the presence of so many sharks in an environment where we have nowhere to hide, and are effectively between a “rock” (lots of big toothy fishes) and a “hard place” (breaking our decompression obligations and risking a case of decompression sickness, or the “bends”). Over the years, however, we have found the sharks to be consistently non-threatening, and we now welcome their presence to make the long decompressions (upwards of an hour or more, following 20-30 minutes on the bottom) more interesting and entertaining. Today, however, things got almost too entertaining. When we ascend from the bottom, 200-280 feet (61-83 meters) down we send inflatable “safety sausages” to the surface to let the topside crew know where we are. These are attached to a reel of line that we spool out as we send the safety sausages to the surface. We then wind the line back on the reel as we ascend back to the surface over the course of an hour or more of decompression time. Most of the time, we hang on to the reels below the floats as we follow our decompression schedules. However, for various reasons I prefer to swim around a bit during decompression, leaving my reel to dangle below the safety sausage. Today, however, a group of Galapagos Sharks — apparently attracted by the shiny metal of my new reel, decided to give it a “taste test” of sorts.
After determining that my reel apparently didn’t taste very good, one of the sharks took the line into its mouth. As I watched this melee unfold through the viewfinder of my video camera, I thought for sure that I would never see the reel again (we always carry a spare reel and float with us).
Amazingly, however, thanks to quick work by safety diver Senifa Annandale, and the AMAZING toughness of the DGX Hi-Viz Dacron line that I use on my reel (recommended to me by my friend Mark Derrick at DiveGearExpress), my reel and line survived the attack. As intimidating as these photos appear, however, it’s important to note that at no time during any of these dives have we ever felt in any way threatened by the sharks. All of us who witnessed the assault on my reel were actually laughing in our mouthpieces. While the sharks mistook my dangling reel for an injured fish, they have never shown any sort of aggression to us as divers.
As it turns out, very near to where the excitement with my reel was taking place, a large “bait ball” was forming. A school of small baitfish were being bombarded near the surface from below by sharks and larger predatory fishes (such as tuna and sharks), and from above by various seabirds. Our safety diver Keo Lopes came over to borrow my camera and managed to film the action. All in all, it was a very exciting decompression!
Although the stories of shark encounters dominated the conversations in the “dry lab” aboard the ship, we actually did accomplish some important science during the deep part of our dives as well. One of our main missions is to complete a checklist of fishes of each of the islands within the Papahānaumokuākea Marine National Monument, which means documenting as many different species as we can. This includes observations of species that have not previously been recorded from each of the islands, which we refer to as “new records”. On the theme of toothy fishes, one such new record at Lisianski that I managed to document (after having it pointed out to me in a cave at a depth of 200 feet [61 meters] by Randall Kosaki) was the Giant Moray Eel (Gymnothorax javanicus).
Another new fish record that I captured on video at a depth of 280 feet (84 meters) over a flat sandy bottom was the Maze Toby (Canthigaster rivulata).
Another specific mission we have on this cruise is to collect algae specimens from the deep reefs. As photosynthetic organisms, it might at first seem that algae would be confined to shallow depths; but in fact there are vast expanses of multiple different species going down well past 330 feet (100 meters). On this trip, we are limited to a maximum depth of 280 feet (84 meters), where we often find many different kinds of algae, sometimes completely covering the bottom. One particularly interesting find is a blade red algae that we have not yet been able to identify. According to our friend and colleague Dr. Heather Spalding at the University of Hawaii, it’s likely a new record, and possibly a new species.
The algae is surveyed both with the photo quadrat system, and also through carefully collected specimens, which are brought to the surface, photographed, and carefully processed along with the data about where and when they were collected, for later study back home.
After our deep dives were completed, Brian Hauk and I made a short dive to a shallow reef near where we had completed our decompression from the last deep dive. Although we selected the spot at random, it turned out to be a magnificent and well-developed reef, rich in corals, fishes, and invertebrates. There were many Galapagos Sharks following us throughout the dive, a few of which I recognized (from scars and other distinctive features) as being the same individuals that accompanied us during decompression earlier in the day. Brian spent the dive conducting a series of photo-quadrat surveys looking specifically for coral bleaching, while I followed along and captured video of the various fishes I saw.
Tonight the ship makes its way to my favorite diving location in the Northwestern Hawaiian Islands: Pearl and Hermes Reef. We’ll have two full days of diving there before continuing on to Midway Atoll. Based on our trip so far, I am sure I’ll have lots of fun and interesting things to report.