For years, legendary tales from Scotland and Western Alaska described large animals or monsters thought to live in Loch Ness and Lake Iliamna. But evidence has been mounting that the Loch Ness and Lake Iliamna monsters may, in fact, be sleeper sharks.
Two exceptionally large Arctic sharks ply northern waters -- Greenland sharks and the Pacific sleeper sharks. During the last few years, scientists have documented Greenland sharks using the St. Lawrence Seaway, lending further credence to the hypothesis that some sharks can survive in freshwater. Bull sharks are also known to swim in fresh water, but this species needs warmer waters.
The idea of sharks possibly using Loch Ness is not new; that's long been one of the hypotheses explaining the Loch Ness Monster. But until now, nobody has suggested sleeper sharks, perhaps because they're secretive and so rarely seen.
Sleeper sharks can exceed 20 feet and weigh upwards of 4 tons. Sleeper sharks probably use rivers and lakes to find food, and there is an abundance of salmon and other fish in Loch Ness and Lake Iliamna.
Sightings are often consistent with descriptions of sleeper sharks in that the monsters' shape and colors usually match that of sleeper sharks. Salmon and lots of other prey species have been found in sleeper sharks' stomachs.
As much as we know about sleeper sharks, there are still plenty of unknowns:
- How long can sleeper sharks cope with freshwater? Can they spend months in rivers and lakes?
- Do they ever over-winter in freshwater?
- What is the timing of their movements in and out of freshwater?
While most sighting descriptions are intriguing, in Lake Iliamna the "monsters" have reportedly been seen in the shallow waters near shore. But hard data is a necessity. Late this summer, I plan to lead a field expedition hoping to capture sleeper sharks in Lake Iliamna, attaching satellite tags to track their movements.
How exactly? Years ago when working in Prince William Sound, we spent the night in one of the bays on board our research vessel. One evening I tossed some fish scraps into a crab pot and lowered the pot to the bottom along with an underwater camera. Several fish visited --black cod, a skate and a sleeper shark.
I plan to try the same technique in Lake Iliamna to catch a shark on video. In addition, I will set some baited circle hooks to catch a shark for photographing, tagging and release.
The third technique I'm investigating is to use a camera device that is baited, dropped to the bottom and takes photos when approached. It later returns to the surface for collection by the scientists.
A subsequent expedition is planned for late summer 2013 to Lock Ness to repeat the exercise on Nessie.
Harbingers of Climate Change
Sleeper sharks are proving themselves very adaptable, so much so that they may become the Arctic's dominant large predator. Global warming is reducing Arctic Ocean ice and critical refuge habitat for ice seals and polar bears. Without ice to haul out on, seals and polar bears may be exposed to predation by these large sharks. In the waters near Tromsø, Norway, Greenland sharks were suspected of killing large numbers of harbor seals. In the stomach of a Greenland shark captured in the North Sea, researchers found the jawbone of a young polar bear. Harbor seals have been reported in stomachs of Pacific sleeper sharks.
In fact, nearly every marine species in the Arctic has been found in the stomachs of these sharks, which makes sleepers a unique predator. Scientists who examined a dozen Greenland sharks from Iceland found that six sharks contained remnants of marine mammals, accounting for a quarter of the total mass of stomach contents and, perhaps, a majority of the energy ingested based on the energy content of marine-mammal blubber.
Greenland sharks have been caught in large numbers in eastern Canada and western Greenland. One researcher estimated that 50,000 individual sharks were caught per year in the Baffin Bay region in the 1940s.
From my research, I would offer one precaution: Don't underestimate the predatory skills of sleeper sharks.
No doubt, sleeper sharks can be easy to underestimate. Fishermen and scientists have described them as sluggish and distinctly unpredatory-like over the years -- based, in part, on how they appear when brought to the surface on a long line or in a trawl. But sleeper sharks have been detected attacking live and active prey such as Pacific halibut and salmon. One sleeper shark captured on an International Pacific Halibut Commission research charter contained six whole adult chum salmon. Each weighed more than 4 pounds and were so fresh and bright they could have been cooked for dinner. Fresh whale tissue is also common in sleeper shark stomachs.
Understanding the role of Greenland and Pacific sleeper sharks on marine ecosystems is critical for managing northern oceans. If they turn out to be the culprits described as monsters in Loch Ness and Lake Iliamna, their somewhat ho-hum reputation based, in part, on their uninspiring name may be due for an update.